How much AC is usually let through a MUR860 rectifier bridge?
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 5th April 2005, 08:14 PM #1 bg4533   diyAudio Member   Join Date: Aug 2004 Location: Ohio How much AC is usually let through a MUR860 rectifier bridge? How much AC voltage is usually let through a MUR860 rectifier bridge? Is it dependent on AC voltage?
 5th April 2005, 09:43 PM #2 Eva   diyAudio Member     Join Date: Oct 2003 Location: Near the sea I think you've accidentally mistaken current and voltage somewhere in your sentence Remember that MUR860 is rated at 600V DC peak and 8A average current Peak current may greatly exceed rated average current as long as a small enough duty cycle is employed. However, rated peak voltage must not be exceeded
 5th April 2005, 09:54 PM #3 bg4533   diyAudio Member   Join Date: Aug 2004 Location: Ohio I am somewhat of a beginner so I don't really know what I am talking about. What I am trying to ask reworded: What would be a normal measurement of AC voltage on the DC side of a MUR860 rectifier bridge? ----- In response to your question and a bit more thinking: Is AC current on the DC side a bigger problem? What would be a normal measurement for this?
 5th April 2005, 10:45 PM #4 BWRX   diyAudio Moderator Emeritus     Join Date: Jan 2005 Location: Pennsylvania it depends on the voltage rating of the transformer secondary it is hooked up to and also the current draw of the load.
 5th April 2005, 11:01 PM #5 bg4533   diyAudio Member   Join Date: Aug 2004 Location: Ohio I am away right now and I can't recall the exact measurements. I am trying to replace the bridge in my DAC-AH. The transformer has 2 taps rated at 18V each (center tapped I think). Each tap is hooked up to one side of the bridge. The DC output I got seemed reasonable. With no load I measured around .5V of AC on the DC side. I really don't know, but that seems pretty high to me.
 5th April 2005, 11:13 PM #6 BWRX   diyAudio Moderator Emeritus     Join Date: Jan 2005 Location: Pennsylvania do you mean the transformer has two secondary windings and they're wired to provide a positive voltage rail, negative voltage rail, and common ground using one bridge rectifier like in this picture: or by two taps do you mean just two wires connected to a bridge rectifier like in this picture: the voltage rating of the transformer secondary is in VAC RMS. if you are using either configuration the DC voltage at the filter cap terminals should be approximately: VDC = VAC * sqrt(2) - 1.4 the 1.4 comes from the 0.7V drops (approximately) across the rectifier diodes. if there is no filter cap and you're just measuring the DC voltage at the bridge rectifier terminals with an RMS multimeter than it will be a little higher than the voltage rating of the transformer secondary.
 5th April 2005, 11:30 PM #7 bg4533   diyAudio Member   Join Date: Aug 2004 Location: Ohio The top diagram is what I am dealing with. Positive, negative and ground. I know how to calculate what the DC voltage should be. The DC voltage I got was basically what I expected. (I estimated in my head, did not calculate) I measured AC voltage on the DC side of the rectifier. My thought was that I should measure little to no AC voltage. ~I measured 0.5V
 5th April 2005, 11:34 PM #8 pinkmouse   diyAudio Moderator     Join Date: Apr 2002 Location: Rotherham, England If you're measuring with no caps, you get pulsed DC, and most DMMs can't measure this accurately. Stick 6800uf or so of capacitance on each rail then try again. __________________ Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
bg4533
diyAudio Member

Join Date: Aug 2004
Location: Ohio
Quote:
 Originally posted by pinkmouse If you're measuring with no caps, you get pulsed DC, and most DMMs can't measure this accurately. Stick 6800uf or so of capacitance on each rail then try again.
Hmmm...that is probably the case then. My soldering station died Sunday. A new one is on the way. When it arrives I will test things out and if there is a problem I will report back.

Thanks for the help everyone.

 12th April 2005, 03:10 AM #10 bg4533   diyAudio Member   Join Date: Aug 2004 Location: Ohio I just recieved a scope, but I still don't really know how to use it. When I look at the negative rail of the PSU things are smooth as expected. When I look at the positive rail things dont looks so good. After a 7812 regulator I get what looks like the top half of a sawtooth. Before the regulator and after the rectifier I get something similar except the lines are blurrier and there are horizontal disconuities between the wave. It is the same before and after the filter caps. Is this how this is supposed to be or did I screw something up?

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