electrolytic capacitor limit voltage

[Harp]

Question for the experts:
I have a commercial battery charger labeled "Output 30V 400mA."
When I turn it in the power, the measured voltage is 40V.
I have electrolytic capacitor marked with 40V 10000uF, and I was wondering if it is appropriate (safe) to connect it to the output of this battery charger?
Thank you!

[sled]

Hi,

probably there is a transformer in your power adapter, the secondary voltage is usually higher than rated if there is no load - that's most likely the cause for the 40V instead of 30V. Attach a load and measure again - the voltage should be closer to 30V then.

For the capacitor it's usually NOT a good idea to use them close to the rated max. voltage because small deviations could punch the isolation material. I always use twice the voltage rating I expect on tantalums and electrolytic caps, means if you expect 10V, use a cap rated for 20V or more.

Another important thing to keep in mind is that you might want to consider limiting the current to the capacitor, since it's a really large cap and your power supply is limited to 400mA !

Here's a good article: https://www.sparkfun.com/news/1271

[Harp]

Yes, there is a transformer in charger.
Thank you for information about capacitor!