I did the same to extend the back up time of a couple servers, I used 2
car batteries because the UPS runs on 24 V.
But be careful, aside for the live battery connection (I couldn't figure
it out and learned that in the rude way, 220 V here), you can go into
another problem: some UPSs, mainly the cheap ones intended for backup a
PC lack the power dissipation capacity to run more than the internal
battery discharge time, about 10 minutes at full load. If you connect
an external battery to extend this time the power transistors can be
cooked. I always wondered why these UPSs were not offered in several
time ranges with the same power rating and this is usually the reason.
Some time ago I used several UPSs manufactured by HP in a project and
they had provisions for connecting external battery packs. They had
the dissipation department well designed.
Ignacio, EB4APL
On 06/04/2011 20:25, Murray Greenman wrote:
Why not just put a bigger battery in your UPS? I have a couple of old
ones, and they run just fine with an old car battery, and thus give me
many hours of backup for my Trimble/Nortel GPSDO.
Just be careful though - in some UPS units the battery is live to the
mains! The APC ones seem to be OK.
Murray
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