Connecting car batteries in parallel?

[Kam]

I encountered a system that uses few 12V standard size car batteries
connected in parallel. All batteries are new, of the same model, and
the entire battery pack is charge by a beefed up car alternator. The
system is in operation for few months and so far it seems to function
very well.

Is it OK to connect batteries in parallel? I always 'knew' that this
is a big no no due to the currents that can be developed between the
batteries but the car expert we are using says that this is a common
practice.

Thanks,

Kam

 

[Sjouke Burry]

sure it is, as long as all batteries are in good shape how ever,
it does pose a problem when one unit decides to have a shorted
cell. i have seen fires from this. those that do it correctly normally
have a large fuse link (fast blow) for each battery..
and in most cases where a cell goes bad, it will grain the other
batteries.
scenario is, you end up replacing all batteries at the same time.

You better buy them from the same manufacturer as
well, because there are slight differences beween
producers and types, like different lead alloys,
causing slightly different topload voltages,
temperature dependencies, ect.
Also make sure that cooling air can reach all
batteries equally,to avoid unbalanced temperature
and charging.

 

[Jamie]

I encountered a system that uses few 12V standard size car batteries
connected in parallel. All batteries are new, of the same model, and
the entire battery pack is charge by a beefed up car alternator. The
system is in operation for few months and so far it seems to function
very well.

Is it OK to connect batteries in parallel? I always 'knew' that this
is a big no no due to the currents that can be developed between the
batteries but the car expert we are using says that this is a common
practice.

Thanks,

Kam

sure it is, as long as all batteries are in good shape how ever,
it does pose a problem when one unit decides to have a shorted
cell. i have seen fires from this. those that do it correctly normally
have a large fuse link (fast blow) for each battery..
and in most cases where a cell goes bad, it will grain the other
batteries.
scenario is, you end up replacing all batteries at the same time.

 

[Michael A. Terrell]

I encountered a system that uses few 12V standard size car batteries
connected in parallel. All batteries are new, of the same model, and
the entire battery pack is charge by a beefed up car alternator. The
system is in operation for few months and so far it seems to function
very well.

Is it OK to connect batteries in parallel? I always 'knew' that this
is a big no no due to the currents that can be developed between the
batteries but the car expert we are using says that this is a common
practice.

Thanks,

Kam

I wouldn't use a mess like that without fusing each battery where it
connects to the buss bars. I watched two morons barely get out in time
when their mini pickup truck went up in a fireball. Their competition
stereo system with with a dozen unfused batteries shorted out and set
the fiberglassed speaker cabinets on fire. Their reason for no fuses?
They loose points in stereo competitions if the judges see fuses.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Homer J Simpson]

I wouldn't use a mess like that without fusing each battery where it
connects to the buss bars. I watched two morons barely get out in time
when their mini pickup truck went up in a fireball. Their competition
stereo system with with a dozen unfused batteries shorted out and set
the fiberglassed speaker cabinets on fire. Their reason for no fuses?
They loose points in stereo competitions if the judges see fuses.

The 'entertainment' system for Swissair 111 was installed by cowboys,
unfused and without the ability of the flight crew to disconnect it. All on
board died when it caught fire.

 

[Dana]

I encountered a system that uses few 12V standard size car batteries
connected in parallel. All batteries are new, of the same model, and
the entire battery pack is charge by a beefed up car alternator. The
system is in operation for few months and so far it seems to function
very well.

Is it OK to connect batteries in parallel? I always 'knew' that this
is a big no no due to the currents that can be developed between the
batteries but the car expert we are using says that this is a common
practice.

Why would it be a big no no.

 

[Homer J Simpson]

Why would it be a big no no.

You could connect them safely via diodes but without there is some concern
about voltage differences and the resulting currents.

 

[Michael A. Terrell]

isn't seeing the smoke released part of the competition ?

No, and neither is being burnt to death.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jamie]

I wouldn't use a mess like that without fusing each battery where it
connects to the buss bars. I watched two morons barely get out in time
when their mini pickup truck went up in a fireball. Their competition
stereo system with with a dozen unfused batteries shorted out and set
the fiberglassed speaker cabinets on fire. Their reason for no fuses?
They loose points in stereo competitions if the judges see fuses.

isn't seeing the smoke released part of the competition ?

 

[PhattyMo]

Kam wrote:

"All batteries are new, of the same model,"


That's the ticket.
All of the batteries must (Ideally) be identical.. Same type,size,age,etc.

 

[Jamie]

Why would it be a big no no.

your batteries much be in happy harmonium balance!

