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Rough Draft -
editing and pics still required
Ever notice how your
Internal Combustion Car starts in the winter? You know, you turn the
key and the starter motor turns over very fast for a few seconds then
slows down as you get that sinking feeling that it isnt going to
start. You let off on the key, sit there a minute or so before twisting
it again. Again it turns very fast and starts! Instinctively you rev
the engine and watch the Ammeter needle pegs the stop then falls back to
slightly above the zero point. Both the hot discharge on the
batteries when you are trying to start and the hot charge when engine
starts are caused by the same thing. Stratification around the plates.
Your EV batteries do the
same thing. As you pull out of the driveway, you have that sets you
back in the seat power that quickly settles to a normal cruise power.
After a quick stop at the red light, bam, youre across the street
before the more normal power levels in. Plug in that charger and power
company smiles, within a few minutes the charger falls to 20 amps, 15
amps, 10 amps and then to 5 or less amp for several hours. How can we
use this phenomenon to our advantage?
The
Science - Since nobody pays me to write this stuff, I dont have a lot
of money so when I talk about batteries in my EV, Im talking about
flooded lead acid type. How these things work in the most basic of
terms is a reversible electrochemical reaction. Put electron in causes
a chemical reaction, later a chemical reaction releases those
electrons. What happens in stratification is the electrolyte right
around the plates completes its reaction then blocks the reaction of
the remaining electrolyte! Now you know why to bump the starter in
your ICE car. In our EV, we want to circulate the electrolyte so that
it doesnt stratify around the plates.
The
Peristaltic Battery.
I didnt invent these but before some
well meaning politicians empowered the EPA to close all independent
battery makers, one could get these made, now you have to make them
yourself. Dont try this with old batteries, you have to use new
batteries that have never had electrolyte. Peristaltic pumps use
plastic (or rubber) tubing that is squeezed by little rollers to make
the pumping action. The pumped material never touches the pump parts
no contamination. They can be purchased or made by a local machine
shop. Our came from rejects from a medical project we were building.
What we are going to do is suck the electrolyte off the bottom of the
battery cell and put it back in on the top far side. Youve guessed
right, there is a pump for every cell and that is a lot of pumps.
Fortunately the pumps can be ganged together with only one drive motor.
Okay, think about this for a moment, do you really want to do this? The
plates do not go the edges of the battery case. We are going to drill a
5/16 hole in the corner of each cell, one on each side of the battery.
Carefully push a stiff plastic tube down between the case and the plates
to within of the bottom. Place a short piece of this material on the
other side of the battery. Epoxy all the pieces in place. Place
batteries in the vehicle, connect them, and connect the pump tubing to
the pump. A nice thing about peristaltic pumps is that they are
self-priming and can run dry. Check to make sure the intake of each
cell goes through the pump and back to the same cell. Fill the
batteries with electrolyte, turn the pump on and refill the one with the
long pieces of tubing.
One can get about a 96% charge in around
two hours with the pumps on. My CitiCar would zip along like it just
came off the charger for about 40 miles before it settled down a normal
cruise for the next 20 miles. Im guessing there was not but about 10
additional miles left in the batteries to find a charging station. I
never tested it. Because the batteries have not stratified there is no
charge left to let it sit and limp home. When they are out they out.
The little Pittman gear motor turning at about 3-RPM draws very little
power and add little weight. The pumps, tubing and extra electrolyte
adds a couple of pounds but it is well worth it for the performance
gains especially when racing.
Our attorney tells us we must tell you
that: this is for information only; we dont recommend building a set of
these batteries; electricity kills. Batteries are dangerous to work
around. Were not responsible for any damage you may do to anything or
yourself; Use eye protection; dont stand on the top rung of a ladder;
fast food is fattening; smoking causes lung cancer; breathing is
dangerous; everybody is going to die sometime. In other words, be
careful and if you do anything stupid, we are NOT
to blame.
Some credit where credit is due. Mr.
Saied Motaei for introducing me to this concept back in the early
80s. If you want to try to contact him, try the Santa Clara chapter of
the EAA. In addition, I stole some of the pictures from Design
News magazine (September 1985).
I didnt care for Mr. Motaeis
design in that he used a drive and pump for every battery and left
exposed tubes down every cell. I had all the baffles and so on put in
when I had a battery maker make them for me. Now with no one to make
these, everyone is afraid of the lawyer and EPA, the do it yourselfer is
better off going in from the top. Just a side note here, a little
filter in the line will get rid of that annoying battery-killing garbage
that normally collects in the bottom of the battery. Go back and
re-read that disclaimer.
Dont forget to visit the Bookmark the
Assembled Products, Inc.s home page for future
information.
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