Can't get BMS alarm to stop going off

R

RPA

100 mW
Joined
Jul 20, 2009
Messages
42
Location
Illinois
I made a 29s2p Headway 38120S battery pack. The BMS is a capacitive balance type. Everything is brand new. As soon as I hook everything up the alarm goes off. The pack voltage is at 95.3 . I have included a "schematic " that was given to me in this post. I checked all my connections at the BMS and I'm getting everything I should. 95.3 volts at the positive input and ground at all three wires. Here are the cell voltage readings I get going to the BMS:

A0: Ground
A1: 3.306
A2: 6.61
A3: 9.92
A4: 13.22
A5: 16.53
A6: 19.79
A7: 23.1
A8: 26.4
A9: 29.69
A10: 32.99
A11: 36.25
A12: 39.55
A13: 42.7
A14: 46
A15: 49.3
A16: 52.6
B0: 55.9
B1: 59.2
B2: 62.4
B3: 65.7
B4: 69
B5: 72.3
B6: 75.6
B7: 78.9
B8: 82.1
B9: 85.4
B10: 88.7
B11: 92
B12: 95.3

Any ideas?
 

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Drunkskunk said:
looks like A11 and A13 are .05 volts low. That would shut down my balancer in a hurry. I don't know what the tollerance is on this BMS, though.
Click to expand...

Drunkskunk,
If yours is really that touchy, you better not get far from home. Balance charging to less than that diff makes sense, but not BMS shutdown while in use.
 
Drunkskunk said:
looks like A11 and A13 are .05 volts low. That would shut down my balancer in a hurry. I don't know what the tollerance is on this BMS, though.
Click to expand...

Thanks for your input. I don't know the tolerance on the BMS either but even when I hook up the charger the alarm still goes off and is not charging.
 
RPA said:
I made a 29s2p Headway 38120S battery pack. The BMS is a capacitive balance type. Everything is brand new. As soon as I hook everything up the alarm goes off. The pack voltage is at 95.3 . I have included a "schematic " that was given to me in this post. I checked all my connections at the BMS and I'm getting everything I should. 95.3 volts at the positive input and ground at all three wires. Here are the cell voltage readings I get going to the BMS:

A0: Ground
A1: 3.306
A2: 6.61
A3: 9.92
A4: 13.22
A5: 16.53
A6: 19.79
A7: 23.1
A8: 26.4
A9: 29.69
A10: 32.99
A11: 36.25
A12: 39.55
A13: 42.7
A14: 46
A15: 49.3
A16: 52.6
B0: 55.9
B1: 59.2
B2: 62.4
B3: 65.7
B4: 69
B5: 72.3
B6: 75.6
B7: 78.9
B8: 82.1
B9: 85.4
B10: 88.7
B11: 92
B12: 95.3

Any ideas?
Click to expand...

My headways are at 3.5v each after being idle for 48 hours. Arent you a little low?

being .2v low times 29 cells might trip the BMS LVC?.
 
deardancer3 said:
My headways are at 3.5v each after being idle for 48 hours. Arent you a little low?

being .2v low times 29 cells might trip the BMS LVC?.
Click to expand...

They are a little low but still above nominal except for A13 (3.15V) which might be my problem. But what I don't get is why I can't charge the battery. I haven't even put a load on the batteries yet. You guys got me thinking and I decided I'm going to first try and charge the pack without the BMS. I really didn't want to but I'm out of choices here. Plus the company that I bought the cells, BMS, and charger from won't help me. It's a well known company so I'm a little pissed about that. I'll let you guys know how it works out. Thanks.
 
You really need to do a balance charge of each cell before you do any riding. If these are new cells they need to be exercised a few times at LOW speed or they will pop.
(I have small a box of them to prove that point) :(

Once you get everything Happy, they will last a long long time.

Been there done that,
Juiced
 
RPA said:
deardancer3 said:
My headways are at 3.5v each after being idle for 48 hours. Arent you a little low?

being .2v low times 29 cells might trip the BMS LVC?.
Click to expand...

They are a little low but still above nominal except for A13 (3.15V) which might be my problem. But what I don't get is why I can't charge the battery. I haven't even put a load on the batteries yet. You guys got me thinking and I decided I'm going to first try and charge the pack without the BMS. I really didn't want to but I'm out of choices here. Plus the company that I bought the cells, BMS, and charger from won't help me. It's a well known company so I'm a little pissed about that. I'll let you guys know how it works out. Thanks.
Click to expand...


3.5V per cell after 48 hours is definitely NOT low for LiFePO4 cells by any means but yeah that one low cell definitely needs looking after. I would suggest charging it up to the level of the others with a single cell charger or a variable power supply.

If a BMS is sensing a low cell (usually under 2.0V for LiFePO4) it will prevent charging of the battery. It happened to me (one cell at 1.89V!) and I had to charge the cell individually to clear the fault before the BMS would allow charging the entire pack.

-R
 
Russell said:
3.5V per cell after 48 hours is definitely NOT low for LiFePO4 cells by any means but yeah that one low cell definitely needs looking after. I would suggest charging it up to the level of the others with a single cell charger or a variable power supply.

If a BMS is sensing a low cell (usually under 2.0V for LiFePO4) it will prevent charging of the battery. It happened to me (one cell at 1.89V!) and I had to charge the cell individually to clear the fault before the BMS would allow charging the entire pack.

-R
Click to expand...

I think you got confused between the two posts. None of my cells are at 3.5V . My highest are at 3.3V . It just finished charging with just the charger so I'm going to try and hook up the BMS to see if it still goes off.
 
RPA said:
I think you got confused between the two posts. None of my cells are at 3.5V . My highest are at 3.3V . It just finished charging with just the charger so I'm going to try and hook up the BMS to see if it still goes off.
Click to expand...

Yeah I did :oops:

3.3V isn't all that low either and should not trip a BMS, nor should 3.15V though you still might want to charge that one low cell individually.

Could your "capacitive balance" BMS be checking the difference between the high and low cell and faulting on that?

-R
 
If you just want to bring up the charge on the low cell I'd get a single cell charger like one;

http://cgi.ebay.com/3-2V-2A-Smart-C...emQQptZLH_DefaultDomain_0?hash=item4ce8a8cd35

I recently purchased a 15S charger from them and they delivered quickly.

You can use the single cell charger to charge each cell individually, which is time consuming and tedious, or use it to bring up the low cell(s) to the level of the other cells and see if the BMS will then allow charging current in from your bulk charger. If it still doesn't then you could hook up your bulk charger across the battery terminals and charge it like that. Be careful if you do this because individual cell voltages can climb too high in an unbalanced pack without the BMS to clamp down on them.

I recently removed a cell from my 16 cell LiFePO4 pack and could not use the BMS any longer so I used a variable power supply set to 3.60V to balance each cell to the same point figuring they'd stay balanced enough were I could use the 15S charger(I'll see this spring when I start riding again). Later I figured out how to use the 16S BMS to balance the 15S pack (needed to jumper one connection) while I'm bulk charging directly into the battery. In essence now my BMS is a balancer only.

-R
 
Thanks for the tip. I just bought a couple of them. I figure I might as well balance them all out.

I plan on using my BMS as a balancer only as well. Not only is the thing huge but it's also to delicate for the environment it will be in. The thing cost way to much for that.
 
Hey guys. I got the chargers and got all the cells topped off but it still goes off! Any other ideas? All I want to be able to do is balance out the pack with the BMS.
 
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