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Old 24th May 2007, 02:52 PM   #1
aud1out is offline aud1out  Canada
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Default Capacitors Voltage Tolerance

What capacitors should I keep in my parts bin?

If it matters, I am currently looking at the square type PP film and metallized film capacitors.

I suppose it may matter for the application:
A- Power supply
B- Signal
C- Speaker

My question as follows for each type of application:
1) Voltage rating as it relates to DA or leakage current or other factors.
- getting all higher voltage would keep my bin to a minimum
- if higher voltage means higher dielectric absorption, is this bad?
- if higher voltage means higher leakage current, is this bad?
2) Capacitance tolerance - does this matter
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Old 24th May 2007, 02:56 PM   #2
Did it Himself
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I higher voltage will mean it's a physically bigger cap.

Tolerance is how close it is to the stated value, pretty important IMO!
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Old 25th May 2007, 03:17 AM   #3
aud1out is offline aud1out  Canada
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Thanks richie00boy.

I've heard that for speaker crossovers, higher voltage caps are preferred.

For power or signal, does Dielectric Absorption or Leakage Current or other factors have any significant effect, thereby, making it necessary to choose a cap with proper voltage ratings?
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Old 25th May 2007, 10:12 AM   #4
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I couldn't comment really. I would just choose based on capacitance and physical size, if the voltage is higher than what I need then so be it.
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Old 25th May 2007, 03:19 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
I think that as the voltage rating goes up the DA and leakage both go down.
But, the size and the cost both go up.
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Old 28th May 2007, 02:20 PM   #6
aud1out is offline aud1out  Canada
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Default Leakage Current goes up

Thanks Andrew.

Purchasing in volume can result in savings. This is one reason why I posed my original situation. Was hoping to keep SOME cap values on hand without duplicating Digikey's inventory.

If the characteristics of a cap (DA, leakage current,...) will affect the performance of a specific application, I would prefer to use the correct part and not just what I have on hand. Goes without saying that I am a noob, as well, I (currently) do not order with enough frequency (Digikey USA) that I can just order a cap when needed.

I suppose caps that are physically big due to higher voltage may not be best solution in tight quarters.

Just found some info, leakage current is higher for higher V rated caps. Digikey shows for Pan FC cap but does not show for Pan square caps. Although, how would it compare when same voltage is applied.

Regarding dielectric absorption, do you have information to support your statement. I was guessing that the larger higher V rated cap would have more DA because (?) it has more dielectric.

Or... does any of this matter
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Old 28th May 2007, 06:29 PM   #7
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It's well worth looking up a datasheet for caps you're interested in. I've been using Evox MMks for coupling ( I like them), but if you look at the datasheet you should heavily de-rate the voltage rating with increasing frequency. eg a 63V part appears only good for 5VAC at 100Khz. It's this kind of behaviour behind why speaker crossovers can end up with 630V rated parts - to deal with maybe 10-20VAC at 20Khz...

So - like any caps - I wouldn't want to run a film cap within , say, 20% of rated voltage, for reasons of safety (what happens if it breaks down?), but you may need to consider the frequency of the signal when picking the part for the applcation.
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