I haven't seen any capacitor with the "Ampere" rating written over its body. Usually they have max. voltage and capacitance ratings, can i know "current" rating from both values?(Supposing AC voltage)
is it simply voltage/reactance ?
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4\$\begingroup\$ From the datasheet, like the rest of the characteristics which won't fit on the body. \$\endgroup\$– Dmitry GrigoryevCommented Sep 7, 2016 at 14:09
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\$\begingroup\$ @DmitryGrigoryev I am not familiar with passive components datasheets, where can i get it?. Do I just use google for any datasheet of capacitor that have the same voltage and capacitance ratings? \$\endgroup\$– iMohanedCommented Sep 7, 2016 at 14:11
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1\$\begingroup\$ @MohannadMaklad: like all other datasheets, you get it from the manufacturer \$\endgroup\$– PlasmaHHCommented Sep 7, 2016 at 14:13
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6\$\begingroup\$ Get the datasheet from the manufacturer's website or from the supplier. If the supplier doesn't have datasheets available, you don't know what you're getting for your money. "No datasheet, no sale" is a good rule. \$\endgroup\$– user16324Commented Sep 7, 2016 at 14:17
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2 Answers
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How can i know current rating of a capacitor?
From the datasheet.
Most capacitors don't actually have a "current" rating, since that doesn't make much sense. You can't put a sustained current through a capacitor anyway. If you tried, its voltage would rise linearly, and then you'd get to the voltage limit where you'd have to stop. Put another way, current through a capacitor is inherently AC.
Capacitors do often have a ripple current spec. Capacitors designed to be used in applications where this matters, like switching power supplies, will have a ripple current spec. Check out the Panasonic FK series, for example. These are designed for particularly low ESR (for electrolytic capacitors). Applications where low ESR is important are likely to subject the capacitor to significant ripple current, so this is specified.
Other capacitors are optimized for different purposes where the maximum allowed ripple current isn't relevant, or is so bad the manufacturer doesn't want to admit what it is. In cases where you care, don't use such capacitors.
answered Sep 7, 2016 at 14:29
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\$\begingroup\$ ** You can't put a sustained current thru a capacitor anyway. If you tried, its voltage would rise linearly, and then you'd get to the voltage limit where you'd have to stop** You mean by this DC current, right?. \$\endgroup\$– iMohanedCommented Sep 7, 2016 at 14:50
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\$\begingroup\$ @Mohan: Yes, otherwise the statement would make no sense. \$\endgroup\$ Commented Sep 7, 2016 at 14:58
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\$\begingroup\$ @OlinLathrop So then what does the "permissible current" (RMS) on page 10 of this polypropylene film capacitor's data sheet mean? The link is mouser.com/datasheet/2/315/ABD0000C255-1131244.pdf . I have seen figures like that for many different film capacitors. Can they be used well beyond their permissible RMS current rating so long as they are within the AC voltage rating? \$\endgroup\$– dcsukaCommented Jun 23, 2023 at 19:37
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All the ratings are not always printed on the components body. The ratings that are not written are given in the datasheet. This is the same for the voltage ratings of resistors, for example: except for a few specific cases, they're never written on resistors.
In your case, the current rating is mentioned in the datasheet as the "ripple current". Beware it is expressed as a RMS value, and it depends on the frequency of the current you're smoothing with the capacitor (they are often given for both 100Hz - for mains rectification - and a few hundreds of kHz for SMPS supplies).
Also note that this value is not always given, depending on the type of capacitor. Ceramic capacitors, for example, usually don't have them in the datasheets because they're not usually appropriate for power supply rectification.
