Hafler DH-500 PS electrolytic ESR

lhquam · 7th April 2011, 10:55 PM

I am not sure if this is the most appropriate forum for this post, but...

While "tuning up" my 26 year old Hafler DH-500, I discovered that there was .6 volts of power supply ripple, mostly due to high ESR of the ageing 100 volt, 20,000 uF electrolytic capacitors. While probing other parts of the amplifier, I accidently shorted the +90 volt supply to ground, causing one of the electrolytics to discharge quickly (making a very loud pop). Putting a scope probe on the +90 supply showed that portion of the ripple due ESR dropped from about .3 volts to about .05 volts.

Since I was considering replacing both electrolytics anyway, I intentionally shorted the other electrolytic which resulted in the same reduction on ripple due to ESR on the -90 volt supply.

Can anyone explain this effect? Are these capacitors likely to retain this reduced ESR for a useful length of time, or should I replace them?

singa · 8th April 2011, 02:32 AM

Hi, Shorting the cap to ground probably passed a heavy current through
and the arcing may may cleaned up the terminals giving better
conductivity,same with the electrodes of the cap.

Normally you will get about 200mV of ripple but if it is now very
much lower than leave it at that.Money don't grow on trees so if it ain't
broke,don't fix it.Unless you are a perfectionist or have excess cash on hand.

singa

lhquam · 8th April 2011, 03:13 AM

Singa:

You are probably correct. I removed all of the screws and carefully cleaned (by scraping with a knife and using emory paper) the terminals and solder lugs. The ESR was reduced a little bit more. It will be interesting to see how long this improvement lasts.

stratus46 · 8th April 2011, 03:26 AM

Quote:

Originally Posted by lhquam

Singa:

You are probably correct. I removed all of the screws and carefully cleaned (by scraping with a knife and using emory paper) the terminals and solder lugs. The ESR was reduced a little bit more. It will be interesting to see how long this improvement lasts.

You're lucky you didn't blow any internal conductors in the caps. I assume you welded your screwdriver to the terminals. My guess is you didn't improve the capacitors with the arcs but you did improve the screw connections.

G²

eclectic2k · 8th April 2011, 04:22 AM

I personally doubt the effect was due to the screw contacts. Maybe in part though. I'd be inclined to guess the effect was internal to the capacitor electrolyte or oxide layer... (something akin to reforming them?)

stratus46 · 8th April 2011, 05:18 AM

I wouldn't expect any electrolyte reforming in just a few microseconds but I could be wrong. But, we all know about aluminum terminals oxidizing very quickly and the oxide is a good insulator.

G²

7th April 2011, 10:55 PM	#1
lhquam diyAudio Member Join Date: Mar 2010 Location: Olalla, Oregon: Land of the 100 Valleys	Hafler DH-500 PS electrolytic ESR I am not sure if this is the most appropriate forum for this post, but... While "tuning up" my 26 year old Hafler DH-500, I discovered that there was .6 volts of power supply ripple, mostly due to high ESR of the ageing 100 volt, 20,000 uF electrolytic capacitors. While probing other parts of the amplifier, I accidently shorted the +90 volt supply to ground, causing one of the electrolytics to discharge quickly (making a very loud pop). Putting a scope probe on the +90 supply showed that portion of the ripple due ESR dropped from about .3 volts to about .05 volts. Since I was considering replacing both electrolytics anyway, I intentionally shorted the other electrolytic which resulted in the same reduction on ripple due to ESR on the -90 volt supply. Can anyone explain this effect? Are these capacitors likely to retain this reduced ESR for a useful length of time, or should I replace them?

8th April 2011, 04:22 AM	#5
eclectic2k diyAudio Member Join Date: Nov 2005 Location: Silicon Valley	interesting... I personally doubt the effect was due to the screw contacts. Maybe in part though. I'd be inclined to guess the effect was internal to the capacitor electrolyte or oxide layer... (something akin to reforming them?)

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8th April 2011, 02:32 AM	#2
singa diyAudio Member Join Date: Apr 2004 Location: near	Hi, Shorting the cap to ground probably passed a heavy current through and the arcing may may cleaned up the terminals giving better conductivity,same with the electrodes of the cap. Normally you will get about 200mV of ripple but if it is now very much lower than leave it at that.Money don't grow on trees so if it ain't broke,don't fix it.Unless you are a perfectionist or have excess cash on hand. singa

8th April 2011, 03:13 AM	#3
lhquam diyAudio Member Join Date: Mar 2010 Location: Olalla, Oregon: Land of the 100 Valleys	Singa: You are probably correct. I removed all of the screws and carefully cleaned (by scraping with a knife and using emory paper) the terminals and solder lugs. The ESR was reduced a little bit more. It will be interesting to see how long this improvement lasts.

8th April 2011, 05:18 AM	#6
stratus46 diyAudio Member Join Date: Nov 2009 Location: Los Angeles	I wouldn't expect any electrolyte reforming in just a few microseconds but I could be wrong. But, we all know about aluminum terminals oxidizing very quickly and the oxide is a good insulator. G²

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