Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on October 03, 2012, 11:28:36 pm

Title: Electrolytic capacitors and overvoltage
Post by: Leevi on October 03, 2012, 11:28:36 pm

This is probably depending on the brand but how much do the electrolytic capacitors
endure overvoltage in general?
/Leevi

Title: Re: Electrolytic capacitors and overvoltage
Post by: PRR on October 04, 2012, 12:02:44 am

If you want them to last a while, do not exceed the nominal voltage for more than the 10 seconds at start-up.

If you want them to last decades, aim lower than 80% of marked voltage.

I know from experience that 140% voltage for 20 minutes goes BOOM!! and makes a stinky smoke-cloud and mess inside the chassis.

However, I have stuff with 37V on 35V caps that has run for decades.

Title: Re: Electrolytic capacitors and overvoltage
Post by: Leevi on October 04, 2012, 01:57:13 am

I have a case where a 450/22uF cap is continuously getting 477v i.e. 6% over the nomina rate.
/Leevi

Title: Re: Electrolytic capacitors and overvoltage
Post by: tubeswell on October 04, 2012, 04:09:53 am

I have run electrolytic caps at or slightly over maximums before with no apparent problems. Factory maximum ratings tend to be conservative AFAICT, probably to do with manufacturer's underwriter requirements or some such thing.

477 vs 450 =  much of a muchness. And besides you could probably form 450V e-caps up to 500V in most cases (you might get the odd one that bangs)

Title: Re: Electrolytic capacitors and overvoltage
Post by: printer2 on October 04, 2012, 05:57:46 am

Might it also depend on the manufacturer? Who says they all make them to the same specifications? 

Title: Re: Electrolytic capacitors and overvoltage
Post by: Madison on October 04, 2012, 09:42:45 am

The question I was trying to address in another thread.
So.... which manufacturer is the best to run at rated voltage or above?????
Would anyone mind naming names on which caps are "lasting years" above specs?

Title: Re: Electrolytic capacitors and overvoltage
Post by: HotBluePlates on October 06, 2012, 11:15:12 pm

Quote from: Madison on October 04, 2012, 09:42:45 am

So.... which manufacturer is the best to run at rated voltage or above?????
Would anyone mind naming names on which caps are "lasting years" above specs?

I would much prefer to tell you how I select caps to have ratings higher than the highest possible voltage that can ever exist in the circuit.

I've seen episodes of "Cops" where a suspect drives on bare rims for miles after having all 4 tires blown out with spike strips. I have a feeling that the approach asked about is akin to asking which brand of wheel will last the longest while you're chased by the police on blown-out tires.

I would prefer not to be in the position to need that knowledge...