Electronics > Beginners

Is 50v cap too high for an amp with 32v power supply?

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Zero999:

--- Quote from: David Hess on April 21, 2019, 07:18:30 pm ---A higher voltage capacitor will work fine and will even have advantages.  The larger size yields higher ripple current rating and longer operating life.  Since more modern capacitors tend to be smaller for the same capacitance and voltage, a higher voltage part may be necessary to meet other specifications.

ESR usually drops with higher voltages up to about 150 volts where a different electrolyte has to be used.
--- End quote ---
You're right, the ESR does reduce if the case size is also increased. My point was that if the case size stays constant the ESR tends to increase, with voltage rating. If you can fit a bigger capacitor, in the same place, by all means up the voltage rating, but if it means having to bodge it, then don't bother, as it can cause other failure points.

The datasheet linked below suggests above 35V, the ESR increases, if the case size remains the same. This is of course assuming the capacitance normally falls too. If the voltage is upped and the case size not increased, I suspect that squeezing a higher capacitor value and voltage rating, into the same case increases the ESR. Yes, if this is an old design, you'll probably be able to get modern, higher voltage, lower ESR, parts with the same capacitance into the same or smaller case style, but I doubt the same applies to modern parts.
https://docs-emea.rs-online.com/webdocs/1500/0900766b815005ec.pdf


--- Quote ---Below is an example where I probably should have used even higher voltage replacements just to get a physically longer part for better mounting.
--- End quote ---
Yuck! In that case lager capacitors should have been used purely to avoid those bodge wires, which should be insulated, to reduce the risk of short circuits.

Rerouter:
should make clear on the voltage margins, you don't want to exceed them, and you can sometimes extend there life by running them at a lower voltage, so if your power supply is very well regulated and low ripple current it generally doesnt matter,

On a device like an amplifier where I presume its more or less straight out of a rectifier, then you need to leave some margin, however this margin should be based on the AC voltage that your multimeter measures before the rectifier, and not the DC voltage measured after it,

Measure AC voltage before rectifiers, times that by 1.414 (Changing RMS voltage into peak to peak voltage)
Measure your mains AC voltage, see where your in your countries power specifications, and add margin to account for it being at that maximum, (its relative, so if you measure 240V and your mains allows up to 250V, then times it by 250/240)

And finally you add your compfort margin, generally atleast 5% to account for surges on the mains,

If you meet this your set, if you exceed it, then so long as you still meet my first 2 points.

innkeeper:

--- Quote from: Mp3 on April 20, 2019, 10:45:29 pm ---Hi everyone, upgrading the caps in my FX Audio D802, but one problem is the power supply is 32v and the main power caps are rated for 35v.... so i want to put in something with a higher tolerance, but all i can find is 40v or 50v, and there are only a couple choices in 40v, my question is 50v too high voltage for use with a 32v power supply? Or should i get some better quality 35v caps?

--- End quote ---
What are you trying to accomplish????
What is the problem your trying to solve, or, what are you trying to improve?

vk6zgo:

--- Quote from: Rerouter on April 21, 2019, 10:10:57 pm ---should make clear on the voltage margins, you don't want to exceed them, and you can sometimes extend there life by running them at a lower voltage, so if your power supply is very well regulated and low ripple current it generally doesnt matter,

On a device like an amplifier where I presume its more or less straight out of a rectifier, then you need to leave some margin, however this margin should be based on the AC voltage that your multimeter measures before the rectifier, and not the DC voltage measured after it,

Measure AC voltage before rectifiers, times that by 1.414 (Changing RMS voltage into peak to peak voltage)

--- End quote ---
You stuttered a bit, ;D-------I know you really meant peak voltage.

--- Quote ---
Measure your mains AC voltage, see where your in your countries power specifications, and add margin to account for it being at that maximum, (its relative, so if you measure 240V and your mains allows up to 250V, then times it by 250/240)

And finally you add your compfort margin, generally atleast 5% to account for surges on the mains,

If you meet this your set, if you exceed it, then so long as you still meet my first 2 points.

--- End quote ---

vk6zgo:
This 6.3v thing happens even in the "best of families".

Sony loved using them, & must have known something, as they did last, (ten years or so), but their capacitance as read on a digital  display LCR meter was usually well down & "losses" (it didn't talk "ESR") were up, so I would replace  them "on principle" with 10v rated caps, which were usually in the same package.
I didn't have the same sources as Sony, 6.3v caps were very rare at my usual suppliers, & the alternative sources didn't inspire confidence.

You can still get caught out with some other manufacturers.
I replaced the faulty "biggish" NP smoothing cap for filtering the "boost HT" on an Electrohome monitor with its "modern equivalent" marvelling at how they had reduced the size, till it started to overheat & blow "steam" out of the end.

Low ESR equivalent NP caps in that value & rating were unobtainium, so it ended up with a "Christmas tree" of polyester "greencaps" instead.
Ugly? Messy? Not best practice?-----Yep! But it worked, & that is the primary requirement.

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