Donald Teed donald.teed at gmail.com
Sun Dec 18 17:33:36 AST 2005

On 12/18/05, Stephen Gregory <nslug at kernelpanic.ca> wrote:

> Measureing the AC voltage produced by the UPS does not prove
> anything. Most affordable UPSs don't produce clean sinusoidal power
> and it is hard to measure properly. At any rate a UPS needs to be
> measured under load.

I'm not going to pass myself off as an expert on electricity.
However I don't understand the above.  If a UPS produces
power that is dirtier than from the electrical company, then
why do we have them?

I'd think that over testing the UPS for load repeatedly would
be a bad idea.  Given that lead acid batteries have a life
span defined by the shedding of materials inside,
you want to reduce the consumption of the compounds.
Anyone who has left their lights on a couple of times
and then needs a new battery is aware of that pattern.

Technically, you might need to test under load to accurately
measure the capacity, but each time you do, you effectively
consume the lifespan of the device.  I don't think you even
need to go that way if you start out with the realization that
the voltage without AC is way too low even without load,
and the UPS software sharply lowers the number of minutes
of charge after the AC power is pulled.  I wouldn't
call it "proof", but enough to realize it is time to
replace something.

In my experience, it is cheaper to buy another UPS
than to replace batteries, with the very low end models.

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