(ET) BB600's in the Elec-trak

[Christopher Zach <czach computer org>]

Well the flooded batteries are out and the BB600 flooded NiCD batteries 
are in. Right now I'm able to fit (easily) 60 cells in the back of the 
Elec-trak. That's a total of 80ah capacity at 36 volts; more than enough 
to run around on. The batteries are in 4 blocks of 15 cells; 5 cells 
wide by 3 cells deep. Between them are 2*4 and 1*2 spacers to provide 
some venting.

I could put another string of 30 in the front, but I can't think of a 
reason why; plenty of capacity right now. Maybe I will put in another 
string down the road or something. In the winter I can put another 30 
batteries in the rear weight box giving me an additional 100lbs of 
weight and another 40ah of power.

An interesing issue will be weight: 4 T015's weigh in at about 250lbs. 
60 BB600 cells (1.3lbs each) come in at more like 150lbs. Thus I have 
lost 100 pounds of weight back there. Might be a problem in the snow.

Capacity wise overall it'a about the same as new T105's: They have a 
150ah reserve capacity at 75a draw; BB600's of the same size would have 
a 120ah reserve. However you should never run T105's down past 80% 
(120ah), the BB600's can be run down to zero no problem.

Not sure what I am going to do about the lift. I could tap the pack, but 
that could lead to some really weird imbalance issues down the road 
(NiCDs don't like to be imbalanced). One thought is to just leave the 6 
volt batteries in the front, use a 600 watt UPS for DC-AC and as a 
charger, and run everything else off that. Or a 12 volt and a 6 volt 
battery or something.

Right now I'm just using the main charger to charge the NiCDs. 
Technically they are "full" at 1.5 volt per cell, or 45 volts for 30. 
Luckily enough I have plotted the E20's charger output: It will put out 
over 15 amps into the batteries all the way up to 44 volts. Then between 
44 and 45 it drops output like a *rock* down to a 2 amp final at 45 
volts. Won't go above that; they did a *really* good job on this 
charger. Note to all: You really should charge the pack to 44 volts.

Another thought is I could use the 45 volt DC power as an input to a 
pair of 18 volt super-smart chargers; each one charging half the pack. 
Or I could buy a pair of Vicor 600 watt power supplies and feed the 
super smart chargers at 24 volts (much easier due to simpler 
components). That would charge the pack at 10ah rate; bit slower but 
still reasonable (8 hours for a full charge). This would also solve the 
whole imbalance problem *very* nicely as each 18 volt side would get 
it's own charge profile and could be drained without blowing anything up.

On a different note, I heard *sparking* coming from under the tractor. 
Checked and sure enough: The wire harness had broken one of it's ties 
and fallen down onto the motor pulley. Which merrily wore out the 
insulation on one of the main wires. Great; more things to work out.

Chris