Installed new battery backup for home alarm

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PJO wrote:

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.
Piss off.

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.

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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 charges.
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!
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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 batteries.
--
Chris Green ( snipped-for-privacy@x-1.net)

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PJO wrote:

None of mine do. They do specify the minimum capacity tho.

Correct. That shows you the state of the battry not its capacity tho.
Otherwise a totally flat 10000000A/h battery would take a zillion amps wouldn't it.
In fact, it takes...3 or 4A...

No, it will be almost preciesly he same no matter what battery is on the end.

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They specify both a maximum and minimum, and the maximum is somewhat over twice the minimum, so 7 and 17 would be ok as in this case with the correct charger.

Car batteries are not sealed gel types. You need a special charger for these.

Perhaps you don't know how to design a current limited charger?
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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 matters more.
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.
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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 Parry.
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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.
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Redtag wrote:

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.
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wrote:

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.
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Peter Parry.
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current
hi there, well peter the internal charger will definatly have some form of current limiter circuit 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 bob
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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 about. 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
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current
And I wouldn't let you look after my alarm system. :-))
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Peter Parry wrote:

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.

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<<snipped>>
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 components.
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.
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John Stumbles wrote:

At last, some common sense!

Not especially, but not as dire as you think.

Overkill, but a neat idea.
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My Gunson charger says it's fine to put two batteries in parallel on a float charger (assumes that neither has any disastrous sort of fault of course).
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But is that refering to two batteries of the same capacity?
I would strongly advise th OP not to connect the two batteries together here...
Sparks...
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Sparks wrote:

No. 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.

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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 of charge
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 happen.
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 charger!
Sparks...
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