Re: I need a low voltage expert

[tourman <robercampbell@xxxxxxxxx>]

On Jun 30, 7:27=A0pm, Jim <alarmi...@xxxxxxx> wrote:
> On Jun 30, 7:05=A0pm, and...@xxxxxxxxxxxxxxxxxxxx (Andrew Gabriel)
> wrote:
>
>
>
> > In article <7bdce4ae-930d-44f5-a05a-8aff9b1b2...@xxxxxxxxxxxxxxxxxxxxxx=
ps.com>,
> > =A0 =A0 =A0 =A0 nick markowitz <nmarkow...@xxxxxxxxx> writes:
>
> > > On Jun 30, 5:00 pm, obmcclintock <f...@xxxxxxxxxxxxxxx> wrote:
> > >> 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? Wi=
ll
> > >> I run the risk of burning something out as I can not afford to repla=
ce
> > >> it now that my work is becoming scarce. Please can someone help me
> > >> with this question, thank you!!!
> > > 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 =A0acid in most panels can handle 7-10 am=
p
> > > battery no problem.
> > > if you do put bigger than that =A0the charger in the alarm panel will
> > > never be able to keep up proper charge and burn out.
>
> > 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.
>
> > --
> > 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.

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.....