Series Capacitors to handle higher voltage

Passives Capacitors
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Hi,

I would like to use Dig-Key Part Number 493-7811-ND, 35 V electrolytic capacitors in series to get an over all higher rated voltage. I see the capacitors vary +/-20%. If these different capacitance capacitors are charged from a high voltage supply, will they charge evenly and not exceed their 35 V rating?

For example, if we put three in series with the hope of reliably holding 3 * 35 V. That equals 105 V. If we put three of these capacitors in series and then connect a current limited 105 DC supply on it, will the capacitors stay within their voltage tolerance if the three capacitors are -20%, 0% and + 20% of their rated capacitance values?

Best Regards,
Chris

2

Because of capacitance tolerances and other factors such as differences in leakage current from device to device, series-connected capacitors cannot be counted on to charge evenly unless provisions are made to ensure this outcome.

A parallel arrangement of 3 LNR2A154MSE would offer a significantly higher capacitance with nearly the same aggregate voltage rating, in a smaller physical size at lower cost and without complications coming from series connection.

3

Hi Rick,

Thanks for responding and for linking that better capacitor. Do you know what provisions need to be made to ensure the series capacitors do not get over charged?

Best Regards,
Chris

4

“Cell balancing” is probably the magic search term for such things. There are different techniques used, ranging from sophisticated monitoring systems incorporating microcontrollers and ADCs to simple systems that are essentially little more than a zener diode, with varying benefits and disadvantages to each.

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With high capacity high voltage capacitors charge balancing should only be used if there are no other viable options, or it’s a one off hand made/checked hobby circuit.

With supercapacitors, where only very low voltage parts are available, it is fairly common. This article from Electronic Design magazine provides a good introduction to the design tradeoffs in common balancing methods.
https://www.electronicdesign.com/power-management/whitepaper/21134743/balancing-supercapacitor-stack-voltages

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