B- cable getting hot on charge

[Gurusi]

Hey, I have a JBD 200amp BMS hooked up to a 16 cell eve 280ah pack and two split phase LV6548's. The BMS came with 4awg high temp silicone cables (states 600v 200c); however I decided to double both cables so there are two X2 4awgs per connection now.

I noticed that during high charging amps the B- cable from the BMS to the neg terminal are getting warm to hot. it seems to eminate from the bms and is getting slightly cooler as it gets to the cell terminal. I believe it is due to my set charging amps, I have checked the torque on the cell/s and BMS. I had the charging set to 80amps per inverter so 160amps which i know is hard and fast for longevity ( I read the BMS will likely last longer running in the 100-120amps range). So i have now reduced the charging amps to 60amps per inverter/120amps and will check for heat on tomorrows charge cycle.

Does this seem better? or should i be charging lower or uprating the BMS cables to a larger guage? It seemed odd that a 200amp BMS came with single 4gauge cables...

Thanks!

 

[chrisski]

Please attach pictures of the wiring, lugs, and where the wiring attached to the BMS.

Also, what temp wire is this? My BMS has 200c wire. Hotter temps could be normal, and it’d be nice to take a heat probe to it and get a reading.

My first guess is one of the doubled up cables is not crimped right forcing more current to go through a cable or a bad solder job to the motherboard.

 

[featherlite]

If it were me, I would measure the voltage drop across each connection. Excessive voltage drop = excessive heat build up.

 

[Gurusi]

Please attach pictures of the wiring, lugs, and where the wiring attached to the BMS.

Also, what temp wire is this? My BMS has 200c wire. Hotter temps could be normal, and it’d be nice to take a heat probe to it and get a reading.

My first guess is one of the doubled up cables is not crimped right forcing more current to go through a cable or a bad solder job to the motherboard.

Hey, see attached. cable is high temp silicone 600v 200c. Yep agreed, unfortunately I havent shelled out for a heat prob/infrared as yet. I tried with a digital thermometer and was getting around 70-75c but I dont trust the results with a meat thermometer! I didnt think to check the BMS board temp sensor, but will tomorrow.

crimping was done with a TH0007 hammer lug crimper, felt pretty good when making them... BMS lug is at a 45d orentation due to space, but has good surface area.

So 160amp charge shouldnt be warming the cable B- cable?

 

[Gurusi]

If it were me, I would measure the voltage drop across each connection. Excessive voltage drop = excessive heat build up.

Any guidance under how/under what condtions would be appreciated. I have a decent multi meter, I also have SA which could show something?

 

[chrisski]

crimping was done with a TH0007 hammer lug crimper, felt pretty good when making them.

Don’t think a hammer can crimp a lug anywhere near a hydraulic crimped.

As mentioned, voltage drop will show if this is bad. When under a load, Voltage drop is measured with voltmeter on top of the lug to the bottom of the busbar. If it’s bad, you’ll see a difference in reading than the others.

 

[Gurusi]

Don’t think a hammer can crimp a lug anywhere near a hydraulic crimped.

Very true, however there is always a budget on a build. I purchased mine very early on before seeing one in action (Andy's off grid i believe).

 

[Gurusi]

Don’t think a hammer can crimp a lug anywhere near a hydraulic crimped.

As mentioned, voltage drop will show if this is bad. When under a load, Voltage drop is measured with voltmeter on top of the lug to the bottom of the busbar. If it’s bad, you’ll see a difference in reading than the others.

Hey, did a voltage test under load. Found a voltage of 52.46 everywhere except at the B- lug which was 52.41. Is this considered enough to be an issue? Whilst underload the cable began to warm from the BMS side (discharging approx 70 amps). BMS temp sensor reads 36.1c, cells are 24.1c

Edit:-
Temp is 42c at the b- Lug and 32c at the neg cell lug terminal whilst under 60-70amp load.

 

[chrisski]

Could be worth checking the torque on the b- terminal. If that is correct, I recommend removing the lug to see if there was damage or corrosion to the board or copper or bottom of the lug.

I honest don’t know the temp the b- lug should be. I’ve found corrosion when I found a 5f temp difference.

Voltage drop on the lug would be measured from the top of the lug when seared and torqued to the copper on the board. You might not be able to do this measurement where the BMS is at. Drop should be nearly 0 and no real difference from other like measurements.

 

[Gurusi]

Could be worth checking the torque on the b- terminal. If that is correct, I recommend removing the lug to see if there was damage or corrosion to the board or copper or bottom of the lug.

I honest don’t know the temp the b- lug should be. I’ve found corrosion when I found a 5f temp difference.

Voltage drop on the lug would be measured from the top of the lug when seared and torqued to the copper on the board. You might not be able to do this measurement where the BMS is at. Drop should be nearly 0 and no real difference from other like measurements.

Thanks for the info and advice. I will remove the bms tomorrow and check.

I have a spare/backup bms exactly the same except it has the stock single 4awg cables. I may put it on to see if it has similar issues. If not then it isolates it to the current bms, if it has similar temps maybe it’s a normal temp and I’m over analyzing.

Incidentally I noticed WatchPower gave some faults of “weak battery” when under load; however no audible alarms or numbers came up on the inverters themselves… this may be due to the large draw on a single pack or maybe it’s related. Draw was at 6K

 

[Gurusi]

My spare BMS with single 4awg cables heated up from the board itself; however not as hot as the x2 4awg indicating heat is produced from the BMS however there is an issue with my cable/lugs.

I’ve ordered a new single silicone 2 awg cable to trade out

 

[Quattrohead]

I wouldn't worry about it, you are charging them pretty damn hard and things are going to get warm. Backing off your charging current was probably a good idea anyway.