BMS randomly swiches loads on and off

[Lukas Zemp]

I built a system in my camper around the SBMS0. So far the system was working well for a few months. But since a week I discovered, that she SBMS0 swiches the loads on and off at random moments (battery charging 80-95%).

Sometimes it swiches on and off and on and off within a minute for a few circels.

Maybee the chargers also get disconected. I can not tell as they are sometimes also swiched off because of the high charge of the battery.

Did someone else encounter ths problem as well?

Thanks and greetigs,

Lukas

[Dacian Todea]

Lukas,

You need to check what error flag is creating this problem. There can be many reason so it will be hard to speculate.

Can be to high of a charge rate and voltage exceeding 3.75V (assuming you use LiFePO4) or can be a bad connection between two cells that results in either high or low voltage on one of the cells. Can be a lose cell monitoring wire that makes intermittent contact. Can be low or high battery temperature limit if you set some limits (default there are no limits).

[Dave Svab]

Hi folks

I have the same issue with my SBMS40. About 2 years old, but only recently installed so its brand new.

How can I best check WHICH error flag is being triggered? Which page of the SBMS40 menu can I navigate to in order to see those flags?

Thanks in advance,

Dave

[Plamen]

Dave, It's Monitoring and scroll to page 3.

[Dave Svab]

Thanks. Here’s my page 3. 

The BMS has just disconnected the load as I watching the screen. No other flags highlighted during the few seconds of disconnect. This is what it looks like with no charging underway. Batts are pretty full. And the load being drawn at the time of the unexpected disconnect was under 5A. Disconnects are happening every 10 or 15 minutes, random intervals.

[Dacian Todea]

There is nothing wrong in that photo it just shows a fully charged battery so charging is stopped.

If your loads turns off for a second while battery is fully charged you can look at your cell connections to make sure there is no bad connection between cells and you can go in advanced parameter setting and set Cell balance max dV to something large like 3999mV to see if that solves your problem.

[Dave Svab]

Hi Dacian,

Thanks. Bumping max dV to 3999mV as you suggested seems to have stopped the load cycling on and off. 

Is there any documentation anywhere where I can read and learn more about these settings in the advanced setup options? I want to learn more about why that worked. I need to understand my equipment more clearly since I’m completely off-grid and depend on SBMS heavily and often don’t have any Internet to resolve issues like this.

Also, where can I find details about the STATUS value. I noticed the value is usually 20480 when not charging and batteries are full, but I’d like to decode the other bits in the integer. Documented anywhere?

Thanks again for your help, your great products and your help and commitment to this community. Much appreciated 😀👍

[Dacian Todea]

There is a scrolling help text explaining each line on screen. The Stat values are nothing else than just a number compressing the flag status on monitoring page 3. Since there is a total of 15 flags the Stat will be a number between 0 and 32768

That way if someone sends a photo where I can see the stat number I can know what flags out of all 15 are set and with are not.

For example when you see 20480 that is calculated from the two flags that are ON the flag 15 and flag 13 that are DFET and CFET  ON so you have 16384 + 4096 = 20480

  

[Dave Svab]

Thanks again 

[Dave Svab]

Aarrgghh !!!!

It just cycled load off then on again. What should I look for or try next?

Can you share the exact conditions under which the SBMS40 firmware would do this? As i reported yesterday … I happened to be watching the screen when a off/on cycle happened and I’m pretty sure no error flag on page 3 went high

[Dacian Todea]

Have you powered OFF the SBMS after you set the max dV ?  Those setting only take effect after a power cycle.

[Dave Svab]

Found my problem. Bad ring connector on my main bus. Nothing to do with SBMS40.

Sorry for wasting your time. I have other questions so I’ll open new post as these have nothing to do with this topic

Thanks all !!!

[B0bD]

Good information.

Not to hijack the thread, but I had a similar problem with the inverter momentarily switching off.  I have a Magnum MS4024 inverter, with their RSA adapter cable that allows a remote switch; its connected to EXTO3.

Eventually traced it to a bad termination inside the RSA cable - Magnum provides a crimp connector to allow customer wiring to be added.  Problem is that the RSA cable itself is a phone cable, and the one connector with a single wire doesn't crimp tightly enough. I got rid of the crimp connectors, and soldered my wires on directly.  Now that I know the cable is nothing other than a RJ11 , wit one side of the switch connected to the white, blue and black, and the other to the red, I am going to eliminates all of the connections and install a RJ11 cable long enough to reach from the inverter to the panel, and install ferrules on the RJ11 wires.

Just thought this might be useful to someone.

[Harold]

Just to say I'm also facing random cutoff load. I noticed it on IntLoad only as I have SBMS120 and that my inverter witch is on ExtLoad has a fairly long temporisation when switch off to actually turn off.