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RE: Battery Chargers, Pulse Units; but what is the REAL problem....
- Subject: RE: Battery Chargers, Pulse Units; but what is the REAL problem....
- From: Larry Elie <lelie ford com>
- Date: Thu, 17 Dec 1998 12:56:55 -0500
- Sender: owner-elec-trak cosmos5 phy tufts edu
I have been in training for the last few days, so didn't have time to
respond. Lots of
good ideas have already been presented, but I'll give you my perspective.
thread was started by Steve Naugler, asking about chargers. First off, he
his batteries are 8 years old and weak. Not bad for the pack; I can get
$45 each at Sam's club; 6*45=$270 + tax for 8 years is $33.75 per year.
spend a lot on chargers, think about what that means. I don't know how
use the tractor, but this is probably the same order as a person with a
machine uses for fuel... and that didn't count what you paid your utility.
As a matter
of fact; chargers aren't all that efficient, and MOST of what the GE
charger is doing
is equalization. THAT is a whole new subject.
I'm a physicist by trade, but picked up a MS-EE along the way. I do
pretty well with
electronics. Ever since the first time I ran a GE, I pulled out the DVM
around under the seat and hood. The GE is NOT wired like we wire our
pickup (not my area of Ford) or like our other electric... er...
'alternative vehicles'. Yes,
we wire the thing in series too, but we do NOT tap off any 12 or 18 V
Because of EQUALIZATION! We literally MATCH batteries to put them in
When you put 6 (or 20 or 38) batteries in series, you solve one problem
but at an
enormous trade off. The higher series voltage means you can make nice,
wires, and make the system efficient. The batteries can be thought of as
The contain charge, like a capacitor. Now there is lots of nice chemistry
going on as
well, but that is all secondary. If you connect 6 electrolytic capacitors
in series, and
discharge them unequally, you will have a terrible time getting them all
back to the
charged state UNLESS you bring them all to a potential beyond where you
need them to go. That is how all series battery chargers work. Bummer.
why it takes so long to equalize them. Besides, it doesn't really work
all that well.
Don't believe me? Check your GE batteries with a DVM next time the
'go dead'. You probably have 5 batteries of 5.5 to 5.85 V and one at 2.3
V. If you
hook up a cheap battery charger to the 2.3 V battery and bring it up to 6
or so volts,
the unit can work for another hour... until the next bad actor drops to 2
or 3 V. You
are not going to win this; I have trickled each up within .1 V, but that
measure the chemistry of the individual battery. Besides, the same
business is going
with individual cells within each battery. di/dt chargers can help this
part, but to do it
right you have to know the history of each cell, which would take a new
It can be done (I have a invention disclosure in the area, but the patent
isn't there yet),
but it isn't trivial. Does it sound like I am being negative? Probably.
Did the GE
folks know? Yep. Have any of you noticed that when the battery pack goes
the tractor won't go forward, that you can still reverse? I believe the
GE folks kept the
forward direction relay (contactor to the purist) from engaging when the
was below a certain point, but they didn't bother for reverse. Why?
Because if you
keep going, you will REVERSE CHARGE one of the cells. That is bad. The
charger will not bring it back very quick if you do. Most of what it will
be doing will be
to heat up the other batteries for a very long time; a trickle charger on
one cell is better.
It isn't just the GE; the 9 to 18 V battery packs for hand tools have this
as their typical
failure mode as well; I opened several to test my invention on and all had
cell reversal as the failure mode.
What to do? Start by looking with a DVM. Don't be afraid to charge a
with a trickle charger. Keep in mind that even if there is a 'worst'
one of the lift batteries) that replacing it won't necessarily make
because now one of the other batteries will be the worst one. Not that
do it; just won't do as well as you could. Do NOT reverse charge a
if you do PLEASE trickle charge that individual battery. Every trickle
have ever seen is floating (you don't need to disconnect the battery from
others near by) even to the point that you can connect a charger to one
WHILE the GE charger is charging. Remember, the GE is going to try to
you about 40 volts across everything, including the 7 or so you will get
trickle charger, so a combination like this will not fully charge the
other 5. These
numbers of course change with current which is itself dependant on the
If you wanted to make an 'ideal' charger, it would have to charge all of
the cells in
parallel, using di/dt techniques, sample the battery acid, and do it while
battery was in operation as well. Not all that easy. All the 'spiking'
rectification are secondary to making each cell carry it's own load.