48V50Ah GM battery pack problem.

[josephkoh]

Anyone with experience with the GM 48V50Ah? I am having problem with my 2X packs.

This is a project to replace a lead acid battery pack for a converted EV car.




On arrival, one of the battery couldn't be charged. I took out the covers and checked the cell voltage, one of the cell is already broken. I've got a replacement cell from GM. Now, before I can deliver to my client, more cells are broken. I suspect the BMS is shoddy. Anyone used the 50Ah before?

[josephkoh]

Here is the status of the cells:
































I used the battery to run static test a Magic Pie once. After that, I left it for 2 weeks. Now so many cells are  at 0V.

[karma]

that's a shame. looks like your bms has dragged your cells down. I would remove the the balance wires before it damages the complete pack.

[Bikemad]

Anyone with experience with the GM 48V50Ah? I am having problem with my 2X packs.
On arrival, one of the battery couldn't be charged. I took out the covers and checked the cell voltage, one of the cell is already broken. I've got a replacement cell from GM. Now, before I can deliver to my client, more cells are broken. I suspect the BMS is shoddy. Anyone used the 50Ah before?

I never even realised this particular battery existed prior to your post, and I haven't seen it advertised anywhere on the web, so I think it unlikely that anyone on this forum has had experience with it.

Your readings give a total battery voltage of approx 21.5V instead of at least 49.5V, due to nine of those cells being almost completely dead and only six out of the fifteen being in a usable condition.

I'm assuming those cells are LiFePO4 cells, and if they're are anything like LiPo cells those nine almost dead cells are unlikely to recover from being discharged that low.

Have you had a response from GM regarding this problem? (Apart from the original dead cell)

What are the cell voltages like on the other battery next to it, are they in a similar state too, or is that other battery still OK?

A fully charged cell should be able to supply 150mA (0.15A) continuously for two weeks before the cell was fully discharged!
Therefore each of the dead cells must have been loosing power at the rate of 0.5 Watt/hour. I would think it's possible that a faulty BMS could consume 4.5W of power (9 cells @ 0.5W) and disperse the resultant heat without becoming noticeably hot.

Alan
 

[josephkoh]

These cells are advertised, but without official pricing. I guess is case to case basis.


These are LiFePO4. I tried to coax one cell back to life from 0V the other day with a power supply. It worked. But the self discharge rate is alarming (even without plugging in the BMS). The drop is as much as 50mV / day. So, it's really high maintenance cells. Really have to check one by one to see if it's okay.

Yes the other pack has the same problem. So now, I ditched the BMS. Also some cells broken.

I wanted to try this on my new project with the 5kW motor on a motorcycle with 1kW hydrogen fuel cell hybrid system. But guess I have to wait a while until I get some feedback from GM.

[Who42]

From my experience with LiFePO4 cells you must get them all about the same voltage to start off with other wise the BMS can't cope basically to get  all the cells on the same foot before charging them in series what I do is when I first get them I hook them up all in Parallel and charge them at around 3.4 volt or just higher than the highest reading of the highest cell voltage with in spec  with a Variable DC power supply say 5 amps max. then drain them to about 3v with a car head lamp  repeat the process several time till you are satisfied that all LiFePO4 cells are equal in voltage and staying that way. You must use a very accurate voltage meter
 
Then connect them in series and connect the BMS then drain them a little bit say 20% then charge them normally keeping a close eye on every thing checking all voltages.

This also helps with lead acid batteries get them to all the same voltage in  Parallel  then chage them in  series  

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[josephkoh]

Thanks Who42 for you kind advice.

I'll try parallel charge first then a discharge. It's take a while because of the high capacity.

I was also advised to charge them up to the same voltage and leave the cells for one month. Then match the similar discharge rate of the cell and group them together in the same pack. This way, the charge and discharge rate is similar can cells in series can last longer. Only problem is, I have only 2 packs, that makes 30 cells. Normally cells packed this way is priced about 30% higher than the normal ones.

I am using http://www.schulze-elektronik-gmbh.de/index_uk.htm charger to charge the single cells one by one. The maximum cells number is 14. So you see the dilemma I am having with 15 cells pack.