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Aluminum electrolityc capacitors operated close to rated voltage

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brumbarchris:
Hello,
Whereas we do have a fair experience with ceramics, we find ourselves in the situation where we need to place some aluminum electrolytic capacitors on our PCBs, in order to ensure a low impedance of the battery pack we are using.

The battery pack consists of 6 x LR6 alkaline cells. Even if the cells are super-charged to begin with, their individual voltage would not exceed 1.65V, which means that the entire pack would be at 9.9V maximum.

Is it "safe" to use 10V rated electrolytic capacitors?

Sure, I know having margin is better, but here this is a "late" addition to the design and we are quite constrained in terms of volumetric space.
Having browsed some datasheets, I have not seen any temperature derating information, but as I said, our experience with this sort of caps is limited, hence the question.

Regards,
Cristian

Siwastaja:
It should be fine. Aluminium electrolytic capacitors inherently have built-in voltage margin (i.e., the dielectric is formed at the factory at higher voltage rating), and leakage current starts to steeply increase only after some 20-30% overvoltage. Contrast this to tantalum capacitors, which have fallacious voltage ratings, and 40% derating is the norm as always explained in the usually separate application note.

For the same reason, alu elcaps used to come with separate working voltage ("WV") and surge/peak voltage ratings in the past. Haven't seen them since 1990's. Nowadays rated voltage is the working voltage.

I always try to derate aluminium elcaps by at least 10-15% as a general principle, but I would not hesitate not to derate it in situation like yours.

1.65V is a decent estimate for initial no-load voltage of an alkaline cell.

Voltage derating helps dissipate heat by increasing the package size, in large ripple current applications, and this way, increase the lifetime. This probably does not apply to your use case.

Go for it.

dzseki:

--- Quote from: Siwastaja on May 25, 2022, 10:15:50 am ---alu elcaps used to come with separate working voltage ("WV") and surge/peak voltage ratings in the past. Haven't seen them since 1990's. Nowadays rated voltage is the working voltage.

--- End quote ---

I have made a new design recently where I selected the filter capacitor from CDE, I was delighted to see on the sleeve of the capacitor that the surge voltage rating was also indicated!

Someone:
https://data.energizer.com/pdfs/l91.pdf
1.8V fresh and excitingly low impedance!

the next common step up at 16V seems a bit high, so a good 10V part that specifies transient or surge voltage rating would probably be the best bet (more common in higher voltage/mains parts but available in 10V).

TimNJ:
Check this: https://www.eevblog.com/forum/projects/impact-to-lifespan-of-an-electrolytic-capacitor-run-near-rated-voltage/

It’s not a problem, in principle. The only thing you might want tp consider is whether or not you can actually trust the manufacturer’s ratings. Probably just don’t use some garbage bottom tier brand.

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