Following help in previous postings I have finally installed my new 17Ahr
Yuasa battery in parallel to the existing 7Ahr battery in my alarm box.
(£38 including delivery from Maplin!)

All looks fine, but can I check on one thing - When connecting the new
battery there are a increased hmmmm coming from the box. This is just the
transforming starting to charge my new (and presumably not fully charged)
battery, isn't it? Its nothing to worry about is it?

Because I have added the extra battery it is just going to take longer to
charge, but there is no other consideration for the charger is there?

Just checking :-)


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Hi Redtag,

I don't know the reasons why or what panel the 17Ah battery is connected to,
but I would disconnect it now!!

If you are referring to a domestic intruder alarm panel, most only have the
ability to charge a 7Ah battery, also, you have connected in parallel
batteries of differing capacity which must not be done due to issues of
equalisation of charge etc.

Regards

Ian
"Redtag" wrote in message
news

Following help in previous postings I have finally installed my new 17Ahr
Yuasa battery in parallel to the existing 7Ahr battery in my alarm box.
(£38 including delivery from Maplin!)

All looks fine, but can I check on one thing - When connecting the new
battery there are a increased hmmmm coming from the box. This is just the
transforming starting to charge my new (and presumably not fully charged)
battery, isn't it? Its nothing to worry about is it?

Because I have added the extra battery it is just going to take longer to
charge, but there is no other consideration for the charger is there?

Just checking :-)


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Redtag wrote:

Following help in previous postings I have finally installed my new
17Ahr Yuasa battery in parallel to the existing 7Ahr battery in my alarm
box. (£38 including delivery from Maplin!)

All looks fine, but can I check on one thing - When connecting the new
battery there are a increased hmmmm coming from the box. This is just
the transforming starting to charge my new (and presumably not fully
charged) battery, isn't it? Its nothing to worry about is it?

Because I have added the extra battery it is just going to take longer
to charge, but there is no other consideration for the charger is there?

Just checking :-)

Hehe - I like your thinking.

The 17Ah battery will have a much lower internal resistance than
your 7Ah. It will draw a much higher current when charging
(unless the charger is constant current, which would be strange
for lead acids).

Having them both in parallel almost guarantees that your charger
(the thing that's humming) will die soon.

Remove the 17Ah, and just have the 7Ah as was. If you really
need more capacity, you need to build a suitable charging circuit.

--
Grunff

I agree with the other two - 7Amp max m8

--
Regards

SantaUK
Mail me at:
arjf (ng) zzvyyne (qbg) pb (qbg) hx === ROT13
Use http://andrewu.co.uk/tools/rot13/ to convert to readable format

"Redtag" wrote in message
news

Following help in previous postings I have finally installed my new 17Ahr
Yuasa battery in parallel to the existing 7Ahr battery in my alarm box.
(£38 including delivery from Maplin!)

All looks fine, but can I check on one thing - When connecting the new
battery there are a increased hmmmm coming from the box. This is just the
transforming starting to charge my new (and presumably not fully charged)
battery, isn't it? Its nothing to worry about is it?

Because I have added the extra battery it is just going to take longer to
charge, but there is no other consideration for the charger is there?

Just checking :-)


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

"Redtag" wrote in message
news

Following help in previous postings I have finally installed my new 17Ahr
Yuasa battery in parallel to the existing 7Ahr battery in my alarm box.
(£38 including delivery from Maplin!)

All looks fine, but can I check on one thing - When connecting the new
battery there are a increased hmmmm coming from the box. This is just the
transforming starting to charge my new (and presumably not fully charged)
battery, isn't it? Its nothing to worry about is it?

Because I have added the extra battery it is just going to take longer to
charge, but there is no other consideration for the charger is there?

Just checking :-)


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

hi there,
i must agree with the person who said that putting batteries of this type in
parrallel is not a good thing for the stated reasons. however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the current
will reduce to a small float level (trickle) when the battery has fully
charged. so i would say disconnect the small battery and the large one will
be ok (just take longer to attain the full, float charge voltage so the
charger will be putting out its max current for longer)
regards
bob

Ok, thanks everybody. My new 17Ahr is now disconnected :-) Hope it was not
too late!

