Combining battery question.

[rutman]

Hi


I have identical batteries. Each are rated at 12v 7amps


I would like to know if its possible to combine both batteries to give
me 12 volts 14 amps.

I am guessing that if I hook them up in parallel it should do the job?


please let me know.

 

[sofie]

Yes.... you are correct.... PARALLEL

 

[DaveM]

Hi


I have identical batteries. Each are rated at 12v 7amps


I would like to know if its possible to combine both batteries to give
me 12 volts 14 amps.

I am guessing that if I hook them up in parallel it should do the job?


please let me know.

Yes, with a note of caution.... The batteries should both be in the same
condition, i.e., brand new, or having been used in the same type of service
for the same amount of time.
The reason for this is to avoid the possibility of one battery discharging
into the other, and to make sure that they both supply current into the load
equally..
Suppose that one battery is new, and the other has seen many
discharge/charge cycles in its life. That means that the used battery may
have deterioriated somewhat so that its internal resistance is higher than
the new battery. When the batteries are connected in parallel, the new
battery will have to supply a greater amount of current to the load,
possibly damaging it. It also may not accept a charge as well as the new
battery, and may cause the new battery to be overcharged.

--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

[James Hahn]

Batteries aren't usually rated in amps. Do you mean they are rated at 7
ampere hours (ah)? In that case, using them in parallel will give you 14
ah, more or less. The fact that the batteries can never be completely
identical may introduce some oddities.

Or perhaps you mean that you have a device that draws 7 amps that you are
running off one battery and you want to know if you can use two batteries in
parallel to run two of the devices? In that case I would ask Why not run
each device off its own battery?

 

[Dave Plowman (News)]

I have identical batteries. Each are rated at 12v 7amps

I would like to know if its possible to combine both batteries to give
me 12 volts 14 amps.

I am guessing that if I hook them up in parallel it should do the job?

If lead-acid you'll probably get away with it - although it won't be quite
as good as a single battery of the correct capacity. But it won't work
well with Ni-Cads, etc.

 

[Bob Shuman]

I do not agree with the reply you were provided by DaveM, although I do
agree with his note of caution if using the batteries in parallel.

Although it is not clear exactly what you mean by "combining" the batteries
(this can be either in Series or Parallel), if the two 12V batteries are
placed in series, then they will produce 24V nominal voltage with no
increase in the maximum current they can supply. If the batteries are
combined in parallel, then the voltage will still be 12V, but the maximum
current they can supply will double.

That said, the ampere rating you provide is most likely not a true maximum
current (in amps as you noted), but is probably a CAPACITY rating for the
battery and if so, would be supplied in amp-hours. For the 12V battery you
cited, a 7AH rating would mean that hypothetically you could supply a
current of 7 amperes for a period of 1 hour. Likewise, if you were
supplying, say 700 milli-amps, then you would expect to be able to do so for
about 10 hours. (This is assuming that the internal resistance of the
battery and its construction/specifications would support these currents for
this period of time - it may be that the maximum spec for current is
substantially less than the 7A I used as an example.) The bottom line here
is that when the batteries are in series, their combined AH rating will not
change. When used in parallel, the AH rating will double. If you do the
math you will see that the energy supplied (in watt-hours, where watt =
volts * amps) is the same as the theory of energy conservation would dictate
must occur.

Bob

Yes, with a note of caution.... The batteries should both be in the same
condition, i.e., brand new, or having been used in the same type of

service

 

[[email protected]]

To: DaveM
cc: James Hahn
Bob Shuman

The simplified answer to DaveM is: YES
..... your hunch was correct, hook up the batteries in parallel which,
in a perfect world, will give you the desired rating of 12v 14A.

electricitym
..
..
..

 

[[email protected]]

Dave Plowman:
Judging from the original rating of 12v 7A..... I would say with
confidence that this is NOT a NiCad or NiMH.... but more than likely a
gel-cell (aka: Lead Acid) therefore hooking them up in parallel is
quite acceptable.
electricitym

 

[Allodoxaphobia]

To: DaveM
cc: James Hahn
Bob Shuman

The simplified answer to DaveM is: YES
.... your hunch was correct, hook up the batteries in parallel which,
in a perfect world, will give you the desired rating of 12v 14A.

Tho', I would not re-charge them in parallel. Recharge'em 1 at a time.

Jonesy

 

[Dave Plowman (News)]

Dave Plowman:
Judging from the original rating of 12v 7A..... I would say with
confidence that this is NOT a NiCad or NiMH.... but more than likely a
gel-cell (aka: Lead Acid) therefore hooking them up in parallel is
quite acceptable.

That's a fair guess if it had been stated as 7Ah. However, it was just a
side comment. ;-)

 

[sofie]

Allodoxaphobia:
The reply posting by electricitym is CORRECT.
Absolutely NOT a problem to charge lead acid (gel-cell) batteries in
parallel ....
....this is done ALL THE TIME with automotive and RV/Trailer batteries.
When the towing vehicle is running it is charging both the engine battery
AND the trailer battery at the same time..... they are in fact connected in
parallel via a mechanical relay/solenoid or a solid state isolator.

 

[Dave Plowman (News)]

Absolutely NOT a problem to charge lead acid (gel-cell) batteries in
parallel ....
...this is done ALL THE TIME with automotive and RV/Trailer batteries.

Gel cell and lead acid ain't the same - and you don't get gel cell in cars
as a rule.

SLA - sealed lead acid - which use a gel as the electrolyte - should be
charged with a maximum voltage of 13.8. They can't gas in the same way as
a liquid electrolyte type can, so mustn't be overcharged.

