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SMPS capacitor test question

I noticed the lithium battery for my nikon camera was acting as it it had a bad cell. It would charge, but just not last very long. The battery is "smart" with a third terminal that the camera talks to. It shows perfect "health" which is total nonsense after 2 years of use and the fact that it doesn't work right.

THe charger itself is is little less smart. It charges the battery at 8.4V and 0.9A or something like that, but using only the + and - terminals from the battery pack.

I also noticed it got pretty hot, so I opened it and found very few parts aside from some 20+ pin charging controller and pretty basic switching power supply. The transformer and filter caps were pretty hot. The older Kodak/Sony AA NiMH chargers seriously look more complex than this charger.

I guess it's expected that that cap will warm up at whatever crazy frequencies they use these days in compact power supplies, however while it would fail my standard for the touch test, it may still be in spec.

Is a capacitor ESR meter of some sort going to be useful for testing the cap? What frequencies do they test at?

While I could just replace the cap and not worry about it, not being able to test it is the issue I'm more interested in solving.

Reply to
Cydrome Leader
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An ESR meter such as the Bob Parker Blue now available from Anatek Corp, would tell you the story. It tests at around 100kHz, as I recall. It's not an expensive instrument, especially if you build it yourself from a kit, and is certainly endlessly useful in a commercial workshop. For non-commercial casual use, still cheap enough to be one of those 'nice to have' items ...

Arfa

Reply to
Arfa Daily

What Arfa said, but an ESR meter is a bit of a luxury if you don't have the prospect of some ongoing use for it (I have one, but I use it in servicing often enough). For one-off problems and no meter at hand, if I had doubts about the cap I'd simply replace it with a 105C low-ESR reputable_brand_and_series one. They are cheap enough, and if that still leaves the thing steaming hot then the problem lies elsewhere.

On the battery pack - there *should* be a protection module within it which will (should) monitor cell voltage differences among other parameters. Assuming that is the case, a LiXX charger with a constant voltage setting of 8.4V is appropriate, and 900mA is within the bounds of reason. If the charger gets hot it is probably due to its supply-side electronics rather than the controller chip or battery side circuitry. An 8W switcher shouldn't dissipate much heat at all. While I would normally expect good stuff from Nikon, who knows.

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who where

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