So, how should I do this? I want to add more capacity for those long
winter power cuts we get out here in the country and I thought dropping in
a new battery would be just the job.

How should I add my new battery? I don't mind buying a new charger but how
should I connect it in relation to the other battery and charger.

Thanks

On Sun, 14 Dec 2003 11:27:09 -0000, Crooksie wrote:


"Redtag" wrote in message
news

Following help in previous postings I have finally installed my new
17Ahr
Yuasa battery in parallel to the existing 7Ahr battery in my alarm box.
(£38 including delivery from Maplin!)

All looks fine, but can I check on one thing - When connecting the new
battery there are a increased hmmmm coming from the box. This is just
the
transforming starting to charge my new (and presumably not fully
charged)
battery, isn't it? Its nothing to worry about is it?

Because I have added the extra battery it is just going to take longer
to
charge, but there is no other consideration for the charger is there?

Just checking :-)


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

hi there,
i must agree with the person who said that putting batteries of this
type in
parrallel is not a good thing for the stated reasons. however the
internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the
current
will reduce to a small float level (trickle) when the battery has fully
charged. so i would say disconnect the small battery and the large one
will
be ok (just take longer to attain the full, float charge voltage so the
charger will be putting out its max current for longer)
regards
bob





--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

On Sun, 14 Dec 2003 11:27:09 -0000, "Crooksie"
wrote:

however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the current
will reduce to a small float level (trickle) when the battery has fully
charged.

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.

--
Peter Parry.
http://www.wpp.ltd.uk/

"Peter Parry" wrote in message
...
On Sun, 14 Dec 2003 11:27:09 -0000, "Crooksie"
wrote:

however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the
current
will reduce to a small float level (trickle) when the battery has fully
charged.

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.

--
Peter Parry.
http://www.wpp.ltd.uk/

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

, Opera's revolutionary e-mail client: http://www.opera.com/m2/

hi there,
i must agree with the person who said that putting batteries of this type
in
parrallel is not a good thing for the stated reasons. however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the
current
will reduce to a small float level (trickle) when the battery has fully
charged. so i would say disconnect the small battery and the large one
will
be ok (just take longer to attain the full, float charge voltage so the
charger will be putting out its max current for longer)
regards
bob

********. The PSU is simply not capable of charging this capacity and it
should be disconnected NOW.

"Redtag" wrote in message
news

Ok, thanks everybody. My new 17Ahr is now disconnected :-) Hope it was not
too late!

So, how should I do this? I want to add more capacity for those long
winter power cuts we get out here in the country and I thought dropping in
a new battery would be just the job.

How should I add my new battery? I don't mind buying a new charger but how
should I connect it in relation to the other battery and charger.

OK, You can either do it properly or do it cheaply. The proper way would be
to have a proper rated PSU/charger in a proper steel cabinet with the
battery. Quite expensive.

The cheap way would be to have a large battery like your 17Ah or a car
battery (that way you can go as big as you like!) and have it on a trickle
charger - although the best way is to simply charge it up ready for use as
it'll hold a charge for many months without trickle.

Now then PLEASE don't connect it to you alarm panel cos your alarm panel
will go bang. Instead you can wire in a relay so that if your mains fails
the relay will switch from alarm battery to car battery. The problem is that
during switch over the panel may activate (alarm) due to PIR's etc. dropping
out of circuit. The SAB too may operate causing a tamper fault. The real
proper way would be to have a control circuit which would monitor the panel
O/P voltage and bring in the car battery at a suitable level. All very
messy.

If I was in your situation where you are expecting lots of power cuts I
would probably do away with the panel battery and disable the panel charging
circuit (usually a simple matter of cutting a link or resistor - speak to
the manufacturer) and then just connect a fully charged large battery to the
panel making sure a proper fuse arrangement exists in the battery feed. That
way the panel won't need to charge anything but will have a damn good
standby power source in the event of a mains failure. You do need to ensure
that the cutting of any charging links does allow the battery to power the
panel. Older panels had a marked link on the PCB for dry cell batteries but
that was many moons ago.

