Capacitor Voltage

[shaiqbashir]

Hi Guys!


well i want to ask you about the voltage ratings of an electrolytic capacitpr. I want to know that why these capacitors are categorized by their voltages. Like there is a capacitor of 100uF of 12V and there is a capacitor of 100uF of 50V. WHat is the difference between the two.

Secondly, in a certain circuit, there is to be used a 0.33uF capacitor of 12V. While in my market, 0.33uF of 50V is avaialable. Can i use the 50V capacitor in the place of 12V one. If not then what should be the replacement. Secondly, please tell me that if a capacitor of a value is not avaiable in the market, then how should we search for its replacement.

Thanks in advance!

Regards,

 

[SM2GXN]

Hi shaiqbashir!

For your first question, the voltage rating given for a capacitor 16V/1000uf means that its maximum working voltage is 16V which you shouldn't exceed, they may withstand higher voltages than the one marked on the capacitor for a shorter period of time but it is always best to stay lower otherwise POFF!!! ???
As you may have noticed, higher voltage rating is equal to bigger can, usually it is as simple as this: you don't put a 50V/1000uF in a circuit were the maximum voltage is 10 volts cause they cost more but if the only capacitor you got on hand is 50V/1000uF just plug it in it will do no harm in most circuits, the can may be bigger so space could be an issue.


For your question number two, in most cases there should be no problem to replace the 12V with 50V capacitor having same capacitance, there may be circuits sensitive enough to upset the function but rarely.
If you don't find the proper value for your capacitor series and parallel is the alternative, one might not be able to get exactley same value but often close enough.

 

[shaiqbashir]

Thanks a lot Mr. SM2

U have helped me a lot!

Regards

 

[MP1]

For your question number two, in most cases there should be no problem to replace the 12V with 50V capacitor having same capacitance, there may be circuits sensitive enough to upset the function but rarely.

In what cases do you see this to be a problem?

MP

 

[oldgrandpainmi]

MP,

Although I can't show this, I can guess:

If there is a circuit where the ESR of the cap is critical, it would be different between the voltage ratings, even though the cap's value is the same.  Even caps with the same rating and voltage, from the same batch, can vary in ESR.

How's that as a guess?

oldgrandpainmi

 

[MP1]

Wow, I totally forgot about this thread since SM2 never answered. Yes, if one was to replace a low ESR capacitor with one which was not low ESR, this could certainly be a problem since ESR is the sum of in-phase AC resistance. However, I read the original post as replacing a standard electrolytic rated at 12 Volts with the same type of electrolytic rated at 50 volts. I do not see where there would be a problem in this scenario, so I had asked the above question. Not sure why SM2 thought there could be a problem in this case. I actually stock the higher voltage electrolytics to keep my stock to a minimum. The only place I see a concern is where the higher voltage rating has a larger physical size, which might take more PC Board real estate.
Nice to see you are bringing some of the older posts back to life.

MP

 

[SM2GXN]

Hi MP!

You and oldgrandpainmi answered your question I apolgize I've missed it  :-[
As you said higher voltage rating is equal to bigger size, let us take one example about size, a crowded pc motherboard usually got their filter caps real close spaced, replacing one of them with higher voltage rating is often not possible because of bigger can size. As most people that repair pc motherboards know dried out caps is quiet common today cause of bad choise of capacitors or bad designed VRM,s.
Say you by a capacitor named something like Rulycon (sounds pretty close to Rubycon) some of these makers of caps has same can size as the original but some of these higher voltage rating, since these caps has higher ESR and badly mixed electrolytic formula they will pop sooner or later probably much sooner than a good cap, higher ripple current will kill the capacitor faster.
It's wise to stay with good brand low ESR caps in SMPS I think you know that better than I do MP 
Another thought, if you replace a mains filter capcitor in a DVD player SMPS which is well screened in a metal box, say you find a capacitor with higher voltage rating but you find that the cap is taller which in turn will put top of the can very close to the screen box, these DVD players does "usually" not have any safety ground connected to its chassie, so what would happen if there is a short to the can? The DVD player might as well have more than 300 volts to its chassie.
I just wanted to guard myself to another question if I had answered like this:
It's just OK to put whatever you have in your junkbox as long as the capacitor has same capacitance and same or higher voltage rating.
However, I didn't finish my job to explane why very well but I guess that there is lot more that can be said about this.
English is not my mother tongue so hopefully you all understand what I tried to explane 

 

[indulis]

Voltage ratings on caps relates directly to the dielectric.
Temperature rating will follow ESR and ripple current.
ESR & ESL will change with frequency.

 

[naushad1]

dear
what is ESR and ESL.
THANKS

 

[indulis]

equivalent series resistance and  equivalent series inductance

 

[aartak]

In order to ensure that the capacitor will not cause problems simply read its
datasheet(of course if you can find it)

 

[Jashimchando]

the voltage rating of capacitor is given by manufacturer to safeguard puncturing of dielectric by peak to peak voltage and damage the capacitor, when it said 50v it means 50v peak to peak. the higher the voltage rating the better it is but more expensive

you have a 9v dc circuit (as measured by dc voltmeter) this means you applied 9v average to the capacitor

AVG volt = 9
PEAK volt = (AVG)(pi) / 2 = 14.12 v
PEAK to PEAK volt = (2)(PEAK volt) = 28.24 v

your minimum capacitor rating is 28.24 v
suggest use 50v capacitor

the capacitor voltage will not affect the circuit operation, it is still 22uf except thicker dielectric material, physically bigger size.

 

[Kevin Weddle]

The voltage rating of a capacitor is proportionate to the value. The construction of high value capacitors results in more tolerance than lower value capacitors.

 

[Hero999]

The voltage rating of a capacitor is proportionate to the value.

No.

The construction of high value capacitors results in more tolerance than lower value capacitors.

Yes, to an extent but that's only because it's less important to have close tolerance of large capacitors, making it an unnecessary expense.

The type of capcitor makes more of a difference to the tolerance, for example large power factor correction capacitors, with values as high as 500V 100

 

[indulis]

The voltage rating on a capacitor is dictated by its dielectric. Thats the stuff between the "plates".

 

[Johnsteave7]

The voltage rating on a capacitor is the maximum amount of voltage that a capacitor can safely be exposed to and can store.

Remember that capacitors are storage devices. The main thing you need to know about capacitors is that they store X charge at X voltage; meaning, they hold a certain size charge (1µF, 100µF, 1000µF, etc.) at a certain voltage (10V, 25V, 50V, etc.). So when choosing a capacitor you just need to know what size charge you want and at which voltage.

At first to understand the voltage rating given for a capacitor 16V/1000uf means that its maximum working voltage is 16V which you not  exceed,it is higher voltages of capacitor and second there should be no problem to replace the 12V with 50V capacitor having same capacitance.

Also try to understand then feel free to go and visit  http://actpcb.com/pcb-calculator capacitance  for your better knowledge.