Yeah. Mire shite from aan electronics designeer of some 320 years
experience, and who has spent more time charging batteries in teh last
two years than he is prepared to mention.
So? The principles are the same. They aen't to YOU, of course, beacuse
your understanding is totally limited.
I have seen things burn out in micro seconds, millisecond, seconds,
hours, minutes days, months and years. All for different reasons. Most
of which I ecventually identified, since it was part of my job to do so.
Your statement says nothing.
320 years eh! Christ, that's before electricity itself was tammed!
Yes, please do. Piss off and learn some manners.
Oh. So why then do manufacturers of PSU's and chargers specify the maximum
size of cell to be used??!
Here's one... take a flat car battery and place it on charge. What will the
meter on the charger tell you? 3A?, 4A? Then it calmes down as the battery
So, this guy places his 17Ah battery in parrallel and the mains fails for a
prolomnged period. The batteries are used and then the power is restored.
What typical current are you expecting the batteries to draw on initial
charge?! Let me tell you it'll be more than the 1.2A that is the typical
fuse rating in the charging circuit!
Any self-respecting battery charger will limit the maximimum current it
delivers to a safe (for it) amount. It thus won't care whether you've
connected a 10Ah or a 1000Ah battery to it, the maximum charging
current will be the same. It'll just take a long time to charge big
No, I haven't a clue. What I do know though, after many years in the
security systems business, that if you overload an alarm panel battery by
installing one of larger capacity that the manufacturer states the fuse will
likely pop or the PSU will burn out. I have seen this so many times and in
some cases the damage to the panel has been beyond economical repair.
So I'm not basing my comments on calculations or a supreme knowledge of
electronics but on over 20 years experience in the field and I think that
Control panel PSU's/charging circuits are generally nothing fancy and
usually just incorporate the bare minimum of components to give a charge.
OK, on some of the top end panels the PSU and charger are top dollar and
will react to abuse accordingly. Some even have status reporting via the
LCD. I think though that someone who is posting here will have something
more basic and will therefore be running the risk of a burned out PSU.
On Tue, 16 Dec 2003 10:31:46 +0000 (GMT), Dave Plowman
To be fair - nor do most alarm panel designers. Some of the designs
are very crude and simply rely upon the resistance of the transformer
windings. Whilst this is usually adequate for the battery specified
if called upon to operate in this mode for a protracted period heat
related failures are common.
Peter, if you try an charge a gel type battery - as all the alarms I've
ever seen use - with the method you describe, it will have a very short
life indeed. At the very least it needs a constant voltage charge, and
since it is left permanently on charge a way of dropping this to a
'float' amount. And ICs to do this very job cost pennies these days.
*What was the best thing before sliced bread?
Dave Plowman firstname.lastname@example.org London SW 12
I really think everyne overreacted.
Lead acid chargers are just a voltage source in series with a
resistance. Using one that delivers less merely means the float charge
is slower, and teh batteries take longer to recharge out of an outage.
My guess is you have panicked needlessly.
This assumes the charger circuitry lasts that long. A lot of alarm
panels are of dubious quality and I suspect the charge circuit is
designed to sustain its maximum output for only a relatively short
time. Making it work at max output for several times the expected
time may well cause things to overheat and expire.
well peter the internal charger will definatly have some form of current
and 'should' be quite capable of sustaining the max current indefinatly. it
matters not how big the capacity of the battery is, this max current is
fixed. the only thing that will vary is the charging time. however if the
unit is of dubious quality as you suggest who knows
I suspect the extra hum from your kit may be due to some metalwork
getting slightly re-positioned by accident, and is nothing to worry
Or there could be a problem not associated with the new battery that
does need worrying about!
It is unlikely IME that fitting the 17AH battery as well as or instead
of the 7AH will have any adverse effect. [as long as it is not faulty]
If you are worried about it, just put a 10 ohm 5 watt resistor in the
+ve lead between the new battery and the rest of the system.
