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Old 27th August 2006, 08:41 PM   #1
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Default Battery Charger

Hey I need something to charge a 12v sealed lead acid batt from a backup ups.


anything quick and dirty? I was thinking lm317, 7805 as a current limiter, and a diode.
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Old 27th August 2006, 10:20 PM   #2
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http://www.bb-battery.com/productpages/BP/BP4-12.pdf

just found the doccumentation on this battery. Seems to be Glass mat type ( not gel type) with a charge voltage of 14.5v aprox @ 1.2 amp max ( id assume lesser current would be best) and 13.5v for standby operation.
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Old 2nd September 2006, 01:55 AM   #3
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I tried using a car charger to charge it at a 2A trickle charge....no juice at all, even left it overnight.
Nothing. Do I need higher voltage/ amperage to clean the crystals off the plates inside?
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Old 2nd September 2006, 02:34 AM   #4
soongsc is offline soongsc  Taiwan
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The UPS should charge it. Why would you need to charge it separately?
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Old 2nd September 2006, 03:41 AM   #5
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because I dont have a ups..... this isnt for one anyways. I'm using it to power a small portable amplifier. I actually have two, which will give me +/- 12v so I wont be as limited on wattage due to rails.
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Old 5th September 2006, 08:36 AM   #6
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Dude 88,
Let me see if I got this straight.

Your trying to charge a SLA battery.
Ran it over night on a 2 amp charger, and it diden't work.

If Ive got that right, good chance the battery is dead. Sorry to report that they don't get better.

Used to happen to us all the time in the chemical weapons radio business. We used SLA cells for the base station battery pack and the customers almost never took care of them. So after two or three years of running and charging, the cell packs burned out and were never coming back.

They 'sulphate' over time. When that happens, they won't take a charge, or if they do, it self discharges quick.

The best thing to do is take the dud cell pack and have it recycled with dead car batteries, and go buy your self a fresh one.

There is a shelf life and a service life, and neither of them get better on batteries.

Good luck there
Jack Crow in Kuwait
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Old 5th September 2006, 05:17 PM   #7
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hey , thanks for the info. The cell I have I pulled from a ups, and the battery was still very much good. Plenty of amperage. I let it sit for about a month or so before using it again, and it was totally dead. I aslo have another one that has some power left in it, enough to run a small motor slowley, think it will charge?
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Old 5th September 2006, 05:25 PM   #8
paulb is offline paulb  Canada
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Maybe your charger is bad. Monitor the voltage while you're charging it. And/Or the charge current if you can. If it draws a whole bunch of current with no voltage increase, the battery is bad.
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Old 5th September 2006, 06:19 PM   #9
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it doesnt draw a whole bunch of current, the voltage increases ( I got the dead one to go up to 11.6v from 5v) but no amperage out of the battery meaning its still dead.

I threw together a charger running off of a 12vac trafo, into a LM7815 regulator, resistor and diode. Out put is about 14.5v @ 1 amp, although the batt wont draw that much from it.
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Old 5th September 2006, 10:02 PM   #10
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Letting the battery sit for a month with no charge applied is the same as draining the charge off with a load, just slower. The self-discharge rate of LA batteries is pretty high and they don't recover well from deep discharges, as you have discovered.

If it won't take a charge from a "normal" level of current, there are safety reasons why you SHOULD NOT try cranking up the charge current. You are liable to boil the stuff inside the battery and if you're very lucky it won't boil-over or even explode and spray nastiness everywhere. If you have to try it, do it outdoors, with the battery sitting at the bottom of a deep, oncovered plastic bucket so that if it does blow/spew it won't mess up anything of value.

It is probably time to go buy a new battery.

I_F
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