SBMS0 current sensors blew up

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JRam

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Apr 20, 2021, 3:38:34 PMApr 20
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I have no idea why it happened, 99.9% sure it was user error but both of the current sensing chips blew out in my SBMS0. 

The SBMS0 was working fine until I noticed one of my 280ah EVE cells (8S) was spiking up. I quickly pushed the red button in the Blue Sea breaker and that's when the SBMS0 made a popping noise and the black smoke followed.

I'm going to try and replace the parts, one says 4080 TAUA but not sure what the second one is. Also it looks like the blue resistor to the left is also damaged. Anyone know what the correct parts are so I can try to revive the SBMS?

Thanks
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Dacian Todea

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Apr 20, 2021, 3:57:35 PMApr 20
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JRam,

That burned one is the Battery current shunt amplifier but the PV shunt amplifier that looks similar also seems to be damaged or at least the 1.3KOhm resistor has a burned mark meaning likely the microcontroller was also damaged.
Your installation was sure incorrectly made and in more ways than one.
First of there should be nothing between the current shunt and battery+ so no fuses, breakers or switches.
What have you used as a charge source as you do not have a DSSR20 ?
The battery current shunt is the LMP8481MM-T  (bidirectional 20x amplification (denoted by that T at the end) )  and the PV current shunt is MAX4080TAUA+T  (unidirectional bust still the 20x variant so is important to have that T in the part number as there are different ones with other amplification numbers).
But I'm sure the STM32F373 microcontroller is also damaged even if it looks like it may still work some parts of it will be damaged for sure based on how that 1.3kOhm resistor looks like.
Not sure what you mean by a cell spiking up but is fairly likely the charger was not controlled by the SBMS0 and SBMS0 needs to have ON/OFF control over all charge sources and separately over all loads.
More details about your configuration will be needed to know what was not correctly setup (likely more than one thing).

JRam

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Apr 20, 2021, 5:47:36 PMApr 20
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Sadly this happened a few months back and I can't find the diagram I did before connecting everything. I also did not take any pictures so I'm trying my best to remember how it was wired. 
I believe It was wired like this: 24v 8S 280AH Positive -> 300A shunt -> Bluesea Breaker -> Growatt 24P. Negative went straight to Growatt.
The reason why one cell was "spiking" was more or less due to the terminal screws not being torqued properly. You can easily strip the M6 threads in the EVE cells so I was way too careful and that led to a poor connection.
The Growatt does not have a way to remotely shut off the charging, I was going to wire a Victron BP but they do not recommend using it between the inverter and battery. So nothing was in place other than the cumbersome settings in the Growatt for low/high voltage, that led to my reaction to trip the breaker. Now I realize I should have used the PV disconnect instead, too late now  but lesson learned.

Thanks for the help, I'm going to see if any other components look damaged before continuing with the repair attempt. 

Dacian Todea

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Apr 20, 2021, 11:50:06 PMApr 20
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If you do not manage to repair ship it to me and I will do the repair. You will not be able to use Growatt as an inverter only same as I use the PIP MPPSolar that is basically the same inverter.  The inverter can be controlled ON/OFF trough the ON/OFF switch that will be controlled by EXT IO3 but the Solar and grid chargers can not be used as they have no separate remote.

Andreas Schröder

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Apr 29, 2021, 2:21:15 PMApr 29
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One question to these kind of problems with current sensors blowing up, when a connection to the battery is lost an the wiring is wrong.
Arent flyback diodes near the SBMS0 a way to protect it, when it comes to these current flows?

Thanks for your work,
Andy (who thinks about getting rid of a daly bms in favour of SBMS0)

Dacian Todea

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Apr 29, 2021, 2:44:32 PMApr 29
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Andy,

If wiring is done correctly meaning no fuse or switch between battery+ and current shunt then the current shunt can not fail.
Inside the current shunt amplifier there is a diode and that is the one that fails but energy when shunt is disconnected from battery is way to large thus the diode fails completely and you will need significantly large external diode and even then is not guaranteed it can protect the internal current shunt diode plus the leakage current a large diode has may have an influence in current measurement accuracy.
What happens is that if the shunt is disconnected from battery+ while current flows through it then the electromagnetic field around the wires that is stored energy will collapse and since shunt is still connected to the loads it will become negative in the sense that voltage will drop below battery- and since current shunt has an internal protection diode between the inputs and GND that is in turn connected to battery- the diode will start to clamp that negative voltage but if current was large that energy pulse from the stored energy will just completely damage the diode and with that the current shunt amplifier that contains it.  If I were to put a larger diode internally then next weakest link will be damaged and that will be the cell balancing wires 1 and 2 that are connected to battery- and that in turn will likely damage much more on the SBMS0 including DC-DC converter, microcontroller and other parts.
The thing is that the simplest thing to do is just make a proper connection between Battery+ and current shunt and so as long as the current shunt is connected there this fault can not happen.

Andreas Schröder

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Apr 29, 2021, 4:33:37 PMApr 29
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Wow Dacian,

thank you for your quick reply and the explanations concerning diodes and the current flows when the connection is lost. Sacrifising current measurement accuracy for security withour knowing that it will help in the end is indeed not a good point. I think i will ask Cem if he still has one SMBS0 he can ship to Germany.
Thanks again
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