JK-BMS B2A8S20P (11.2 version) temperature 86.3°C (187.34°F) too high ?

[LaFabrik]

Hi guys, I need your opinion please
I am testing a 12V230Ah battery with a JK-BMS (B2A8S20P).
I discharge with a total current of 169A (125A through a victron Phoenix inverter + 45A through a DCDC to another battery)
The MOSFET temperature reaches 86.3°C (187.34°F) I find it high, knowing that in the JK-BMS data sheet it is indicated "Operating temperature range: -20 ℃ ～ 70 ℃ (-4°F ～158°F )
I use 2x7AWG wire and I tightened the connection screws to 4 N.M
What do you think ?
Thanks

 

[timselectric]

Very high in my opinion.
Mine rarely see 40c.

 

[LaFabrik]

Very high in my opinion.
Mine rarely see 40c.

40°C, yes that is good
It corresponds to what current intensity (A) ?

 

[timselectric]

40°C, yes that is good
It corresponds to what current intensity (A) ?

Yes, more current generates more heat.
But, heat is the enemy.

 

[LaFabrik]

i agree heat is not good ! that's why i would like to understand what's happening here

 

[timselectric]

i agree heat is not good ! that's why i would like to understand what's happening here

Check all connections.
But it's mostly due to high amperage.

 

[timselectric]

I charge and discharge at less than 20% of capacity.
Everything stays at room temperature.

 

[LaFabrik]

I charge and discharge at less than 20% of capacity.
Everything stays at room temperature.

What is your BMS please ?

 

[time2roll]

Are the power terminals hot? 4 Nm seems light, is that the specification?
Wire seems thin for 170 amps.

Is that silicone wire? That stuff is rated more amps due to the high temp insulation but will get real hot if wire is pressed near the rating. 100 amp should be closer to max (2x 50 amps)

 

[LaFabrik]

Are the power terminals hot? 4 Nm seems light, is that the specification?
Wire seems thin for 170 amps.

I admit I also had a doubt about 4N.m so I tried 6N.m and the result is exactly the same!
yes the screws are hot too
wires are 7AWG x 2 (double wire each time)

 

[timselectric]

What is your BMS please ?

JK-B2A20S20P

 

[Steve_S]

I purchased a Batch of JKBMS B2A24S15P when I switched all of my packs over to that BMS. I had 1 fail out of that batch with an identical fault, the MOS Temp was reporting 130C Overtemp. There were no issues with the bank, no heavy draws or anything that could cause any issues yet the 1 of 8 failed this way. I have not opened up the failed BMS but I'm sending it to UpNorthandPersonal as he's interested in diagnosing the cause.

While I really like the JK's, their Quality Control testing I feel is just not up to snuff.
They do seem to have peculiar quality issues and are fairly lackadaisical when it comes to product support.

 

[RV10flyer]

I have JK’s on nearly 200kWh. All are rated for 200A. I don’t push any Chinese engineered/sourced electronics over 50% or 100A. Mine rarely see 50A. You need two batteries/BMS’s if you want to pull 169A.

 

[LaFabrik]

I purchased a Batch of JKBMS B2A24S15P when I switched all of my packs over to that BMS. I had 1 fail out of that batch with an identical fault, the MOS Temp was reporting 130C Overtemp. There were no issues with the bank, no heavy draws or anything that could cause any issues yet the 1 of 8 failed this way. I have not opened up the failed BMS but I'm sending it to UpNorthandPersonal as he's interested in diagnosing the cause.

While I really like the JK's, their Quality Control testing I feel is just not up to snuff.
They do seem to have peculiar quality issues and are fairly lackadaisical when it comes to product support.

Thanks Steve
i really like JK-BMS but you right sometimes the quality control is not ok
i will try another one, to be sure the problem is really this device

 

[LaFabrik]

I have JK’s on nearly 200kWh. All are rated for 200A. I don’t push any Chinese engineered/sourced electronics over 50% or 100A. Mine rarely see 50A. You need two batteries/BMS’s if you want to pull 169A.

Hi
i hope i can go more than 100A, this BMS is sell for 200A, so i can expect at least 150A

 

[time2roll]

Swap the wire to 2x #4

 

[LaFabrik]

Swap the wire to 2x #4

exact, i can try this. thx

 

[timselectric]

Hi
i hope i can go more than 100A, this BMS is sell for 200A, so i can expect at least 150A

You can.
But that doesn't mean that you should.
200a is the max. But it shouldn't be the constant.
If you have enough capacity, you should be drawing less than 20% most of the time. (Lower is better)
Even 20% only gives you 5 hours of run time.
If you don't stress your system, it will be there for you for many years.
You definitely need more battery capacity.

 

[HRTKD]

I have the Overkill Solar 4s 120 amp BMS (aka JBD). I've run it at 100 amp discharge for three hours with no issues. I charged my EV as a test of the system to make sure everything was working. I found no hot spots, the BMS was doing well. I've charged at 60 amps with no problems.

The Overkill Solar BMS has been tested to run continuously at the rated 120 amp discharge/charge amount. It seems to be one of the few BMS that is well designed/built.

 

[LaFabrik]

I have the Overkill Solar 4s 120 amp BMS (aka JBD). I've run it at 100 amp discharge for three hours with no issues. I charged my EV as a test of the system to make sure everything was working. I found no hot spots, the BMS was doing well. I've charged at 60 amps with no problems.

The Overkill Solar BMS has been tested to run continuously at the rated 120 amp discharge/charge amount. It seems to be one of the few BMS that is well designed/built.

Thanks, i use to use JBD BMS before, but now i need more discharging current, that is whay i choose JK

 

[HRTKD]

Change the way you connect the cable to the BMS. Instead of allowing the cable to come in at a ~45° angle, change it to be perpendicular to the BMS. By allowing it to be 45°, you're reducing the surface contact area. More surface contact area means less resistance. It isn't a huge difference in contact area, but at those amps, you need all the contact surface area you can get.

Two 7 awg cables in parallel is effectively a single 4 awg. Using 4' as the round trip distance, my wire gauge calculator says you should be using a single 2 awg, or two 5 awg cables.

How hot are your cables getting?

 

[RCinFLA]

Appoximate prediction based on 25 deg C ambient air environment. MOSFET's will be much higher temp than outside case. There is only one overtemp sensor on one of the four strings of MOSFET's.

Measure voltage drop across BMS. If you have some blown MOSFET's, solder joint fractures, or current shunt resistors failures the voltage drop will be greater than chart for given current and the BMS will get even hotter for given current.

 

[Berseker]

Same experience, my 150amps jk bms mosfet overtemp warning comes on when charging at 60amps AC

 

[LydMekk]

My 200A versions stay under 30c during charging.
Consider passive cooling for your battery box.
See my battery build thread in my signature.

 

[Berseker]

My 200A versions stay under 30c during charging.
Consider passive cooling for your battery box.
See my battery build thread in my signature.

The cell temps stay a cool 32 deg C.hence why i suspect the issue may have to do with how i extended the P cable .
I only added a 7inch extension using 35mm cable to the P cable and nothing to the B cable. Could this be an issue?