 

[Dana]

You could connect them safely via diodes but without there is some concern
about voltage differences and the resulting currents.

I was assuming safety and other cautions were being observed.

 

[jasen]

I encountered a system that uses few 12V standard size car batteries
connected in parallel. All batteries are new, of the same model, and
the entire battery pack is charge by a beefed up car alternator. The
system is in operation for few months and so far it seems to function
very well.

Is it OK to connect batteries in parallel? I always 'knew' that this
is a big no no due to the currents that can be developed between the
batteries but the car expert we are using says that this is a common
practice.

The more you hook in parallel the bigger the mess when one gets a shorted
cell, drops 2 volts and sucks all the energy out of the other batteries.

2 or three is probably OK, but I'm not the one taking the risk.

if you isolate the batteries using diodes so that current can't flow from
one battery into another there should be no problems as a failed battery
cant damage its neighbours.

Bye.
Jasen

 

[Richard Henry]

You could connect them safely via diodes but without there is some concern
about voltage differences and the resulting currents.

What effect would a failed battery have on the common charging
equipment?

 

[feebo]

I encountered a system that uses few 12V standard size car batteries
connected in parallel. All batteries are new, of the same model, and
the entire battery pack is charge by a beefed up car alternator. The
system is in operation for few months and so far it seems to function
very well.

Is it OK to connect batteries in parallel? I always 'knew' that this
is a big no no due to the currents that can be developed between the
batteries but the car expert we are using says that this is a common
practice.

Thanks,

Kam

technically there is no problem if all is working as planned... minute
differences in voltages soon iron out and when on load make a marginal
difference

The problems start when faults arise and good batteries can provide
all the power needed to start fires etc when a cell goes short.

A good parallel system should have some circuity to protect against
this - at it's most simple, some really beefy diodes hower a better
solution is with power MOSFETs so individual batteries can be taken
out of circuit on discharge or failure. Charging would require a
similar set-up but reversed and watching for excess charge current and
general signs of batteries in distress.

 

[feebo]

What effect would a failed battery have on the common charging
equipment?

depends on how the equipment and charge circuit were designed. If you
just have a load of parallel batteries and an alternator connected to
their common output as long as everything stays fine, there would be
no real consideartion... prob is, things seldom "stay fine" and if you
get a short in a cell in one battery, the voltage will drop and the
remaining batteries (and alternator if charging) will pour power into
that battery... fires start like this. At the least, it will discharge
your setup over time. Ammeters (centre zero) in series with each
battery output will at least give an indication of what each is doing
and so help pinpoint the fault.

Why break your back? just design a nice simple controller (based
around a micro-controller witha few a2d inputs) and control the whole
caboodle with good thyristors and a display for feedback.

 

[Rich Grise]

The more you hook in parallel the bigger the mess when one gets a shorted
cell, drops 2 volts and sucks all the energy out of the other batteries.

2 or three is probably OK, but I'm not the one taking the risk.

if you isolate the batteries using diodes so that current can't flow from
one battery into another there should be no problems as a failed battery
cant damage its neighbours.

I wouldn't use diodes - for one thing, you've got their forward drop, and
for another, you'd need a whole nother set for charging.

I'd just slap some fusible links in there.

Cheers!
Rich

 

[Ian Malcolm]

I wouldn't use diodes - for one thing, you've got their forward drop, and
for another, you'd need a whole nother set for charging.

I'd just slap some fusible links in there.

Cheers!
Rich

Extremely common to parallel 2 to 4 IDENTICAL batteries in marine
leasure applications. Fusible links between the batteries and the bus
bars are *strongly* reccomended. The batteries should be from the same
batch and must be kept as a set. If one fails, you are supposed to
replace the *whole* set. High circulating currents are somewhat of as
myth as the impedence of a 'flat' lead acid battery is fairly high and
surface charge rapidly reduces any initial voltage difference. However
as mentioned by others one bad cell will kill the whole set.

 

[Roger Hamlett]

I wouldn't use diodes - for one thing, you've got their forward drop,
and
for another, you'd need a whole nother set for charging.

I'd just slap some fusible links in there.

Cheers!
Rich

Yes.
If you look at a lot of vehicles with 'larger' engines, it is common to
have the electrics using two 12v batteries, and parallel them during
normal running, but series connect them for starting. Rally cars, and
things like the Hummer diesel, do this. The norm, is to have heavy duty
fusible links, rated just a little above the highest likely starting
current, built in close to each battery. Often pigs to get and and
replace, when a problem appears, but without them, the wires between the
batteries become the 'limiting factor', and can give some 'exciting'
effects....

Best Wishes