(ET) Battery pack rebuild on E20

[Chris Zach <cz alembic crystel com>]

Well, after getting the E15 going I figured it was time to fix the 
battery pack on the E20. Earlier this year I had something happen that 
took out one of the three battery strings. I had isolated the string, 
now it was time to figure out what happened.

In a nutshell, bad. Several cells had melted spots which usually means 
they went dry and shorted out. One cell had melted to another and when I 
pulled them apart electrolyte came out of the damaged cell showing that 
there was electrolyte in at least one of the blown cells. This happened 
on charge, but I was using the normal 44.5 volt terminating voltage 
(just under 1.5 vpc which is less than the 1.55 vpc max) so I'm not sure 
why things went bad. However once a cell shorts the rest of the pack can 
discharge into the now one-cell-less string which might have started a 
chain reaction before the string fuse blew.

Anyway back to work: I pulled 18 of the cells and replaced them with 18 
cells I had sitting around for years in the yard. I did remove all the 
interconnects, cleaned them up, cleaned up the battery terminals with 
the wire brush, cleaned up the stainless steel bolts, and in cases where 
the bolts were hard to remove re-tapped the threads. Tapping the threads 
takes *forever*. But now I have 18 in, and will charge it for 15 hours 
at 3 amps (c/10) to see what the water levels look like (most cells had 
no water, but that's not unusual when the cells are totally discharged).

Will work on the other side tomorrow. I wish I had more contactors, I 
might use a pair of Leaf contactors (which trigger on 12v not 36v) as a 
way to isolate two of the strings with the pack off. I also need to 
re-connect the old Link-20 so I can watch the current draw on these two 
packs and see if they are staying in balance with the front pack.

C