CHAPTER ONE THE POWER SUPPLY Every project needs POWER. Power is ENERGY (actually: Power over a period of TIME is energy) and it comes from a battery or a POWER SUPPLY. We are going to describe a POWER SUPPLY that connects to the mains of your house. A Power Supply provides TWO THINGS. It provide a VOLTAGE and a CURRENT. The voltage can be oscillating "up-and-down" or "reversing" and we call this ALTERNATING VOLTAGE and it is given the letters AC. The letters AC actually mean ALTERNATING CURRENT and the term comes from the very beginning of supplying energy to houses when two rival companies had a war. One company supplied DIRECT VOLTAGE and the other supplied ALTERNATING VOLTAGE. The first was called DC and the second called AC. The voltage at all power points of a house is ALTERNATING and to convert it to DC requires a transformer, a rectifier and a smoothing capacitor called an electrolytic. We will not be concerned with any of these components but the three values we will be covering is: THE VOLTAGE    THE CURRENT and if the output is AC or DC. A POWER SUPPLY plugs into your wall socket and delivers a VOLTAGE, a CURRENT and lets you know if the output is AC or DC. A Power Supply can also be called a Wall Wart, Plug Pack, Adapter or "Converter." A POWER SUPPLY FOR YOUR MODEL RAILWAY You will need at least 2 or 3 different power supplies for your layout. This is because a layout requires at least two different voltages. Normally, these are very expensive, buy we are going to show how to use all sorts of "junk" and "discarded" power supplies from computers, shavers, toothbrushes, toys, printers, faxes, mobile phones, old electric drill chargers and anything you no-longer use, and convert them into a power supply. They will cost you little or nothing and they will work PERFECTLY. But you need to know what you are doing as there are lots of different options. The Li-ion 4-cell power supply we will be describing is equal to $100 power supply (from a model railway supplier) and the $35 Power Supply (we will be describing)  using 5 Li-ion cells can be used as a BENCH POWER SUPPLY for all your testing and is equal to a $100 product. And some of the other power supplies we will be describing will cost you either nothing or just a few dollars. Once you have a power supply, we will describe the next item on your list, a THROTTLE. (This is covered in Chapter 4 - halfway down). This is the module that connects between a power supply and delivers a voltage and current to the track to control the speed of the loco. A typical "Wall Wart" or "Plug Pack" or "Adapter" Power supplies are also called wall warts, plug packs, chargers or adaptors and must be of the type that is SAFE. In other words, you must be able to touch the output wires and the tap in the kitchen and not get killed. This is not a joke. If the adaptor is only designed to be used with a fully plastic item, it may be lacking isolation as you cannot touch any of the wiring. This will only refer to very old devices where a simple capacitor was used to convert the household voltage to a situation where the output current and voltage was fairly low when you measured across the two output wires. But when you measured between either wire and the frame of a toaster, the voltage was 315 volts !!! Throw out anything that you are not absolutely sure is safe. I had one customer blowing up one my modules because he has two plug packs and one was leaking. It put a high voltage on the module and damaged the microcontroller 5 times. I asked him to put the module on batteries to prove the problem was the plug packs. He changed the plug packs and fixed the problem. Suppose you have a handful of say 10 different, old, unwanted, useless adaptors. We are going to show how to connect two or three together to produce a voltage suitable for many of our railway projects.   Make 4 piles. The first will have current ratings from 100mA to 500mA. The next will have current ratings from 600mA to 1 amp The third pile will be 1 amp and higher. And the fourth pile is for those adaptors that deliver AC. From these piles you will be able to make a power supply using two adaptors by wiring the outputs IN SERIES. Many of the CDU projects from Talking Electronics need an input of 20v DC to 25v DC.  The current can be as low as 100mA as the electrolytics in the CDU will take up to 1 amp if the the power supply can deliver this current, but if the available current is 100mA, the CDU will simply take longer to charge the electrolytics. So, almost any power supply can be used and it is the voltage that is needed so the electrolytics charge to the maximum. If you have two 12v DC adaptors with a current rating from 100mA to 1 amp, they can be combined together by connecting the output wires IN SERIES. If one adaptor is 100mA and the other 1amp, they can be combined and all that will happen is the output current will be limited to 100mA. You can even connect 3 adaptors in series to get a total voltage of 25v. This is one way to use low-output-voltage adaptors to power the CDU project on your model railway. Some adaptors are only 3v to 4v to 5v and they can all be combined.  USING DC ADAPTORS IN PARALLEL You can also connect adaptors in PARALLEL - DC adapters. This involves connecting the negative output of one to the negative of the other and the two positives together. Ideally, the output voltage of each adaptor should be the same as this will equalise the load-sharing. But many adaptors have a high output voltage that drops as the load is applied. For instance a 12v 500mA adaptor can be as high as 17v on no-load and this voltage will drop to 12v when 500mA is flowing. The other adaptor may be 14v on no-load and 12v when 500mA is flowing. These two adaptors can produce a 12v 1 amp power supply ONLY IF the actual sharing between the two is EQUAL. Otherwise the output voltage will be 17v on no-load and gradually drop to 12v as the current flowing to the load increases to 1 amp. And the current-sharing will change from 0:100 %  to something nearing 50:50 % It is pointless placing a 12v and 5v adaptor in parallel as the 5v adapter will never deliver any current. THE SOLUTION: The two adapter share 50:50 when the output voltage is exactly the same. This will never be the case but no damage will be done if each adapter has a diode on the output that prevents one adapter passing any current to the other. You will lose about 0.7v and the output voltage will be 0.7v lower than previously, but it will allow two adaptors to be placed in parallel. What will happen is this: The adapter with the higher voltage will deliver ALL the current. As you increase the velocity of the loco, the increased current will cause the output voltage to reduce and when it matches the output voltage of the second plug-pack, the two will share the current. In reality the second plug-pack will simply "start-delivering" and the voltage will not reduce much further.  If you want to see if each adaptor is supplying equal current, replace the diodes with two small "one ohm" resistors (one in each line) and operate your loco. Feel each resistor and see if they are getting "equally-hot." Here is a typical 18v power supply for a model railway.  This is the ideal supply, but it is expensive and our aim is to show how to produce the same output voltage by using much cheaper items (Plug Packs etc.) 18v Power Supply USING AC ADAPTORS IN PARALLEL You can connect AC adapters in parallel, providing they produce the same output. The only way to check this is to connect them together at one end and flick the other two leads to make them spark. If they produce a large spark, you need to change the leads from one adapter. If you flick the leads and a small spark is created, they do not match perfectly and one or both will get hotter than normal as current will flow through the secondary windings. It is very difficult to make any other tests without using a multimeter. When you connect one end of each together and connect a multimeter (set to low AC voltage) to the other two leads, the meter should NOT SHOW any voltage. This means the output of each adapter is rising and falling at the same time and with the same amplitude.  USING DC ADAPTORS IN SERIES Here are two Plug Packs connected in series: You can connect any TWO or THREE together and the output voltage will be the sum of all the voltages and the current will be determined by the lowest current of the 3 adapters. This is very handy for CAPACITOR DISCHARGE UNITS as they need a voltage of approx 16v to 25v DC to fully charge the capacitors. If you do not have any old Plug Packs, you can buy new ones on eBay for a few dollars. You can buy 1Amp or 2Amp Plug Packs. You will need: 1 x 12v adapter  and 1 x 5v  adapter for a THROTTLE. 