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How could I modify alarm system to be kinder to SLA batteries..

Hi,

It seems to kill a battery every couple years. Pulled battery today, warm to the touch, 11.3V.

If I read the voltage of the wires going to the battery when disconnected, it reads 13.71V.

It has some sort of detection to indicate when the battery is dead, it issued a fault today because of it.

I bought a replacement for it today, but I am wondering, is there anything I can do to make it be kinder to the battery?

If I do something, obviously it:

1) Must not affect the bad battery detection circuit (probably just checks voltage? or maybe it does a test load on battery?)

2) Must not affect switchover or operation on battery.

3) Perhaps lower the charging voltage if possible to make the battery last longer. This is just a regular SLA, not a gell cell or anything. What would be the ideal voltage?

What type of circuit could I put in place between the 2 wires from the alarm and the 2 battery terminals that would make it a less aggressive charger, but allow full use of the battery if need be?

Thanks,

Alan

Reply to
Anonymous User
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Not untypical for SLA batteries in that sort of application. I get about the same life out of the batteries in my UPS.

Sylvia.

Reply to
Sylvia Else

Hmm..i get roughly ten years life with the battery in my UPS (APC

330-XT+).
Reply to
Robert Baer

Some of those things have poor charging circuits that end up cooking the battery. One quick fix that might work for you: Add a resistor and bulb between the charge/alarm circuit and the battery. Use a relay whose normally closed contacts short out the resistor & bulb combination, and have the relay energized when line voltage is present. When the line voltage drops out, the relay drops out and removes the resistance from the circuit; when the line voltage is present, the resistor & bulb combo is in circuit between the battery and the charge/alarm circuit.

It's tough to specify the value of the resistor, with no details on the battery or the charger. Most likely it's a trickle charger, and a small capacity SLA, under 10 amp hours. You might try 10 ohms at 10 watts.

The bulb (a 12 volt auto brake light bulb) in series with the resistor protects the resistor from overheating in the event that the battery is flat when line voltage returns. If the charger is already current limited to under 1 amp, the bulb is not needed.

Your battery might not be maintained at 100% charge with the modification, but it will be close.

Ed

Reply to
ehsjr

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