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Capacitor substitution values?

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ChadTower:

I've looked high and low for this info over the weekend... no luck...

...when working on old boards, and you have to substitute modern values for some old dead caps... how far is acceptable in either direction for capacitance?  I know voltage can go up just fine but never down... but the capacitance rating?  Say you have to replace a 500mfd cap but you only have 470mfd caps on hand... or would you be better off swinging up?  If so, how far up?

Level42:
The problem is that there is no universal answer to this question. I guess it depends on what circuit the caps are used.
And are we talking electrolytic caps only or also regular caps ?

If I had to  choose, I'd stay as close as possible, but choose the one with the higher value instead of the lower (Farrads).

Voltage can be anything as long as it's equal or higher.

SirPeale:
Stay as close as possible.  If we're talking electrolytic caps here, 500 to 470 isn't that bad.  Remember that values drop anyway as they get older.  In order to be really bad, they'd drop way down before they're bad.

I'd meter the cap anyway to see what kind of shape it's in.  Even though it's older, they made them better those days.  It may be just fine.

ChadTower:

--- Quote from: Peale on January 27, 2008, 03:50:41 pm ---I'd meter the cap anyway to see what kind of shape it's in.  Even though it's older, they made them better those days.  It may be just fine.

--- End quote ---


Don't have an ESR meter... everything I read everywhere says the capacitor checker on a DMM isn't all that useful in proving anything.

sarge:
Usually + or - 20% of the rated capacitance is considered acceptable when dealing with electrolyitics.  If you were too concerned with matching the original you could always connect a 470 and a 22 or 47 uf capacitor in parallel and that will bring the total capacitance up.  Electrolytics rarely fail abrubtly but will instead gradually die out due to capacitor drying up.

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