Cell Socks

Short update: The battery assembly is moving forward slowly with a few set-backs.  The main setback was I changed my mind on the tab connections.  I assembled part of a back with rivets which worked pretty well but reconsidered as I wanted to be able to replace cells relatively easily.  I have tested all of them but these gray market cells...

One other thing while assembling I brushed a tab with a rivet and got a bit of an arc. No damage done but with 250 of these cells the chances are I would do it again. To prevent that I made up some covers (which my wife called cell socks).  It's just some fairly dense packing foam that I cut a slit in so it would slid over a cell tab.

Meanwhile it's back to peeling stickers and assembling packs.  Though I did recently discover EVTV so I have been watching it on YouTube and it has been *interesting* watching the shows.  The show is kind of like a Thirsty Traveler stays home and tinkers in his garage.  It's entertaining and makes this more tedious work go by faster. :)

Pack assembly

Right now I am grouping the cells together.  I was able to balance the capacities within ±0.15ah which is probably withing the uncertainty of my testing.

The most time consuming thing is peeling off all the stickers and getting all the pressure sensitive adhesive off.  PSA is not known for it's high conductivity.  :) So I get to sit in front of the TV with rag and some rubbing alcohol.

For making my connections I was able to modify a 3 hole punch with a simple MDF block to make all the holes in the tabs.

Works well but I might put a better spring in the punches because they often get stuck and I have to wiggle the cell to get it back out.

While I was away UPS left some presents

While I was away working in Spain for 2 weeks the UPS driver left a few boxes on my doorstep.  So after unpacking the bags it was time to unpack the new toys:

The first is the EMW EV Android Dashboard.

http://www.emotorwerks.com/emw3/product/ev-dashboard-by-emw-basic-edition/

It measures the current flowing from the pack to the controller in order to estimate the state of charge (SOC) of the battery cells.  Unlike other batter chemistries you cannot estimate SOC from the voltage.  Lithium has a very flat voltage curve from 10-90%.  Great for performance but it's hard to know how many electrons you still have in the tank.  This uses a hall effect sensor to measure the current flow.  It is designed to work with a android device so I was able to get a good deal on a new Toshiba 10.1 thrive tablet.   It has bluetooth to communicate with the current sensor and a GPS chip for navigation and a nice bright screen. It's not the best tablet in general because it's a little bulky and not the most robust case.  But none of that matters for me as I am mounting it in the center dash.

One other cool feature is that there is an output on the Bluetooth unit so it will drive the stock fuel gauge too. 

I need to play with it more but it doesn't seem to work in landscape mode. Hopefully this is something that I haven't figured out yet or will get added soon.  The other thing is that I wish the gauges were more adjustable as far as ranges and it would be really nice to add the option for warning lights (for high batt temp, SOC < 10% etc).  It seems like this would be easy to add but I have only used a android device for 15 minutes....

The second item was my BMS system:

I went with Lithiumate Lite, EV Li-Ion Battery Management System (BMS).

http://elithion.com/lithiumate_lite_overview.php

It monitors each cell group (in my case 3 cells in parallel) and make sure that the cell doesn't get over charged or over discharged.  I went back and forth on needing a BMS and I think bottom balancing a pack that has had the capacity matched would be fine.  But this is my first time with lithium and wanted the "insurance" of the BMS.  I knew I at least wanted monitoring of all of my gray market A123 cells and going to a full blown management system wasn't anymore expensive with the Lithiumate Lite.  Also on the bright side, not only are they made in the US, they are made here in Colorado!

To be honest having the EMW dash and the Lithiumate is redundant but I wanted to try out both and see how they compared.