Non-Polarized Electrolytics

[Findm-Keepm]

I've run across something I've never encountered before. In testing a non-polarized electrolytic, all checks are ok except one - the value is double or better in each and every one I tested.

I needed to replace a blown yoke return cap in a Zenith BW set. Easy - I've got the replacement Zenith 4.7uFd cap in my parts stash, so just to be safe, I thought I'd run it across my Sencore LC102. ESR, leakage at full voltage and dielectric absorbtion are A-OK. Value? 4.7ufd it should be, but measures 10.9ufd. Wait - lemme check another I have in the used parts stash. Same thing - double the value at 10.7uf. Yes, I know the value can be high for electrolytics (Sprague TVL's are +80/-20 tolerance), but these are clearly labled with the tolerance - 10%.

Opening up a new (packaged) NTE 2.2Ufd non-polarized cap (actually a United Chemicon by the logo on the cap) it too measures 100% higher, and the tolerance on the cap is stated as 20% (M after the value, corresponds with the 20% rating on the United Chemicon datasheet)

Ok, so let me check against a standard cap I have - 10uF (actually 10.0138uFd by the cal label) - dead on. Next, a common Nichicon 4.7uf 100V cap - 5.8uf, well within the 20% tolerance.

Now here's what I think is happening: Non-polarized electrolytics are made by placing two polarized electrolytics of the double the desired value in series. I'm surmising the Sencore LC102 can't discern that they are in series and somehow reads things high. My EDC cap checker (value only, but spot on with other caps) also checks all my non-polarized electros at 200% or higher.

Anybody out there have any non-polarized electros they'd be willing to check for value?

BTW, I put the first cap I checked in the Zenith - it's now got sweep and working fine. All voltages (per Tekfax) all check out just fine as well. Cap runs cool, so no issues with the double value.

Any help is appreciated. Although my original problem is solved, I'm still wondering.

Cheers,