What is a proper BMS for 48v (16s) 15Ah A123 pack?

[Zeropointbug]

I have a 48v 15Ah prismatic A123 pack that's going to need 5 new cells bought for replacing 4 weak cells, and one dead one. I don't really know why 5 cells would be damaged that bad with only ~1000km on them and a small 3A charger... doesn't make sense as they 'should' be almost fine without any BMS. Also, the pack has only really been drained 70% DOD average, and maybe 85% upper limit.

Are the cell_man cells reject cells or something? Has anyone else had this same problem with these?

Any and all help is greatly appreciated

 

[Zeropointbug]

Also, the pack construction is as follows...

I had a PP bracket machined along with aluminum 'tabs' cut with holes drilled into bracket for said tabs to be screwed down. With slots machined between the two screw holes for the cell tabs to come through from the other side and be clamped down by the aluminum tabs. While building the pack, I used that very strong tape with fiber in it (glass?) to strap together every 4 cells; put 4 more cells in, tape it, etc..... then once the pack was built, I cut 5 pieces of Lexan for the 5 sides of the packs, for impact resistance (works VERY well BTW), really tough.

 

[redorblack]

How are you charging them and have you done any balance charging /individual cell charging before taping them all together and running them 1000 KM with no BMS? What you put them in isn't the issue, how you wired/connected them, how you are loading them, how you are charging them is the issue.

What are they being used for and how many amps are you drawing average and max?

 

[Spacey]

1,000 miles with no BMS? That's where you went wrong if you were not monitoring the cells properly?

 

[NeilP]

As Spacey said, if you have not used a BMS, and not monitored individual cell voltages on a regular basis, then that is where you went wrong.

Those weak and the dead cell were probably just slightly out of balance to start with, and each successive charge/discharge cycle has taken them more and more out of balance till they finally were getting under/over charged on each cycle.

Regular monitoring is essential no matter what chemistry you are using from those really cool and great LiPo cells that evey one should use if they want a great performing bike...to those big heavy weight things that some people rave about...what are they called again...LivePoo or something....

 

[Pure]

As Spacey said, if you have not used a BMS, and not monitored individual cell voltages on a regular basis, then that is where you went wrong.

Those weak and the dead cell were probably just slightly out of balance to start with, and each successive charge/discharge cycle has taken them more and more out of balance till they finally were getting under/over charged on each cycle.

Regular monitoring is essential no matter what chemistry you are using from those really cool and great LiPo cells that evey one should use if they want a great performing bike...to those big heavy weight things that some people rave about...what are they called again...LivePoo or something....

From what I understand, those with large Amperage cells (headway/A123) need to pay special attention to balancing the pack during the first few charge cycles. That getting every cell in perfect balance has proven to be difficult and needs your attention to ensure no one cell gets too far out of whack.

 

[Zeropointbug]

Ok ok,

They have been charged with a 3A charger that cell_man provided, I did monitor cells once in a while, and right before this happened, I DID check them all out and they all seemed fine, within an acceptably tight balance. The MAX current would spike at 45 - 50amps, with average top speed cruising current at around 20 to 25 amps, depending on variables. Prior to building the pack I cycled every cell twice to be sure of capacity and cell resistance. Then once the pack had been built, I let it sit for a day then cycled the entire pack once on the charger, while monitoring cell voltages.

Anyways, should I scrap the entire pack for new cells, or replace the damaged cells in hopes that the new cells will work the older ones properly with a decent balancing BMS?

 

[999zip999]

At this point I would replace the bad cells and put a bms as signalab 60a 10fet model or the one that headway uses. What is the one cellman has for sell ?

 

[Zeropointbug]

Just a small $30 unit that as far as I know doesn't balance the cells, only has voltage cut-off and charge cut-off. But I am not sure on this.

I will do some digging.

 

[kriskros]

cell man has both...a 30amp and 50amp ,and they balance cells... i have the 30amp on a 36v,20amp battery... often spikes to 50+amps... over 700 miles and all cells perfectly balanced

 

[Zeropointbug]

Ok, well if you recall I made another thread, and I mentioned that I had a 30A BMS unit from cell_man, but had not installed it yet (idiot). So if the cell_man BMS will work, then that is what I will use then.

I have to make the purchase of 5 new cells now. I just want this bike running again! I'm running a 9C 26" 'FAST' kit on 48V, I hit 56kmph.

 

[Zeropointbug]

Where is A123RC.com physically located? I hope it's not China.

 

[Zeropointbug]

Anybody?