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Topic: 100 uf capacitor voltage rating (Read 1 time) previous topic - next topic

pwesson

In the  Arduino example, a 100 uf capacitor is used.

http://arduino.cc/en/Tutorial/SFRRangerReader

I can easy buy a 100 uf capacitor - but I'm a novice at electronics and wondered should I be concerned about the capacitors stated voltage?

For example, should I purchase the 100 uf 10V capacitor, or should I be looking for a 5v or 3.3v one.


Kind regards,
Paul  :~

Magician

Cap connected to +5V line, so 6.3V rating should be fine. Of course, you can use cap with higher voltage rating, 10V or 16

RoyK

Good working practice is to use a voltage rating of at least twice the expected voltage. More is better.


majenko

The voltage rating on a capacitor is the voltage level above which it is likely to explode and get very messy.

The voltage doesn't affect the capacitance in any way.

As long as you stay well below the rated current all will be fine.  The closer you get to that rated current, the more likely you are to run into manufacturing tolerances and defects and have a capacitor explode, or vent.  I for one always use at least double the required voltage if possible.

Many modern motherboards have capacitors that are rated at just over the required voltage, and it is amazing how many motherboards die with vented caps.  You can always tell a vented cap - the top of it is bulging outwards.

For more information: http://en.wikipedia.org/wiki/Capacitor_plague
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James C4S


The voltage doesn't affect the capacitance in any way.

Well, for ceramic capacitors voltage does matter.  Ceramics (excluding C0G/NPO) have a voltage (and temp) coefficient associated with them.  The closer the applied voltage is to the rated voltage, the less effective capacitance you get.  For cheap dielectrics like Y5V and Z5U the loss can be as high as 60%.


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majenko



The voltage doesn't affect the capacitance in any way.

Well, for ceramic capacitors voltage does matter.  Ceramics (excluding C0G/NPO) have a voltage (and temp) coefficient associated with them.  The closer the applied voltage is to the rated voltage, the less effective capacitance you get.  For cheap dielectrics like Y5V and Z5U the loss can be as high as 60%.


Yes, but we're not talking ceramics here - we're talking electrolytics.
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MarkT


Good working practice is to use a voltage rating of at least twice the expected voltage. More is better.


Working voltage is not the same as an "absolute maximum rating".  Semiconductor datasheets often highlight the abs max ratings rather than recommended working conditions.  Capacitor datasheets are more sensible.  Choose a working voltage greater than the maximum actual in-circuit voltage it will be exposed to, factor of two is unnecessary.  The device is spec'd to run at working voltage continuously.  Higher voltages upto the "surge voltage" rating are tolerable for brief periods (but may lead to greater leakage current).
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James C4S


Yes, but we're not talking ceramics here - we're talking electrolytics.

The capacitor type was never mentioned in this thread.  Which is a dangerous  when talking about capacitors because different dielectrics have different behaviors and guidelines.

(You already deleted the comment, so I assume you realize 100uF ceramics do exist.)
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

majenko



Good working practice is to use a voltage rating of at least twice the expected voltage. More is better.


Working voltage is not the same as an "absolute maximum rating".  Semiconductor datasheets often highlight the abs max ratings rather than recommended working conditions.  Capacitor datasheets are more sensible.  Choose a working voltage greater than the maximum actual in-circuit voltage it will be exposed to, factor of two is unnecessary.  The device is spec'd to run at working voltage continuously.  Higher voltages upto the "surge voltage" rating are tolerable for brief periods (but may lead to greater leakage current).


Voltages closer to the capacitor rated value generate more heat.  Capacitor longevity is a function of heat - more heat = shorter lifespan.  Selecting a capacitor with a higher voltage isn't just about what voltages it can cope with - it's also about getting a good lifespan out of your capacitor.
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majenko



Yes, but we're not talking ceramics here - we're talking electrolytics.

The capacitor type was never mentioned in this thread.  Which is a dangerous  when talking about capacitors because different dielectrics have different behaviors and guidelines.

(You already deleted the comment, so I assume you realize 100uF ceramics do exist.)

There are certain assumptions one has to make with this site.

1. The people asking questions are generally novices.
2. The fact the question is being asked shows a lot about the knowledge levels of the user.
3. You have to ask yourself what kind of capacitor it is most likely to be given the simple fact the question is being asked, and the way the question was asked.

Balance of probability:  Wet electrolytic.  It would be a freak occurrence if the OP was asking about anything else given the style of question.

Also, if you would care to click the link the OP provided - that looks very much like a drawing of an electrolytic to me - and the schematic clearly shows it's polarised.
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