RE: Battery Chargers, Pulse Units; but what is the REAL problem....

[Larry Elie <lelie ford com>]

Very long.

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.  
The new 
thread was started by Steve Naugler, asking about chargers.  First off, he 
mentions 
his batteries are 8 years old and weak.  Not bad for the pack; I can get 
batteries for 
$45 each at Sam's club; 6*45=$270 + tax for 8 years is $33.75 per year.  
Before you 
spend a lot on chargers, think about what that means.  I don't know how 
much you 
use the tractor, but this is probably the same order as a person with a 
gasoline 
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 
and poked 
around under the seat and hood.  The GE is NOT wired like we wire our 
Ranger Electric 
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 
accessories.  Why?  
Because of EQUALIZATION!  We literally MATCH batteries to put them in 
vehicles.  
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, 
small 
wires, and make the system efficient.  The batteries can be thought of as 
integrators.  
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 
really 
need them to go.  That is how all series battery chargers work.  Bummer.  
That's 
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 
batteries 
'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 
doesn't really 
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 
technology.  
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 
'dead', and 
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 
pack voltage 
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 
series 
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 
a single 
cell reversal as the failure mode.

What to do?  Start by looking with a DVM.  Don't be afraid to charge a 
single cell 
with a trickle charger.  Keep in mind that even if there is a 'worst' 
battery (usually 
one of the lift batteries) that replacing it won't necessarily make 
everything fine 
because now one of the other batteries will be the worst one.  Not that 
you can't 
do it; just won't do as well as you could.  Do NOT reverse charge a 
battery, and 
if you do PLEASE trickle charge that individual battery.  Every trickle 
charger I 
have ever seen is floating (you don't need to disconnect the battery from 
the 
others near by) even to the point that you can connect a charger to one 
battery 
WHILE the GE charger is charging.  Remember, the GE is going to try to 
give 
you about 40 volts across everything, including the 7 or so you will get 
from the 
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 
degree of 
charge.

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 
the 
battery was in operation as well.  Not all that easy.  All the 'spiking' 
and 
rectification are secondary to making each cell carry it's own load.

Larry Elie