Testing or Replacing BMS

[lakespyder]

I actually bought a GTK pack for my golf cart from Ali Express and have been battling with the manufacturer ever since.

Battling even to the point that the company Foxelion created a fake SMS/text message to use as evidence in the dispute so Ali Express would deny my dispute and not allow me to return the battery. Now the BMS keeps tripping when I give the cart some throttle, making it unusable. Your videos inspired me to open it up and seek to change the BMS, but I did not find quite what I was expecting when I opened the case. Instead of 16 cells, there appear to be 48 individual cells each measuring approx 3/8" x 5.5" x 7".



The BMS is JBD-HP28SA and the pack is supposed to be 100AH 48V Lifepo4.


At this point, and being a newbie to lifepo4 I am hesitant to dig in any farther. I am hoping to get any advice that can be provide as to testing and possibly replacing the BMS. I would be comfortable swapping out the BMS as there are just 2 soldered connections and 2 plugs, but is there any good way for me to test to see if that is the problem before I do so? Would it be worthwhile to buy an upgraded BMS to replace this one? and if so, will the balancing wire plugin be the same? Is there a certain order that the BMS would need disconnected and reconnected if I do replace it to do it safely?

Thanks in advance!

 

[sunshine_eggo]

The BMS is limited to 100A. Increase in throttle will have an associated surge where the motor is likely drawing >100A for longer than the BMS allows thus tripping the BMS.

You need a BMS with higher current capability.

 

[lakespyder]

The BMS is limited to 100A. Increase in throttle will have an associated surge where the motor is likely drawing >100A for longer than the BMS allows thus tripping the BMS.

You need a BMS with higher current capability.

I got a coulomb meter and installed it. It is tripping well below 100A, which is why I think the BMS may have gone bad. At least that is what I am hoping as the manufacturer is not helpful at all.

The battery has also been working for the past month in the cart and just started this last week. Even if I ease into the throttle it trips somewhere in the 60amp range. It also trips immediately when it gets to that current range, so no 3 or 5 second or even any delay for it to trip and turn the battery off.

 

[sunshine_eggo]

Are you observing any of the individual cell voltages dropping below cutoff?

 

[lakespyder]

Are you observing any of the individual cell voltages dropping below cutoff?

No I have not. I was expecting a pack of 16 batteries, which I did plan to voltage test each individually, but when I opened it up there are 48 individual batteries. That kind of made me nervous as a newbie, so I have not opened them any farther than in the picture as i am not sure what to expect and I don't want to screw them up.

 

[lakespyder]

I guess my biggest concern is what do I do with this? Based on the pic and knowing that it is 48 individual cells, is this even a decent and safe battery pack for my golf cart? Is my best option to swap out the BMS and give it a go? Should I consider opening up each of the 48 individual cells & test (I really prefer to avoid that unless absolutely necessary).

Also, are the BMS plugs the same if I buy a different BMS? or should I be sure to buy the exact same so I don't have to rewire things? And, if I do replace BMS, is there a certain order I need to do things in to be safe or do I just unplug & unsolder, then re-attach as it sits?

 

[sunshine_eggo]

Picture is way too small.

If they were 48 cells in series, they wouldn't be anywhere near 48V.

They are likely 3P16S, i.e., 3 cells are in parallel acting as 1 "cell." Then those groups of 3 are in series to form a 16S 48V battery.

In this case, there should be 17 wires running from the BMS sense plug to the cells.

Please provide us with any battery specifications you may have to be certain.

 

[lakespyder]

Picture is way too small.

If they were 48 cells in series, they wouldn't be anywhere near 48V.

They are likely 3P16S, i.e., 3 cells are in parallel acting as 1 "cell." Then those groups of 3 are in series to form a 16S 48V battery.

In this case, there should be 17 wires running from the BMS sense plug to the cells.

Please provide us with any battery specifications you may have to be certain.

You are correct in that there are 3 cells in series acting as one, thus 16 sets of those to equal 48V. It sits at about 53.4V when fully charged, although the manufacturer says that 52.8 is full charge. I have attached a larger pic, you can also see the setup in my initial post. I am happy to enlarge or take any additional photos if you want to see anything specific.

 

[acdoctor]

I believe you can get a replacement bms JBD from Overkill. ALWAYS remove the sensor cable first and reconnect it last.
I would start by charging if it will. Unplug the sensor cable and check the voltage of the parallel packs. DC volt meter is required. Care must be given not to short leads while testing. Black wire is entire battery negative. Each white wire moving away from it voltage increases plus 1 cell. Example black to the first white is 3.4 volts black to second white is 6.8 and so on. Black to red is total pack voltage. I would be looking for any cells that are higher or lower than the rest. 0.25 volts could be a problem. If that checks out discharge it and check in the same manner.
This is why I don’t like parallel cells in a pack. You could have a dead cell and the other 2 could be carrying it to some degree. If it were 16 cells it would be fairly obvious. When you load it the voltage of the 2 cells may be dropping enough to trip the BMS like it is supposed to do.
If you don’t fully understand the BMS it monitors the cell’s voltage 16 of them. If any 1 cell reaches the minimum allowed cell voltage it disconnects the whole battery. If any 1 cell reaches the maximum allowed cell voltage it also disconnects the entire battery.

 

[sunshine_eggo]

You are correct in that there are 3 cells in series acting as one, thus 16 sets of those to equal 48V. It sits at about 53.4V when fully charged, although the manufacturer says that 52.8 is full charge. I have attached a larger pic, you can also see the setup in my initial post. I am happy to enlarge or take any additional photos if you want to see anything specific.

To clarify, the 3 cells are in PARALLEL. When they are in series, their voltage increases.

