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.

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