Need help converting 120 vac to 18 vdc

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Thread Starter


Joined Nov 30, 2019
Ok... So I'm attempting a Full bridge rectifier build supplied with AC electricity off of your typical home power outlet with a final output of 18vdc at no less than 15A. (~270 watts) Can anyone tell me how to step down AC voltage without lossing much amperage? (transformer alternative) Here in the U.S. most outlets are 120vac at 60 hz on a 20A circuit breaker so I can't sacrifice much amperes if any.

Side note: Would it be more efficient (as far as current loss) to rectify the AC voltage to DC then step down the DC voltage to my final output?

Thank you for any and all the you choose provide.


Joined Mar 30, 2015
Welcome to AAC!

You misunderstand how transformers work. For an ideal transformer, power in would equal power out. Transformers aren't lossless, but the efficiency isn't low enough to make getting 18VDC at 15A from a 15A 120VAC circuit all that difficult.

I don't use many transformers, but my recollection is that the "standard" voltages in the range you need are 18VAC and 24VAC.

If you want to do a transformerless supply, that's a disallowed topic at AAC.


Joined Oct 7, 2019
A transformer is efficient.
120vac at 15A is probably all you should pull from the wall. A transformer can change that to 12vac at 150A.
120V at 1.5A from the wall = 12V at 15A.


Joined Aug 23, 2012
For the safety reason, the transformerless issue which doesn't allowed to discuss, so this thread will be locked, if you change your mind and willing to use transformer then please click the "Report" button and we will reopen the thread, thank you.
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