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Author Topic: capacitor capacity in crossover  (Read 4830 times)

David Parker

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capacitor capacity in crossover
« on: April 08, 2011, 08:43:41 pm »

capacitors are rated in voltage. The ones in question are rated 250v. 250v in music works out to 15,625 watts at 4 ohms. Will a 250v capacitor hold up in a low pass crossover, 800 watts rms, 4ohms?
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Ivan Beaver

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Re: capacitor capacity in crossover-Math
« Reply #1 on: April 08, 2011, 08:53:30 pm »

capacitors are rated in voltage. The ones in question are rated 250v. 250v in music works out to 15,625 watts at 4 ohms. Will a 250v capacitor hold up in a low pass crossover, 800 watts rms, 4ohms?
Untill you start doing the proper math.  Take your RMS voltage-multiply it by 1.414 (to get a peak) and then double it to get the peak to peak voltage.

So working backwards you take 250V divide by 2=125V.  Now multiply by .707 and you get 88 volts.

So now you are in the range of 1944 watts.  Of course that does not allow for any peak power etc.

It also depends on how/where it is used in the circuit and what the actual applied voltage is.

But the short answer is yes, it should be OK, but not with as much "headroom" as you think.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

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David Parker

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Re: capacitor capacity in crossover-Math
« Reply #2 on: April 08, 2011, 10:35:35 pm »

capacitors are rated in voltage. The ones in question are rated 250v. 250v in music works out to 15,625 watts at 4 ohms. Will a 250v capacitor hold up in a low pass crossover, 800 watts rms, 4ohms?
Untill you start doing the proper math.  Take your RMS voltage-multiply it by 1.414 (to get a peak) and then double it to get the peak to peak voltage.

So working backwards you take 250V divide by 2=125V.  Now multiply by .707 and you get 88 volts.

So now you are in the range of 1944 watts.  Of course that does not allow for any peak power etc.

It also depends on how/where it is used in the circuit and what the actual applied voltage is.

But the short answer is yes, it should be OK, but not with as much "headroom" as you think.

this is a truly frustrating endeavor. Just when you think you've figured something out, you find out there's another twist.
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Bob Leonard

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Re: capacitor capacity in crossover
« Reply #3 on: April 08, 2011, 10:39:36 pm »

capacitors are rated in voltage. The ones in question are rated 250v. 250v in music works out to 15,625 watts at 4 ohms. Will a 250v capacitor hold up in a low pass crossover, 800 watts rms, 4ohms?

And to add to what Ivan has stated above be very sure you understand that not all capacitors are created or rated equally. I go through capacitors like water rebuilding guitar amplifiers, and suggest you do your best to stay away from Chinese caps and use good old American brand caps, Mallory and Sprague whenever possible. You'll pay more but be much happier in the end. One of my suppliers for capacitors is MOJOTONE. You'll be very happy with their service.
 
http://www.mojotone.com/amp-parts/Capacitors
 
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John Roberts {JR}

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Re: capacitor capacity in crossover
« Reply #4 on: April 09, 2011, 09:03:13 am »

capacitors are rated in voltage. The ones in question are rated 250v. 250v in music works out to 15,625 watts at 4 ohms. Will a 250v capacitor hold up in a low pass crossover, 800 watts rms, 4ohms?

All 250V capacitors are not alike, just like a 9V transistor radio battery is not in the same time zone as a car battery. The current the capacitor has to deal with in a crossover matters too.

Simple over voltage will cause a capacitor to fail because the dielectric breaks down. Over current causes the capacitor to fail from internal overheating. Note: polar capacitors only block that rated voltage in one direction. so be sure to use non-polar types.

Useful specifications for caps in a crossover would be ESR (series resistance), ESL (series inductance), ripple current (rated current usually at 120 Hz), and a few others.

=====

Another reason I like active crossovers.

JR
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Re: capacitor capacity in crossover
« Reply #4 on: April 09, 2011, 09:03:13 am »


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