Remember too that any short circuit of a large battery will melt the wiring
so please fuse well.

On Sun, 14 Dec 2003 19:18:32 -0000, PJO wrote:


OK, You can either do it properly or do it cheaply. The proper way would
be
to have a proper rated PSU/charger in a proper steel cabinet with the
battery. Quite expensive.

Pete, I am fine with doing it properly - it will still be cheaper than the
£228+VAT that the alarm people wanted!

If I do source the properly rated charger (a 3A one should do it) then how
to I connect this? I would still like to keep the existing 7Ahr battery,
and add this in parallel but if I do this then how to I charge it? I want
to do as little as possible in "their" cabinet and to add my own with this
new battery.

Cheers

"PJO" wrote in message
...
, Opera's revolutionary e-mail client: http://www.opera.com/m2/

hi there,
i must agree with the person who said that putting batteries of this
type
in
parrallel is not a good thing for the stated reasons. however the
internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the
current
will reduce to a small float level (trickle) when the battery has fully
charged. so i would say disconnect the small battery and the large one
will
be ok (just take longer to attain the full, float charge voltage so the
charger will be putting out its max current for longer)
regards
bob

********. The PSU is simply not capable of charging this capacity and it
should be disconnected NOW.

Even with the lower-capacity battery the panel is designed for its power
supply/charger is going to have to sustain its max output current for many
hours: long enough to cook a poorly designed PSU (not that I'm saying the
PSU might not be poorly designed :-). So with the larger battery the PSU
_should_ not suffer.

Putting two batteries of different ages and capacities in parallel is
probably not a good idea.

If you want a serious backup supply (maybe for emergency lights as well as
the panel) you could get a caravan/boat leisure battery (circa £30 for 85AH
from motorists discount centres) and a charger from Argos (£25 IIRC) which
will drop back to a maintenance charge for maintaining a float supply.

--
John Stumbles
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-+
Thank God I'm an atheist

Peter Parry writes
On Sun, 14 Dec 2003 11:27:09 -0000, "Crooksie"
wrote:

however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the current
will reduce to a small float level (trickle) when the battery has fully
charged.

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.

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
--
roger
del x's to email

In article ,
PJO wrote:
********. The PSU is simply not capable of charging this capacity and it
should be disconnected NOW.

The charger for a sealed lead acid device should be constant voltage, and
will restrict the amount of charging current.

--
*A closed mouth gathers no feet.*

Dave Plowman London SW 12
RIP Acorn

"Redtag" wrote in message
news
On Sun, 14 Dec 2003 19:18:32 -0000, PJO wrote:


OK, You can either do it properly or do it cheaply. The proper way would
be
to have a proper rated PSU/charger in a proper steel cabinet with the
battery. Quite expensive.

Pete, I am fine with doing it properly - it will still be cheaper than the
£228+VAT that the alarm people wanted!

If I do source the properly rated charger (a 3A one should do it) then how
to I connect this? I would still like to keep the existing 7Ahr battery,
and add this in parallel but if I do this then how to I charge it? I want
to do as little as possible in "their" cabinet and to add my own with this
new battery.

Cheers

Get hold of a Power Supply Unit / Charger that will comfortably take your 17
A/hr battery, and comes complete with a relay switch that operates on mains
failure.

The relay should be wired with the open no voltage contacts connected to
your alarm panel. The voltage side of the relay will be connected from
charger to battery when mains power is present, and then drop from battery
to appliance if a mains failure occurs.

These people should be able to point you in the right direction:

http://www.ktassemblies.co.uk/products.html

If I do source the properly rated charger (a 3A one should do it) then how
to I connect this? I would still like to keep the existing 7Ahr battery,
and add this in parallel but if I do this then how to I charge it? I want
to do as little as possible in "their" cabinet and to add my own with this
new battery.

