I have some lead-acid gel cells that have been removed from UPSes due to aging and reduced capacity. They still charge to full voltage.
Short of actually charging them up and running them down - which would take a long time - is there a way I can judge their quality? Some are worse than others. Internal resistance test of some kind, maybe?
Put a significant load on them and measure how the current changes over time.
With a correctly chosen load, 10 - 30 seconds should be more than enough to get a good idea about their capacity.
I normally use light bulbs as loads -- they're cheap, easy to obtain, come in a great variety, and got a very good overload indication and protection. :-)
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Useful idea. Thanks.
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Seems to me that the higher internal resistance means that the plate area is much less than the fresh cell. Same goes for the capacity.
That makes sense. I may try an internal resistance test (low-level dynamic AC or something) and see what it reveals.
I have a question that is not related, but perhaps you posters know: Is there adverse effect to mounting a gel cell battery in a manner other than vertical? I see nothing on the cell that says it must remain a certain way.
The manufacturers own recommendations are that they can be used in any orientation, but check that you haven't got the one make that doesn't allow that!
Regarding testing, we always use a high-rate discharge test, at least 1C and monitor the voltage over 1 minute to see what discharge slope we get.
While you can use open-circuit terminal voltage as a rough guide to the state of charge, the battery must have been standing off-load or off-charge for an hour, and it is a rough guide only.
We just shipped out a special charger for an experimental battery research application, 0-600V @ 150A and 0-50V @ 150A, hand or PC voltage and current control, weighs about 1100kg or just over a ton, 3-phase input 415/440V 3-wire. We took some pictures as we were building it and will put them up on the company website next week. I'll advise url when we get them finished.
Peter
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