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Testing an uninterruptible power supply (UPS)

I would like to buy a battery for my UPS which has failed. But there is no clear indication that the sealed lead-acid battery is dead. How do I test?

Should I hook a multimeter to the positive battery terminal? The 10 amp DC multimeter setting should do? Put the black multimeter probe to the battery positive terminal and the red multimeter probe to the UPS charging output? I expect that will measure charging current flowing into the battery and provide an indication of whether the UPS is attempting to charge the battery.

Any idea of how much charging current there should be?

This is the 12 V sealed lead-acid battery model number: BP7-12 7AH/20HR I guess "20HR" means that it takes 20 hours to recharge.

Thank you.

Reply to
John Doe
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The 7AH/20HR means that the battery will put out 7AH if it is discharged at a 20 hour rate, 7/20 = .35 amps. If you discharge the battery with a .35 amp load, it should be dead in 20 hours. In a UPS though they normally drain them at a much higher rate. As for charging I would estimate something less than 2 amps. maybe slightly more. As far as testing the battery goes, if you want to spend less money than a new battery would cost (about $15 for a 7AH), I would suggest taking a 12V light bulb and hook it up to the battery and monitor the voltage till it drops to about 10 volts. Then do the math and see how many amp hours you got out of the battery. Then compare that to a similar energy curve on the spec sheet for a new battery like this one....

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If you don't know the wattage of the light you are using, you could use your 10A amp meter to measure current draw and another meter to monitor voltage. The current will also change as the voltage drops.

If you really want to know how all your batteries are doing you could get this thing

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or this thing

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The second one is cheaper but you need to provide the load to discharge the battery.

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Chris W

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Reply to
Chris W

Thanks.

That was my best wild guess.

I messed with it for a while, but the charging light in my Tripp Lite UPS does not even come on (blink) now, like it did before.

Oh well.

It is being replaced with a line conditioner (APC LE1200). I think that is what I want. I am not very concerned about loss of data (I do backups frequently in Windows). I am concerned about possible damage to my hardware caused by brownouts.

Ideally, I would like something without a battery that would sustain my system for a few seconds. I am sure the LE1200 will not do that, but hopefully it will help.

Thanks for helping me get on with replacing the thing.

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Reply to
John Doe

No, I was thinking it might mean 20 hours to charge, as in "hour recharge". Thanks for the correction.

Reply to
John Doe

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