You really do need to read properly (!!). You CANNOT connect the large
battery in parallel with your 7Ah - period.

If you do as some say and use a standby PSU with a relay (I mentioned this
too) then the alarm will probably activate on change over as the PIR's etc
will go into alarm, the SAB will operate and the panel may go into "power
up" in which case it'll activate itself too!!!!

If you do away with your 7Ah and just use the large battery in "dry cell"
mode then all will be well. Reading between the lines... is you alarm on a
maintenance contract? because if it is then you obviously can't cut the
charging link out although you could always cancel the contract and come
here for advice when it fails!

Others have suggested a caravan battery - brilliant idea. A boat battery is
another. These are designed to hold a charge for many months without use and
a gel filled as opposed to liquid acid.

You can buy a simple "battery maintainer" from the likes of halfords for
around £20 and that will keep the battery topped up OR, if you're into
playing, buy a small windmill charger like boat owners use and use that to
keep the battery up to scratch!

In any event you need to discard the 7Ah!

In article ,
PJO wrote:
You really do need to read properly (!!). You CANNOT connect the large
battery in parallel with your 7Ah - period.

It's common with caravans. You use a diode between them to stop one
discharging the other.

--
*If you try to fail, and succeed, which have you done?

Dave Plowman London SW 12
RIP Acorn

Redtag wrote:


Ok, thanks everybody. My new 17Ahr is now disconnected :-) Hope it was
not too late!



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.

Peter Parry wrote:

On Sun, 14 Dec 2003 11:27:09 -0000, "Crooksie"
wrote:


however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the current
will reduce to a small float level (trickle) when the battery has fully
charged.


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.


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.

PJO wrote:



********. The PSU is simply not capable of charging this capacity and it
should be disconnected NOW.



******** is right. Any cahrger will be able to charge any similar
construcytion battery of a HIGHER capacity.

The daneger is over charging a small battery. Under - or cvery slow
charging - of a larger is never a problem, unless the charger simply
never gets it to charge at all..

Ive charged bloody lorry batteries on a cheap 1A charger designed for
scooters etc. No probs at all, if you don't mind waiting some days...

"roger" wrote in message
...
Peter Parry writes
On Sun, 14 Dec 2003 11:27:09 -0000, "Crooksie"
wrote:

however the internal
charger in the alarm panel will be a constant voltage type with current
limiting, designed to float charge the battery, this means that the
current
will reduce to a small float level (trickle) when the battery has fully
charged.

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.

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

roger


And I wouldn't let you look after my alarm system. :-))


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Redtag wrote:

On Sun, 14 Dec 2003 19:18:32 -0000, PJO wrote:


OK, You can either do it properly or do it cheaply. The proper way
would be
to have a proper rated PSU/charger in a proper steel cabinet with the
battery. Quite expensive.

Pete, I am fine with doing it properly - it will still be cheaper than
the £228+VAT that the alarm people wanted!



Don't listen to him. He is seriously talking through his arse.

If your charger didn't go bandg withing 5 minutes of hooking

up the bigger battery, I would lay you odds of 50:1 that it

will never go bang in a day or five, or however long it takes.


If you are concerned, charge the bigger battery up elsewhere, and then
comnect it fully charged.

John Stumbles wrote:


Even with the lower-capacity battery the panel is designed for its power
supply/charger is going to have to sustain its max output current for many
hours: long enough to cook a poorly designed PSU (not that I'm saying the
PSU might not be poorly designed :-). So with the larger battery the PSU
_should_ not suffer.


At last, some common sense!



Putting two batteries of different ages and capacities in parallel is
probably not a good idea.



Not especially, but not as dire as you think.


If you want a serious backup supply (maybe for emergency lights as well as
the panel) you could get a caravan/boat leisure battery (circa £30 for 85AH
from motorists discount centres) and a charger from Argos (£25 IIRC) which
will drop back to a maintenance charge for maintaining a float supply.


Overkill, but a neat idea.

