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please explain these dmm readings on bridge rectifier

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mrbuell

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Hi all,
on my 240v welder the input power is routed to 2 bridge rectifiers one for each leg. It then goes to a bank of large capacitors and then outputs to the inverter board. My DMM reads +110VDC and -110VDC as expected when referenced to ground and 330VDC with a probe on each. The odd thing is, I read 240VAC on each leg with reference to ground. Is this a normal reading? I wasn't expecting a AC voltage at all.
 

You are correct not to expect AC but your meter is probably responding to changes in voltage and interpreting them as AC. The voltage from each bridge will be un-smoothed DC, basically lots of half cycles so the DMM will see what looks like a distorted AC waveform and give you the reading it thinks it would be if it was a sine wave.

Brian.
 
That makes sense. Thank you for your response.
 

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