# Renew an Old Power Supply



## T-Man

This supply has 20 volts AC and 12 volts DC at 4 Amps. The DC didn't work and blew my amp for the Diesel Horn Project. So I had to regroup and work the Power Supply. I replaced the old rectifier with a new itegrated circuit and with a 12 volt chip and two capacitors I created my 12 volt DC power source.I was getting 18 volts with just the bridge rectifier. I could of used some larger diodes to bring the voltage down to 16 volts and use it to throttle engines but that is another project and I needed a good 12 volt DC supply.








The circuit is fed from the bridge rectifier from the left and out on the right to the terminal strip.








I used RTV to hold the circuit board on a foam board.








Parts
Bridge Rectifier 276-1146 4 amps and 50 volts
7812 12 volt DC regulator 1 amp 276-1771
100 micro farad capacitor 272-1028
1000 micro farad capacitor 272-1032
This is a Kalmbach Book Project "Easy to Build Electronic Projects for Model Railroaders", By Peter Thorne 1988
page 9

I don't use mine a lot but to place a load on the transformer a heat sink for the regulator is reccommended. Just a piece of metal to distrubute the heat.
DOn't forget the heat sink.


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## stream4ever

Nice hope it works.


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## T-Man

*Of Course*

 
Yes it does. I get 12.6 DC volts off the terminals and 20 Volts AC off the other. I am in good shape. My regulator is rated at only 1 amp but since it runs only momentary and not constantly I should be fine. The box also has a power switch and an old circuit breaker. It does power my diesel horn project. It still sounds sick.hwell:
I need to check out two more things. I need a heat sink for my 12 volt regulator.A metal strip will do fine. I am not sure how hot it gets. In general I use old transformers and I need to update or install new circuit protection. I have read that the old Lionel circuit breakers should be replaced and upgraded.
I am also ready to start my auto reverse circuit for a HO trolley. Sure you can buy one but they are easy to make. We have had questions on them before. I just can't resist the challenge.
This is my way of mixing the old and new. I started with LEDs,flashers, a 5 volt power supply to run the flasher of the track, and now making the 12 volt power supply.That reminds me this only powers my testing. I had a large transformer and was limited by the voltage regulator capacity of 1 amp. For more power you start with a smaller voltage transformer 12 to 16 and with the bridge rectifier the voltage will drop. So it all depends on the specifcations of the components used.
I let an opportunity pass at the last train show. I saw a very old dual transformer. The little voices said "BUY IT" but I didn't.:lol_hitting:
One of my books had the method to upgrade it with a transistorised throttle.
The picture of the transformer was in the book.My little voices remembered but I didn't at the time.hwell:


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## stream4ever

Nice did you say you can make a HO trolley?


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## T-Man

Not exactly, a circuit to reverse the trolley on a line to go back and forth automatically. It is not part of the Trolley. It's a timer with a relay.


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## stream4ever

oo ok


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## T-Man

*Easy as Pi (3.141592)*

I have started it and will post it when completed and working LOL.
I installed a part backwards. So ar I have had three mistakes.



This later thread is about converting AC to DC with a transformer.


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## stream4ever

Good luck cant wait to see it.


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