The cell count and specs confirm 3P16S LFP config.

You simply need a 16S LFP (3.2V) 100A BMS. As @acdoctor indicated, overkillsolar sells that exact unit with their own sticker on it. It has a lifetime warranty on it even if you screw it up, but he often runs out of stock. You can also order it with multiple leads installed for lower resistance. You can order it with the bluetooth dongle that allows you to access the BMS and display very detailed data and configure it as you like.

 

[mmame]

You need a 16s LiPo, not a LFP BMS - or a BMS with adjustable voltage settings!

Edit: my claim was wrong, just read the screenshots above...

 

[sunshine_eggo]

You need a 16s LiPo, not a LFP BMS - or a BMS with adjustable voltage settings!

Supplied specs indicate LFP with 51.2 nominal voltage. Why are you saying LiPo?

 

[mmame]

Ouch, looks I was wrong.... - seems to be LiFePo, not Li(Co)Po

 

[lakespyder]

I believe you can get a replacement bms JBD from Overkill. ALWAYS remove the sensor cable first and reconnect it last.
I would start by charging if it will. Unplug the sensor cable and check the voltage of the parallel packs. DC volt meter is required. Care must be given not to short leads while testing. Black wire is entire battery negative. Each white wire moving away from it voltage increases plus 1 cell. Example black to the first white is 3.4 volts black to second white is 6.8 and so on. Black to red is total pack voltage. I would be looking for any cells that are higher or lower than the rest. 0.25 volts could be a problem. If that checks out discharge it and check in the same manner.
This is why I don’t like parallel cells in a pack. You could have a dead cell and the other 2 could be carrying it to some degree. If it were 16 cells it would be fairly obvious. When you load it the voltage of the 2 cells may be dropping enough to trip the BMS like it is supposed to do.
If you don’t fully understand the BMS it monitors the cell’s voltage 16 of them. If any 1 cell reaches the minimum allowed cell voltage it disconnects the whole battery. If any 1 cell reaches the maximum allowed cell voltage it also disconnects the entire battery.

Thank you for this awesome info!
So what is the black & red wire that are by themselves below the larger bank?
Do I use the top black wire of the large bank as ground when testing or test to the main ground or does it matter?
BTW: you are absolutely correct in that I am limited on understanding on this. I do know that the BMS monitors and controls the cells, but I am very much at the learning stage of all of its connections and how they work....... Yes, I will choose to upgrade if I replace it. Tomorrow I will pull the main bank and begin testing. I will share the results. Thanks again and have a good night!

 

[sunshine_eggo]

Thank you for this awesome info!
So what is the black & red wire that are by themselves below the larger bank?

Likely a temperature sensor.

 

[lakespyder]

I fully charged the pack and was able to access the bus bars where the batteries are all connected so I was able to test the voltage of each pack at the pack. It finished charging approx 8 hours ago and has been sitting unused since.
In order from + to - the 16 cells tested
3.342
3.341
3.343
3.341
3.342
3.341
3.343
3.342
3.342
3.343
3.343
3.500* When I re-tested this one it was 3.499
3.343
3.557* When I re-tested this one it was 3.556
3.342
3.344

Total voltage at output tests at 53.79, while this all adds up to 53.849 so there is up to 0.059 possible total error in my testing.

Total voltage difference between the highest cell and lowest is 0.215

I plan to pack it all back up and put it back into the cart to test again. There have been a couple of times where I took it off of the charger before it was fully charged, so I am going to try it again and see if that could have caused some cells to not have received enough charge.

Could pulling it off the charge before the final stage or stopping then restarting the charge cycle before it has completed have caused the problem I am having?

 

[sunshine_eggo]

3.500 and 3.557 cells are essentially full, while the others are not. Your battery is notably imbalanced.

 

[lakespyder]

3.500 and 3.557 cells are essentially full, while the others are not. Your battery is notably imbalanced.

As far as notably imbalanced, is that usually an issue of the cells or something that the BMS can fix?
The good news is that after a full charge I took the golf cart for a ride and it is not tripping the BMS so far. The voltage would go down to about 46 under load, and the current up in the range of 115-130 on a hard take off, but would level off quickly after initial take off. I will now have to see how long it will last and at what point it may try to trip the BMS and strand me. I am really hopeful that the issue is that some cells were just not properly charged from the charger not fully completing its cycle. I only did a short test, but so far so good.....

I do appreciate all the help!

 

[acdoctor]

All of the cells are fairly close except those 2 rogue ones. If it were me I would use a load like a head light from a car to bleed those two during charge. Will probably take several charges to correct.
The next question is what do they look like at the bottom?
What is happening is the highest cell is disconnecting the BMS when it reaches the maximum cell voltage. While the other still need considerable change. The result is the total capacity from the artificial top to the bottom is a lot smaller than the advertised capacity.

 

[sunshine_eggo]

All of the cells are fairly close except those 2 rogue ones. If it were me I would use a load like a head light from a car to bleed those two during charge. Will probably take several charges to correct.
The next question is what do they look like at the bottom?
What is happening is the highest cell is disconnecting the BMS when it reaches the maximum cell voltage. While the other still need considerable change. The result is the total capacity from the artificial top to the bottom is a lot smaller than the advertised capacity.

Concur.

If you can regulate your charge current, you can expedite the process by charging at a rate slightly lower than the load, that way you're catching the lower cells up as you bleed down the high ones (which actually stay near full since you're charging at nearly the same rate the load is pulling down.

If this were a DIY pack, you'd break it down and charge 'em in parallel.

Once you've top balanced the pack, you should be able to fully charge it without issue. Then you would want to know how it performs as you discharge it per @acdoctor .