New capacitor esr value query

[sam67]

Just bought some caps that are 0.1uf 100v caps ..just tested with esr meter and the esr is about 25 ohms ..Is this about right for such a low cap.. The caps are suppose to be low esr ... they are not branded but they were all i could get.

Thanks

[Huckfinn]

Re: New capacitor esr value query

sam67:

A high quality nonpolar polymer or mica cap at .1 and 100v reads about 12 ohms esr value. You did not state whether or not your new .1 units are electrolytic or not. Most commonly, .1 units at 100V rating are not aluminum electrolytics, but some are. If your units are small round aluminum cylinders with plastic shrink labels, they are electrolytics. These can read about 25ohms esr when new. If they are discs or rectangular shaped blobs or boxes, they are very likely nonpolar nonelectrolyte types, using ceramic, mica or polymer for the dielectric [insulator]. Electrolytics can also be configured to be nonpolar, this is accomplished by putting two polar electrolytics inside the "can" and hooking them up in series with the two negative leads connected to each other internally while the two positive leads come out of the case, giving you a nonpolar electrolytic equivalent. Externally, these NP caps look just like a regular electrolytic, except that they do not have polarity markings, and sometimes they actually put the "NP" designation on the plastic over-sleeve. Flipping the polarities of the internal and external hookup also gives the same results, as long as the two leads that come out of the case always have the same polarity as both minus or both plus. Keep in mind that to get a nonpolar electrolytic equivalent, two capacitors are connected in series that each have twice the capacitance of the desired end value. That hookup of course doubles the esr value. If your units are electrolytics, they may have about 25 ohms esr even without being NP electros [anotherwords, they have a polarity marking ]. If your units are not electrolytic, but are one of the other mentioned technologies, then 25 ohms esr indicates a not-so-great new cap.

Huck

[sam67]

Re: New capacitor esr value query

Hey thanks Huckfinn for the run down it's appreciated..Sorry i forgot the golden rule and did not post what type of caps they are..

They are indeed electrolytic caps so i guess these should be ok with the 25 ohm esr..There is about 10 of them and all measure same readings.

Thanks again for your time

Best

sam67