On 2/11/2013 1:41 AM, Cor van de Water wrote:
the input side of a UPS would make for a backup charger, in fact
it might charge faster than the charger I have in my EV today.
Maybe yes; maybe no.
I've played with a few UPS (Sola, APC, SL Waber). The ones I looked at
would have some significant shortcomings if you tried to use them as a
battery charger, or as an inverter with your EV's battery pack.
The Sola could not start generating AC unless there was already AC on
its input. It used the AC from the AC line, or from its own inverter
output, to power its logic section. Without AC, the inverter could not
start. It depended on the AC to "precharge" the power supply, so when it
went away, there was enough power to start the inverter.
The SL Waber had a "hot" non-isolated charger for its battery pack. I
destroyed one by thinking I could use it to charge a battery that had
its negative side grounded! It also would not start inverting without a
source of AC just prior to the inverter switching on.
All of them had really miserable chargers. They delivered a very low
charging current (like 1 amp max), and it was a constant-voltage "float"
charger, fixed at 13.8v max.
All of them also had very poor heatsinking, intended only to run at full
power for maybe 5-10 minutes (only as long as the batteries would
normally last).
But these are all smaller "consumer" UPS. The big commercial units are
(hopefully) better designed and more versatile. Before I bought a UPS to
use as a charger or isolated inverter, I'd want to hear from someone who
has tried that particular make/model (like Cor did on the 3kv Powerware
9125).
--
The most dangerous enemy of a better solution is an existing one that
is just good enough. -- Eric S. Raymond
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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