2 x 12v 1Amp adapters for a Capacitor Discharge Unit. Total of 4 Plug Packs. Here are some examples: THE BEST ADAPTOR:   The best DC adapter for all the CDU modules is a 24v or 30v supply made from two  12v adaptors in series of three 10v adaptors in series. If the CDU module has an on-board regulator, the 30v supply is the best as it will charge the electros to a maximum of 27v. For all the other CDU modules, you should use two 12v adaptors in series and the electros will charge to about 23v.  5v, 10v, 15v POWER SUPPLY You can use your unwanted phone chargers to make a 5v, 10v or 15v power supply of 500mA, 1 amp or 2.4 amp. You can only use one of the outlets from each charger as each lead must have the positive and negative leads isolated for the other leads as you are adding one voltage "on top" of the other. You can combine any 500mA, 1Amp, or 2.4 amp devices and the lowest current will determine the final current you will be able to get.  Simply connect the red lead of one to the black lead of another as shown in the diagram below to get the voltage you want. I put 1,000u 25v electrolytics across each 5v output to improve the current sharing. (not shown) NOTE: Sometimes you will use a charger (wall wort) (or two in series) to charge a Capacitor Discharge Unit and the inrush current will be more than 1 amp and one of the chargers will "close-down" and fail to deliver its voltage. The solution is to add a 12 ohm resistor for 12v, 18 ohm for 18v or 24 ohm for 24v that is soldered to the positive lead. This will limit the current to 1 amp on turn-on.  The $2.50 plug Pack above was purchased as 12v @ 1 amp.  It was easily opened-up via a screw and clip, to reveal the PC board shown below. The output voltage is determined by the zener diode at the front of the board. The 12v zener was replaced with 15v and now the output is 15v DC. I would limit the current to 800mA, but a 15v supply can be connected to many of the throttle circuits covered later in this article to give 0v to 12v DC output.  The zener diode is "sitting high" to show the diode in this discussion and also to allow test chips to measure the voltage across it. It was then resoldered close to the board and the cover replaced. This module is LIVE when out of the case, so don't touch anything. The new 15v zener converts this power adapter to 15v output. You can also use a white LED in series with the 12v zener diode to get 15v output. Note the cathode of the zener is connected to the cathode of the LED and the 1k current-limiting resistor is linked with a jumper (it is not used). Thus the 15v output drives the LED (3v drop) and the 12v zener drops 12v. The anode of the zener is connected to 0v. The result is 15v output. CONNECTING A BATTERY CHARGER A 12v battery charger is NOT a 12v DC power supply. Firstly, it is NOT DC but a voltage called PULSING DC or PULSATING DC. It can also be called UNFILTERED DC. One lead is always considered to be at 0v and the other lead rises from zero to about 18v and falls to zero. For 50Hz mains it produces 100 peaks per second. If you measure this voltage with a DC multimeter you will get a reading of about 12v because the meter is trying to read the maximum but it is rising and falling so fast that the needle only gets the chance to get to about 12v. If you put a large electrolytic across the output, you will see the 18v reading. The electrolytic is storing the peaks. If you connect this battery charger to a project, the electrolytics in the project will store the voltage and the project will see 18v. If the electrolytics are large (say 1,000u for each amp required), the voltage will be quite smooth and suitable for the project. But you must remember, the input voltage is about 18v. When you connect a battery to the 12v battery charger, each cell produces a characteristic voltage of about 2.1v  This is called the electro-negativity of the cell to produce 12.6v for the 6-cell battery. It is the battery that prevents the reading rising above about 12v. When the battery gets fully charged, this reading will rise to about 13.6v but when the battery charger is removed the voltage is 12.6v. A battery connected to a charger can rise to nearly 15v and at this point the "overhead"  (the difference between the charger voltage and the battery) will be say 3v. This 3v will only allow a very small current to enter the battery and it may do two things. It may electrolyise the water in the cell to produce Hydrogen and Oxygen and thus "evaporate" the water or the current may be so small that it just replaces the self-discharge of each cell. To prevent this, the battery charger should be removed when the charging current falls below 100mA 36V !! Some of the CDU projects can be supplied with 30v to 36v DC to fully charge the electrolytic(s). You can make a 36v supply very cheaply by using 24v and 12v plug packs and these are available on eBay for less than $10.00 (for both) including postage.     Simply connect the leads as shown in the following diagram to get 36v. Some of these plug packs have a current detecting overload circuit and "shut-down" if the current is more than 1 amp (even for a millisecond). To prevent this we add a 47 ohm resistor. This "trick" only applies when you are using the plug packs for our CDU modules as the high current is only required for a few seconds and then falls to a very low value and the resistor will not get warm when used for this particular application.   We now supply a pre-voltage module that takes 12v DC to 20v DC and converts it to 26v DC seeBOOST CONVERTER THE ALTERNATIVE TO A WALL WORT Because a Wall Wort producing 13v AC or 27v DC is fairly difficult to obtain (almost impossible) Talking Electronics has produced a number of CDU modules that accept almost any voltage (AC or DC or DCC) from 9v to 15v (either AC or DC) and the on-board voltage generating circuit will produce an output of exactly 27v DC. The latest module to have this feature is JIM's CDU MkII and it has a mini trim pot to adjust the output voltage from 13v to 27v DC to cater for all different types of solenoid points.  This module has on-board push-switches to control the position of the point and each module is designed to be connected to a single point or two or three points that ALL need to be activated AT THE SAME TIME.   You can see the project HERE. This is just one way to get around the problem for the moment, but at some point in your plans to produce a large layout, you will need a POWER SUPPLY. You can spend a lot of money on a POWER SUPPLY but Talking Electronics is always aiming to show the cheapest and best way to get something at the lowest cost. Let's look at what we are talking about: BENCH POWER SUPPLY A Bench Power Supply is the name given to a power supply that looks like the following images: They come in all sorts of arrangements and offer current limiting and output voltages from 0v  to 35v (or higher) at 1 amp to 10 Amp or more. But these cost a lot and you can build a similar "instrument" (a piece of test gear is called an INSTRUMENT) for less and since it will be "out of a case" you will be constantly reminded of how it has been put together. Power Supply MkII 0-12v DC(voltage adjustable)   0-1Amp(current adjustable) Power Supply MkII kit from Talking Electronics for $20.00 plus $7.50 postage.  Click HERE for details. (see the full article HERE) The following project is a 0v to 12v BENCH POWER SUPPLY  with current limiting and has an output of 1 amp. This is sufficient for all types of testing and you can increase the values by referring to the circuit. The whole idea is to create projects at the lowest cost and have them open for viewing so you can remember how they were assembled.       This is the cheapest, safest Power Supply you can get. It will deliver 0-12v at 1amp and you can limit the current to a few milliamp so you will not damage a project you are designing. It has 14v at 5 amp  - called an AUXILIARY OUTPUT  - that connects directly to 4 cells and you need to be careful as the Li-ion cells are capable of delivering up to 50 amps if the wires are shorted. This project is called a BENCH POWER SUPPLY as it is a handy piece of TEST EQUIPMENT that is designed to deliver a controlled voltage for a project you are developing. It is not a continuous power supply as the cells need to be charged (when the indicator LED does not illuminate). The Li-ion cells are available on eBay for a few dollars each and you can buy a single-cell charger for a few dollars. These chargers are microcontroller based and they stop charging when the cell is fully charged. You cannot charge the cells from a "battery charger." You can also get a single-cell charger PCB that connects to your laptop USB socket and it will charge a cell very quickly. But you will only be able to charge one cell at a time. All these things are covered later in the article. POWER SUPPLY MkII Circuit You can use 2 x 470R @ 0.25watt or 1 x 1k @ 0.5watt The new PC board uses 1k (in place of 220R shown above as the current limiting resistor for the white LED) to keep the brightness low to stop blinding you.   