Capacitor voltage ratings?

xcsp800

I’m looking to update my crossovers’ on my 11Ts’. My question is, on the 34MFD capacitor, the voltage rating is 250V on the old one, but can it be replaced with a 200V? I’m not seeing the 250V available anywhere from Sonic Craft.

Thanks.

FestYboy

In short: yes. The capacitance value is the important part.

daddyjt

xcsp800 wrote: »

I’m looking to update my crossovers’ on my 11Ts’. My question is, on the 34MFD capacitor, the voltage rating is 250V on the old one, but can it be replaced with a 200V? I’m not seeing the 250V available anywhere from Sonic Craft.

Thanks.

All due respect, but NO, you cannot. You can go with a higher voltage than spec, but never lower.

The capacitance (uf) of a capacitor in a crossover must always be to spec (unless you are modifying the crossover, and really know what you are doing).

If you cannot find the spec you need, you can parallel multiple capacitors to meet the spec. In your case for example, you could parallel a 250v 30uf and a 250v 4uf (just pay attention to physical size constraints). OR, you could go with a 300v 34uf... just a couple options...

pitdogg2

daddyjt wrote: »

xcsp800 wrote: »

I’m looking to update my crossovers’ on my 11Ts’. My question is, on the 34MFD capacitor, the voltage rating is 250V on the old one, but can it be replaced with a 200V? I’m not seeing the 250V available anywhere from Sonic Craft.

Thanks.

All due respect, but NO, you cannot. You can go with a higher voltage than spec, but never lower.

The capacitance (uf) of a capacitor in a crossover must always be to spec (unless you are modifying the crossover, and really know what you are doing).

Slow down Mark this is a passive XO, he is looking at the bipolar electrolytic. Yes he can use 200volt the music voltage will NEVER get that high.

do not use any bipolar electrolytic caps. You should be looking at poly film caps MUCH better than the old electro and Mylar caps. You can also go up in resistor wattage use 10 or 12 watt instead of the 5 watt that they came with but keep the ohm's the same.

I'd also think that when you parallel caps you need to be as close to half as possible or you end up with a bypass cap in essence.
I've used all 200 volt sonicaps in all my XO's. 300 and 400 volt caps are HUGE like pepsi/soup can huge.

xcsp800

Thanks gentlemen.

mhardy6647

I'd opine (FWIW) that there's no good reason to put in lower voltage capacitors than were originally present, but I'll also opine that 200 V rated capacitors shouldn't be a problem at least in the MR and HF sections of a crossover. There are plenty of loudspeakers out there in the field rockin' ridiculously cheap and low-quality 50 V non-polar electrolytics in their crossovers

Capacitors exposed to lower frequency signals (if there were any in a given XO) might well end up fielding the full power output of an amplifier, and if the originally-spec'd parts were borderline in terms of voltage* rating (which is a regrettably common 'problem' due to cost-cutting!), one might be asking for trouble.


(generic image of some exploded electrolytics -- not for the squeamish)



The e-waste depositories of the world are full of components (e.g., flat-screen TVs) that "failed" due to nothing more than failure of power supply capacitors that were not really robust enough for their intended application. This, unfortunately, reflects both cost-cutting and planned obsolescence
______________
* P = V^2/R (for DC) and P = V^2/Z (for AC, where Z = impedance), per "Ohm" and his Law

RTally

Let's be reasonable. That pic above with the failed cap is for an amplifier, not a speaker crossover. Different situation entirely.

Using the nice wheel mhardy6647 provided, power is equal to the square of voltage times resistance (or impedance).

Assume a 100 V cap that is exposed to full voltage applied to a speaker. Such a cap would be across (parallel with) the woofer. A 100 V cap, used for an 8 ohm impedance speaker, results in P = V*V/R = 10,000/8 = 1,250 watts. Few, non Pro speakers, will ever see that much power, and if they do, the voice coil is in more danger than any cap. That voltage squared relationship is why many home speakers use electrolytic caps rated at 50 V (312 watts applied to 8 ohm speaker).

Because most film caps are only available with ratings much over 100 V, anything over 100 V would be acceptable for use in a crossover unless you are talking pro applications.

F1nut

Welcome to Club Polk.

daddyjt

Damn - rebuilding SDA SRS crossovers just got A LOT cheaper and easier! 50v caps are much smaller than the higher voltage spec caps, and easier to fit on the boards.

THANKS!

westmassguy

Most vintage Polks had 100 volt, 34uf caps. Nothing to worry about using Sonicaps.

mhardy6647

Most of the photos of scorched crossovers on the internet show toasted power resistors, in fairness. As I said, a low-ish voltage rating in an XO cap (especially in MR or HF sections of an XO) isn't much of a practical concern.