Elec/Poly cap replacement rules?

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Steve
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Elec/Poly cap replacement rules?

Post by Steve » Wed Feb 07, 2018 6:03 am

Hey guys,

This guy in the following video replaces all of his mobo caps with poly replacements:



He keeps the voltage the same but goes for half the capacitance, is this wise? He says it is perfectly fine.

Thx,

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exxos
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Re: Elec/Poly cap replacement rules?

Post by exxos » Thu Feb 08, 2018 8:11 pm

Well spotted video that! I've not seen those poly caps before, I always look though the caps list when I research new caps and never seen them come up in farnell, though they are there it seems.. anyway..

Capacitors ESR is generally dependent on the physical size of the capacitor. For example a 1,000uF 10mm x 20mm could be 2,000mA ripple, but Companies like Panasonic normally do a "Long" version , say, 10mm x 35mm, where ripple can be 2,500mA. So generally I avoid smaller capacitors because of that..

Though seems the new poly caps are cramping in some series spec into a small package! Normally those small SMT caps are terrible ESR and I have mostly avoid them.. again due to physical size and poor ESR rating. Also ripple current generally goes up with uF value also.

So its possible that guy replaced caps which may have only been 500mA ripple 2,200uF for example, and replaced them with 1,000uF 5,000mA ripple.. more ripple power is always good, and technically you wouldn't need the same uF for the ripple power. Of course its "acceptable ripple" based on load and frequency of the PSU.. both could be guessed at but I doubt anyone cares enough to look into it :lol:

I've not looked at all the caps, but quick look and 1,000uF seems to be the max value farnell stock anyway. Normally I would go for the same uF value or a little higher when changing caps, basically to get a better ESR value. Also as caps age, uF will go down, so I like to add in a little "ware-room".

So yeah, normally going for half value is a no no with such things, but the poly caps spec looks a huge jump better than normal caps. Really he should have compared both types of capacitors and showed scope results so we can see what's really going on.. In anycase, in this particular instance, I would think it should be fine and the jump in ripple power will definitely add up!
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Steve
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Joined: Fri Sep 15, 2017 11:49 am

Re: Elec/Poly cap replacement rules?

Post by Steve » Thu Feb 08, 2018 11:38 pm

Thanks Chris for your very educational response :) Good to know!

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