As they say Flame suit on - seems some aggression around.
Not so sure the resistance in the lead is so small, it is though probably
unimportant on an 80 series with the parallel connection, as you said in
your post small voltage differences are all that is required on batteries to
make one do all the work and 2V difference is charged to flat.
On generators we are always mindful of the run from the charger to the
batteries, a) because it is often not protected by a fuse etc, it is on the
charger but not on the battery side b) on a 25A charger the volt drop will
be appreciable as the charger connections are of a limited size.
Occasionally, normally with nicads, we use a sensing connection that
compensates for the voltage drop.
I think UHu is referring to the equalisation charge as used in fork lifts
etc. I seem to remember on a fork lift the equalisation charge voltage is
slightly higher than the normal charge voltage, the principal being that it
will "reset" the battery voltages to the same level (so they do more work),
but that is perhaps more for series connected batteries?
I have to say that as the batteries in parallel with a hefty connection I
don't see how one could have a different voltage and stop the charger while
the other was not fully charged? I have always imagine that if two similar
batteries of different charge levels were connected in parallel they would
even out? All of the installations I deal with are in series to give 24V,
although sometimes we have two pairs of series batteries in parallel.
With regard to different capacities - I understand your point - I would
still be cautions, different capacity batteries, and or different
manufacturers are likely to have different internal resistances, I wonder if
during high current draw there might be a lack of output from one battery,
of course when the voltage drooped on one the other would come into effect
but I don't know if on a 50% load you would see and equal split in the work?
For reference I am no real expert on batteries, I hate batteries, chargers
and battery leads - just ordered =A37K's worth batteries and leads today -
need 720l of acid to fill them - using 8 off 140AH batteries on a generator,
6 generators, 48 batteries, each holding 15L of acid and weighing something
like 57KG filled.
Malcolm
Stafford (UK)
FJ45 '75 & FJ45 '76
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of Clive Marks
Sent: 18 December 2007 19:11
To: [Email address removed]
Subject: Re: [ELCO] Charging batteries
And some more rubbish.
The resistance in the circuit may be small and unimportant, that is
correct, but don't come the crap about the batteries equalling out. It
is the fact that they are connected in parallel that stops one from
charging early.
Basically the battery with the resistance, or the older battery having
a reduced voltage because of age, will not get a full charge. This is
because the charger is looking for a set voltage. When it sees this
voltage it stops charging, so we have one battery at the correct level
(stopping the charger), and one that hasn't quite made it. When you
remember that a 'flat' car battery still has about 10 volts in it you
realise that a small difference is of more significance. To be sure of
charging them both to optimum charge them seperately. This is probably
of little significance with a pair of car batteries, unless they did
not start out as a pair and one is behind the other in voltage before
you start.
While I am on the topic of batteries I will expose another silly idea.
You can connect together two batteries of differing AH rates as a
pair and use them just as you would a matched pair. The batteries are
using power based on the voltage, not the amperage. Taking one battery
of 100 amps and one of 50 amps and connecting them will work fine as
the power take off will be done with reference to the remaining
voltage. This means that the batteries will both be half empty at the
same time and they will both be flat at the same time.
The worst thing that you can do for battery life is to use a new
battery with a half good one. Because of the above the good one will
do more of the work and its life will be shortened considerably.
Regards,
Clive Marks
Home: +44 1293 514600
Mobile: +44 7821 491897
Crawley, West Sussex, UK.
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