PARTS LIST Power Supply MkII $20.00 plus $7.50 postage.  Click HERE for details 4 - 1R      0.25 watt resistors 1 - 4R7 1 - 100R 1 - 220R to be replaced with 1k (the old board shows 220R - new board uses 1k) 2 - 470R (or use 1k @ 0.5watt resistor) 1 - 1k (as shown in circuit above) 1 - 22k 1 - 150k 2 - 500R trim pots 2 - knobs to suit 1 - 3v9 zener 1 - 6v2 zener 1 - 9v zener 1 - BC338 transistor 1 - TIP31 transistor 1 - BD679 transistor 1 - 3mm white LED 4 - 2-screw terminal blocks 2 - heat fins 4 - sets of nuts and bolts and 5 washers 4 - hook-up wire for battery boxes (to replace      the rubbish on the battery boxes) 2 - side-view panel meters and 2 stickers and         foam tape to hold them in position 1 - toggle switch 10cm 0.5mm tinned copper wire for meters 30cm fine solder Backing card and 4 feet and foam tape 1 - Power Supply MkII PC Board Trickle Charger Components are included: 2 - 180R 4 - 3v9 zeners 2 - 9v zeners 3 - 3mm white LEDs Trickle Charger PCB Single-cell charger kit $7.00: 1 - USB voltage/current monitor module 1 - single cell charger PC board 1 - single cell battery box 1 - 1R0  5-watt wire wound resistor These parts are not included in the kit: 5 - 18650 Li-ion cells 1 - 4-cell battery box 1 - single cell battery holder 1 - 4 cell charger 1 - single cell charger or USB charger module and single cell battery box These items can be bought on eBay.   Here is a set of 4 Li-ion cells. Just use the 4 lower cells in a 4-cell carrier. The top cell is just to increase the voltage slightly so the project will produce slightly more than 12v at 1 amp. You can buy Li-ion cells for about $2.50 each on eBay. They have a capacity of about 2 Amp-hour to 3 amp-hour. The 4-cell carrier can be bought on eBay for about $2.50 The following 4-cell charger can be bought on eBay for about $3.50. This will charge the cells at about 70mA to 150mA and it will take about 24 hours to fully charge a depleted set of cells.  The charger below will charge a single cell at about 500mA to 700mA and connects to your USB port on a laptop. You can only charge one cell at a time with this arrangement. The 1 ohm resistor will discharge the cell quickly. The cell voltage must not go below a minimum voltage of 2.8v. You need to place a voltmeter across the resistor while discharging to make sure you do not discharge the cell below its recommended minimum.  The module in the photo charges the cell quite quickly and at 4.2v the cell is charged to 90% (or more) and the circuit turns OFF. You must use a charger that turns OFF when the cell is charged as this type of cell cannot be left charging on a "trickle charger" as the cell will produce internal "whiskers" and it will get damaged. More details of the project shown above can be found HERE.  It describes a 1 amp adjustable POWER SUPPLY that can be used to power your locos or as a BENCH POWER SUPPLY for all your testing.  18650 BATTERY CAPACITY This simple circuit tests the capacity of a 18650 cell. Connect the circuit to the terminals of a clock mechanism and fit a fully charged rechargeable cell. Set the hands to 12 O'Clock and the clock will let you know how long the cell lasted until the voltage reached about 2.4v. Now fit another cell and see how long it lasts. You cannot work out the exact capacity of a cell but you can compare one cell with another. The initial current is about 450mA. BATTERY CAPACITY TESTER TEST FAKE CELLS !! This circuit tests the capacity of a rechargeable cell. Lots of cells are FAKE. Just like the UltraFire cell below. It weights 30gms !! You cannot get 6amp-hr capacity into 30gms!! But what is the capacity of the cell?  Our cell had less than 0.5 amp-hr. Use this tester to find out: The resistors and diodes are simply easy-to-get components that make up a load to discharge the cell at about 600mA. This is a load of about 2.4watts and the resistors and diodes add up to a capability to dissipate 2.5 watts. The voltage of the cell drops from 4v to 2v and the current drops too. You can measure the voltage across the resistors and work out the current-flow. Don't fit an ammeter as the voltage -drops across it will reduce the current considerably. Don't use jumper leads as they drop about 350mV !! You can use any component(s) for the load, provided they don't get too hot. The buzzer starts to buzz when the voltage drops to 2v. You will need to adjust the value of the biasing resistors to reproduce this value if you are using a different transistor as the detection voltage can change by as much as 200mV with different makes of BC547.   Our cell lasted less than 2 hours and was obviously FAKE. Some cells have a much smaller  cell inside and that's why they weight only 28grams !! CHARGING A CELL A Li-Ion cell must be charged on a charger that cuts off when the voltage reaches about 4.2v. If you charge a cell from a variable power supply and do not monitor the terminal voltage of the cell, it will rise to over 5.5v and get damaged. CURRENT How much current do you need?  That is: how many AMPS do you need? A small loco takes 300mA to 600mA and you need a 1AMP supply to make sure the necessary current can be supplied as the motor will take 800mA to 900mA when starting and accelerating and when hauling a number of coaches. For a DC layout, you will generally only be running one loco at a time and a 1-Amp supply will be sufficient. The current values mentioned above apply when the supply is 12v. If the supply drops to say 10v, the current will be less and if the supply increases to 14v, the current will increase by a considerable amount (when the same motor is connected). It is impossible to state the actual values because the current taken by a motor increases and decreases due to the load and this load is not only the velocity of the train, but the acceleration and inclination of the track and also the rpm of the motor (as it takes more energy to rotate at higher rpm) and lots more current when the motor is "loaded." AC TO DC Before we finish, there is a bit of theory that needs to be understood. We have mentioned the AC voltage and DC voltage on (or for) many of the projects. The two values are a little bit different and you may be wondering why. The technical reason is this: When you deliver 10v AC to a circuit that has diodes and capacitors (electrolytics) that convert the voltage to DC, the output is 40% higher than "10" because the 10v AC is actually 14v at the instant when the voltage is rising to a maximum and the capacitors get charged to this value.  There is a loss of about 1.5v across the diodes in the circuit and the output becomes 12.5v Quite often the manufacturer of the 10v AC transformer will add a few extra turns and the voltage will be 13v AC (under no load).  This is done because the output drops when full current is delivered (because the transformer is very poor quality) and this will ensure the output never goes below 10v AC. It drops from 13v to 10v - under full load. However the 13v AC will produce 18.2v AC minus 1.5v = 16.7v DC when unloaded and if you deliver more than 13v AC, the resulting unloaded voltage may be too high for some of the electronic components - especially IC's. CONCLUSION You need to buy or make 2 POWER SUPPLIES: 15v to 17v  @ 1 amp POWER SUPPLY for a throttle (to drive a loco - suitable for 1 or 2 locos). 24v POWER SUPPLY for a Capacitor Discharge Unit. (less than 100mA needed) Cost will less than $15.00 for up to 4 Plug Packs. (see above for details of the Plug Packs you need to buy. If you build a Bench Power Supply (see Power Supply MkII) you will have an adjustable output voltage (0v to 12v DC) and you will be able to limit the current (from 30mA to 1 amp) so the project you are testing will not be damaged. When you have the 2 Power Supplies, you can decide on the Capacitor Discharge Units and the Throttle module. Under NO circumstances should you build a power supply with soldered wires or bare joints or bare leads going to the mains or any wiring with bare MAINS connections. One day a child may come and play with your equipment and touch exposed wires and get thrown across the room. Always use Plug Packs (Wall Warts) or Power Supplies in a professional case. They are called "double insulated" and that means they do not have an earth lead. It also infers they do not have a metal case and this makes them extremely safe.   