02-01-2015, 05:12 PM
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Merry Christmas to all
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Join Date: Apr 2009
Location: North Central Florida
Posts: 53,224
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Quote:
Originally Posted by tdelahanty
This is a good question for Dan. I have 650mv dc on the AC line. I checked this because things just didn't sound right. Dan how much dc is acceptable ?
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Tom.......First, how are you coming up with the 650mv measurement? Are you measuring with a DMM or an oscilloscope? Which wires are you measuring, i.e. hot to neutral, hot to ground, or neutral to ground?
It is not unusual to have some level of DC offset on AC lines in your home. This is often caused by variable speed AC motors like those found on a hair dryer and by switch mode power supplies in electronics and computers that create DC by chopping half the AC sine wave to make a pulsing DC output. This causes the other half of the sine wave, also a pulsing DC, to be back fed onto the neutral which generates heat in the cores on transformers. Under perfect conditions the neutral tap on any transformer should have zero AC or DC when referenced to ground.
650 millivolts (0.65 VDC) is not a serious problem on a AC line but ideally zero DC would be the best. You can probably reduce the DC offset on your home power by turning off (unplugging) anything with a switch mode power supply when not in use.
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Dan
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Last edited by jdandy; 02-01-2015 at 05:45 PM.
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