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chef
11 December 2010, 1521
I'm looking for 3-4 Thunder Sky LFP 40Ah cells to fix the pack in my bike. Used are fine as long as they have at least 90% of original capacity. Would prefer the older style LFP cells to match the existing ones (I think the newer LFYP cells have slightly difference specs.. 2.8-4.0v instead of 2.5-4.2v).

Skeezmour
11 December 2010, 1543
I'll check at work on Monday and see if we have 4 that are in at least good shape. Did you have 4 complete failures?

Richard230
11 December 2010, 1556
Hi Chef. Are these batteries for your GPR-S? My electrical engineering friend is trying to get my bike back on the road. Yesterday he received the 6 of the transistors that he needed to repair my under-tank battery BMS. (He claims that he now has cornered the US supply of these transistors.) He only needs one to fix the BMS board, but decided to buy the rest just for fun. He claims that they sell wholesale for 6 cents each, but the seller, Littlediode.com wanted $4 each.

Anyway, he tells me that my bike did not have a DC-DC converter and was pulling the power for the chassis from the 4-battery under-tank battery pack. He speculates that he extra electrical strain of this application is what sagged my HP batteries in this pack. So far I have replaced 5 cells (before I discovered that the BMS board was toast) in this pack, two of which died after the transistor blew up and killed the BMS board.

Perhaps Harlan can help you. He was able to sell me three of his used 50 AH HP cells when I contacted him. I gather that he has a bunch of used batteries in his backroom.

chef
11 December 2010, 1557
Thanks Skeez. At least one of the cells is at half capacity and very limited power output (the most I can get out of the pack is 21Ah). When the pack is run down, that cell sits at a dangerously low level, something like 2.0v. Two other cells are lower than expected while all the other cells are above 3.0v. I really need to pull the old thread out of Google's cache as I recorded every cell's voltage.

Richard - yes it's for the GPR-S. Mine does have a DC-DC converter so I'm surprised they didn't put one in yours. It's like playing the lottery with EMS...
Is that 5 out of 20 cells you've replaced? Yikes. My suggestion to you is to dump that buggy Modalis BMS, it lets cells get far too high. I'm planning to switch it out with the MiniBMS.
Good idea contacting Harlan, thanks!

Richard230
11 December 2010, 1613
Chef, what you are describing is exactly what my bad cells were like when I finally got around to inspecting them with a volt meter. When my cells dropped to 2.0 volts, two developed beer bellies and the other three just plain shorted out when I tried to recharge them. The other thing they would do is to charge very quickly to 3.4 volts and then discharge down to 2.0 volts after just a couple of miles of running. I kept replacing the batteries until I saw the small black hole in the top of one of the transistors.

Richard230
11 December 2010, 1626
My bike has 24 cells in 5 packs. The last pack, directly under the tank, is the one that had the cells that kept going bad and was where the 12V chassis power was coming from. I agree about the Modalis BMS. I suggested to my friend that he take a look at the mini-BMS board, but he wants to see if he can repair the Modalis board. You know how electrical engineers like a challenge. :)

chef
11 December 2010, 2308
I've watched in disbelief as the Modalis allowed the weak cells to shoot up to 4.2v. While that's technically in line with TS spec, it's well known that charging up that high reduces the cell's life while only adding a negligible amount of energy. The longer you stick with that BMS, the more likely you'll continue to replace cells.