A blowing fuse problem with JK BMS.

[Michael36]

Hello everyone,

I've never really experimented with forums and such, so hope I chose the right section of the forum for this topic, apologies in advance if I placed it somewhere wrong.

Using a JK-B2A24S20P for testing and eventually implementing it within a 5kW, later upgraded to 10kW solar system.

I have a situation, with a battery bank of 12S4P, with 237 Ah modules.
Everything is wired according to the diagrams provided, checked and double checked for shorts, and then wired to a Victron Energy, 48V/5000/70A Mutiplus II series inverter.
The BMS balancing leads as well as B+ and B- are wired individually through a 2 AMP fuse.

The BMS turns on without an issue, either from the inverter charging or using a 5V across the P- and B- terminals of the BMS, as I've eventually found out searching through the forums.
Once on, the functionally appears to be normal, showing the status of each cell and the pack together. As well as charge and all the other various bits and bobs.

The charging of the cells works fine without any issue with a constant current of 60A.

The issue arrives when trying to discharge the cells, the 2 AMP fuse that is connected to the BMS B+ and the 12th cell of the pack, blows up the second the inverter turns on to draw power.

Verified the circuit for shorts, multiple times, and by second hands.

Reading through the specsheet/datasheet of the BMS, I couldn't find anything pointing to a large current draw on the B+ terminal, as the BMS should be drawing in the neighborhood of tens of milliamps, which shouldn't blow the fuse.

I also understood that there are some discrepancies in the manuals, are there any updated (Recent) versions of the manual?

Could it happen when it's turning the MOSFETS on, or trying to balance a cell? (All cells showed less than 10mV of total deviation between them).
A friend suggested that the internal resistance of the battery might be at play here, but I'm not sure about that.

Does anyone have any idea what could be causing this?

I’ve attached a drawing of the schematic, (The balance leads are not all wired in the schematic but are wired on the BMS unit).

Any info is much appreciated,

Thank you all for the assistance!

 

[Don B. Cilly]

5A fuse? Of course it blows. Even a minimal surge current when turning the inverter on would do it.
Also, 12s is quite an uncommon configuration, it's usually 15s or 16s for 48V.
-

 

[Nobodybusiness]

Hello everyone,

I've never really experimented with forums and such, so hope I chose the right section of the forum for this topic, apologies in advance if I placed it somewhere wrong.

Using a JK-B2A24S20P for testing and eventually implementing it within a 5kW, later upgraded to 10kW solar system.

I have a situation, with a battery bank of 12S4P, with 237 Ah modules.
Everything is wired according to the diagrams provided, checked and double checked for shorts, and then wired to a Victron Energy, 48V/5000/70A Mutiplus II series inverter.
The BMS balancing leads as well as B+ and B- are wired individually through a 2 AMP fuse.

The BMS turns on without an issue, either from the inverter charging or using a 5V across the P- and B- terminals of the BMS, as I've eventually found out searching through the forums.
Once on, the functionally appears to be normal, showing the status of each cell and the pack together. As well as charge and all the other various bits and bobs.

The charging of the cells works fine without any issue with a constant current of 60A.

The issue arrives when trying to discharge the cells, the 2 AMP fuse that is connected to the BMS B+ and the 12th cell of the pack, blows up the second the inverter turns on to draw power.

Verified the circuit for shorts, multiple times, and by second hands.

Reading through the specsheet/datasheet of the BMS, I couldn't find anything pointing to a large current draw on the B+ terminal, as the BMS should be drawing in the neighborhood of tens of milliamps, which shouldn't blow the fuse.

I also understood that there are some discrepancies in the manuals, are there any updated (Recent) versions of the manual?

Could it happen when it's turning the MOSFETS on, or trying to balance a cell? (All cells showed less than 10mV of total deviation between them).
A friend suggested that the internal resistance of the battery might be at play here, but I'm not sure about that.

Does anyone have any idea what could be causing this?

I’ve attached a drawing of the schematic, (The balance leads are not all wired in the schematic but are wired on the BMS unit).

Any info is much appreciated,

Thank you all for the assistance!

12s 4P? Are you sure? It’s usually 15 or 16 in series?

Are you using NMC or LI-ION cells?

Are you talking about the sense lead for one of the cells keeps blowing a fuse?

B- is the same terminal the BMS is hooked to and B+ is the same terminal the positive cable to the inverter is hooked.

Can you post a picture of the wiring?

 

[RCinFLA]

The forty large MOSFET's gate drive activation may have a short duration surge current when both charging and discharging sides are simultaneously turned on.

If the 2-amp fuse is a fast blow fuse it might blow during series MOSFET turn on.

Try a slow blow fuse or higher amperage fuse.

 

[Michael36]

12s 4P? Are you sure? It’s usually 15 or 16 in series?

Are you talking about the sense lead for one of the cells keeps blowing a fuse?

It is 12 cells in series, I'm using 4 recycled LG batteries bought locally, from the same batch. Each module is rated for 2.6Kw.
Fairly enough, the nominal voltage per module of 3 cells in series, is 11Volts.

Found this seller from the UK for second hand batteries:
https://www.secondlife-evbatteries.com/collections/ev-battery/products/jaguar-ipace-11v-60ah


The fuse that is blowing is wired to the final cell off the pack, from the 4th battery module. This cell is also connected to the B+ terminal of the BMS and to B12.












The main issue with the fuse blowing, is that it's inside the battery module, which cannot be opened without damaging or destroying part of the assembly.

What I can do to 'replace' the fuse, is to wire the balance lead as well as the B+ lead (bms power lead) directly to the module terminal, as the terminal has a common point directly with the last cell in the pack, the one with the blown fuse. (Last, as I'm counting from the B-, the negative terminal of the pack).

 

[Michael36]

The forty large MOSFET's gate drive activation may have a short duration surge current when both charging and discharging sides are simultaneously turned on.

If the 2-amp fuse is a fast blow fuse it might blow during series MOSFET turn on.

Try a slow blow fuse or higher amperage fuse.

That was the end solution, changed the fuse to a 5AMP slow blow fuse, and it is working like a charm.

Might need to add a slow starter somewhere in the circuit for future proofing but for now, it is alright.

Thank you very much for the help!

 

[RCinFLA]

You don't want to curtail any surge current to switch the MOSFET's on and off.

When you use the manual charge and discharge disable, which I recommend you only use sporadically for testing, it creates an extra diode drop in the series path due to the turned off MOSFETs' body diodes.

When charge or discharge mode is disabled, the BMS monitors pass current and when it gets above a couple of amps it overrides the manual charge or discharge disable user setting and turned both back-to-back MOSFET's back on to avoid overheating the body diode of the disabled MOSFET's. If current drops again or reverses current direction due to discharge or charging current showing up, it re-engages the disabled path selected by user.

It needs the gate drive to do this quickly.