[NBLUG/talk] OT: Anyone ever replaced a battery in a UPS?

[Bob Blick]

Dave Sisley wrote:
> I don't want to hijack this thread, but want to pose a question of my 
> own.  I have quite a few UPS's piled up - and I have no way of knowing 
> if they are any good (although some have 'failed' and now I know maybe I 
> can replace the battery).
> 
> What's the best way to test a UPS?  I don't have any sort of voltmeter 
> or whatever (but if that's what I need, I'm off to Radio Shack).   
> Obviously, battery-time is dependant on how many things you have plugged 
> into it, but is there a way to quantify how much juice a charged UPS can 
> deliver?

Hi Dave,

I was at Harbor Freight today, digital multimeters are $2.99 until Xmas...

If you have a known good battery you can put it in a UPS and start 
plugging more and more things into it until it shuts off, that will give 
you an idea how much power it can deliver. UPSes are rated in 
volt-amps(VA) and actual wattage is less than that(the ratio varies from 
manufacturer to manufacturer, but is usually somewhere around the square 
root of two). How long it can run a load is pretty much dependent on the 
capacity of the battery. Sealed lead-acid batteries are rated based on a 
20 hour discharge and have much less capacity when discharged at high 
rates(like a UPS will do). So any calculations will have little relation 
to your actual uptime under load.

If you charge a sealed lead-acid battery and then let it sit overnight, 
the static voltage will relate quite well to the overall capacity of the 
battery, but will not tell you how it will hold up under heavy load - 
the load test is the only real way to tell.

Also, although most consumer UPSes use a single 12 volt battery, there 
are variations. I have a rackmount Tripp-Lite with three 6 volt 
batteries connected for 18 volts. But the battery voltage is printed on 
the battery so it's usually easy to tell what's going on.

Warning: most UPSes do not have the battery isolated from the AC line, 
so if the UPS is plugged in, you can get a shock touching one of the 
battery terminals. So do your testing carefully and if you cobble a 
battery outside of the UPS(maybe because it's the wrong battery and 
won't fit inside) you are creating a shock hazard.

Cheerful regards,

Bob


Cheerful regards,

Bob