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RE: Testing a battery float charger

To: <>
Subject: RE: Testing a battery float charger
From: "Randall" <>
Date: Wed, 15 Nov 2006 10:50:39 -0800
> Anyway, is there a way to test an automatic battery float charger?
> I've got about 5 of these that I can't figure out if they are 
> draining the
> batteries or if the batteries went bad (but I don't want to risk them
> eating any more batteries)
> Is there a way to test if they are behaving properly?  Thanks.

First, easiest test would be to hook them to a  known good, fully charged
battery.  Monitor the voltage directly at the battery.  If the charger is
working, you should immediately see the voltage rise as it starts charging
the battery.  If we're talking 12v lead-acid (car battery), the voltage
should continue to rise into the 14.2-14.6 range.  Then you should see the
voltage drop back over some time (minutes usually, might be longer depending
on the charger) to around 13.1-13.5 and hold there.  If it continues to drop
below 13v, then the float circuit is probably not working.

As long as you keep an eye on it, and remove it promptly if it starts to
discharge or overcharge the battery, then it won't hurt the battery.

To get much more thorough, I think you'll need to know how the charger is
supposed to work, and what kind of battery it's designed for.  Gel cells,
for example, usually need current limits and/or temperature limits.

BTW, if these are those cheap float chargers from Harbor Freight; every one
of mine has failed.  Turns out they should only be connected to an
already-charged battery ... connecting them to a heavily discharged battery
will burn up the transformer.  And then it will, as you say, run the battery
flat over time & ruin it.


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