CAPACITOR-INPUT POWER SUPPLIES You may find instructions or a circuit on the web for a CAPACITOR-INPUT POWER SUPPLY. This is a power supply with just a single or even 2 capacitors connected to the mains, followed by a bridge and an electrolytic. There is no transformer in this type of power supply and although you think the capacitor separates the mains from the 12v output, IT DOES NOT. It does reduce the voltage of the mains to say 12v DC after the bridge, but if you touch either of the output wires and a water tap or kettle or toaster, you will get a jolt of 240v AC and although the current may be less than 100mA, you only need 15mA to kill you. It's the duration of the electric shock that is finally fatal and if you are under a railway layout and cannot remove your hand fast enough, you will get fried. Another point to remember. This has NEVER been mentioned before. The output of a cap-fed power supply is only 12v when the diode bridge and 12v zener is connected. If any of these wires are cut, the "12v section" becomes 336 volts !! The 12v zener is called the LOAD and when you connect your project to this power supply, the current passing through the zener is now diverted from the zener and to your project. But if the zener "blows up" and then your project "blows up" you will have 336volts on your project. This type of power supply is illegal in many countries and hopefully you will never see one. BUT this comment is to inform you: NOT TO BUILD A CAPACITOR-INPUT POWER SUPPLY.             ooooooooooooooooooooo0000000000000000000000000oooooooooooooooo BOOST CONVERTER Finally we have a module that will answer a lot of your problems. It is a DC to DC converter that converts a low voltage DC to a higher voltage DC. Commonly called a BOOST CONVERTER.  (A converter that converts a high voltage DC to a low voltage DC is called a BUCK CONVERTER). All our Capacitor Discharge Units now come with a Boost Converter module connected to the input terminals of the CDU module. Here is an example: The input wires (on the right) will accept a DC voltage from 5v to 20v DC (from a plug pack or wall wort) and produce an output voltage that has been adjusted by the 10-turn pot. We set the output voltage to 26.5v so the electrolytics on the CDU module see a voltage of 25v (after the input diodes). This has now solved all our problems of getting the right voltage for the CDU modules so they produce the full output. The boost module can deliver up to 2 amps and this means the CDU module will charge very quickly (if required).  However any plug pack can be used and even a 200mA plug pack @ 5v  will charge the module in less than a few seconds. The speed of charge (recovery) will depend on the voltage and current capability of the plug pack and the number of electrolytics on the module and the microfarad value of each electrolytic.

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POINT MOTORS Here are 4 common POINT MOTORS. They can be connected to our CDU Modules to produce fast switching of the rails and at the same time the CDU Module prevents the solenoids getting hot or warm.

CHAPTER THREE THE POINT Controlling a SOLENOID point using a CDU module This is PART "B"  of our discussion on controlling a point. This part uses a Capacitor Discharge circuit to control a solenoid on your point to prevent it "burning out." You must read all of this discussion as some modules can be wired to operate many points (one after the other) while some modules can only be connected to ONE POINT. Talking Electronics is gradually phasing-out all the older modules and concentrating on those with indicator LEDs and the modules that also activate a 2-Aspect signal. This has been done because we now supply a pre-voltage module with all CDU's so you can connect any voltage from 9v to 20v and the CDU will get 25.5v from the pre-voltage module.  This means the CDU modules will operate at maximum output and if you have a delicate point motor, you can reduce the voltage from the pre-voltage module to get the action you want. The new designs also have a front panel so you can mount 2 or more Capacitor Discharge Units on your console and have visual indication of the position of each point. The CDU modules are designed to activate a solenoid point-motor, but if you have a manual point, Talking Electronics has a number of activation devices to operate the point. These come in the form of a small servo or a miniature servo that can be placed on the top of your layout or on the under-side.   These servos can operate quickly or slowly, depending on the electronics module you purchase. We also have linear-actuator versions for HO  and Z-scale layouts. The whole range of requirements has been covered and you need to enquire before buying. [Here is the module to operate a KATO point motor.] (see PART "A" to control a point with a motor) The most common type of point motor is a solenoid that moves the rails from one position to the other. It is also called  a TURN-OUT MOTOR: This is s PL-11 Point Motor Here is the inside of a PL-11 POINT MOTOR. It must be activated for less than 1 second.  It was activated for 4 seconds and it MELTED !! The plastic core melted and bubbled through the coil and the activating rod is FROZEN. That's what this article is all about. If you add a CDU module to activate these POINT MOTORS they will not get damaged.   PECO PL-10 or PL-34 POINT MOTOR and the 3 wires needed to activate the two solenoids. They are called PULL SOLENOIDS because the core is not a magnet. (it is called an ARMATURE) The SOLENOID Point Motor consists of two coils of wire that alternately pull a metal rod into the middle of the solenoid and at the same time change the position of the point. It is also called a double-acting solenoid because it will both PUSH and PULL. The "core" or "plunger" is not a magnet and it will only PULL into a CORE. A core is a coil of wire and it is also called a solenoid. The solenoid will accept AC or DC and it can also be called an ELECTROMAGNET. Because an electromagnet only "pulls," you need two to produce PUSH and PULL motion.  It is really PULL-PULL motion. The core only PULLS into a solenoid. (When the core is a magnet, you can get push-pull action with a single winding) But because the core in the solenoid point motor is classified as a SOFT IRON CORE,  you need 2 coils. But the problem is the coils have very low resistance. The resistance of the coil is about 4.5 ohms for some types and 11 ohms for others and when connected to 12v, the current will be nearly 1 to 3 amps. They must only be activated for less than half a second and if the 12v is connected for more than 10 seconds, the plastic case will start to smell and melt. In a few more seconds the solenoid will be completely damaged. The photo above was damaged in 4 seconds !! To prevent this from occurring, you need an electronic module that delivers the current for a very short period of time (so that nothing gets warm). This module is called a CAPACITOR DISCHARGE UNIT and it contains 2 or more 1,000u (or 2,200u or 4,700u) electrolytic capacitors that deliver the required energy. These capacitors get charged slowly and when they are fully charged, you can press a switch and operate the point. It does not matter how long you hold the switch because the capacitors are drained in less than a second. If you operate some of the solenoid point motors DIRECTLY from the 12v train supply or the 16v AC supply from the train transformer, some  will take more than 3 amps and produce a more than 30 watts of heat.  This is equal to a small soldering iron and it will quickly melt the plastic case. If you already have a PASSING SWITCH or a "spring return toggle switch" with a centre-off position, it will work perfectly, but if you have visitors working the control panel, they may leave the switch ON or change it very slowly and it can cause the solenoid to heat up. To prevent any of these catastrophes, we have designed a number of CDU - CAPACITOR DISCHARGE UNITS to operate the points safely. These CDU modules are connected between the PASSING SWITCH and the power supply to give you double protection. So, it's: POWER SUPPLY, CDU MODULE, PASSING SWITCH, POINT. PRE-VOLTAGE MODULE  - see the new version (dual) for $18.00 After 20 years of selling CDU modules, we found a pre-voltage module in the form of a BOOST MODULE that will convert any voltage from 3v DC to an output of 27v DC. This has changed our range of CDU modules enormously. The photo shows the pre-voltage module connected to CDU Module MkIIB however it can be connected to ALL our modules to make them operate at full output, no matter what voltage power supply you are using. Previously it was very difficult to get 16v to 24v supplies but now the problem is solved. You can ask for the pre-voltage module for any of the CDU modules you have already purchased. The output voltage of the pre-voltage module is increased when the screw of the 10-turn put is rotated ANTICLOCKWISE and and you have to keep turning and turning and turning the screw as the voltage only increases when the wiper inside the case is very very near the end of its travel. You need to monitor the output voltage as it will increase to 40v from some modules and this is too high for the electrolytics in the CDU module.   