240SX EV Conversion

Talk about tedious work. I refinished 3 packs worth of cells (96) in a week. the refinishing process goes as follows:

• Disassembly
• Preparation
• Treat
• De-prep

For the fist packs-worth of batteries I prepped the cells by applying masking tape to the top 1/4 of the cell side then adding a rubber-backed metal washer to protect the contact area. The treatment phase was 2 steps. First dipped the ends into a phosphoric acid-based rust conversion solution followed by a dip in a thinned POR-15 silver paint. Once the paint cures I remove the tape and washer. This process takes quite a while.

The new process is much simpler. Dis-assemble and dip into thinned POR-15. Wipe off excess with paper towel. Done. The threads get treated as well, but it doesn’t stop the screws from getting inserted. I will need to prep the contact area before assembly, but that will only be a scuff with fine sandpaper and some a rust inhibitor called NO-OX ID.

Stay tuned.

For the first pack I wrapped the end of the cell with masking tape, placed a rubber coated washer on the contact area of the cell.

Well, it has been a month and still no word from Headway. Not all that surprising.

I’m going to have to restore each of the cells on my own. The process I’m considering is as follows:

1) Remove all cells from packs.
2) Polish contact ends and attach a steel backed rubber washer to the ends of each cell.
3) Dip the ends of each cell in a rust converter solvent like Ospho
4) Dip each end into a thinned clear POR-15
5) Remove washers and reassemble.

At 3 minutes a cell, 512 cells should take me only about 40 hours. What fun!

Charlie

I opened up two more of the packs today, #7 and #8. I’m not too happy about what I found.

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I purchased a set of LiFepo4 batteries from Headway Battery in China. http://www.headway-cn.com/

I have 512 of the the 38120-S cells. These are 10Ahr cells with an operating Voltage of 2.5V-3.65V
Dimensions 38 (mm) x146 (mm), Weight 307g Max continuous discharge 5C Max pulse discharge 15C

At my request they were arranged into 16, 32 cell packs configured as 8P4S. Each pack is should deliver 10V-14.6V at 80 Ahr.

The issue I’m having is RUST. About half the cells have formed some serious rust on the positive cell terminals. I’ve discussed this issue with Headway and they claim the batteries were stored incorrectly. This is not the case. The long term storage specification for the batteries is 35 degrees C, which was not exceeded.

The packs were delivered in July 2009 and have been stored in my garage here in South Florida since. They were stored on a metal cart about 10″ off the ground inside the garage. The location is an non-air conditioned attached garage. It sure can get humid here in South Florida but the packs were never exposed directly to water.

Here are some pictures taken a few weeks ago.

http://is.gd/97Apl
http://is.gd/97AFB
http://is.gd/97AKp

The 240sx was at display at the 12/13/08 Park Vista auto show along with 4 other Electric Vehicles from the Florida EAA. It was a great show.

The controller would not fit in the planned location so displaced one of the front batteries which was relocated to a rack in front of the right wheel. This turned out pretty well since I needed to repair that rust hole anyway.

An emergency disconnect was mounted below the rear front rack. An all-thread rod in the passenger compartment is used to pull it open. This kept with the design goal of having no pack voltage in the passenger compartment.

A voltage prescaler and DC/DC converter needed to be added to the Link 10 E-meter. The maximum input voltage for the link 10 is 50V, so the pack voltage needed to be reduced before entering the meter.

Since I had to relocate the engine compartment fuse box, I also took the liberty to remove some unused wires. This include removing the ECM and harness as well as many other unused circuits.

The battery charger was trial fitted to a plywood sheet in the hatch. This is not the final location of the charger since it’s too close to the batteries and their venting gasses.

The electric motor was mounted to the original ICE motor mounts. A clam-shell clamp was fabricated to clamp the motor. 1/4″ bar stock was used to mount the clamp to the mounts. A trial fit in the car showed too much sag on the mounts so an additional under-support was fabricated and welded in place.

The 18 batteries were arranged over 4 battery racks, 1 in the back and 3 in front. 9 batteries were placed in the back rack and 9 in the front. Placing 9 batteries in the front kept the front at roughly original weight. The rear will be a few hundred pounds heavier.

I had to move one battery into the hole in front of the front wheel to make room for the controller.