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 Post subject: How much extra uF is too much?
PostPosted: Sep Wed 29, 2021 4:32 am 
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Location: Redlands CA
Working on a Westinghouse TV, C3 a7b are 40@500, the closest thing Mouser has (that's not absurdly priced) are 56@525.

Will the extra 16uF (total of 32) be a problem in this circuit?

I can get 40 or 47uF caps from eBay, but prefer to get them all from Mouser if possible.

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 Post subject: Re: How much extra uF is too much?
PostPosted: Sep Wed 29, 2021 11:44 am 
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Location: Belrose, NSW, Australia
56uF should be fine.

Electrolytics have a VERY wide tolerance range, -20%, +100% is not unusual.

It isn't wise to use too large a value cap as the "input to filter" because it stresses the rectifier unnecessarily. But 80 or even 100uF is not uncommon in this position.

So, no problem here.

Larger electros used elsewhere do no harm.

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 Post subject: Re: How much extra uF is too much?
PostPosted: Sep Wed 29, 2021 10:53 pm 
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Great, thank you!


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 Post subject: Re: How much extra uF is too much?
PostPosted: Sep Wed 29, 2021 11:37 pm 
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Or install a poly cap.

Granted they aren't cheap. 47μf @ 630VDC is $22.95 each.

https://www.tubesandmore.com/products/c ... ylene-fast

I honestly don't trust an electrolytic to hold up long term to voltages above 450 VDC

-Steve

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 Post subject: Re: How much extra uF is too much?
PostPosted: Sep Thu 30, 2021 5:00 pm 
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Location: Crystal Bay, NV 89402
Unlikely that 500v working voltage is needed in this application.
Maybe the manufacturer had a big supply of 500v cans.
Reasonably sure that 450 will do the job.
I did not understand the comment about failure of 450v capacitors.
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Ron.


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 Post subject: Re: How much extra uF is too much?
PostPosted: Sep Thu 30, 2021 6:18 pm 
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Somewhere I read that due to the physics of the aluminum electrolytic capacitor the highest effective voltage rating ends up to be around 450 VDC.
I've seen many rated at 475 and even 525 VDC, but I believe that was surge voltage.

I recently came across an old electrolytic rated at 600 VDC, but discovered it was actually two in series inside a cardboard tube.

I have seen modern electrolytics also rated at 600 VDC and wonder if they are also two capacitors in series inside one package?
This is fine as long as their leakage currents stay balanced.

-Steve

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 Post subject: Re: How much extra uF is too much?
PostPosted: Sep Thu 30, 2021 9:57 pm 
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I was able to find 47@500 from Mouser after all so I went with that.


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 Post subject: Re: How much extra uF is too much?
PostPosted: Oct Fri 01, 2021 1:32 am 
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Location: Pewaukee, WI
azenithnut wrote:
Somewhere I read that due to the physics of the aluminum electrolytic capacitor the highest effective voltage rating ends up to be around 450 VDC.
I've seen many rated at 475 and even 525 VDC, but I believe that was surge voltage.

I recently came across an old electrolytic rated at 600 VDC, but discovered it was actually two in series inside a cardboard tube.

I have seen modern electrolytics also rated at 600 VDC and wonder if they are also two capacitors in series inside one package?
This is fine as long as their leakage currents stay balanced.

-Steve

Sometimes I'll do series lyrics in recaping. If 2 series make a much cheaper replacement than a single part with a oddly high voltage sometimes that makes more sense than a $20 part. Having 220K or higher voltage equalizing resistors across each cap.


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 Post subject: Re: How much extra uF is too much?
PostPosted: Oct Fri 01, 2021 7:16 am 
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Location: British Columbia
From what I was reading you don't really need the equalizing resistors across electrolytics connected in series anymore, something to do with improvements in the electrolyte I think. Also it would be good to get 105 C rated caps, of a good brand, like one of the Japanese makes, and not a Chinese mystery brand, or a Lelon brand one. Film caps are a waste of time, and money here, unless you gang several small ones together in parallel, but then there is the bulk, a motor run cap maybe?
Regards
Arran


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 Post subject: Re: How much extra uF is too much?
PostPosted: Oct Sat 02, 2021 3:18 am 
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The equalization resistors may not be necessary anymore, but having them to bleed down over 450V sure seems like a good idea if you have ever been bit by a charged lytic.

Most motor run caps I've seen are over 20 years old, but they all seemed excessivelyy big relative to their capacitance and to vintage can lytics...


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