STRENGTH OF A CDU Here's a way to understand the "strength" of a CDU. It's only an approximate comparison, but it will help you. We take the simplest CDU with 2 x 1,000u electrolytics and charge them to 25v. We say this will operate ONE POINT. If we have 2 x 1,000u electrolytics and charge them to 35v, we can operate TWO POINTS at the same time. This is because the voltage has increased from 25v to 35v and the voltage plays a BIG part in producing the energy.  If we have 2 x 2,200u and charge them to 25v, we can operate TWO POINTS at the same time. If we have 2 x 2,200u and charge them to 35v, we can operate FOUR POINTS at the same time. If we have 1 x 4,700u and charge it to 25v, we can operate FOUR POINTS at the same time. If you have an old-style point, it can require more energy than a new style. And N-gauge points may require less energy than HO-points. It is not wise to operate 3 or more points at the same time from a single supply-line (from a CDU) as there is nothing in the system to share the energy equally. It may work, simply because you are over-supplying the energy. Here's another way to understand the energy stored in an electrolytic - especially in a CDU Module. If we charge 1,000u to 25v, we can say the energy stored is ONE UNIT OF ENERGY. If we charge 1,000u to 35v, we can say the energy stored is THREE UNITS OF ENERGY. If we charge 2,200u to 25v, we can say the energy stored is THREE UNITS OF ENERGY. If we charge 2,200u to 35v, we can say the energy stored is FIVE UNITS OF ENERGY. If we charge 4,700u to 25v, we can say the energy stored is SIX UNITS OF ENERGY. If we charge 4,700u to 35v, we can say the energy stored is ELEVEN UNITS OF ENERGY. REDUCING THE ENERGY If the point "bangs too hard," the energy from the CDU can be decreased by reducing the voltage. You can use a lower voltage supply. If you are using AC, the voltage on the capacitors will be about 40% more than the AC reading of the supply you are using. This is because the AC voltage is rising and falling and the CDU detects the "top of the wave" whereas the multimeter reading is a value below the top of the wave. And the CDU charges the capacitors to the peak voltage produced by the AC. If you add a diode between the wire going to the positive terminal of the CDU and the actual positive terminal of the CDU, the voltage will be reduced by 0.7v. The cathode of the diode must be connected to the positive of the CDU. Keep adding diodes in series and after about 5 diodes it will start to have an effect.  If the voltage is AC, the voltage will reduce by about 1v per diode. OVER-VOLTAGE Capacitor Discharge Units (CDU's) contain electrolytics with a high capacitance and it is important NOT to charge them to a voltage higher than the VOLTAGE RATING on the component. For instance, a 4,700u 25v electrolytic should not be charged to a voltage higher than 27v.  And a 1,000u 35v electrolytic should not be charged to a voltage higher than 38v. A customer charged a 1,000u 25v to 42v and it got very hot !!!!   I had to replace it as it started to leak internally and continued to get hot, even at 25v. So, it was permanently damaged. When you connect a CDU to a power supply, take a reading of the output voltage as this will be the voltage across the electrolytics and do not exceed the voltages I have suggested above. If the end-cap is bulging and not FLAT, is has been overheated and may leak or explode at any time. If it gets hot, even if the rated voltage is across it, the electrolytic is leaking internally and may explode. An electrolytic in our modules should remain cold at all times. Using a DC supply (such as from a wall wort or plug pack) is the easiest way to deliver the right voltage. You can get 24v 1 amp wall worts on eBay for less than $5.00 delivered and this will give you 23v to 24v on the electrolytics. Some CDU's have voltage doubling on the AC input terminals and a voltage as low as 12v AC will produce up to 40v DC on the electrolytics because the 12v AC can be 15vAC on no load and when this is doubled and converted to DC it will become as high as 40vDC. This is too high for any of our electrolytics. That's why the CDU specifies 8v to 12v AC as this will produce 22vDC to 34vDC. Our CDU's put virtually no load on a power supply and this definitely occurs when the CDU is fully charged and thus the power supply will deliver it no-load voltage and the electrolytics will be charged to a maximum.   THE SIZE OF WIRE The size of the conductors in the wring to a point-motor is not very critical. You can buy light-duty, medium-duty and heavy duty hook-up wire. The resistance of these will be different but it will not affect the operation of a point. A point motor may be 3-4 ohms resistance and the wiring may be less than 0.5 ohms and the point motor will get less energy. But the reduction will not be noticeable.  The reason why we have three different gauges of hook-up wire is this: The thickness of any type of wire and wiring is worked out when a constant current is flowing for a long period of time. This current will gradually increase the temperature of the wire and it must not get too hot. A point motor may take 3 amps and when delivered via a 1 amp light-duty cable, the operation will be so short that the wire will not have time to heat-up. Thick wires and leads are only needed when supplying current to the track when you are driving a train for a few minutes or longer.    Gauge is not important for short-term currents. TYPES OF CDU's We have designed more than 15 different CDU modules to cater for hobbyists requiring to operate new or old points and also KATO points. Every new model is cheaper to keep the customers happy and offer different mounting features. They also cover AC and DC supply-lines and a whole range of voltages. They all do exactly the same job when you compare the total capacitance and the operating voltage of 25v or 35v.  It's just the CDU's with higher capacitance will operate larger point motors and will drive 2 or 3 at the same time. HOW THE 'ENERGY' WORKS A CDU delivers ENERGY to a point motor. A Point Motor is a SOLENOID and it can be called an ELECTROMAGNET and is similar to the crane that picks up scrap metal via an electromagnet and delivers it to a ship at the dock to take overseas for re-manufacture. But an electrolytic is not like a battery. A battery delivers a high voltage and a high current for a considerable period of time at the beginning, when it is full charged. And its fully-charged voltage remains high for a reasonably long period of time. An electrolytic delivers a high voltage and high current for a very short period of time. And this applies to our CDU projects. That's because it stores only 1/1,000th the energy of a battery. And just about all this energy is released in less than one second. So we have to take this into consideration. A point motor takes time to move from one position to the other. During this time the voltage delivered by the electrolytics will fall and the current will decrease. If the voltage drops too much before the point reaches the other position, it will no travel the full distance. This can be fixed by increasing the voltage to the maximum of the electrolytics or adding more electros. You need to listen to the "click" "click" of the point before fitting the CDU and maintain the same sound. The aim is to get the point to "click" and stay in the position via what we call a "toggle mechanism" or "over-centre cam" where the armature of the solenoid keeps a very small amount of pressure on the point so the loco is not derailed. This is one of the features built into the actuating arm of the point - from the actuator to the rails that change the position of the point. Too much capacitance can cause the armature to bounce away from the end position and too little capacitance can prevent the armature reaching the end of its travel.  