I have a list of values of capacitors and i also know their material types! But i don't know how to figure out their voltage rating? "Ratings have been removed in the capacitors for this purpose"

Also for my inductors, i have their value.But i have no idea how i can find their current ratings? "Ratings have been removed from the inductor for this purpose"

I have a RCL-METER if that can help me out. I used it to find the capacitance and inductance value!

Thank you!

  • 3
    \$\begingroup\$ It is written in their datasheet. It's unfortunate you don't have one... \$\endgroup\$
    – Eugene Sh.
    Oct 26, 2017 at 20:00
  • \$\begingroup\$ What are the type of capacitors you have? Tantalum, electrolytic or else? \$\endgroup\$
    – dirac16
    Oct 26, 2017 at 20:08
  • 5
    \$\begingroup\$ It is unclear what you are asking: "Ratings have been removed in the capacitors for this purpose". Removed by whom? For what purpose? \$\endgroup\$
    – Transistor
    Oct 26, 2017 at 20:08
  • \$\begingroup\$ @Transistor I think the purpose is for educational practice? Or define the ratings for a new product? \$\endgroup\$
    – Nazar
    Oct 26, 2017 at 20:28
  • \$\begingroup\$ Only one way I know of.... destructive testing on a decent sample size! \$\endgroup\$
    – Trevor_G
    Oct 26, 2017 at 20:29

2 Answers 2


I was not sure whether this should be an answer or a comment, but a good breath of fresh air cleared my mind:

You cannot guess rating based on short-term, small sample-size observation.

That is simply not what a rating is.

A rating is the manufacture saying

I promise that within X years, not more than Y‰ of our devices will malfunction by a deviation of D from this set S of specified properties, if operated, stored and transported under these environmental conditions E.


  • X will be in the order of years. If you test only for hours or days, it will be hard to infer anything, unless your caps die horribly. Then you know "way to much", but nothing else, really
  • Y is something that you'll need to define yourself. What failure rate is acceptable? Nothing in your question indicates you've given that any thought!
  • apropos failure: what is a failure? Fire? A reduction of capacity by 10% A two-fold increase in leakage current? An increase in ohmic resistance? Susceptibility of any parameter to air humidity? D and S would answer that, and your application would define those, but again, no trace of consideration
  • only one small part of E is what you seem to care about, but that's simply a misunderstanding of what it means to have a rating for anything.

Generally, unless very expensive components got accidentally packaged wrongly by accident (never saw that happen), there is no good reason to scrape off markings on a package. I've heard of counterfeit components, which someone tried to import, so they scraped off the markings and imported them as "no-brand". Those devices are either stolen, or actually of inferior quality. You would never use them - capacitors are a commodity device, so just throw yours away and get well-rated ones.


Exceeding the voltage rating on caps usually ends up shortening their life (a lot). You don't specify the type of capacitor, which would have an impact. In any case, if I had a heap of a given capacitor, I'd take one and slowly increase the voltage across the leads, measure leakage current, and note when it gets destroyed. Then wager an educated guess on that data, divide by two, and use that as my rating.

It's a bit the same idea with the inductors, but potentially less destructive, since you can monitor their temperature. As far as I know, the DC current rating of inductors is actually established by a give delta T vs ambient. So you can swipe the current getting in the inductor until you reach a temperature increase you are comfortable with (eg. 10°C)

or at least that is what I'd do presented with the problem.

  • \$\begingroup\$ Divide by 2. Or 200. Depends. In the end, devices are also speced to a failure probability within a speced life time, and how would you know your capacitor at the voltage you're using it with dies after 1 year instead of 20 years, if you don't test a couple hundred caps for a couple years? \$\endgroup\$ Oct 26, 2017 at 22:01

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