Shunt reading are not correct, displayed voltage jumps.

[MG]

Hello,

I installed the SBMS0 last year. I had strange shunt readings ​​since the beginning but I haven't looked into it yet, also because the OVP and UVP works fine all the time. But recently the BMS shows strange voltage jumps and I think slowly maybe my BMS has a malfunction.

As a said the shunt readings are not correct. The pictures below are all taken immediately after switching on the BMS. Only the BMS was connected (no loads or charger) to my Battery (4S 12V 160Ah Lifeypo4)  Also with Loads and Charger connected I got false readings, sometime the Loads get up to 750A.

 

The second issues are the  you can the see in the short video. I measured all cells individually its only on the BMS. When I reconnect the BMS it works again for a while.

Is my BMS broken?

[Dacian Todea]

MG,

Check your ADC1n shunt sense wire connection both on the shunt side and on the SBMS0 side as it is open circuit and that is why you see that -600A (that is when that wire is not making contact open circuit).

Then when you fix that go to ADC menu and set you current shunts correct resistance value as that is the reason your current value was always wrong.

For the battery shunt you say you have a 150A 75mV shunt so Resistance will be 75mv/150A = 0.5000mOhm so that is what you will set in the ADC menu then for PV shunt you will set 75mV/75A = 1.0000mOhm

After you are doing this go to Device settings ans push the Save device settings so this are permanently stored so even if you do a power cycle the current shunt settings will remain saved.

As for the video. What you see there is voltage drop on sense wires while cell balancing is active. Those voltage drops seems a bit high so please check you sense wires connections. Make sure all 12 cell sense wires are connected as it may look like you did not connected all 12 wires or some are not making good contact. In any case during cell balancing there will be some voltage drop just slightly less than what you see in that video.

Nothing is wrong with the SBMS0 you just need to check your connections as you have some bad connections and also make the correct settings.

[MG]

Hello Dacian,

Thank you for your great support, you are right about the shunt readings. Despite I measured everything it seems as the contacts were corroded, I treated them with sandpaper and now the shunt readings works like a charm.

Two more questions:
According to the manual I need a resistor (1kOhm to 10kOhm) when I connect an EXT IO to DSSR20. Do I need the resistor also when I connect an EXT IO to a Ronegy battery to battery charger?

I saw that the new SBMS0 has a new fancy monitor screen. I have SBMS Version 0.2b Software 4.0p. When I update my BMS with firmware sbms0-v02b-v50d.bin do I get this monitor screen with this version?

[Dacian Todea]

-Yes you will need a resistor also for the battery to battery charger as you will have vehicle ignition signal then resistor then EXT IOx+ then the EXT IOx- will connect to the battery to battery ignition connector.

The resistor is there so that if the EXT IOx wires are shorted to GND you limit the current below 50mA and protect the Toshiba optoisolators.

-Yes when you update the firmware you will get the new monitoring screen. 

[MG]

It worked, thanks a lot