Capacitor Leakage, and ESR Explained

[Yorkie]

Thanks David for the clarification. This makes more sense now. I did see the table you have posted but at the bottom of the page, you did write that the values may be different. I am just wondering, how would you find out the ESR value of a capacitor? Will they be mentioned in the spec of the capacitor or that’s something Bob came up with? In the ESR meter, does it display the expected ESR value for a cap and the actual ESR value for it? I am quite curious how this thing really works before throwing some money around, that's all.

Welcome to the forum, and thanks for reading the thread

All new capacitors should have a very low ESR - a good capacitor should show up as zero or just a fraction of an Ohm, so there's no stated value. Some electrolytic capacitors are especially designed for critical applications such as in switched mode power supplies and are marketed as such.

If you test a capacitor and it has an ESR of much more than 1 Ohm - up to 10 Ohms (see Bob Parker's table for worst case values considered acceptable for a range of capacitances), then the advice is to compare that old cap with a new one. If the ESR of the old one is say 8 Ohms and a new one of the same capacitance is say 1 Ohm or less, then fit the new one and chuck the old one away! Really, anything with an ESR much above 10 Ohms, has stopped being a capacitor and is doing a good imitation of a resistor.

As to 'not wanting to throw money about' an ESR meter needn't be an expensive item. The homebrew meter that I built can (in the UK anyway), be built for about £15.00 GBP (less than $25 Canadian). The thread I wrote about the development of that homebrew meter became very untidy, so Joe (forum archivist), kindly created a PDF of how to build, test and use that meter, which can be found at the link in post #50 here:

http://golbornevintageradio.co.uk/forum/...hp?tid=411&page=5

In another thread, Nick DS highlighted an excellent little ready built and tested meter module that tests capacitors (electrolytic and non-electrolytic), showing their capacitance and ESR, which also tests transistors, diodes, inductors, resistors, and costs only £16.00 GBP ($25 Canadian), including post. Several forum members have bought these little meter modules and built them into boxes including myself. Mine has worked fine, though very occasionally it does state: 'no known/faulty part' when other meters give a reading of some sort.

http://www.ebay.co.uk/itm/151021743457

You can see my boxed up version in this thread at post #19:

http://golbornevintageradio.co.uk/forum/...p?tid=3296&page=2

It’s far cheaper than other ESR meters that are favoured by many restorers and has the advantage of being multi-function. Had it been available when I developed and built my homebrew ESR meter, I probably wouldn't have bothered - I'd have bought one of those modules instead!

Hope that helps.

(BTW, I was embarrassed to note that in my original thread about ESR/Leakage I'd made several grammatical errors, so I must have been asleep at the wheel when I wrote it. On some forums I'd have been ordered to the Head's Study for admonishment, but everyone is too polite here, so I've corrected the errors - I hope I spotted all of them!).