# Electrolytic capacitor rms and peak current

1. ## Electrolytic capacitor rms and peak current

Can electrolytic capacitors can have higher peak current than their max RMS or ripple current ratings as long as RMS current is below the specified current value?

Such as a capacitor with a rating of 1.5amp RMS max which conducts 4amps peak but 1.2A RMS.

2. ## Re: Electrolytic capacitor rms and peak current

Hi,

It's the nature of AC, that the peak value is higher than the RMS value.

Klaus

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3. ## Re: Electrolytic capacitor rms and peak current

Originally Posted by KlausST
Hi,

It's the nature of AC, that the peak value is higher than the RMS value.

Klaus
But electrolytics don't work with AC the peak currents might be from switching an inductive load with constant peak current greater than specified RMS current from datasheet.

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4. ## Re: Electrolytic capacitor rms and peak current

Hi,

But electrolytics don't work with AC
For sure every capacitor can work with AC current.

For voltage:
Electrolytics can't work with "negative voltage".
In usual power supply applications, there is DC voltage combined with AC voltage (ripple) in a way that there is no negative voltage.

Klaus

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5. ## Re: Electrolytic capacitor rms and peak current

The peak current can be any value as long as RMS current isn't exceeded?

6. ## Re: Electrolytic capacitor rms and peak current

Hi,

If there is an additional current limit, then I'd expect it to be specified in the datasheet.

Klaus

7. ## Re: Electrolytic capacitor rms and peak current

Originally Posted by KlausST
Hi,

If there is an additional current limit, then I'd expect it to be specified in the datasheet.

Klaus
Yeah? Cap datasheets can be among the worst.

I would assume 4A peak for a 1.2rms rated cap is fine. 5x or 10x might have me thinking more carefully about it.

But also consider the whole picture. If you also have a handful of ceramic (or films) with lower esr/esl they'll start taking the higher frequency pulses away from your electrolytics. It's good practice to have them anyway.

8. ## Re: Electrolytic capacitor rms and peak current

The peak current can be any value as long as RMS current isn't exceeded?
You must also consider the rated voltage of the capacitor. An electrolytic capacitor always have some series resistance (ideal capacitor has zero equivalent series resistance) and that can limit the initial current.

Consider you are using a low duty cycle square wave (positive going narrow pulse train) that will have high peak current but low RMS current. Such a case you will have the peak current limited by the capacitor series resistance. The ESR contributes to the internal heating that also must be limited.

In short, the answer is YES!

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9. ## Re: Electrolytic capacitor rms and peak current

Originally Posted by Zak28
Can electrolytic capacitors can have higher peak current than their max RMS or ripple current ratings as long as RMS current is below the specified current value?

Such as a capacitor with a rating of 1.5amp RMS max which conducts 4amps peak but 1.2A RMS.
I believe the current specification of caps is limited by their ESR, where excess heating might destroy it. Heating is directly related to Irms, and not Ipeak. Hence working below the Irms with high Ipeak should be ok.

Voltage on the other hand is related to electrolyte breakdown, so peak values must be well below voltage ratings.

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