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Old 18th February 2006, 12:21 PM   #1
jpg is offline jpg  Germany
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Default Is it normal that my MUR860's ...

(Hi Cloners)

... differ greatly* by means of both forward and backward resistance (I'm talking of the difference between the diodes, not between the fwd and bwd resistance, obviously)? I've never used MUR's before.

I started wondering when my DMM gave me unexpected readings when I tried to measure the DC (and AC) of my provisional PSU (2*25V toroid, one secondary used, 4 MUR860's forming a full wave rectifier): instead of 35VDC and 0VAC, I measured 25VDC and 10VAC. (When measuring different selfmade PSUs, I always got perfectly expectable DC and AC readings on my DMM.)

I'm lost as to where the problem resides and if there is a problem at all and the next best thing to do seemed (to me) to measure the MUR860's resistance.

Can anyone help?

Thanks,
Peter

*I don't recall the exact values, but I'll repeat the measurement later.
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Old 18th February 2006, 01:38 PM   #2
moamps is offline moamps  Croatia
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Default Re: Is it normal that my MUR860's ...

Quote:
Originally posted by jpg
..... instead of 35VDC and 0VAC, I measured 25VDC and 10VAC. (When measuring different selfmade PSUs, I always got perfectly expectable DC and AC readings on my DMM.)...
Did you place a smoothing capacitor at the output?
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Old 18th February 2006, 05:17 PM   #3
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Thanks, moamps.

By "capacitor at the output" you mean a (polar electrolytic) cap between the positive and the negative lead? No, I didn't use one.

And that seems to have made the difference. Now that I've connected pos and neg with a 1kF I'm measuring 33,9VDC. Lesson learnt: a smoothing cap is mandatory when measuring a rectified voltage.

The reading on my DMM still isn't 0VAC, but is constantly cycling. I guess this is due to the remaining DC ripple that the meter can't interpret.

I take it that it's save to connect the PSU and the GC?

Peter
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Old 18th February 2006, 05:57 PM   #4
moamps is offline moamps  Croatia
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Quote:
Originally posted by jpg
....Lesson learnt...


Quote:
I take it that it's save to connect the PSU and the GC?
Yes.
Regards,
Milan
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Old 18th February 2006, 07:31 PM   #5
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Thanks, Milan, the CG is up and running.

With the toroid, the 100Hz sinus sounds considerably better at higher levels than before with the 2*50mA PSU.

Peter
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