That's why you have to match the capability of the CDU with the point. oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 8:   - see the new version (dual) for $18.00 The simplest and cheapest CAPACITOR DISCHARGE UNIT MkIIB is shown in the following image:  CDU MkIIBM  $14.50 plus $6.50  (BM means built and tested - made up) Click  Here to order. This is CDU MkIIBM  $14.50 plus $6.50   fully assembled The screw terminals make it easy to fit to your layout. Here are the connections to the Power Supply and point: The two push switches in the wiring diagram above are also shown in the two following diagrams: The PECO Passing switch only makes contact when the red lever touches and pushes the contact. This occurs when the lever is in the  "12 O'Clock" position and you must move it past this position to prevent the point motor "burning-out." The green wire is called the COMMON A single CDU can be used to operate 2 or more point motors provided you allow a few seconds been each activation, for the CDU to re-charge. Our CDU module fits between the Power Supply and the switch or switches to a SOLENOID POINT MOTOR. It is designed to deliver a short pulse of energy to the solenoid to change the position of the point. A Passing Switch will deliver a pulse of energy but if it gets stuck in the mid-position, our CDU will prevent the point motor "burning out." If you do not include a Capacitor Discharge Unit, and you activate any type of switch for more than 10 seconds, the flow of current will heat up the solenoid and "burn it out." The CDU prevents this. To go over it again, the CDU module can be used with a PECO PASSING SWITCH so that if the lever is moved too slowly or kept at "12 O'clock" too long, the CDU will only allow a short pulse of energy. And you have double protection !!  CAPACITOR DISCHARGE UNIT MkII - MODIFICATION If your transformer does not supply 15vAC to 16vAC, you can increase the input voltage by adding a 100u to 220u electrolytic and 1N4004 diode to the input to create a voltage doubling arrangement. You can also change one or both the 1,000u electrolytics for 2,200u. This will deliver a much larger pulse to the point-motor and guarantee operation. By adding one power diode and 220u electrolytic, the 16v AC input will be "doubled."  You need to ask for 35v electrolytics before you do this as the final voltage on them will be very close to 30v to 35v DC If you ask for 35v electrolytics, you can supply the module with 35v from one or two plug packs. You cannot get a single 35v plug pack but you can get 12v and 24v  or use 3 x 12v plug packs. Here is the authors solution to providing 36v: The image shows a 24v plug pack and 12v plug pack from this supplier: https://www.aliexpress.com/item/33019625426.html?spm=a2g0s.12269583.0.0.20bf3cb13mMIx6 Universal EU US Plug Switching Adapter AC 220V-240V To 5 V 12 V 24V Volt Power Supply DC 5V 12V 24V 1A 2A 3A 5A Power Adapter Output Voltage 12v   Current 1A   $2.30 Universal EU US Plug Switching Adapter AC 220V-240V To 5 V 12 V 24V Volt Power Supply DC 5V 12V 24V 1A 2A 3A 5A Power Adapter   Output Voltage 24v US Plug  Current 1A   $3.60 The adapter costs less than $1.00 (you need 2) and you need to order the type to suit your wall socket: https://www.aliexpress.com/item/32842341038.html?spm=a2g0s.9042311.0.0.27424c4d2OjUuW This gives you a 36v supply for less than $10.00  You just need to wire the outputs in series. If one of the plug packs does not turn on when connected to a Capacitor Discharge Unit, it will be due to the high in-rush current being detected by the over-load section. The answer is to add a 22 ohm or 27 ohm resistor in series. This will limit the current to 1 amp and the resistor will not get warm because the current reduces to a very small value within 5 seconds. oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 8A:  This module replaces Choice Number 8 above.   It incorporates a pre-voltage module, a high-value of capacitance and two CDU units on the same Printed Circuit Board. CDU MkIIB- dual  $18.00 plus $6.50  Click  Here to order. It has a front panel with four 2mm x 7.5mm self tapping screws and toggle switches and combines everything you have wanted for $18.00 - fully built and tested.   The input should be between 9v and 20v DC. (It can be AC up to 15v AC as the module has a protection diode on the input.)  The input current has been limited to 1amp (via 10R and 18R hidden resistors) for a very short period of time at the beginning of charging to prevent damage to the pre-voltage module. The pre-voltage module produces 25.5v and you should not touch the screw on the 10-turn pot. If you increase the voltage 27v, the module fails and dies. If you want to DECREASE THE VOLTAGE - turn the screw CLOCKWISE.  Yes Clockwise - this is a CHINESE Module!! This will reduce the impact (activation) of the solenoids at each turnout on your layout but the 10-turn pot will not tell you the output voltage, so if you intend to increase the voltage after experimenting, you must put a multimeter on the output terminals of the pre-voltage module. The operation of the pot is not liner, so be careful. The advantage of this module:  you can reduce the voltage for "N-gauge" and Z-gauge" points.  OUR LATEST 4,700u CDU - with 2 CDU's on the board. Comes built with toggle switches (just standard switches without rubber grips) and a front panel with 4 screws.  oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 8B:    FOR 2-KATO POINTS CDU MkIIB- dual  $18.00 plus $6.50  Click  Here to order. You can use the CDU MkIIB - dual to operate KATO points by connecting the two outer screw terminals together and taking to the KATO point.  The middle terminal is then taken to the KATO point.  Here is a diagram to show how the voltage reverses from the CDU MKIIB - dual to allow this to work: To operate a KATO point connect the two outer screw terminals together and take to the KATO point.  The middle terminal is then taken to the KATO point. USING A PLUG PACK This "trick" is only for the following problem because it has unique problems. Some plug packs - switch-mode plug packs - also called adapters - have an inbuilt overload protection and when the current is higher than 1 amp (for a 1 amp adapter) it switches OFF and you have to turn OFF the adapter to reset it. If you connect this type of adapter to some of our CDU modules, the inrush current will be more than 1 amp and the adapter will fail to power the module. The solution is to add a 12 ohm (or 15 ohm) resistor to one of the leads and this will reduce the inrush current to less than 1 amp and the adapter will power the module. The resistor can be 0.25 watt or 0.5watt as the current will only be present for a very short period of time as the electros charge in about 1 second. CHOICE NUMBER 9: If you want to use a toggle switch and 2 LEDs to show the position of a point, this POINT MOTOR CONTROLLER Module offers these features. POINT MOTOR CONTROLLER  $13.50 plus $6.50 Click  Here to order. You can also buy the module fully built and tested with toggle switch on an extension lead for $20.50 plus $6.50 postage. Note: The common to the solenoid is fitted to the top screw terminal.  The amount of energy delivered to the solenoid depends on the voltage delivered to the module. For 12v DC supply, the solenoid will work very delicately and will be suitable for small solenoids used in "Z-scale." Supplying 16v AC will deliver FOUR times more energy and will be suitable for larger scales and can operate 2 points. The 100R resistor determines the amount of energy delivered. Increasing the 100R to 150R or 220R increasing the timing and thus the amount of energy delivered. See the full article: HERE oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 10: Talking Electronics has an In-line version that takes up less space on your console. This In-line CDU module has two LEDs that show the position of the point. It is fitted to your control panel and the LEDs show the position of a point. This very handy for a point that cannot be seen from the control area. The module is very slim and more than one can be placed side-by-side to control all the points in your layout. Each module is connected directly to a point. It is called CDU In-Line and costs $12.50  plus $6.50 postage. It is shown in the following image: Click  Here to order. The input voltage needs to be 12v to 16v AC or DC and you may need two adaptors in series to get this voltage. See Chapter 1 for the Plug Packs (or Choice Number 11). oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 11: For layouts that need 2 or more points changed at the same time, a larger version is available with 2 x 4700u electro's: It is CAPACITOR DISCHARGE UNIT MkIII  and is shown in the following image: CDU MkIII fully built and tested $16.50 plus $6.50 postage Click  Here to order. CDU MkIII fully built and tested $16.50 plus $6.50 postage Connecting CDU MkIII to 24v DC supply   Connecting CDU MkIII to 14v - 16v AC supply You can use the "accessories" output of a train transformer if it is DC (14v DC to 24v DC) or if the accessories output is AC (14v AC to 18v AC). The module has been tested up to 20v AC but it is best to keep to 18v AC max. If you use a 24v plug pack and 12v Plug pack, the voltage to the module will be too high and the zeners will get HOT. Here is a solution from Steve Galka: This principle applies to all CDU's but it does limit the "inrush current" and you can email me if you are adding a VOLTAGE DIVIDER to another project to see if any reduction in operation will occur. oooooooooooooo0000000000000000000000000000oooooooooooooooo A larger CDU is also available from Talking Electronics, to change up to 8 points at the same time: CHOICE NUMBER 12: It is CDU 18,000u Flat version (built and tested) and costs $18.50  plus $6.50 postage. It is shown in the following image: Click  Here to order.   