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lead acid batteries in parallell?

F

Frank White

Jan 1, 1970
0
I have seen this a few times now and have always felt that it is a bad
idea because if one cell in one of the batteries is worn out more than
the others then you will always be discharging one battery with the
other.

The first time I saw this was on tractor starting batteries, and
recently on a scissorlift.
How common are parallell battery arrangements and is this something
worth worrying about?


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R

Rich256

Jan 1, 1970
0
Floyd said:
I've seen 48 VDC battery plants in telephone offices with 3 and
4 different strings in parallel. They might be described as
relatively similar in type, somewhat similar in size, and very
different in age and make.

The point of similarity is necessarily the voltage ratings,
which essentially means they all must be able to operate with
the same charge voltage, the same float voltage, the same cutoff
voltages, etc. etc.


Unless one has a shorted cell there should be no problem in parallel.
My Diesel Truck has parallel batteries.


It appears to me that if they are not the same size the one with the
larger capacity will supply most of the current. Since the voltage will
always be equal they should discharge to the same state of charge even
though they are different size.

When being charged they will charge according to their size, the voltage
determining their state of charge.
 
S

Spokesman

Jan 1, 1970
0
Frank White said:
I have seen this a few times now and have always felt that it is a bad
idea because if one cell in one of the batteries is worn out more than
the others then you will always be discharging one battery with the
other.

The first time I saw this was on tractor starting batteries, and
recently on a scissorlift.
How common are parallell battery arrangements and is this something
worth worrying about?


Most emergency light systems that supply more than two or three remote
units use multiple series/parrallel batteries. If they are allowed in
this
application they must be quite reliable.
 
D

daestrom

Jan 1, 1970
0
Pablo said:
US Navy submarines have been using batteries in parallel for
decades...same aH, rating, no problem !!

BULL!!! Want to tell me were on a submarine you think the lead acid
batteries are in parallel?? Battle-lanterns (6V primary cells that are
never recharged) ??

Nuc boats only have one ships battery and it's over a hundred cells in
series. Diesel boats (of which the US Navy has zero) had two ships
batteries. Yes, those could be connected in parallel, but only during
discharge, they charge separately (various connections could be set up from
the manuevering room)

Parallel operation can work well for small batteries like your typical
marine engine starting application. But it isn't the best choice. One
battery can go bad and 'hog' all the charging current. Many marine
applications include a switch to allow switching from one battery, to the
other, both, or neither (nice to be able to disconnect the batteries when
working in the engine compartment)

daestrom
(former Chief Electrican's Mate, USNavy Submarine Service)
 
R

Ross Mac

Jan 1, 1970
0
Frank White said:
I have seen this a few times now and have always felt that it is a bad
idea because if one cell in one of the batteries is worn out more than
the others then you will always be discharging one battery with the
other.

The first time I saw this was on tractor starting batteries, and
recently on a scissorlift.
How common are parallell battery arrangements and is this something
worth worrying about?


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Should work fine as long as you use the proper isolation system. Here's one
link of many that explains it in the event you don't already know of such
devices..
http://www.thejump.net/fishingarticles/Ship-Shape.htm
Good luck....Ross
 
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