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# rectify electricity before transformer? Answered

can you rectify the US mains (120vac, 60hz) as it, and used the pulsed dc to feed into a transformer and get a dc voltage out of the transformer? I'm asking this because it would be much much more efficient for high current situations. Here's my specific situation:

I want to build a capacitive spot welder and a capacitive discharge cutter in an all in one device. To charge the enormous capacitor rapidly (1.5 farads in my case), I need a very high current power supply. I'm using a modified microwave transformer that was rated at 1kw, and it is now modified so that it outputs 12 volts AC at around 80 amps (probably less because of losses). This must be rectified to charge the capacitor.

Assuming a perfect transformer (for arguement), it would have:
120volt, 8.34 amp input
12volt, 83.34 amp output

the following is with full bridge rectifiers, assumed voltage drop: 1.4v
If the power was rectified before the primary, the loss on the bridge rectifier would be: 11.67 watts
If the power was rectified after the secondary, the loss on the bridge rectifier would be: 116 watts

huge difference

so once again, the final question is: Does rectified input of a transformer = rectified output? Does the 120hz pulsed dc (as opposed 60hz ac) matter? Could this setup charge a capacitor?

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## 1 Replies

muttyfutty (author)2009-11-25

Sorry!
I'm afraid transformers only work on AC.
Well, actually pulsed DC will work, but wont be as efficiant.
as to pure DC, then no chance.
Capaciters charge best on DC,