 

[sofie]

Dave Plowman:
.........
Many motorcycle shops will substitute sealed Gel Cell batteries in dirt
bikes to avoid spilling acid when the bike is laid down...... and
motorcycle charging systems operate much the same as automotive charging
systems..... running anywhere between 13.2 to 14.7volts depending on the
load and the engine RPM.

 

[Dave Plowman (News)]

Many motorcycle shops will substitute sealed Gel Cell batteries in dirt
bikes to avoid spilling acid when the bike is laid down...... and
motorcycle charging systems operate much the same as automotive charging
systems..... running anywhere between 13.2 to 14.7volts depending on the
load and the engine RPM.

Yes - as will AWD vehicles used for off road where they may overturn. But
using a charging system designed for 'wet' lead acid where the voltage may
go up to well over 14 volts will result in a very short life.

However, if a bike or AWD is regularly being overturned, the cost of a new
battery is likely to be insignificant.

 

[steve]

Gel cell and lead acid ain't the same - and you don't get gel cell in cars
as a rule.

SLA - sealed lead acid - which use a gel as the electrolyte - should be
charged with a maximum voltage of 13.8. They can't gas in the same way as
a liquid electrolyte type can, so mustn't be overcharged.

Agreed. Charging gel-cells at over rated voltage kills the capacity.
The battery will still have proper voltage, but if you do a capacity
test, it will be drastically less than rated. We see this all the
time on ATC-601's. Aircraft mechanics are told to keep equipment on
chargers at all times, which is fine for old NiCd packs, but these
charge at 14 volts and constanly come in with ruined packs. They
won't last more than 5 minutes at rated capacity. I've been told that
the cause is because they can't "vent", as you say. They seem to work
perfectly as a replacement for lead-acid, as in they charge in exactly
the same manner, but they do lose their capacity if charged at too
high a voltage too often. As Daniel Sofie says, they put them in dirt
bikes, which makes sense. They charging system charges the batteries
just as it should, but I can guarentee that it won't last as long as a
lead acid would in its place if it wasn't vibrated and jarred to
death. The capacity loss is just an acceptable sacrifice for no
battery acid spilling. Possibly a bold statement, just my thoughts.
I bet the gel-cells still last at least a year in that situation, but
they probably have to be replaced prematurely due to capacity loss.
But, there is no perfect battery pack, and gel-cells are definantely
nice.
Steve

 

[Dave Plowman (News)]

Agreed. Charging gel-cells at over rated voltage kills the capacity.
The battery will still have proper voltage, but if you do a capacity
test, it will be drastically less than rated. We see this all the
time on ATC-601's. Aircraft mechanics are told to keep equipment on
chargers at all times, which is fine for old NiCd packs, but these
charge at 14 volts and constanly come in with ruined packs.

Yes. The accepted way is to charge at constant voltage of 13.8. This, of
course, takes more time than blasting a non sealed liquid electrolyte type

They
won't last more than 5 minutes at rated capacity. I've been told that
the cause is because they can't "vent", as you say. They seem to work
perfectly as a replacement for lead-acid, as in they charge in exactly
the same manner, but they do lose their capacity if charged at too
high a voltage too often. As Daniel Sofie says, they put them in dirt
bikes, which makes sense.

Or anywhere where they might be overturned. So called sealed no
maintenance liquid ones still have a vent and can leak if overturned.

They charging system charges the batteries
just as it should, but I can guarentee that it won't last as long as a
lead acid would in its place if it wasn't vibrated and jarred to
death. The capacity loss is just an acceptable sacrifice for no
battery acid spilling. Possibly a bold statement, just my thoughts.
I bet the gel-cells still last at least a year in that situation, but
they probably have to be replaced prematurely due to capacity loss.
But, there is no perfect battery pack, and gel-cells are definantely
nice.

The big snag for auto use is that they can't be re-charged so quickly
without shortening their life. But for many other applications they're
still quite competitive.

I'm a sound engineer and will use them where I've got a reasonably static
location where I can't easily get mains. One car sized one will run all my
gear all day with capacity to spare. And re-charge overnight. Ni-Cads,
etc, are of course used where weight and space are a consideration, but
the overall running costs of the much higher initial price per Ah - and
the lack of large capacity ones at a sensible price, so more changes
during the day - make the ancient technology of lead acid still attractive.

 

[none]

Yes. The accepted way is to charge at constant voltage of 13.8. This, of
course, takes more time than blasting a non sealed liquid electrolyte type


Or anywhere where they might be overturned. So called sealed no
maintenance liquid ones still have a vent and can leak if overturned.


The big snag for auto use is that they can't be re-charged so quickly
without shortening their life. But for many other applications they're
still quite competitive.

I'm a sound engineer and will use them where I've got a reasonably static
location where I can't easily get mains. One car sized one will run all my
gear all day with capacity to spare. And re-charge overnight. Ni-Cads,
etc, are of course used where weight and space are a consideration, but
the overall running costs of the much higher initial price per Ah - and
the lack of large capacity ones at a sensible price, so more changes
during the day - make the ancient technology of lead acid still attractive.

Gel cellls are lead acid. What makes them burn out so easily when
overcharged is that they use "micro-cell" technology instead of the
older lead plate arrays. Micro-celling give them greater density but
requires a bit of care when charging.
My SLA smart charger starts out at a peak voltage rating of 13.1 with
my larger SLA's and 12.3 with my smaller packs.
As for life in four wheelers/dirt bikes you usually get 2-3 years of
use if properly maintained.( trickle charged during the winter months
or periods of non-use greater than 30 days.)
They do make great packs for use in all sorts of apps. I use them with
my video cameras and lights as well as with cordless power tools.( I
have a 12v 8ah pack on a belt pack that I use for all my 12v power
tools, drills, skil saws etc... and they'll run most all day on on
charge. Much cheaper than the oem nicad packs.