PJO wrote:

If I do source the properly rated charger (a 3A one should do it) then how
to I connect this? I would still like to keep the existing 7Ahr battery,
and add this in parallel but if I do this then how to I charge it? I want
to do as little as possible in "their" cabinet and to add my own with this
new battery.


You really do need to read properly (!!). You CANNOT connect the large
battery in parallel with your 7Ah - period.



You can actually.

Lots of things like cars and caravans regularly connect the batteries in
parallel. They charge just fine. They even discharge just fine, but its
obviously advantaegous in e,g. a camper to discnnect teh primary engine
battery from teh camper to ensure you can start the engine the next day
if you flatten the lesiure cells.

In article ,
The Natural Philosopher wrote:
Lots of things like cars and caravans regularly connect the batteries in
parallel. They charge just fine. They even discharge just fine, but its
obviously advantaegous in e,g. a camper to discnnect teh primary engine
battery from teh camper to ensure you can start the engine the next day
if you flatten the lesiure cells.

There are diodes available that do this automagically...

--
*Why isn't there mouse-flavoured cat food?

Dave Plowman London SW 12
RIP Acorn

In article ,
PJO wrote:
********. The PSU is simply not capable of charging this capacity and it
should be disconnected NOW.

Lead acid cells have a *very* low resistance when discharged and without
some form of current limiting between a simple charger and the battery -
even just a resistor - they would draw a very large current indeed, far
more than the puny power supply in an alarm could hope to supply.

--
*I have my own little world - but it's OK...they know me here*

Dave Plowman London SW 12
RIP Acorn

"The Natural Philosopher" wrote in message
...
Peter Parry wrote:

On Sun, 14 Dec 2003 11:27:09 -0000, "Crooksie"
wrote:
snipped
time. Making it work at max output for several times the expected
time may well cause things to overheat and expire.


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
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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The Natural Philosopher wrote:

Putting two batteries of different ages and capacities in parallel is
probably not a good idea.



Not especially, but not as dire as you think.

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).

--
Chris Green )

Don't listen to him. He is seriously talking through his arse.

If your charger didn't go bandg withing 5 minutes of hooking

up the bigger battery, I would lay you odds of 50:1 that it

will never go bang in a day or five, or however long it takes.


If you are concerned, charge the bigger battery up elsewhere, and then
comnect it fully charged.

More ****e from the philosopher above!

We're talking a 1A psu here... not a car or a caravan.

I have seen overloaded PSU's burn out after months but burn out they do -
fact.

Lots of things like cars and caravans regularly connect the batteries in
parallel. They charge just fine. They even discharge just fine, but its
obviously advantaegous in e,g. a camper to discnnect teh primary engine
battery from teh camper to ensure you can start the engine the next day
if you flatten the lesiure cells.

Fine BUT we're talking low current capability alarm here - nit car.

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).

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...

Dave Plowman wrote:

In article ,
The Natural Philosopher wrote:

Lots of things like cars and caravans regularly connect the batteries in
parallel. They charge just fine. They even discharge just fine, but its
obviously advantaegous in e,g. a camper to discnnect teh primary engine
battery from teh camper to ensure you can start the engine the next day
if you flatten the lesiure cells.


There are diodes available that do this automagically...


There are relays that do it 10000% better automgically. Diodes DON'T
work BTW. You need full volts on charge, not full volts -0.6v or whatever.

Dave Plowman wrote:

In article ,
PJO wrote:

********. The PSU is simply not capable of charging this capacity and it
should be disconnected NOW.


Lead acid cells have a *very* low resistance when discharged and without
some form of current limiting between a simple charger and the battery -
even just a resistor - they would draw a very large current indeed, far
more than the puny power supply in an alarm could hope to supply.


So what happens when the puny power supply comes across a discharged
7A/h battery?

ALL lead acid chargers are current limited in some way. Not all are
capable of handling a direct short, but a fully dicsharged battery is
not a dead short. Its a plastic bin job. Its finished as a battery. No
lead acid battery is ever fully discharged in operational life. Only
right at the very end of its operational life :-)

PJO wrote:

Don't listen to him. He is seriously talking through his arse.

