question about capacitor voltage rating?

[samy555]

Hello
When the working voltage is say, 12 volt, then the suitable capacitor is 25 volt, i.e the double
what if i use 16 volt cap?
what will happen if i use 10 volt cap??

thanks alot

 

[tpetar]

Hello
When the working voltage is say, 12 volt, then the suitable capacitor is 25 volt, i.e the double
what if i use 16 volt cap?
what will happen if i use 10 volt cap??

thanks alot

Rated voltage is maximum allowed continouous voltage with which capacitor can work safely.

Its not good to use capacitor in over rated voltage design, that can lead to capacitor damage with side effects of explosions and leakages.

16V rated capacitor can work on 12V if there is no spikes, high ripples, and other extreme situations in voltage. With other words, you need good stabilized and steady voltage.

Often that can be seen in situations when designers dont have much space on PCB, and use lower voltage rating of capacitor but still in safe range of capacitor working voltage. For example: capacitor rated for up to 6V is used for 5V circuit powered with Li-Ion single cell battery, and there is no need to use 25V or 35V rated capacitor.



Read this additional materials:

Capacitors Tutorial
http://www.facstaff.bucknell.edu/mastascu/elessonshtml/LC/Capac1.htm

Types of Capacitors
http://www.learningaboutelectronics.com/Articles/Types-of-capacitors

What does the Voltage Rating on a Capacitor Mean?
http://www.learningaboutelectronics.com/Articles/What-does-the-voltage-rating-on-a-capacitor-mean




Best regards,
Peter

;-)

 

[samy555]

thank you very much

 

[tpetar]

You will find a lots of videos on YouTube portal, where people playing with capacitors and higher voltages. Just type in search field "exploding capacitor" or something similar.


Best regards,
Peter

 

[ftsolutions]

There is also a relation to projected MTBF (reduced) of designs where the capacitor is operated at close to its maximum rating. As a general rule of thumb, choose a capacitor such that the maximum voltage you expect to see on it is no more than 70-80% of the capacitor's maxium rating. Depending upon the modeling and criteria used, more margin may be necessary, but this is a reasonable starting point.

 

[samy555]

There is also a relation to projected MTBF (reduced) of designs where the capacitor is operated at close to its maximum rating. As a general rule of thumb, choose a capacitor such that the maximum voltage you expect to see on it is no more than 70-80% of the capacitor's maxium rating. Depending upon the modeling and criteria used, more margin may be necessary, but this is a reasonable starting point.

thank you

Someone told me that when he useed a 10u/250v cap in a 555 timing circuit he got very bad results. but when he used a 10u/16v cap he got results exactly as he calculated them
He was working with a 12-volt battery
I am surprised that, is there a logical explanation?
thanks

 

[ftsolutions]

There are so many possible variables with such a generically worded question without specifics on what "bad results" means...
Does "bad result" mean that the time on/off interval was out of spec, was the timer oscillating, or not resetting, or ???
It is possible that the ESR of the high voltage cap was significantly different from the 16V cap, and that had an effect on the charge/discharge time of the circuit. Or maybe it was not the same tolerance. Or the right temperature rating. This is only a guess and it may only be tangentially related to the voltage rating of the part. Specifying a capacitor ONLY by the voltage rating isn't sufficient for all applications.

 

[Venkadesh_M]

thank you

Someone told me that when he useed a 10u/250v cap in a 555 timing circuit he got very bad results. but when he used a 10u/16v cap he got results exactly as he calculated them
He was working with a 12-volt battery
I am surprised that, is there a logical explanation?
thanks

That doesn't make sense may be the capacitor is leaky or damaged....

 

[tpetar]

thank you

Someone told me that when he useed a 10u/250v cap in a 555 timing circuit he got very bad results. but when he used a 10u/16v cap he got results exactly as he calculated them
He was working with a 12-volt battery
I am surprised that, is there a logical explanation?
thanks

Probably he use polypropylene capacitor which is not good for higher frequencies.


Best regards,
Peter

 

[samy555]

Probably he use polypropylene capacitor which is not good for higher frequencies.


Best regards,
Peter

Thank you Peter
no, it was an electrolytic capacitor.

 

[tpetar]

Thank you Peter
no, it was an electrolytic capacitor.

In that case maybe he reverse polarity.


Best regards,
Peter

 

[samy555]

No, he is good in basic electronics, So I do not think he misses this point.
He claims that when using, say 10u/160v capacitor in 555 timing circuit, then the capacitor reduced its capacitance by a considerable amount!!!

 

[tpetar]

No, he is good in basic electronics, So I do not think he misses this point.
He claims that when using, say 10u/160v capacitor in 555 timing circuit, then the capacitor reduced its capacitance by a considerable amount!!!

Maybe he try to use Chinese Kinder Surprise Egg :

Best regards,
Peter

 

[samy555]

LOL
may be,,,,,,,,,,,,,,,,,,

thank

 

[tpetar]

There is one more possibility that capacitor is very old or its not used recently. Longer resting of electrolytic capacitors can increase internal resistance and can reduce capabilities of capacitors.


Best regards,
Peter

:wink:

 

[kripacharya]

Probably he use polypropylene capacitor which is not good for higher frequencies.


Best regards,
Peter

In that case maybe he reverse polarity.


Best regards,
Peter

Maybe he try to use Chinese Kinder Surprise Egg :

Best regards,
Peter

There is one more possibility that capacitor is very old or its not used recently. Longer resting of electrolytic capacitors can increase internal resistance and can reduce capabilities of capacitors.


Best regards,
Peter

:wink:

The last one is the usual suspect for electrolytics. Typical tolerance range is anyhow very wide, and an old cap is likely to have degraded. Experienced hacks would "rebuild" the electrolyte before using an old electrolytic.

However even this does not directly correlate to a higher voltage rating resulting in a poorer capacitance value. More needs to be understood here.