Peri Hartman via EV wrote:
First, thanks for everyone's replies. Appreciated.
The unit I bought is rated for 900w and 1500VA. The specs don't list the
Wh but, again, my guess is around 100Wh.
The idea of hacking the unit and putting in a larger battery is
tempting. Theoretically, if it is rated for a 900w load, it seems that
100w or even 200w should be safe continuously. But who knows. And that
assumption has no relation to charging, where the charger is probably
the minimum to safely charge the existing battery.
900w sounds big enough; but like I said, there is a lot of fantasy in
small home UPS specs. I think they assume you'll never test it. A UPS is
a bit like a fuse -- if you never have a problem, you'll never know if
it's a real fuse, or a cheap fake!
It's not that hard to connect a bigger battery and see what happens. It
might be entertaining to experiment. :-)
I put an ammeter and voltmeter on my UPS battery, and measured the
voltage and current during charging, to see what kind of charging
algorithm it was doing. The ones I've tested are just s stupid
float-voltage charger -- it applies a fixed "float" voltage, limited by
whatever the charger's max current is (which was 2-3 amps on the UPS I
tested). Also check around to be sure nothing is getting hot. I didn't
have any temperature rise problems during charging.
Then try a discharge test. See how long it runs, how hot things get, and
what its cut-of voltage is. I found I needed to add fan cooling for
anything over 10-15 minutes.
The two models I tried had cut-off voltages around 10v. That struck me
as a bit low. The APC models have a pot to set the cut-off voltage, so I
set it to 11v to give the battery a break.
Warning: The battery in some UPS is *not isolated* from the AC line! I
found this out the hard way, and destroyed a Sola UPS. The SL Waber
UPS-250 is built this way; but the two APC are not.
Happy hacking,
Lee Hart
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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