# Transformer on a (quasi)DC line

P

#### PiRho Tech

Jan 1, 1970
0
I'm wondering: Would it work to rectify 120v ac before dropping it into a
transformer?
Reason: my output is 13.8v, and I'd hate to lose 10% (especially when
running ~15A) just to rectify it on the side of the secondary.
I'm thinking it should work: You'd have a 120Hz ac, just raised by ~60v,
di/dt would still be present to induce a field.

Any thoughts?

Mark D.

R

#### Robert Baer

Jan 1, 1970
0
PiRho said:
I'm wondering: Would it work to rectify 120v ac before dropping it into a
transformer?
Reason: my output is 13.8v, and I'd hate to lose 10% (especially when
running ~15A) just to rectify it on the side of the secondary.
I'm thinking it should work: You'd have a 120Hz ac, just raised by ~60v,
di/dt would still be present to induce a field.

Any thoughts?

Mark D.

Me thinks that you should *learn* about some electronics before you
put your tongue into the AC power outlet...

S

#### Some Guy

Jan 1, 1970
0
Silly.

First, you aren't talking about rectifying here, if you will still have
120vac floating on a 60vdc level... that's called adding a dc offset.
Rectifying either cancels or inverts half of the wave.

Second, if you did put 120vac floating on 60vdc into a transformer, the
effect would be: The transformer would perform exactly as it did before you
added the dc offset, except that it would also GET HOT. The output would be
exactly the same as it would have been without the offset. At least until
the transformer got hot enough from the 60vdc to melt...

On the other hand, if you did rectify the ac, then effectively you would be
putting half the voltage into the transformer, and altering the input
waveshape to boot. This would have the effect of halving the output
voltage, and causing voltage spikes on the output which might just destroy
the components on the output side...

The other guy is right. You should pick up a TEXTBOOK (not just something
off the shelf at Barns n Nobles) on electronics, and read through the
chapter on how transformers work.

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