# EEVblog Electronics Community Forum

## Electronics => Repair => Topic started by: RayRay on June 30, 2022, 12:29:52 am

Title: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: RayRay on June 30, 2022, 12:29:52 am
Hey guys.
So, I need to replace a faulty 63v 47uf capacitor, but it's an uncommon value that I don't have handy.
I do however have 22uf 50v ones, which I could combine to get the capacitance, but I'm not sure how that'd work in terms of voltage divide, would the voltage be split in half across the 2 caps in such a scenario, or should I bother obtaining caps with the needed value? I've made a drawing of how I was thinking of connecting em (attached)
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: bdunham7 on June 30, 2022, 12:54:13 am
That's just parallel and you'll have 44µF and 50V--both under spec.  44µF is close enough and it will work as long as your actual circuit is operating at less than 50 volts.
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: RayRay on June 30, 2022, 01:02:16 am
Thought that might be the case. Thanks for your help!
What if I connect 4 in series though, will that support up to 63v?
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: abdulbadii on June 30, 2022, 01:49:24 am
22uf 50v is not fulfilling C rate as sum < 47uF

get of greater one, instead of series, put each || to other

___|___
_|_   _|_
___  ___
|____|
|

so top and bottom terminal represent the required C
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: mariush on June 30, 2022, 05:54:01 am
You should first determine what voltage is in that circuit.

It's quite possible that the voltage is much lower than 63v but they went with 47uF 63v because they used such value in another part of the circuit or because they wouldn't have gained anything by using a lower voltage rating one.

For example, they often make 47uF 35v, 50v and 63v in the same diameter - 5mm or 8mm - and the only difference may be a small difference in height ex 8x11 mm for 35/50v and 8x13mm for 63v - the designer could have left a 5mm diameter for this capacitor but 2-3mm of diameter is not much savings and leaving 8mm makes it possible to use 5mm or 8mm capacitors so they'd be able to use different series if one becomes unavailable.
Sometimes they use a thicker version (ex 8 mm instead of 5mm diameter) and taller one because it would be more resilient to temperature, the bigger metal can handle temperatures better and the capacitor will last for a longer time.

Unless the capacitor is used for some very specific purpose (timing for example), in a lot of cases it's possible to increase the capacitance a bit without any negative effects .. so you could probably use 56uF or 68uF without any worries.

So basically, going a bit higher in capacitance is fine, going lower is risky.  Going a bit lower in voltage rating should be avoided unless you're sure of the maximum voltage that would be across the capacitor, but going up in voltage rating is fine - your limitations would be dimensions (diameter and height) and the technical specifications - a bigger size capacitor may have much better technical specs that could affect the stability of the circuit (depending how the capacitor is used)

Capacitors in parallel give you more capacitance, but same voltage rating.  Capacitors in series gives you same capacitance, higher voltage rating (but with big voltage rating / capacitance capacitors you also need balancing resistors)

So with your 2 capacitors, in parallel you'd have 44uF 50v - 44uF is close enough to 47uF (all capacitors are +/- 20% so 44uF is well within +/- 20%)  but 50v is below the 63v rating.  IF you're lucky the capacitor never sees a voltage close to 50v in which case you can use the capacitors in parallel.

In series, you'd get 22uF and 100v rating - voltage wise it would be safe, but capacitance is too low.
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: wraper on June 30, 2022, 06:02:09 am
22uf 50v is not fulfilling C rate as sum < 47uF
Does not matter. It's less than 10% difference while the vast majority of electrolytic caps have at least 20% tolerance. Nor they are used with precise capacitance in mind.
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: Kleinstein on June 30, 2022, 06:09:22 am
44 µF is usually close enough. Many circuits are not very picky with the capacitance choosen: even a single 22 µF may work in quite a few circuits.

Another alternative can be 2 x 100 µF in series. This could than also be lower voltage caps. Ideally one would have high value resistors in parallel to help balancing the voltage, but it depends on the circuit if this is OK.
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: vk6zgo on July 03, 2022, 07:14:39 am
You should first determine what voltage is in that circuit.

It's quite possible that the voltage is much lower than 63v but they went with 47uF 63v because they used such value in another part of the circuit or because they wouldn't have gained anything by using a lower voltage rating one.

For example, they often make 47uF 35v, 50v and 63v in the same diameter - 5mm or 8mm - and the only difference may be a small difference in height ex 8x11 mm for 35/50v and 8x13mm for 63v - the designer could have left a 5mm diameter for this capacitor but 2-3mm of diameter is not much savings and leaving 8mm makes it possible to use 5mm or 8mm capacitors so they'd be able to use different series if one becomes unavailable.
Sometimes they use a thicker version (ex 8 mm instead of 5mm diameter) and taller one because it would be more resilient to temperature, the bigger metal can handle temperatures better and the capacitor will last for a longer time.

Unless the capacitor is used for some very specific purpose (timing for example), in a lot of cases it's possible to increase the capacitance a bit without any negative effects .. so you could probably use 56uF or 68uF without any worries.

So basically, going a bit higher in capacitance is fine, going lower is risky.  Going a bit lower in voltage rating should be avoided unless you're sure of the maximum voltage that would be across the capacitor, but going up in voltage rating is fine - your limitations would be dimensions (diameter and height) and the technical specifications - a bigger size capacitor may have much better technical specs that could affect the stability of the circuit (depending how the capacitor is used)

Capacitors in parallel give you more capacitance, but same voltage rating.  Capacitors in series gives you same capacitance, higher voltage rating (but with big voltage rating / capacitance capacitors you also need balancing resistors)

So with your 2 capacitors, in parallel you'd have 44uF 50v - 44uF is close enough to 47uF (all capacitors are +/- 20% so 44uF is well within +/- 20%)  but 50v is below the 63v rating.  IF you're lucky the capacitor never sees a voltage close to 50v in which case you can use the capacitors in parallel.

In series, you'd get 22uF and 100v rating - voltage wise it would be safe, but capacitance is too low.
Nope, you will have 11uF and 100v rating.
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: tooki on July 03, 2022, 02:49:33 pm
Capacitors in parallel give you more capacitance, but same voltage rating.  Capacitors in series gives you same capacitance, higher voltage rating (but with big voltage rating / capacitance capacitors you also need balancing resistors)
I’m sorry, what? That’s absolutely wrong. Capacitance falls when you put capacitors in series, using the same formula as parallel resistors:

Ctot = 1/(1/C1 + 1/C2 + … + 1/Cn)

(Does anyone know if there’s a general name for this formula, the reciprocal of sums of reciprocals?)
Title: Re: Replacing a single 63v cap with 2x (uncommon value) possible?
Post by: Zero999 on July 04, 2022, 11:22:09 am
Get the correct value. 47µF 63V is a very common value. It really isn't worth bodging it.