Dumb question: minimum cap voltage requirement?

[greg7]

Are caps rated at 50V adequate for using in series in a crossover? I've stumbled across some polycarbonate film caps I'm dying to try in series with my tweeter but they're only rated to 50V. I've never seen film caps rated less than 100V

 

[dotneck335]

Depends on how much POWER you are driving them with. 10,000 watts or 10 watts?

 

[rayma]

Yes, a 50V bipolar rating is pretty standard for a tweeter capacitor, and allows for 100V peak to peak,
or 150W into 8 ohms. Also check the current rating. Metallized film capacitors have much less
current capability than film/foil types, and some may be inadequate.

 

[greg7]

30 watts max, probably far less, like 1-5 watts at normal listening levels

 

[dotneck335]

Well, at 30 watts power into an 8 ohm speaker, you need ~22 peak AC volts; less voltage (more current) for a 4 ohm speaker. So I'd say a 50 volt rated cap would be just fine. And, BTW, it's NOT a dumb question!

 

[Michael Bean]

Power rating on even a tweeter circuit is very important, just as important as voltage rating. Capacitors that are expose to higher current levels will run hot, and most likely be damaged. I made that mistake once, and started to notice the sound quality from the tweeters was deteriorating and distorted in a really irritating way. Replacing them with the proper cap fixed it immediately.

Mike

 

[newvirus2008]

Yes, their core temperature (like semiconductors) climbs higher and remaining useful lifetime (RUL) starts running out much faster due to the increased stress. Besides, smaller voltages across a capacitor with larger rating is best for linearity, even for film capacitors.

And I agree with dotneck, it's definitely not a dumb question, but an important point to be taken care of.

 

[waxx]

the formula to calculate volt RMS from speaker is V = sqrt(P * R) where P is the watt and R the (nominal) impendance of the speaker. So it's about 22v AC like said above. For the voltage needed for your cap, it's best to double that (headroom/safety) so i would say a 50v cap (as 44v caps hardly exist) or higher is suited.

 

[bansuri]

I made some calculations with different caps in a tweeter circuit. All are 4,7uF, the film types are 200V and the bipolar electrolytic has 100V nominal, 35Vrms.


20Vrms 20kHz 100W continuous into a compression driver that is heavy duty

bipolar 2.10€ tan delta 0.1 heating loss 23.6W will explode (even if the loss goes down with frequency)

MKT 1.95€ tan 0.01 loss 2.3W also too much

MKP 2.50€ tan 0.004 loss 0.09W


https://www.tdk-electronics.tdk.com...1513474ba/pdf-generaltechnicalinformation.pdf