I really wouldn't go for separate chargers etc
May, but not will.
But I doubt it.
What a partially dicsharged battery looks like is a low voltage source
in series with a bit of resistance - fairly negligible in comparison to
the charge currents being used. What happens if you stick a bigger
battery in the vcharge circuit is that it will run at the same charge
current (cos its voltage is the same) for longer.
I have xcharged car batteries with trickle chargers from one amp up to
15 amps. The battery is no different. The little chargers will still
charge the bigger batteries. Just takes a couple of days, is all.
Any charger is going to run full charge on all butteh smallest cells for
at least an hour...and if it hasn't blown in an hour, it won't blow in
three...its up to working temp in that hour.
The alarm panel will only have a transformer that supplies just enough to
keep things going at their designed working ratings, so making it work
harder can, and will, make it overheat inside the casing. This rise in
temperature inside the casing can, and will, have bad effects on other
Most panel instructions will give a maximum battery capacity allowed for
that design of power supply, so to increase this capacity can, and will,
have effects on the design of the system and will void any warranty.
The charger system may well be a voltage / current source with a bit of
resistance, but you have to take into consideration the environment that the
source and resistance are working in. The system expels heat into its
surrounding space. The space within, and the connected heat dissipation
appliances, should be enough to safely exhaust that heat away from the
appliance. Increase the heat, or close in the space, and you have to
consider what effect these change will have within the working parameters
that have already been designed into the system.
The increase in the "HUM" sound heard, probably means the power supply is
working harder to keep the increase in battery capacity up to the system
ratings. So this means an increase in heat produced by the power system.
This increase is probably not designed for by the makers, so it can, and
will, effect the designed for working state of the system.
The power supply is rated to take what the makers allow for in the design of
the panel, so making changes to these parameters will affect what is allowed
for in the design. If the power supply has to work harder at charging the
battery, then it is probably not supplying other parts of the system with
the correct power source they need to work properly.
Whast happens in practice is that the voltage obviously settles around a
common point. However you have to over voltage to charge, and under
discharge, the volts drop, so there is no huge explosion when you e.g.
stick jump leads on a car to start it, even if you use a tractor battery
to do it (provided its not a 24 or 48v battery of course).
Under charge, the voltage rises...the more discharged battery will hog
current till both batteries are at an eqqual state of charge,
concomitant with the applied voltage. At that point they appear as a
simple larger single battery. And stay that way until seperated.
The only remaining issue is one of peak current. But any abttery has a
pretty low impedance, so teh charger will be designed to supply a
certain current to a certain voltage that reflects teh discharge state
of teh battery. It doesn't KNOW how big the battery is. It just KNOWS
that a 60% flat battery will be at - say - 12.5V under charge, and it
will deliver its rated current to that voltage whatever.
The cfact that the OP's charge hummed a bit merely shows the battery was
fairly discharged. Unless you are into super fast charging (one hour or
less) currents will never be high enough to risk battery damage, and the
current into a larger battery will be no higher.
The greater danger is over currenting a small battery.
OK, say this happens...
The small battery is flat
The large one isn't
The large battery will charge the small one until they are at equal states
Trouble is, there is no current limiting in between the two batteries, so
the small one will be charged at "cor blimey" amps, which is not good for
the battery, or the wires interconnecting them.
Caravans and boats have a special split charging system, so this doesn't
Look in any multi battery UPS, and you will see the batteries are all
connected in series, not parallel because of this.
As people have said before, just connecting the big battery will be OK if
the charging circuit is of a suitable quality, prolong periods of higher
current charging *WILL* cause the voltage regulator to heat up more than it
would with a smaller battery
Things are made cheaply, so they will just about do the job they were made
for, but no more - I recently bought a cheap electric car tyre inflator,
there are warnings you need to only use it for a shot while, then turn it
off to cool, then you can use it again - yes it will inflate a tractor tyre,
but not in one hit - it would overheat - the same may well go for the
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