Eva Håkansson - with passion for electric drive

Eva Håkansson - with passion for electric drive

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New batteries for the Wabbit!

Blog - in EnglishPosted by Eva Håkansson 08 Sep, 2009 00:47:43

Bill's beloved electric "Wabbit" has been stranded with dead NiCds for almost a year, but it will soon be out on the street again! 54 brand new ThunderSky 90 Ah lithium-iron-phosphate cells are being installed!

Before Bill built the KillaCycle, he used to drag race his electric Rabbit, or "Electwik Wabbit" as he call it. Converted in 1996 it had first Optima Yellowtops and later on SAFT NiCds. Photos from the conversion process can be seen here http://www.haritech.com/wabbit.html and in the EV Album you can see Bill smoke the tires http://www.evalbum.com/014.html.

Picture: Bill's electric Rabbit will soon smoke the tires again...

Anyway, the NiCds have now seen their best days, and when they barely could take Bill the 35 miles to work, it was time to get something better. 54 ThunderSky 90 Ah lithium-iron-phosphate cells have been waiting in their shipping crates the entire summer while we have been busy with KillaCycle and ElectroCat.

The Rabbit is a very fun little car, and both Bill and I have missed it a lot. Bill has been insanely busy with work and the KillaCycle, so I had to work on the Rabbit to get anything done at all. This weekend we finally had some time to work together and make a big leap towards a functioning car. While Bill shared his time between battery boxes and answering emails, I made battery packs. 18 packs of 3 cells is the most we can fit in the car.

Picture: 7 of the 18 packs of 3 cells that will be installed. The ThunderSkys fit perfect in the boxes that originally were made for Optima Yellowtops.

ThunderSky cells, as all large prismatic lithium cells, have to have "pressing plates", a sort of corset that prevents the cells from swelling and deforming during charge and discharge. The original ThunderSky plates are a pain to install, so I made my own instead. ~1/8 inch aluminum and the kind of steel bands that one use around shipping crates make perfect pressing plates. Much quicker and cheaper than the originals, and it also makes the battery packs smaller.

Picture: Machining to get nice, straight edges on the pressing plates. My dad always told me to use machines if possibles; and I agree - it is much less work and the result will be much better.

Picture: The machined edges are sharp as a razor blade. The belt sander and then the scotch brite wheel is the reciept to perfect smooth edges.

To get really nice joints on the steel bands, a special banding tool is required. We bought at high-quality used "Titan" banding tool on eBay for about $100. The retail price for a new is $1,000 - but then it is a German quality tool! It tightens, crimps and cuts - all with one tool. It is awesome! The only drawbacks are that it can't make smaller packs than 3 cells due to its size and the joint needs to be under tension to stay closed (which isn't the case with the tools that use a little clip).

Picture: This simple jig made of G10 holds the cells in place while I strap them. But remember - the jig MUST be made of a non-conductive material or you will short them all. Also remember that the bolts are live - put a piece of tape on top of them before you start to strap.

Picture: Holding the plates in place with a strap. Notice the volt meter - don't forget to check the health of the cells before you build the pack. It is no fun to discover a dead or sick cell when the pack is built and installed. ThunderSky LFP should be at 3.30-3.31 V out of the box if they are healthy.

Picture: Strapping! The German banding tool "Titan" is awesome! $100 used on eBay, $1,000 new...

Picture: Done! Only 17 more to go...

Picture: Finished battery packs next to ElectroCat. Wonder why the tape on top looks so strange? It is reused, the grey and white paint is since I painted something on the race trailer. Why throw away tape that still works..? That is just wasteful... ;-)

It will take about one more day of work, and the Wabbit will be back out on the street!

// Eva :-)