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AC to DC Variable Bridge Circuit

AC to DC Variable Bridge Circuit

AC to DC Variable Bridge Circuit

Looking for some tips on making a nice little circuit breaker test box for work. I run across circuit breakers that have all sorts of charging motors, shunt trips and spring release coils that operate on all different voltages. I'm looking to make a nice little test box that will put out both variable AC and DC. I think 10A will be enough to do whatever I need. Input to the box would be 120VAC maybe to a variac. I have a 600V 50A full wave bridge I dug out of an old transfer switch. Where I'm only operating a coil here and there do I need a filter capacitor on the DC output? If so how big? The variac, is there a relatively inexpensive one I could find? I would ideally like to put it on a selector switch so I could vary the AC output from 120V down to 12V or lower. Then switch it to a DC through the bridge and have a variable DC from 120VDC down to 12VDC. Any thoughts on this? Good idea, bad idea? Just a simple little "cheater box" is what I'm looking for so I can test breaker functions while primary injection testing.

RE: AC to DC Variable Bridge Circuit

I wouldn't trust the results if you're using unfiltered pulsating DC to test a DC circuit breaker. The results might not be valid.

If it's only up to about 10A, then it might be better and easier to use an old variable DC power supply. YMMV, but adjustable DC power supplies even up to 40A class (19-inch rack, two knobs, two meters, often HP) are seemingly widely available surplus. I've seen them thrown out as unwanted junk.

You'd still need to add some switching and perhaps calibrated metering.

RE: AC to DC Variable Bridge Circuit

Had to build some test jigs for production current monitors. I used a 50W or so toroid power transformer and just wound a couple of turns of #12 through them. A variac fed the primary, easy to get 0-20A.

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