JBD BMS discharge issue

[L0veless]

just took my golf cart out for first ride.
started Battery was at 92%, ran around for a bit very happy with everything averaging 37 amp draw, climbed the steepest hill amps climbed to 55.
battery level read 88 % then all of a sudden it drops to 11%
I get home throw it on the charger and it starts the charge total battery voltage 53.61. charge starts to climb at 13 %
my cells were balanced before building this pack. low cell is 3.332 high cell is 3.355 then one cell starts to fluctuate between 3.332 and 3.772
now bam it jumps from 13% to 93% this is all in about a 30 minute time span. from start charging to now currently low cell is 3.350 high cell3.355 with one cell (9)fluctuating between 3.354 and3.850
currently total volt is 55.13
this set up is 16s, 105 ah battery with JBD bms set at 250amp. charger is set at 56 volts. floats between 1amp and 30 amp depending on the draw.

any ideas what is going on I do NOT want the wife stuck out on the course.
thank you

 

[Alkaline]

Check voltage wire on the cell that is jumping, if its secure and so is the connection you have a wonky cell that can trigger the SOC. The Soc can be triggered by low or high voltage on any cell, even if all the others are good.

 

[TomC4306]

Loose connection somewhere or wire insulation caught in a crimp.
And don't just look at the BMS connections check everything.

 

[L0veless]

Loose connection somewhere or wire insulation caught in a crimp.
And don't just look at the BMS connections check everything.

will do, I did check everything before installing with multi-meter for continuity and voltage. but will check again.

 

[TomC4306]

A picture of the top of your battery would be helpful

 

[L0veless]

I turned the charger off and my cells are now at high cell 3.337 low cell 3.335 I set my charger at 56 volts. Only wanting to get in one or two rounds. I'm guessing I only need about 20% to accomplish this range.

thank you

 

[Bob B]

For a bad connection to show itself.... there needs to be current flow.

 

[L0veless]

I went through and tightened all connections, they were snug. loosened 9 and re-tightened it. checked everything with multi-meter cell to cell was3.3 then went from cell 1 through cell 16 with the proper voltage increases. Tomorrow will take it back out and see what happens. there is a lock down cover on this pack to keep it secured in my cart.

 

[HRTKD]

Half the cell voltage issues seen on the forum are due to bad connections. A dirty connection is just as bad as a loose connection. All connecting surfaces must be clean and level.

This may be a bit ticky tacky but it looks like the cable lugs you used on the battery cells are too big for the studs they're on. The lugs look like they are skewed to one side of the cell terminal which is only possible if the lug is too big. A lug with a smaller hole makes more surface contact.

The gray cable that connects the two columns of cells appears to be much smaller than the red and blue cables that go to the rest of the system.

After exercising your system, check all the connecting points with your finger, feeling for points that are hotter than the rest. When you find a hot one, you know where to start. If you have an infrared thermometer, that's more objective.

 

[L0veless]

I will change out the lugs on the reused battey cable that was off the wet batteries in the cart.
this is also the same cable that was used in the cart for previous battery and yes it is smaller. This BMS out of the factory is 300 amp/500 amp this is why those cable are so large. My thoughts are always go bigger not to create stress this is why the larger BMS. but upgrading that cable is not an issue. in the most extreme use I was only drawing 55 amps I was guessing I would be up around 125 amp draw but not even close.

do my parameters look right?
one other thing I noticed. on another screen.
Nominal capacity 100000.0 mAh
cycle capacity 80000.0mAh
full charge capacity 25000.0mAh is this right?

 

[HRTKD]

Why such a large BMS on a 105 Ah battery?

 

[L0veless]

they are 4c thinking I "might" need 300 amps, knowing really maybe just 200. plus I'm of the nature cant have too much.old railroad here. thinking I can program it down to what I really need. now I know 75 amp is probably more than I need for my cart and my situation. some carts take up to 6oo amps depending on the motor. plus the little in price difference, buy it once and forget about it. now If down the road I change out to a bigger motor I will have the BMS to match my needs up to 300 amps.
thank you for your response.

 

[TomC4306]

Why so many wires attached to cell 14?

 

[RCinFLA]

Main battery terminal connections looks good. Mid-stack jumper cable and its terminal lugs are feeble.

Realize each BMS sense wire is shared between two cells so the resistance of mid-stack jumper cable will add resistance that, under high load current, will affect the voltage reading on adjacent cell that includes the mid-stack jumper cable between BMS sense wires. That would be cell in lower left hand side of first picture.

 

[L0veless]

this JBD BMS goes from 7-21 series cell 14 gets the extra leads, I soldered them together then crimped into connector.
Jumper cable I will change out to a new heavier cable

 

[L0veless]

last night turned off charger was at 92% SOC. nothing hooked up so very little draw .014 according to my meter. this morning went out and its at 76% could this be to first time of use and just absorb? turned charger on set it o 57.7 volt, 7amp after 10 minutes jumped from 76% right up to 100%. nothing incremental. I'm using the JBD BMS app on android phone.

 

[TomC4306]

What are you using to charge?

 

[L0veless]

Huawei R4875 adjustable charger, 0-60v 0-50A​

Reading up on charging I thought adjustable would be best to set it at 56v to extend battery life as opposed to standard 58.4 volt chargers.

 

[Tom.tang]

Maybe some battery cell is bad or is less than others

 

[TomC4306]

I think you need to FULLY charge to 56 volts and hold that voltage on the charger for about an hour of absorption time. Stop turning off the charger in mid charge.
The BMS will read 100% for a little while, IGNORE THIS.
Watch the CURRENT.
When the battery is full at that voltage, current going in will dwindle. THAT is how you know the battery is fully charged.
This process is what resets the BMS coulomb counter to 100%.
Cycle battery. Observe behavior.