Sunday, December 27, 2009

Cleaning the Battery Posts

Since aluminum oxide is quite non-conductive I decided to clean all of the battery posts on my new TS-LFP100AHA batteries. You can see the surface oxidation on each of the battery posts in the sample photo below. The post on the left is the negative post, and on the right is the positive.Even though copper oxide is relatively conductive I decided to clean it as well. I preparation to do the cleaning I had ordered a stainless steel wire brush, fine single cut file, and a bottoming spiral M8x1.25 tap for the post threads. I first used the wire brush to clean off each post. I could have stopped there but I wanted to make sure I had a smooth surface for the copper straps to rest against. I put a thin layer of NOALOX on each post and then used my file to smooth off the top of each post. The NOALOX helped keep the aluminum from sticking to hard in the file grooves and also put a thin layer back immediately on the aluminum to minimize oxidation. Using the fine turned out to be a good thing. I found a battery where the center post didn't stick above the nut which holds the post in place. I found the nut on each post significantly looser than on other batteries. I'm glad I discovered this since I wouldn't want the post to allow air inside and/or work loose.

After filing the tops and putting a coat of NOALOX on each post. I then put NOALOX in each hole using a cotton swab. I followed this with the tap then a cotton swab again to get any filings out of the hole followed by NOALOX again. This may have been overkill but I did find that there was a significant amount of inconsistency in the threads. I don't think it would have made a difference in getting the bolts to work but I wanted good conduction to the bolts. I'm using a BMS from Black-Sheep Technology which mounts on top of a brass bolt with a tapped hole for a screw which holds the BMS module. I have the BMS version for the TS-LFP90AHA which has the same post spacing as the 100AH battery. The brass bolt makes sure I get good conduction to the BMS module and having the screw in the bolt makes sure I don't over stress the pcb.

Right now I have the batteries hooked up in two separate parallel strings getting their initial 4.2v charge as required by the TS documentation. I have one string hooked up to my bench top lab power supply and the other set hooked up to a 4.2V smart charger. I initially did a bulk charge up to around 4 vpc using my Zivan NG-1. So far I have pulled well over 14KWh from the wall. [edit: I do not recommend charging any LiFePO4 cell to 4.2V. Even TS has lowered their max voltage to 4.0V. It shortens their life and there is very little energy above 3.45v any way. I'm now only charging to 3.485vpc. See my January 2011 blogs.]

Now I'm working on a way to mount the batteries in the Gizmo battery box. The lead acid batteries were not bolted down, nor was the battery box. It just sat in the Gizmo frame. I don't want the Li batteries bouncing up and breaking a BMS board or something if I hit a big bump.

Thursday, December 24, 2009

Lithium Batteries Finally Arrived!

Thanks to the hard work of EV Components I finally have 40 TS-LFP100AHA cells for use in the Gizmo. I placed the order in September 2009 but due to several circumstances out of their control the shipment didn't arrive until now. Fortunately they were able to find a shipper who would ship to Seattle and customs didn't take a full month like it did on earlier shipments. Dave Kois, of EV Components was kind enough to let me drive up to pick them up today. I arrived while the truck was still unloading. They sure have their work cut out for them. Look at all those boxes of cells!

While unloading the forklift ran out of propane so they had to run fill the tank. They are anxious to get an electric forklift so this doesn't happen and also so they don't have to breath the fumes. Below is another picture. You can see the brand new Toyota RAV4 that Dave is converting.

Below are pictures of my cells in my 2000 Honda Insight. It was definitely over gross. I'm glad I'm not that heavy of a person. There wasn't much spring travel left.
The box in the back is the battery box out of the Gizmo. I took it out and had it sand blasted. The bottom and corners were badly eaten by battery acid. It will last much longer with Li batteries in it. I'm going to paint it black inside and out. I'm also planning on plugging the drain holes so that water doesn't get in from the bottom. I still need to put in a splash guard in front of the box so the batteries stay clean and dry. Last time I had the batteries out I put baking soda on the bottom of the box. When I pulled them out the entire bottom was wet with baking soda crystals on the sides of most of the batteries. I determined that most of the water entered from the two front drain holes which are right where the tires would splash water on the box.

Well, I'm off to get my batteries ready to install. I still have several things to do.
  • Primer and paint the battery box
  • drill mounting holes in the battery box to match up with some threaded holes in the frame of the Gizmo so the box doesn't bounce around. Even 500lbs of batteries would bounce on some of the bumps I've hit.
  • clean off the battery posts and coat with NOALOX. I'm going to use a very fine file for this with NOALOX on the file so the aluminum won't have time to oxidize.
  • Run an M8x1.25 bottoming tap down each hole to clean the threads. I'll use NOALOX here too. The BMS I'm planning on using will mount to the top of brass bolts which hold the connecting straps so I want good conductivity through the bolts.
  • connect the batteries up in parallel and give them their 4.2V initial charge. I have a lab power supply I can use. I also picked up a 4.2V Chinoz Smart Charger from EV Components to do this.
  • Rebundle the batteries in the arrangement I need to buddy pair them.
  • finalize my mounting design and mount the the batteries to the battery box.
  • It may not matter much but I'm going to put NOALOX on the ends of all of the connecting straps. They are four layers laminated with some shrink wrap. See the picture below.

I have several other things to do but I'll post about them later.