[danh818]

The first four cells were clamped to their test boards and cycled today. This first round of testing will be done at 1.5c discharge and 1c charge. Once I have baseline data for each cell, they will be grouped by capacity and again cycled at a higher rates.

[danh818]

I've made some changes to my cell testing parameters, so I thought I would post the whole procedure from beginning to end.

After a couple of trial runs, I found that my lead acid supply bank just wouldn't take a 4x 40amp regenerative discharge, so I had to drop down to 35amps.

To start off the process, I number each cell with a paint marker as well as its corresponding plastic tray. The sticker from the negative tab of two cells is then removed by hand and I place those two cells side by side with the tabs resting on a 3/32" thick piece of Acetron GP (aka Delrin). I then use a shop rag with a bit of WD40 to remove the leftover adhesive from the sticker. Next a different rag with rubbing alcohol is used to remove the oil and ensure the contacts are spotless.

My cell testing station is setup with four 6volt deep cycle golf cart batteries arranged in a 2p2s group using larger copper ring terminals and 1/0 copper stranded cable. All four PowerLab6 chargers are daisy chained using servo extensions and 'y' harnesses with a single USB interface connecting them to a PC for control and logging. I have wired the PL6's in a 2x 2p arrangement by removing the factory bullet connectors and using copper crimps to to attach the input leads to some 4awg stranded copper cable I had around the shop. I have chosen to terminate the positive end of the chargers with a 'jumper cable' clamp, so that I can easily disconnect them when not in use, this also lets me power up each set independently if necessary.

Cycling parameters are as follows:
Charge - 3.6v 38amps C.C.C.V C/20 I.R. is marked on each cell at the end of the charge cycle
Regenerative Discharge - 2.5v 35amps C.C. Amps out are marked on each cell

I run only one cycle beginning with charge and ending in discharge. Cells will be left at discharge voltage until I have tested them all this way, then grouped by capacity and bottom balanced using C.C.C.V discharge to 2.5v before assembly into modules.

The purpose for this procedure is simply to weed out weak/damages cells and begin to break the cells in without fully taxing them.

[Bowser330]

Seeing as you have several hundred cells when you discharge cells down to 2.5V, then wont they self discharge while they are sitting and waiting for the last ones to discharge, before grouping them? Or do they not self discharge much?

[danh818]

They really do not have any issues with self discharge, although in my opinion long term storage should be somewhere around half state of charge. Also, since I am drawing the cells down to 2.5v with a constant current output, they bounce back up to between 2.9-3v almost instantly and after a few minutes, some are reading over 3.1v

[Bowser330]

Originally Posted by danh818

They really do not have any issues with self discharge, although in my opinion long term storage should be somewhere around half state of charge. Also, since I am drawing the cells down to 2.5v with a constant current output, they bounce back up to between 2.9-3v almost instantly and after a few minutes, some are reading over 3.1v

interesting, i clearly have more learning to do

[danh818]

Feel free to stop by tonight Bowser. I'll be here late testing. You can have a look at the data for yourself, it's always good to have a second set of eyes. So far I've got 44 cells done, I'm shooting for at least 50 by tonight.

If any other forum members that are in the LA area want to come by and check out the build progress feel free to send me a PM .

[danh818]

Not much to report in the last week. The car is out at my fabricators shop getting the rear end installed. They will also be welding in some gusset plates into the front end to strengthen the strut towers and act as a attachment point for the front most motor mount.

I have now tested 102 cells, all with very good results, even the few so far that have slightly wrinkled tabs, or a bit of curvature to the pouch. Even with my very conservative testing settings, the lowest capacity I have come across has been 18.3aH.

[danh818]

New Blog post is up!
Sorry to all you that have been waiting with baited breathe.

My laptop decided it had taken enough abuse and gave up on life. After a couple trips to the Apple store they decided to replace the hard drive cable, but alas that wasn't quite it. Since I had replaced the hard drive with a non-apple one, I was on my own at that point. Although I back up all my data, starting from scratch and transferring files was and absolute last resort. I used Spin Rite, a hard drive recovery tool that I have had great success with in the past, and after eight straight days of running, my machine was again bootable, not having lost a single file. I immediately cloned the drive installed a new, solid-state hard drive and transferred all the data. Finally back up and running.

Throughout the ordeal we became swamped at work and I was left with zero free time and no computer to dump all the new fabrication photos onto. But all the while Empire Fabrication of Simi Valley Ca. was hard at work bending and welding, getting us a few steps closer to a finished car.
Without further ado:


Check out my blog for more pictures of the whole fabrication and mounting process.

Rear end mounting is complete! - Now for the motor...

[rwaudio]

Awesome progress, the rear end looks sweet!! It's odd not seeing the transmission there. I assume you are going to put some of the batteries back there similar to what I did? What kind of weight balance are you looking for? Keep the stock 50/50? Mine has turned out a bit rear heavy and although that works very well for traction I'm not sure how it will affect the handling in the end. I'm going to move the charger, dc/dc converter and 12v battery up in front of the motor as low as possible to redistribute some weight.