# Regulator AC or DC



## Patrick1544 (Apr 27, 2013)

Hi

I am interested to know if the MC7812 voltage regulator or any other similar regulator is designed only for DC voltage or can I use it with an 18Volt AC constant input. The 7812 will cut the input down and output 12 volts.

Thanks


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## rkenney (Aug 10, 2013)

DC only.

It would be easier to get a 12v transformer than try to regulate 18v down to 12v.

On the other hand if you have a constant load you need the 12 v for you could put something in series with the load to achieve the 12v.


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## Patrick1544 (Apr 27, 2013)

Im thinking about cutting down the voltage in a Passenger car light, so that the constant 18VAC on the track for TMCC use, wont blow the bulbs out. They are Lionel Passenger cars and use a 14 volt bulb. Guess I could use resistor to achieve this, also.


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## Hutch (Dec 19, 2012)

all you need is a bridge rectifier


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## Patrick1544 (Apr 27, 2013)

OK. Ill look for a rectifier with with the ratings I need. Thanks


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## gunrunnerjohn (Nov 10, 2010)

Actually, if you want to cut the voltage to the bulbs in a passenger car, it's as simple as a single diode. It'll run them at roughly half the voltage of the track voltage. The bridge rectifier is overkill and not necessary.

A 1A diode is all you need for each passenger car, they're very common. 1N4001 through 1N4005 are common types, typically available for a few cents each.

A resistor is the WRONG way to do this, as you'd have a pretty large resistor getting quite warm in the car.

Of course, a much better way is to convert them to LED's, they don't use any significant power and you can make them totally flicker-free quite simply.


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## Patrick1544 (Apr 27, 2013)

I do have some 1N5402 diodes. Ill try that. The diode dropped the 18VAC down to 10VAC. Just about the right brightness I"m looking for. Now, Is flicker free possible using incandescent bulbs?


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## gunrunnerjohn (Nov 10, 2010)

Overkill for this job, but they'll certainly work! 

One tip. Alternate the polarity of the diodes in the individual cars so you have an even, or close to even distribution. That is, the band on half of them should face the pickup rollers, and away for the other half of the car lot. This minimizes the DC offset on the track which could start blowing your horn in conventional mode if you have half a dozen cars with the same polarity.


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## Patrick1544 (Apr 27, 2013)

......


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## Patrick1544 (Apr 27, 2013)

Great tip.
Would never have thought of the effect it might have.
Thank you


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## gunrunnerjohn (Nov 10, 2010)

It's the little things that sometimes get you.


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