# BUILD a converter to convert AC to DC



## nemo (Aug 20, 2011)

Any body have instructions and a parts list on building 120volt ac to 12 volt DC


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## T-Man (May 16, 2008)

Yes we do!


First you start with a transformer then use parts to convert to DC and then get a voltage.

If you want 12 volts you will need a transformer of at least 14 volts AC becuse you get avoltage drop. 16 would be better. I think Radio Shack sell one, A 12 volt DC one. That's probably the best bet. One member uses it, I just remember while looking up my old thread.
ANyway you can go shop or look at this thread. The shopping part will be cheeper to do.


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## NIMT (Jan 6, 2011)

Do you want fixed voltage or variable?
And more importantly what amperage?


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## gunrunnerjohn (Nov 10, 2010)

My plan is simple, 120V -> 12V transformer, bridge rectifier, a couple of electrolytic caps, and a three terminal regulator. If you want variable voltage, you can get 3 amps from the LM317 regulator in the TO-3 package. For fixed voltages, the TO-3 fixed regulators are a bit simpler.

For variable voltage, I use a potentiometer with the LM317. I have a bench supply I built that way about 35 years ago, still working today. I did have to give it a new LM317 regulator a few years ago, too many coils providing inductive kickback killed the old one. Now I have a 36 volt TVS across the output to protect the regulator.


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## T-Man (May 16, 2008)

I understood everything except the "TVS"? 
I have never done the variable voltage, with a pot, it's interesting.

Did we scare him away?


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## gunrunnerjohn (Nov 10, 2010)

TVS is a transient suppression diode. I put them in all my TMCC locomotives to protect against spikes.

Here's the TVS Diode I use for trains.

The LM317 and LM338 are variable voltage regulators that just require a pot to vary the voltage, very handy.


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## T-Man (May 16, 2008)

Ah Yes, you used on with the strip lighting in the coach.


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## gunrunnerjohn (Nov 10, 2010)

I keep the little TO-92 ones around for use wherever I need a regulated voltage. 

I'm trying to get my latest lighting control board finalized and I'll have some new build pictures.


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## NIMT (Jan 6, 2011)

You two do know your scareing the kids like TJ, Reckers and Big ed with the grown up tech talk!


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## T-Man (May 16, 2008)

Yeah it's habit forming. This fall I have reviewing electronic notes and past projects. So I'm up on the conversation for once.


Nemo, if you are still with us! The easiest way with out any modifications is to use a wall wart with a DC output. Try a charity shop or yardsale and get em for a buck. It would cost about 15 buck s worth of parts from a Radio Shack.


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## tankist (Jun 11, 2009)

nemo said:


> Any body have instructions and a parts list on building 120volt ac to 12 volt DC


while building might be fun, why not just go with ready solution - old power-brick? i bet you can get one from ebay nearly at cost of parts. and then bunch of stuff are given away on craiglist. and i guess it is a funny coincidence , as i was walking with kid around neighborhood i spotted a electric massager (the one you put on a chair) at curb. and the power brick it has is exactly 12 volts.
moral of the story: look around before spending any money


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## gunrunnerjohn (Nov 10, 2010)

This is why every time something dies that uses a power brick, the brick gets tossed into my "brick box". I've had many occasions where someone (or even me) needed a brick, and I usually have one that will work. Many times I have to lop off the connector and steal the proper one from another brick and splice the wires. There must be at least half a dozen reclaimed bricks in service here any any given time.


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