SBMSO Showing No Battery Current

[Dexter Anderson]

Hello,

I'm currently in the testing process and looking for help with my SBMS0 not showing a battery current, or balancing.

- SBMS0 wired correctly to the battery shunt and PV shunt along with the sense wires to 5P4S battery setup. (I even swapped the shunts to see if one was faulty).

- Shunts are 300A 75mv, SBMS0 is set to .25 mohms for both.

- DSSR50 connected to the PV shunt, to test solar panel charge.

- The charge coming in is shown going to the load and not the batteries, but it is charging the batteries because there is no load and the DSSR50 cuts out when the batteries are charged to 99%. I have tried load on and off settings in the monitoring with the same results.

- 

[Dacian Todea (electrodacus)]

Can you take a photo of the Diagnostic screen on SBMS0 ?

Also a photo of how the shunts are connected may be useful.

[Dexter Anderson]

[Dexter Anderson]

[Dexter Anderson]

[Dacian Todea (electrodacus)]

The ADC1n wire is not making contact. You need to connect the wire properly and you will need to restart (power cycle) the SBMS0 as when it was last powered ON that wire did not made contact so the zero offset was wrong. But it is still not making good contact as seen from Diagnostic screen it shows 65535 meaning the max value instead of around 32700

Looking at the SBMS0 connector it looks like maybe the PVp may also not be properly inserted but that one is making electrical contact so maybe the push button stays lifted due to gravity and that may be fine.

[Dexter Anderson]

Thanks, Just fiddled with it again as you suggested but no change. I have tried different types of wires these being the second set which have deep contact into the SBMS0 (10mm) with the same result.

could there be something wrong with the internal connection?

[Dacian Todea (electrodacus)]

After you fix the connection you need to power-cycle the SBMS0 else it will not work. During the power-up the SBMS0 will do a zero offset calibration and if the connection is good it will work.

[Dexter Anderson]

I did power off and back on. No change.

[Dexter Anderson]

[Dacian Todea (electrodacus)]

Can you please remove both ADC1p and ADC1n wires and power the SBMS0 then take a photo of the diagnostic screen.

[Dexter Anderson]

[Dexter Anderson]

Double checked the wires are unhooked and the SBMS0 has been reset because it still looks like the battery shunt is still connected.

[Dacian Todea (electrodacus)]

That is not good it means that SBMS0 is most likely damaged. Either some sort of damage internal to the current shunt amplifier or the corresponding ADC pin on the micro controller.

What is that you have between the battery+ and the shunt ? I see there is a red heatshrink tube over something cylindrical that may look like possibly a fuse.

[Dexter Anderson]

Just a short 4/0 cable, no fuse. This SBMS0 has done this since initial hook up unfortunately.

[Dacian Todea (electrodacus)]

I'm sorry you will need to ship it to me to see what went wrong and repair and I ship it back to you as soon as possible.

Once I have it I can see what happened and if it was my fault I will refund you the shipping cost. In any case the repair will be free as I never charge for repairs.

[Dexter Anderson]

Sounds like a plan Dacian, send it to you Findlater address?

[Dacian Todea (electrodacus)]

Yes the Findlater address.

[sailingharry]

Just a comment.  The SBMS0 is an amazing product at a bargain price.  But Dacian's support is priceless.  He responds quickly, with incredible insight into the workings of the unit (duh, he designed it).  The customer service is just awesome.

[Dave McCampbell]

We concur, and always mention the customer service, daily forum, and repair help to anyone looking for a BMS.  For over seas cruisers this is priceless and unique among companies selling BMSs.

Dave and Sherry SV Soggy Paws in Malaysia

[Dexter Anderson]

Received the unit thank you!

The good thing is now it is balancing the batteries, but on the monitoring screens the SBMS0 is showing a positive charge to the batteries when there isn't one.

On the diagnosis screen it shows more accurately with a slight discharge from self consumption.

I have done a factory reset hoping to resolve the issue but nothing changed.

[Dacian Todea (electrodacus)]

The current shunt amplifier was damaged so it was replaced. Best guess is that damage happened due to the huge battery 1600Ah and a small 300A 75mV current shunt so when connecting something like a large capacitive load like an inverter without precharging the capacitors will create current peaks large enough that voltage drop across the current shunt exceeded 1V.

When do you get this +2.8A battery current ? Immediately after power up of the SBMS0 or does it take a few minutes/hours ?

Factory reset has nothing to do with this. It will just reset your own settings like the shunt resistance value.

Can you please show a better photo of your battery?  You mentioned a 4s5p battery but in the photo you provided showing the current shunts I could only see a single cell.

That must be an older photo when you may have tested with just a 4s1p configuration.

[Dexter Anderson]

Thanks again for the repair,

Please see attached for battery pics. This layout is chosen do to space constraints.
It appears the +2.8a shows up after the APC1 shunt is connected. Otherwise the battery current reads negative.

These batteries are not installed yet or currently connected to an inverter. The inverter is a 3000 watt multiples 22 with a resistor to reduce the inlet current to the capacitors. The most this system will see is 200 amps.

[Dexter Anderson]

[Dexter Anderson]

On Tuesday, 22 July 2025 at 20:28:59 UTC-6 Dexter Anderson wrote:

[Dacian Todea (electrodacus)]

The stunts need to be connected before powering on the SBMS0 not after.

Something happened that damaged the current shunt amplifier and the most common thing is having the shunts disconnected from battery while under load or the other less likely will be to exceed 1V peak voltage drop across the shunt. To exceed 1V across your shunt it will require 4000A easily done with a 1600Ah battery and that particular shunt.

This is the worse possible orientation for the cells and not recommended by manufacturer as it is a liquid electrolyte cell and due to the way it is constructed it will be dry and degrade very fast if installed in this exact orientation.

The cells use capillarity to soak the electrolyte everywhere but this only works if the cells are installed standing up (connectors facing upwards) most recommended or at least standing on the narrow side as capillarity will still work that way.

Here is a diagram that maybe better explains the problem

[Dexter Anderson]

Thanks for the information, I read somewhere that you were suppose to connect the shunts after adding power to the SBMS.

I had no idea about the batteries, do not want to degrade, i'll have to come up with another design.

Thanks again, glad we cleared these issues up!