250 V or 630 V woofer capacitor?

[jimjimbo]

 Given the choice between a 250 V or a 630 V woofer capacitor which one would be the proper choice? Can the 250 V Handle pretty much any load? 

[Deang]

250Vdc is fine. 

[moray james]

in a passive crossover the caps at maximum only ever look at the rail voltage and most smaller amps are 50 - 60 volts with large amp running 90 volts, a few might run as much as 120V but you don't see those often and it would not make a difference. Remember that even the cheapest cap is good for at least double its rated voltage. 250 volts is lots.

[Peter P.]

100 watt output into an 8 ohm woofer is only 28V. You're plenty covered with a 250V capacitor.

[jimjimbo]

Thanks gents!

[Davecv41]

On 10/2/2017 at 4:57 PM, moray james said:

in a passive crossover the caps at maximum only ever look at the rail voltage and most smaller amps are 50 - 60 volts with large amp running 90 volts, a few might run as much as 120V but you don't see those often and it would not make a difference. Remember that even the cheapest cap is good for at least double its rated voltage. 250 volts is lots.

Not a good rule of thumb for capacitors. In today's throw away society, parts are frequently used that are running at the edge of their rated voltage specification. My Pentium motherboard had 6 volt electrolytics in the 5 volt circuit. They dried out and shorted. I pulled them off the board and replaced them with higher voltage caps and got the board running again. In researching the problem online afterward, it appeared that most electronics is made that way now to save a few pennies for the bottom line. Apologies for changing the subject from crossover caps to something else.

[JohnA]

Power = I (current) x V (voltage)

Ohms Law is V = I * R (resistance)

so, P = V^2/R

(250*250)/8 ohms = 7813 watts. 

100V = 1250 watts

50V = 313 watts. 

Pretty much any cap you can buy will be sufficient, but go for 100V, maybe save a little $$. 

[moray james]

2 hours ago, Davecv41 said:

Not a good rule of thumb for capacitors. In today's throw away society, parts are frequently used that are running at the edge of their rated voltage specification. My Pentium motherboard had 6 volt electrolytics in the 5 volt circuit. They dried out and shorted. I pulled them off the board and replaced them with higher voltage caps and got the board running again. In researching the problem online afterward, it appeared that most electronics is made that way now to save a few pennies for the bottom line. Apologies for changing the subject from crossover caps to something else.

I really think that you were dealing with crappy caps, a six volt cap on a 5 volt rail is just fine. Cheap little speakers usually have 35 volt caps to save money you can run them on any size amp with no problems what so ever. that's not to say you could not blow them up but the drivers would likely fry before the caps blew up and you would know you were doing wrong long before that even from another room or the basement. Never the less your amplifiers rail voltage is all you speakers will ever see unless of course it dies and go DC.