I need a low voltage expert

I have a technical question about low voltage in an alarm system. I have a 10 year old radio shack 8 zone burglar/fire alarm panel with a small rechargable back up battery. I would like to replace it with a larger wet cell battery just in case our power is out for quite a length of time. I will place it in a vented box close to the panel. My question is; Can I use a battery much larger in size and amp hours than the little one as long as the voltage is the same- 12 volts? Will I run the risk of burning something out as I can not afford to replace it now that my work is becoming scarce. Please can someone help me with this question, thank you!!!

Reply to
obmcclintock
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No can do must use a lead/gel acid battery or risk of fire. the panels charger is not designed for wet cells.

could put a bigger lead/gel acid in most panels can handle 7-10 amp battery no problem. if you do put bigger than that the charger in the alarm panel will never be able to keep up proper charge and burn out.

you could set up a wet cell and separate charger and then shift it over with a relay to burg panel but not economical to do so and must be done so very carefully or risk of fire damage. best bet would be to get 1000 or bigger VA UPS uninterpretable power supply and plug alarm into it . about $150.00 this way UPS battery will hold panel up then when its battery runs out the panels battery takes over have done this many places and it works very well.

Reply to
nick markowitz

Thank you very much Nick, I appreciate it !!! obmcclintock

Reply to
obmcclintock

The charger circuit limits the charging current, and the current won't increase with a larger capacity battery - it will simply take longer to fully charge. This is most unlikely to damage the charge circuit.

Note that lead/gel acid batteries used in alarms don't like being run completely flat (whipes out some of the capacity each time you do it), and the alarm may behave unpredictably as the battery voltage drops too low. Some alarms have a battery protection function to switch off and cease current draw before running the battery too low, but probably not a 10 year old radio shack system. If you are using the system in a situation where you expect the battery to run out, you might want to investigate a battery protection circuit, although it might not integrate well with the alarm if it wasn't designed with this in mind.

Reply to
Andrew Gabriel

Andrew, read Nick's reply. I think you missed the fact that the OP wanted to use a wet cell battery, presumably a car battery. Aside from the things that Nick pointed out, the fact that liquid lead acid batteries emit hydrogen is important to note also. Lack of proper ventilation and/or a little open flame can cause quite a "pop" and the ignition of anything flamable. Not to forget about the corrosion factor with wet cells.

Gel cells that are normally used in alarm panels control the venting of gas and the UPS also has gel cells. I too have used UPS's to extend the standby time of alarm panels. Works great and pretty inexpensive too.

Reply to
Jim

When a charger is being kept on hard full charge because a battery is over sized and can not keep up it is just like when it keeps charging into a dead dried up gel cell the charger will get hot and overheat when it is constantly being called on there are times when I have gone to change out a low battery the panel board and heat sink is so hot you can not touch it with a bare hand.and plug in transformer has burn marks on it as well from overheating. see it all the time.

Reply to
nick markowitz

RHC: Yes, UPS's are also very useful for extending the backup battery time of cable modems. They are advertised as having a longer backup battery time than they actually do in reality. Put the cable modem on a UPS and you have your monitoring continuous for far longer times. No power, no cable modem, no monitoring.....

Reply to
tourman

I didn't miss that point. I agree with what nick said about that, so didn't see the need to comment further on it.

SLA batteries for float use are normally charged at a max current of C/7, so you're looking at 7 hours minimum to recharge (probably 10 hours because charging isn't 100% efficient). The charger will have got up to temperature within an hour or two of starting to charge, and stay there until the battery approaches full charge some hours later and the charging current reduces. If you put in a larger battery, it won't get any hotter, it will just stay hot for longer (when charging a completely discharged battery), because with a larger C, the charging current will be less than C/7 and take longer to charge.

There's no "not keeping up" - the alarm is not suddenly drawing any more current or the charger providing less current, just because you increased the battery capacity. It will take longer to charge, but it will more than keep up.

A shorted cell in a battery is a different issue, and that isn't what a larger capacity battery will look like to the charger. Of course, the charger shouldn't end up in a dangerous condition because of a shorted cell, but if you buy a cheap product, that's the sort of place you might find [lack-of-]design compromises were made. Poor quality chargers often result in short battery life too, and may well be the cause of the dead cell in the first place.

Reply to
Andrew Gabriel

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