EVFR 2.0: Building the pack

It’s been a slow summer. I’ve been too busy this summer to get much done and David moved his shop. I haven’t posted lately, but I have been doing things on and off. I’ve also been riding my SV650 a bit. Really glad I got this to practice on while the bike is being finished. I’d rather learn on this than the eVFR. I wouldn’t want to drop either, but I’d rather drop the SV650 (Has frame sliders) than the eVFR with rare fiberglass fairings.

A few weeks ago I decided I wanted to bin my cells. I borrowed an IR meter from a friend. It’s an AC impedance meter and I realize it won’t accurately give me the DC impedance, but it will allow me to organize the cells into groups of similar IR values. I spent a few nights with my girlfriend testing the cells and writing their IR value on them (she’s awesome!). I got ~150 cells that measured between 5.0-5.9mOhm and like 30 between 6.0-6.9mOhm. One I thought was above 7, but was just the leads not attached correctly. I had some cells that were test-cells and some that were showing low voltage, so I set those aside for testing and further study/destruction.

Now that I had boxes of cells, I noticed some had a tiny number of rust specs on them. None of the rust was very bad, but I wanted to get a pack with as little or no rust on it as possible. Some of the ends where the epoxy is applied seems to have been contaminated, and in some cases appeared between the case and blue plastic covering. After organizing the cells, I have ~165 cells that are near 100% and are between 5.0 and 7.0mOhm. The rest are extras and will be used if I need to replace a cell. I plan on putting a small pack of 16 cells together in a 4s4p 1/2kwh arrangement as a test pack that I can also use with an inverter for portable power (could be used as a small emergency pack to charge the bike).

So after sorting the cells, I got the water-jet cut copper buss-bar de-burred and ready for assembly. I used groups of the same IR value to assembly each parallel group. This will ensure that all of the cells share the current as equally as possible. I think I need some longer Stainless Steel screws. The screws that came with the cells seem to be all over the place with regards to quality, and some of the threads were easily stripped. Despite 2 screw issues, the pack went together well and It measured 36.38V (~3.3V/cell). Here are some pictures of building the 11s5p smaller pack (located above the motor):

I’m going to David’s tomorrow and turning the pack over to him so we can start on the plastic holders/battery box.

I also re-started my Discharger project. I’ve gathered most of the pieces and put together a schematic. I’ve gotten help from a few friends Bob Simpson and John Muchow (designed the CC400 discharger I’ve got). I think we’ve addressed any issues that were lingering and figured an easier way to stop charging when an alarm is triggered. I’ve got a sort of Interlock right now. The Low-voltage alarm, Over-current alarm, Over-temperature alarm and Emergency Stop are all wired to a latching relay. If any of them trigger, the gate of the FET is pulled low, and the discharging stops. The contactors are only there to connect/disconnect the battery, and not to stop the test. Here’s a pic of the parts and of the schematic:

Anyway, that’s it for now. I’ve cut down on my social obligations and renewed my motivation for the discharger and eVFR. I’ll probably start building up the larger front pack this week if I’ve got time.