Voltage drop BMS

[seamad]

I'm installing a new Lithium batt in my camper trailer. I have a Chinese BMS the same as the solar overkill one, 120A.
Connected up battery voltage is 13.9V, BMS output 13.1V. When BMS connected to Shunt for battery monitor ( no loads ) it drops to 5.5v or lower.
No idea what's going wrong ?

 

[Freep]

Where are you getting your 5.5v value from?

I have had issues in the past where my BMS harness had a poor connection to the terminals.

 

[seamad]

From the output wires ( 3 of) coming out of the BMS. Also same Voltage when probe was on the soldered section of the board itself.

 

[seamad]

Finished wiring up a CTEK DS250SE in the camper without the BMS, everything working. Tried the BMS again after double checking all the wiring and now the voltage drop across the board is 1 VDC ( 14.2 at input, 13.2 output ), that's without connecting the BMS output to anything. Is the BMS stuffed ?

 

[snoobler]

BMS have a very small resistance, so a sensitive meter might pick up a very small voltage drop under heavy current flow.

I vote stuffed.... unless you've hooked something up wrong.

 

[HRTKD]

Picture of how you put terminals on the ends of your wires?

 

[Gazoo]

I'm installing a new Lithium batt in my camper trailer. I have a Chinese BMS the same as the solar overkill one, 120A.
Connected up battery voltage is 13.9V, BMS output 13.1V. When BMS connected to Shunt for battery monitor ( no loads ) it drops to 5.5v or lower.
No idea what's going wrong ?

I noticed the same thing with my 8S BMS. The app was stuck in driving mode and it was locked. I reinstalled the app and put it in monitoring mode. Now it works perfectly in either mode.

 

[seamad]

Picture of how you put terminals on the ends of your wires?

Lugs hydraulically crimped.

 

[seamad]

Contacted seller.
Said I have to " activate " BMS by connecting battery to charger.
Didn't think this was a thing, but did so. Output on BMS now 1.1VDC

 

[seamad]

I noticed the same thing with my 8S BMS. The app was stuck in driving mode and it was locked. I reinstalled the app and put it in monitoring mode. Now it works perfectly in either mode.

Thanks.
I've changed the mode to monitoring but will have to remove the mattress to get back at the BMS, It's 40C inside the camper, so I'll try later. Does this change in mode effect the internal functioning nof the BMS ?

 

[Gazoo]

Thanks.
I've changed the mode to monitoring but will have to remove the mattress to get back at the BMS, It's 40C inside the camper, so I'll try later. Does this change in mode effect the internal functioning nof the BMS ?

It doesn't change the settings or internal functions of your BMS. I thought there was something wrong with my BMS until I reinstalled the app and discovered the settings. Not saying that will solve the problem you are having, but your BMS is showing the same symptoms mine did.

 

[seamad]

Lifted up the mattress to get access to the BMS. Changed app setting to monitor, Input side BMS 14.11 VDC, output 13.26 VDC. That was measured without connecting the output leads to the -ve shunt. Changed the app setting back to driving and exactly the same voltage.

 

[Gazoo]

Have you locked and unlocked the app while it's in driving mode? Does the lock open and close? That's what wasn't working on mine and is what forced me to uninstall and reinstall the app. Other than that I don't know what to suggest if it still isn't working other than HRTKD's suggestion to post some photos.

Contacted seller.
Said I have to " activate " BMS by connecting battery to charger.
Didn't think this was a thing, but did so. Output on BMS now 1.1VDC

I didn't have to do that. I know that's required for some BMS's. I hooked up my BMS after I top balanced my cells.

 

[seamad]

I didn't notice a lock or unlock function on the app, just changed from driving to monitor. I've packed up the camper as we're heading off on Monday and I can't get the app working as the bluetooth won't work through the packed camper. Will have another look when set up.
Thanks for your assistance.

 

[Gazoo]

I am attaching a photo that shows the lock. Tapping on it will open and close it. I am using an android phone.

 

[seamad]

I am attaching a photo that shows the lock. Tapping on it will open and close it. I am using an android phone.

OK, back from camping.
The lock symbol on my phone flashes on briefly, hadn't really noticed it before, but holding finger on the circle brings it up. Changed to unlock then monitor mode.
Without connecting the BMS to -ve shunt, voltage was the same on input/output of BMS.
When connecting the plug for the cell leads, the power comes on briefly for a second or two then back to low voltage on the output side of BMS. Error message flashes on app

Some progress but still not working. Tried plugging charger in but no luck.

 

[HRTKD]

It looks like the BMS is in low voltage protection mode. Do you have the Ah capacity set right? Post a picture of your parameter settings.

 

[seamad]

 

[seamad]

Some more :

 

[HRTKD]

Your BMS external temperature sensor is jacked up. It either isn't connected or it's broken. The BMS thinks your external temp is -30° C, so it has turned off the ability to charge the battery. You may be able to turn that sensor off in the BMS.