SBMS0 Shunt Currents Both Near Zero

[Stefan Hall]

Hi All,

I'm finally replacing my DALY BMS with SBMS0 on a portable solar battery ( 4s LiFePo4) I put together and am having some trouble getting current readings for both PV1 and Battery.

I attached an image with all relevant connections. A brief summary of the problem is:

• PV1 and Battery Current Read near zero (PV1 is zero, Battery current shown is near zero)
  • This is the case even when I put 12A charge current into the PV1 connector which should pass through both shunts to get to the battery
•  I tried swapping the twisted pair to the battery shunt on the off chance that both shunts had damaged twisted pairs.
• I swapped the SBMS0 with a second SBMS0 from the same order and confirmed I get the same results
• Battery shunt is 500A 75mV (=0.15mΩ), PV shunt is 40A 75mV (=1.875Ω)

I'm hoping someone here can help! 

It's my first time setting up the SBMS0, so hopefully I just made a silly mistake that's easy to fix.

Thank you,

Stefan

[Dacian Todea (electrodacus)]

Stefan,

The shunts need to be connected on the positive side of the battery. There is no damage to SBMS0 from connecting to negative but it can not measure anything this way.

So you will have Battery+ terminal no more than 30cm of appropriate size wire then the battery shunt and then from battery shunt no more than 20 or 30cm wire to the PV shunt .

Only after the shunts you can install fuses or breakers ideally immediately after the shunts as they are designed to protect the wires in case of faults.

Also when SBMS0 powers up it will do a zero offset calibration so it will expect there will be zero current flowing trough the shunts.

ADC1p will be connected on the side of the shunt closest to battery+ and the ADC1n to the side where you connect the Load.  The PVp is towards the PV for the PV shunt.

[Stefan Hall]

Hi Dacian,

Thank you. My fault for not looking closely enough at the diagrams (I've only used BMS with low side shunts so far). Thank you for clarifying the wiring for the shunt sensing as well. 

I'll fix this when I find more time to work on the battery and will hopefully be good to go to get accurate current and SOC going forward. 

Thanks again,

Stefan