Where do I go to buy replacement battery cells?

[zitron]

Hi guys,

I have an old 36V front hub motor with a 36V 12Ah pack. It's got ~3000km on it (~100 charge cycles) and lately the BMS has been cutting off on me. I've checked the pack and found that one set of cells are ~0.2 below the rest and also gets charged much faster than the rest. I think that's a sign of bad cells, but where do I go to buy the cells? I don't think my pack is under warranty any more...

Thanks,

-Z-

[simplyfly]

The issue is of course, matching the cells, likely you will need to replace the entire battery. Depending on how many good cells you have, there is the potential of making a new battery out of them. In my case, I took cells from the same 36V battery you have and made a 48V 5Ah battery from it. I did this by series connecting 4 cells together 4 times, 12 cells x 3.3v =39V @5Ah I charge each pack separately on quad 6A charge / balancer. Larger voltage, lighter battery, a little pedaling and you have an effective system!

New A123 LiFeP04 cells have come down in price by half. Now a very reasonable $9 ea. 30 cells, a quad 20A charge / balancer and an external 20A 12V power supply will be : about $450USD. The charger is ten times as powerful as the one you have, the balancer is far more accurate and the A123 cells are rated for 60A cont, with 200A peak. By far the best thing you could do to wake up your mini motor....

Kinda like energizers vs. dollar store batteries....

[zitron]

Hi Simply,

Thanks for the quick reply. Unfortunately I can't afford $450 for a new pack, I converted my bike in order to save money on bus tickets!! Plus it seems like a such a waste to throw away a whole pack just because a couple of cells. Also, I wonder how many charge cycles do most people manage to get out of their GM packs? According to their website I should be getting well over 800 cycles.

Since my cells are 3.7V 4Ah, I suppose I could take the good cells and make a 40V 8Ah pack, but that will put more stresses on the cells because of the reduced capacity means increase discharge C rate. I still think the best option is to replace the bad cells. Surely GM should sell them individually?

If all else fails, I might get a couple RC LiPo flight packs...

[simplyfly]

Turnigy LiFeP04 8.5 Ah 30C pack, $75 ea..... hobbycity.com

[trike]

I am trying to buy 4 cells from Golden Motor, for my faulty battery pack. The cells are advertised on their web site. I have emailed Golden Motor but get no responds.  Why.

[Bikemad]

Turnigy LiFeP04 8.5 Ah 30C pack, $75 ea..... hobbycity.com

I couldn't find a  Turnigy LiFePO4 with that capacity, but I did find this:
A ZIPPY Flightmax 8400mAh 4S2P 30C LiFePo4 Pack for $107.17.


But it's not much good for replacing a few faulty cells though.


At $4.00 each, these 4Ah 3C C-Rate 26650-G Lithium Manganate LiMn2O4 Cylindrical Battery Cells might be more suitable.

Alan
 

[simplyfly]

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16575

a little bit more...$$
a lot more current delivery....

The zippy is a good pack! I like them because I don't need to assemble the packs. I just use series connection between four packs...

[zitron]

Hi Guys,

Just to update you guys. I ended up getting 3 replacement cell from ebay for $30, and replaced the bad ones (what a pain in the neck!). It worked fine for 150km, but now two more sets of cells have died!!! My pack is probably about to die completely. I guess the moral of the story is, if some of your cells are bad, chances are the rest are about to die too very soon. I am not very impressed by the quality of the cells at all !

I decided to get 2 of these for now: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14321. 5Ah should be enough since my trips are only 12-14km on fairly flat roads. I would have to charge them separately on my 6S charger for my RC planes until I figure out some kind of a BMS.

[Bikemad]

I decided to get 2 of these for now: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14321.

$42.64 is a big saving for the same items direct from HK, but I guess you save some postage and time buying from the "Euro Warehouse".

It's a shame the prices aren't the same from both locations.

I would have to charge them separately on my 6S charger for my RC planes until I figure out some kind of a BMS.

Aren't you forgetting something? you already have a charger, BMS board and a housing that will easily accommodate two of those packs.

I'm sure you could find some heavy duty polystyrene foam to fit inside the aluminium housing and safely hold the packs in place

Voila, a neat, light weight, cost effective 36V 5Ah rack mounted pack all ready to go.

Alan
 

[zitron]

Yeah I know I can probably save ~$15-20 by getting it from HK int., after taking into account of shipping differences. But I'm kind of worried about airmailing 10000mAh of lipos getting stuck in customs. Stuff in DE is more expensive because of the import duty/tax and what not, so there's my contribution to solving the EU debt crisis .  

I'm a bit worried about the Golden BMS board not actually balancing the cells properly, because while I was trying to fix my dead cells I found out that if there are weak cells in the pack, they end up being over charged to 4.25-4.27V before the BMS shuts off charging, further damaging those cells. This definitely can't be good for cycle life in the long run.

BTW I was wondering is 5Ah really enough for 14km on fairly flat land? I weigh ~70kg with the stuff I carry to uni. I guess the only way to know for sure is to try it myself!