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Reply to "Accessory DC Power Supply"

For DC to run LED lights you probably have a load of sources laying around the house. Any AC adaptor from defunct electronics like cell phone/computer power supplies can provide lots of DC. They run in various voltage/amperage ratings. I've been collecting 12 VDC units. Then you need to determine if the LEDs in the signals are current protected or not. If they are, you may be able to power them directly from the power supply. If not, you can go two ways. You can put a current limiting resistor in series with the negative lead. The value is determined by the number of LEDs in series and the applied voltage. In other words, there's a different resistor value for each voltage and LED quantity.

The other way to go which I'm doing now is to use a CL2N3 LED driver chip. They're cheap (about $0.25 each). And they're sort of magic. Most LEDs can handle only 20 milliamps. (0.020 amps). Anything over that and they go "POOF" really quickly. With the CL2, you can apply any DC voltage from 5 to 90 volts and out the other end comes 20 milliamps. That's it. The number of LEDs you can string in series is dependent on your supply voltage. Each LED drops  around 3 volts. So with a 6 volt supply you can string 2 in series before they would start getting dim. If you have a 90 VDC supply you can string 30 of them in series with the same CL2 chip modulating the current.

The lead on the right goes to your supply. The lead on the left goes to the LEDs. The center lead isn't connected to anything, but provides extra support if you're soldering it to a circuit board.

Screen Shot 2021-03-02 at 6.40.03 PM

Armed with a CL2 and a surplus electronic power supply you can run lots of LEDs. If you have a 1 amp power supply, you can power 50 LEDs when they draw 20 milliamps. Lately, due to running more and more building with LED lights, I've been buying these nice 12 VDC dedicated supplies. At 30 watts, it can run tons of LEDs.

Screen Shot 2021-03-02 at 6.44.11 PM

Old laptop power adaptors have pretty good outputs and can be used to drive LEDs on train layouts. I've found that Apple power adaptors don't work, or don't seem to. There seems to be a circuit that prevents them from providing power when not hooked up to the Apple charging circuit, but I may be wrong. I've used PC laptop power supplies with no problems whatsoever.

I bought some Chinese LED street lights and they are unprotected LEDs and needed current limiting. They had very fine-gauge leads and I didn't want to solder them below the layout, but the hole 3/32" was too small to put on my crimped ferrules and getting them through the hole to the underworld. Instead I built little circuit modules that have input and output Euro-style terminal blocks and a CL2 N3 driver chip between the positive lead in and out terminals. I put double-sided servo tape on the block and just stick them under the layout where the light leads come through. These are over-engineered to facilitate using stuff I had lying around, namely those Euro-style connection blocks left over from my layout initial construction in Germany. This was my first version. I stopped trying to use insulated wires and went to heavy gauge solid conductors without insulation since they weren't ever to come in contact with each other or other conductors.

Street Light Power Start

This is how I soldered the later versions. I used the adhesive copper foil as a soldering base. I just bent the conductors 90 degrees and used my resistance soldering unit to apply the solder. The middle CL2 lead is just crimped below to help support the chip.

Street Light Power Final

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  • Screen Shot 2021-03-02 at 6.40.03 PM
  • Screen Shot 2021-03-02 at 6.44.11 PM
  • Street Light Power Start
  • Street Light Power Final
Last edited by Trainman2001

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