Click  Here to order Module and switch module. CDU Module 18,000 fully built and tested $18.50  plus $6.50 postage  This Capacitor Discharge Unit is easy to connect to your layout with screw terminals. You need two push switches to change the position of the point. The LED on the board shows the electrolytics are charged. SPECIAL FEATURES Input voltage can be AC or DC. But you MUST use the correct set of terminals. It did not work for one customer because he connected DC to the AC terminals. There is a 100u electrolytic on the AC terminals and "it will not let the DC in."  The 100u is for a voltage-doubling network at the side of the board as shown in the image above.  Three sets of input terminals are provided. 8v to 12v AC 13v to 20v AC 12v to 30v DC The project comes with instructions for connecting to a plug pack (wall wart) plus information to connect two plug packs (in series) to get the required voltage. The CDU 18,000u has zener-diode regulation to prevent over-charging. If you supply a DC voltage above 25v, this voltage is called "OVERHEAD." It is voltage that is not needed by the module and will be "lost" in the resistors. However it will allow the module to charge quicker as it will supply current right up to the time when the electros are 99% charged. And then they will charge to a full 100% very quickly. If you supply 32v, for example, the electros will charge to 26.5v and the remaining 5.5v (slightly less than this) will be dropped across the 330R combination of 1k resistors to allow a "bleed current" of 16mA to flow. This will also flow through the zeners but nothing will get hot. However it will protect the electros from seeing a voltage of 32v as this will leak through the dielectric of the electros and they will heat up and explode. A Switch Module can be fitted to this CDU to activate the solenoid point and also show the position of the point via two LEDs:   The SWITCH MODULE (shown in the images above) connects to 18,000u CDU for $7.00  extra. This switch module shows the position of the point via two high bright LEDs and it controls (limits) the energy to a point to prevent the rails "bouncing back" due to too much energy being supplied. oooooooooooooo0000000000000000000000000000ooooooooooooooooo CHOICE NUMBER 13: A slimline version of CDU 18,000u is available from Talking Electronics, to change up to 8 points at the same time: It has the same capacity (4 x 4700u electrolytics - the same storage capacity as choice number 12) but only one input option: 15v AC.  It is CDU 18,000u Slimline and costs $19.00  plus $6.50 postage. It is shown in the following image: Click  Here to order.  Click  Here to order Module and switch module. oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 14: A NEW version off CDU 18,000u Slimline MkII has both AC input and DC input and you can decide which input to use. The DC input can be 12v DC to 16v DC and the AC input can be 15v AC from a train transformer. The circuit on the underside of the PC board DOUBLES the DC voltage and the chip has a maximum operating voltage of 18v. But we do not want to exceed 15.5v as the chip will be damaged if it sees more than 18v. The on-board zener regulator limits the voltage on the electro's to 25.5v  and 15.5v will deliver 25v, due to 5v losses in the circuitry.  CDU 18,000u Slimline MkII costs $19.50  plus $6.50 postage. It is shown in the following image: Click  Here to order. The DC input voltage for CDU 18,000u Slimline MkII must be 16v MAXIMUM and each module comes with a VOLTAGE REDUCER module so you can adjust the voltage on the module to 15.5v VOLTAGE REDUCER The VOLTAGE REDUCER MODULE consists of a 3-terminal block and 4 power diodes and screws into the 3-terminal block on the module. This is how the Voltage Reducer Module works:  Each diode reduces the incoming voltage by 0.75v, making a total of 3v. When you get CDU 18,000u Slimline - MkII, check the voltage of your power supply (before touching the module) and make sure it is less than 18v. The voltage reducer module only works for voltages: 16v, 17v and 18v. If it is 18v, connect the VOLTAGE REDUCER to CDU 18,000u Slimline - MkII as shown in the following image: If the input voltage is 17v, you can remove one of the diodes by soldering a link across one of the   diodes (to short it out), as shown in the following image: If  the input voltage is 16v you can remove 2 diodes and if it is 15v, you do not need the VOLTAGE REDUCER MODULE. If you want to deliver 15.5v DC to CDU 18,000u Slimline - MkII with two plug packs, here is the circuit: An easy way to get 15.5v for CDU 18,000u Slimline - MkII  is with two plug packs - 5v and 12v.   You can also use three 5v plug packs and you will find many of these in your parts-bin from old mobile phones !!!! A Switch Module can be fitted to this CDU to activate the solenoid point and also show the position of the point via two LEDs: The SWITCH MODULE (shown in the images above) connects to 18,000u SLIMLINE CDU for $7.00  extra. This switch module shows the position of the point via two high bright LEDs and it controls (limits) the energy to a point to prevent the rails "bouncing back" due to too much energy being supplied. oooooooooooooo0000000000000000000000000000oooooooooooooooo CHOICE NUMBER 15: 1,000u Capacitor Discharge Unit with SPDT Switch SLIM Click HERE  to buy. Fully built and tested for $10.60 plus $6.50 postage. We are constantly updating and improving and adding to our range of modules and this one combines three features at a LOWER COST -  amazing  !! The name: Capacitor Discharge Unit with SPDT Switch - SLIM has been chosen to identify it from all the other CDU modules made by Talking Electronics.  It combines a number of features with a clever circuit to allow a single 1,000u to be charged to 35v and produce sufficient energy to operate a point. It also has an on-board mini toggle switch and two indicator LEDs - this reduces your wiring. The circuit also includes a voltage doubling arrangement for 12vAC to 15v AC - (from a train power supply) and two indicator LEDs to show the position of the point. The mini toggle switch can be easily fitted to your console and small holes on each side of the switch used for the LEDs to shine through the console. All these features are in this narrow PC board so that a row of these modules can be aligned on a panel to show the position of the points. This module reduces your wiring considerably as only 3 wires are needed for each point and a common "bus" of positive and negative to the modules.     A close-up of the switch, showing the leads soldered to the tabs on the switch All the components fit on the PC board and the module comes with 2 x 1,000u electrolytics. The input can be 12vAC to 15vAC or 20vDC to 35vDC. You can make a 12v 24v or 36v supply very cheaply by using 24v and 12v plug packs. These are available on eBay for less than $10.00 (combined) including postage.     If you are making 36v, simply connect the leads as shown in the following diagram. Some of these plug packs have a current detecting overload circuit and "shut-down" if the current is more than 1 amp (even for a millisecond). To prevent this we add a 47 ohm resistor. This only applies when you are using the plug packs for our CDU modules (like this project) as the high current is only required for less than a second and then falls to a very small value.   The resistor will not get warm when used in this particular application.   