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Topic: Do I need to reform electrolytic capacitors with Variac? (Read 10701 times) previous topic - next topic
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Do I need to reform electrolytic capacitors with Variac?

I came across some information: 
http://www.allegrosound.com/index21.html
Quote
If equipment is over 10 yrs old and has not been used in the last 24-hrs, powering ON without the proper use of a VARIAC will drastically shorten the life of the power supply capacitors. The older the caps and the longer they've been unused, the worse the problem.


I would apprciate some advice on this. Is this necessary? Does someone have experience with
Electrolytic capacitors? I have never heard of anyone I know doing this over the years with
an amplifier. Would this make a big difference?

Thanks.

Do I need to reform electrolytic capacitors with Variac?

Reply #1 –
There may actually be something to this. Electrolytic capacitors have a limited lifetime, especially if they are not used for long periods. When you apply voltage, they "reform", which is to say that their properties had degraded but will return to (hopefully) near original within a fairly short period.

Eventually their properties will degrade no matter what, but this could be a matter of decades. It is never a bad idea to replace them in very old equipment.

I have never heard of increasing the voltage gradually with a variac, and would probably not bother myself. On the other hand, if you have a variac then this probably wouldn't hurt.

Do I need to reform electrolytic capacitors with Variac?

Reply #2 –
My equipment is 18 years old. Sometimes wasn't switched on for a couple of months. Still alive and in perfect condition. Maybe because it isn't noname boombox.

Do I need to reform electrolytic capacitors with Variac?

Reply #3 –
I would say that if your equipment has modern "plastic tube" type electrolytic capacitors then they are probably fine unless there is an obvious failure or reason to suspect them.  Capacitors do fail, but modern ones are pretty reliable.  There have been some bad batches in recent years, so if your capacitors look like they are swelling or leaking then they need replacement.

If your equipment has older metal can or cardboard tube capacitors then they should be treated as suspect.  I wouldn't bother trying to reform them.  If they are bad then replace them with modern ones.  You can even "re-stuff" old capacitors with new ones if appearance is important to you.  The newest equipment I've personally seen with these types was from the mid 80s.

Do I need to reform electrolytic capacitors with Variac?

Reply #4 –
I won't dispute it, but I've never heard of this.  Who in the heck has access to a variac?  OK... I do...  I'm an electrical engineer.

And, I did have some capacitors "blow" a couple of years ago when I powered-up an old power amp that had been stored for a few years!  (This amp is probably 30 years old.)  I don't remember if it made a noise, but I remember some very toxic-smelling smoke.  And, I remember a sick feeling...  Unrelated to the smoke.  I unplugged the thing, and got out of the room where I could breathe.  I thought the amp was completely fried, but I took a look inside anyway.  I replaced a couple of (obviously burned-up) low-voltage electrolytics, and the it started working again!  (It wasn't the big main power supply capacitors.)

I have no idea if powering-up slowly with a variac would have prevented (or possibly delayed) this.

Do I need to reform electrolytic capacitors with Variac?

Reply #5 –
Quote from: DVDdoug on
I won't dispute it, but I've never heard of this.  Who in the heck has access to a variac?  OK... I do...  I'm an electrical engineer.

And, I did have some capacitors "blow" a couple of years ago when I powered-up an old power amp that had been stored for a few years!  (This amp is probably 30 years old.)  I don't remember if it made a noise, but I remember some very toxic-smelling smoke.  And, I remember a sick feeling...  Unrelated to the smoke.  I unplugged the thing, and got out of the room where I could breathe.  I thought the amp was completely fried, but I took a look inside anyway.  I replaced a couple of (obviously burned-up) low-voltage electrolytics, and the it started working again!  (It wasn't the big main power supply capacitors.)

I have no idea if powering-up slowly with a variac would have prevented (or possibly delayed) this.


If you try that Variac thing with a switching supply, it WILL FRY. I'm sitting near an Ampex AVR-3 2" videotape machine built in 1978. It sat in storage for over 10 years when we got in in 2005. We turned it on. It worked. No problems with capacitors. My Phase Linear autocorrelator sat in the garage for 12 years. It had some dried out 'lytics which didn't do anything 'bad' except to not work correctly so I replaced them. Dried out caps will not 'reform' and need to be replaced in any event.

G²

Do I need to reform electrolytic capacitors with Variac?

Reply #6 –
Quote from: Glenn Gundlach on
If you try that Variac thing with a switching supply, it WILL FRY.

I have seen many switching supply designs in the last 35 years, and I don't think I have seen one that would have been damaged by low voltage. Not saying it's not possible, just that I have not come across it.

Your point about dried-out electrolytics is a good one.

Do I need to reform electrolytic capacitors with Variac?

Reply #7 –
With a switching supply, the (input) current goes up as the (input) voltage goes down.  I suppose that could cause trouble in a poorly designed switching supply.  But, a properly designed power supply of any type should be able to survive a brownout.  In general, switching supplies are less fussy about what you feed them...  Whenever you see a product with a "universal worldwide"  power supply that's rated to work from 90 to 250 VAC (without the user changing a setting), that's a switching supply. 

Where I work we have a unit with an on-board switching supply.  When we power it up for the first time, we bring-up the voltage slowly.  This allows us to monitor the current (and output voltage), and if something isn't working, we can (hopefully) shut it off before anything "bad" happens.  It's kind of weird to watch the current go down as you increase the voltage!  Well...  It looks weird to anyone who's studied electronics... Ohm's Law is the first thing you learn and it almost becomes intuition that increased voltage means increased current...  (For the non-engineers reading this, this is not a "violation" of Ohm's Law.  It's a special case where the resistance is not constant, so you don't get the "usual" relationship between voltage and current.)