PSN-L Email List Message

Subject: Re: Gas Generator recommendations / standby power
From: "Charles R. Patton" charles.r.patton@........
Date: Tue, 08 May 2001 21:38:37 -0700

Al wrote:
"I have a 250 watt UPS that I put Binding Posts on the back so I can
add more battery capacity when needed. It uses 12 volts."

A warning might be needed here.  I agree with your advice on taking out
the batteries and using a fan and so forth.  But the line above suggests
paralleling the internal with external batteries.  It isn't advise that
wet cells (car batteries for instance) in parallel with gel cells (UPS
supply internal batteries) because they don't equalize well due to
slightly different cell voltages.  Even if the cell chemistry were to
give equal voltages, a large change can also be easily caused by
different thermal environments, with the hotter battery's terminal
voltage dropping, and getting hotter as it adsorbs more charging
current.  I.e., batteries in parallel should be similar in size,
location, charging/ usage history and chemistry, and even then you can
have problems without careful attention.


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Larry Cochrane <cochrane@..............>