If your charger didn't go bandg withing 5 minutes of hooking

up the bigger battery, I would lay you odds of 50:1 that it

will never go bang in a day or five, or however long it takes.


If you are concerned, charge the bigger battery up elsewhere, and then
comnect it fully charged.


More ****e from the philosopher above!



Yeah. Mire ****e 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.

**** off.


We're talking a 1A psu here... not a car or a caravan.


So? The principles are the same. They aen't to YOU, of course, beacuse
your understanding is totally limited.



I have seen overloaded PSU's burn out after months but burn out they do -
fact.



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.

PJO wrote:

Lots of things like cars and caravans regularly connect the batteries in
parallel. They charge just fine. They even discharge just fine, but its
obviously advantaegous in e,g. a camper to discnnect teh primary engine
battery from teh camper to ensure you can start the engine the next day
if you flatten the lesiure cells.


Fine BUT we're talking low current capability alarm here - nit car.



So what? The principles - that its fine to slap two lead acid batteries
in parallel to both charge and discharge, holds.

Just examine the voltage current characterists of lead acid
accumulators, under both carge and discharge, do the maths, and work it
out for yourself. If you are capable.

Sparks wrote:

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).


But is that refering to two batteries of the same capacity?


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.






I would strongly advise th OP not to connect the two batteries together
here...

Sparks...

In article ,
The Natural Philosopher wrote:
Lead acid cells have a *very* low resistance when discharged and without
some form of current limiting between a simple charger and the battery -
even just a resistor - they would draw a very large current indeed, far
more than the puny power supply in an alarm could hope to supply.


So what happens when the puny power supply comes across a discharged
7A/h battery?

It has some form of limiting built in to restrict the charge current to
what it can cope with. A simple lead acid battery charger is a DC source
of around 16 volts open circuit with a suitable series resistor. Of course
modern ones will have some electronics.

ALL lead acid chargers are current limited in some way. Not all are
capable of handling a direct short, but a fully dicsharged battery is
not a dead short.

Didn't say it was - I said it had a very low internal resistance - and any
practical lead acid battery would take more than a burglar alarm power
supply could provide without some form of limiting.

Its a plastic bin job. Its finished as a battery. No
lead acid battery is ever fully discharged in operational life. Only
right at the very end of its operational life :-)

--
*Middle age is when it takes longer to rest than to get tired.

Dave Plowman London SW 12
RIP Acorn

In article ,
The Natural Philosopher wrote:
There are diodes available that do this automagically...


There are relays that do it 10000% better automgically. Diodes DON'T
work BTW. You need full volts on charge, not full volts -0.6v or
whatever.

Wonder why they're sold expressly for this purpose, then?

--
*If love is blind, why is lingerie so popular?

Dave Plowman London SW 12
RIP Acorn

But is that refering to two batteries of the same capacity?


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.

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...

Sparks wrote:

But is that refering to two batteries of the same capacity?


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.


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.


Actually there is a considerable amount of current limiting.
Due to the fact that a battery that is off charge is - say - at 12.5v,
where as it takes over 14V to charge it at any sort of current.

Go and do some real world tests on voltage versus current in both
directions - charge and discharge - and then come back with figures to
justify your statement.



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.



Its not ideal to parallel batteries agreed, because its cheaper to get
bigger ones and put them in series instead. However, it works.


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


No, that agian is untrue. At a given discharged satte, the chargingf
curent on a big, or little, battery will be almost identical. Unless teh
charger is rekyung in thermal inertia for its sole source of cooling, it
will rise exponetntially to a temperature concomitant to its power
dissipation and the rate it can get rid of heat.

A mass of concrtete surrounded by a ploystryrene box may take longer to
get hot, than an empty box, but it doesn't get any less hot for the same
continuous power input...



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!



So you reckon that the alarm charger hasn't got fully hot in an 20 hours
of trickle charging its battery?

Strange world you live in.


Sparks...