After leaving the packs sit for a few days, most of the cells in the 28s and (3) 7s packs are around 3.57v-3.58v, one was 3.55v.
I accidentally let the bulk-charge run too long on one of the 7s packs, and I ended up with some cells at 3.68v and some at 3.5v. I used a light bulb to discharge the highest cell down to 3.4v, and then used the balance chargers to bring them all up to 3.65v, and left them on all night - and all of those cells are still sitting around 3.63v. I thought I saw something similar when building the Headway pack on my Vectrix, it seemed that after a charge/burn off part of the fluff charge/re-charge, or maybe it was sitting on the balance charger for an extended time, the cells held voltage much much longer. Because charging to peak voltage is hard on the cells, and as texaspyro demonstrated it does not yield significant WH, I would NOT want to do on a regular basis. Further, I'm not entirely sure I am not whacky and mis-correlating events... but if I am not, I wonder if holding voltage means that this opens pathways in the cells, or helps with top balance.
Anyhow, I built some cables to connect the batteries, using 4ga wire and lugs with 1/4" hole, crimped, soldered, with thick adhesive shrink-wrap for strain relief. Since there are two holes on each terminal, I ran two of the cables for each connection. Per the '3-up' rule, the two 4ga are equivilant to a 1/0 cable. I am running 4/0 cable through the rest of my VW bus, but the runs between the modules are so short it shouldn't matter. I also like the redundancy - if one of the cables comes loose at 175v, instead of a plasma-ball-generating arc, the other cable should still be connected.
It is really impressive to see a 9kw pack take up so little room, shown against a 17" car rim for scale. Next, I'll make power cables for either end of the pack, slap it in my VW Bus, and see what it can do.
-JD
That's enough variance that a direct connection to a DIY solar panel made up of .5V cells might just work. I didn't test many, but each of the cells I did test in varying amounts of sun put out .5V , and the current output is what varied. 7 solar cells in series + 1 low voltage drop diode repeated for each series cell in my pack and I've got a solar powered balance charger made up of single cell solar chargers.