Using an old Printer Power Supply You can use a discarded Printer Power supply for many of the CDU modules.  Make sure the electros are 35v. I have highlighted the voltage and the current capability (625mA) of this printer supply and it is ideal. You cannot use it on any of the throttle modules as the current is not very high but it is ideal for a CDU module as the current requirement is less than 100mA to charge the electros. There are lots of other power supplies from discarded electronic equipment and you just have check everything before you throw it out.  CHOICE NUMBER 15A: 2 MODULES This CDU now comes as 2-modules with a face place and 5 modules with a face plate. This module requires 25v supply and to get the required energy to change a point, the electrolytics are now 4,700u.     2 MODULES 1 - faceplate   $2.00 1 - power supply module  $5.50 first switch module $5.00 second switch module $5.00 Click  HERE to buy 2 MODULES fully built and tested: $19.50 Click  HERE to buy ooooooooooooooooooo000000000000000000000ooooooooooooo 5 MODULES CDU with output for 2-Aspect signals: This is the latest design with in-built control for 2-Aspect signals. The image shows the 3-wire connection Here is 20 CDU's installed by Kevin Dawson You can also fit 5 CDU modules to the Track Layout above The circuit for the activating part of the CDU module and the outputs for the 2-Aspect signals.  It needs the power-supply module for the CDU to work for both Siding and Main It will not work without the 4,700u power supply module This module comes with a pre-voltage module to make things easy for you. You just need a supply of  9v to 20v DC and the pre-voltage module will output 25.5v to the CDU modules.  Here is the second advantage. The output voltage of the pre-voltage module can be reduced by turning the screw on the 10-turn pot CLOCKWISE. (yes! Clockwise - the module is from China!! ) and this will reduce the energy to a delicate point motor.  Do not turn the screw anti-clockwise as this will output a very high voltage and damage EVERYTHING ! 5 MODULES 1 - faceplate   $3.50 1 - power supply module  $5.50 first switch module $5.00 second switch module $5.00 third switch module $5.00 fourth switch module $5.00 fifth switch module $5.00 Total: $34.00 Click  HERE to buy 5 MODULES fully built and tested: $39.50 Click  HERE to buy You can mount 2 or 5 modules "side-by-side" and use the face-plate shown in the photo below to connect them together and fit them to your console. Here's what you need: 1 - faceplate   $2.00 for 2 modules    $3.50 for 5 modules 1 - power supply module  $5.50 1 - switch module $5.00 1 - switch module $5.00 1 - switch module $5.00 1 - switch module $5.00 1 - switch module $5.00 You can operate 5 points for a total of $34.00 and that is less than $7 per point. The face-plate means there is no drilling needed and a simple cut-out in your console will allow the face plate to be added.  A new face-plate with track ID has been introduced: The 2-module face-plate costs $2.00 or 5-module face-plate $3.50 The circuit for the 5-Modules version has 2 x 4,700u electrolytics in the power supply section because the charging of the 2,200u (in the second part of the circuit shown above), when the switch is in the "MAIN" position, will take a lot of energy from the 4,700u in the power supply and the voltage across it will dip 50% (theoretically). When 5 modules are connected to the power supply, this will be passed to the other modules and affect the operation of the other points at a time when they should not be affected. To prevent this we have used two 4,700u electrolytics in the power supply. The voltage will theoretically drop 30% but the other points are not affected. When 5 modules are connected, the 1,000u in each module will reduce the "dip" considerably. One customer wanted to use a 2-leaded bi-polar LED.  Here is the modification: FITTING A BI-POLAR LED  Use 2 x 4k7 resistors and note the lower resistor fits into the holes identified for a LED. A jumper wire is needed to complete the mod. USING ATLAS #56 SWITCH At first inspection, this switch may not appear to be suitable. But here is the secret of its operation. When you slide the switch to the left or right NOTHING HAPPENS. You need to push the switch for 0.5seconds for it to make contact and the energy from the CDU changes the point. If you push the switch for more than 1 second, all the energy from the CDU will pass to the point in less than 1 second and the extended time of pressing will not damage anything. CHOICE NUMBER 16: CDU 4700u Slimline Buy a kit:  CDU 4700u Slimline $10.50 plus $5.50 post Fully assembled and tested This CDU (Capacitor Discharge Unit) module has been designed with voltage-doubling components so you can use the 12v DC or 15v AC terminals of your train power supply. It also has voltage regulating to prevent over-charging the electrolytic and an indicator LED to show when the electrolytic is fully charged. The 4,700u electrolytic is adequate for a single point and can be connected to two points at the  same time, if needed. You just need two push-buttons (switches) and twin flex (wire) to activate your solenoid point  (point motor).   The advantage of this module is the input voltage. It can be 12v to 16v DC or up to 15v AC and the circuitry will double the voltage CHOICE NUMBER 17:   Jim's CDU MkII Buy a kit:  Jim's CDU MkII $24.50 plus $6.50 post Fully assembled and tested: $30.50 plus $6.50 post This project combines a number of features from three of the projects we have previously designed for Model Railway Hobbyists.  It is available as a kit or fully built and tested. Now you can have 3 features in one module. The first feature is the power supply. This module connects to your track and you don't have to provide 15v AC or a higher voltage to charge the electrolytics. The module has an on-board charging and voltage generating section that accepts almost any voltage and charges the electrolytics to a maximum of 27v. The next feature is the variable voltage (or maximum voltage) for the electro's. You can reduce the voltage to as low as 13v for those solenoid points that do not need a large amount of energy for their activation. The third feature is the reed switch inputs. This allows the module to be used automatically to control a solenoid point so the point gets changed correctly when the train approaches from the other direction. And lastly, the kit comes with a TRACK-PICKOFF MkII connector that fits between the sleepers and connects to the rails with springy connectors.      THE CIRCUIT All the work is done with the microcontroller. The charging of the electro's - the timing to activate the solenoid and the detection of the reed switches. The rail voltage is passed to the project via a bridge and this allows AC, DC or DCC to be converted into DC and stored to a small extent in the first 100u. The 100u on the output of the 78L05 provides a small amount of reservoir for the micro and we are assuming the train will be moving most of the time to maintain supply for the micro. The micro drives a BC 338 transistor with short pulses to allow current to flow into (through) the inductor and produce magnetic flux. When the transistor turns OFF, the magnetic field collapses and produces a very high voltage spike. This spike passes through the high-speed 4004 diode and into the 4,700u electros. The spike is really about 50v but the energy in the spike is converted into charging current and the electros would charge to more the 40v. But they will explode if the voltage rises above 30v so the voltage on the electros is monitored by the 100k resistor and 10k pot. The PIC micro detects a HIGH when an input is 2.2v and the 10k pot can be adjusted produce a voltage from 13v to 27v. The project takes a very small amount of energy from the track during the charging process and this will not be noticed when powering a train around the layout. The indicator LEDs on pins 2 and 5 are output devices as GP2 and GP5 are constantly changed from input to output lines. They normally illuminate one of the LEDs, but every 100mS, the program converts the lines to input to detect if a reed switch has been activated.   When they are input lines, we want them to have 0v on them and the 10k resistors across the LEDs provide this feature. Without the 10k resistors, the impedance of the LEDs is very high and the input lines can "float" and if a white LED is used as an indicator, this "float" voltage can be as high as 3.3v. The micro sees any voltage above 2.2v as a HIGH and the circuit would not work correctly. If a reed switch is activated, the line will be HIGH and the program will respond accordingly.