New DIY 12V Build - low battery voltage from BMS issue

[ski3pin]

Did you try putting a charge on the battery through the BMS?

I have not. I will give it a try.

 

[ski3pin]

Did you try putting a charge on the battery through the BMS?

I put a charge on the battery last evening - 14.4V until the DC unit's amps were near .0 and then disconnected. I checked the battery this morning and the voltage is still low - the same as above - through the BMS.

Here is what the BMS app shows -

 

[MisterSandals]

I checked the battery this morning and the voltage is still low - the same as above - through the BMS.

13.6V is 99% full. Is it acting like it’s not full or are worried about the surface charge (<1% of capacity) discipating overnight?

Looks good if acting normal. Enjoy your full battery. You don’t need to bounce the voltage off the ceiling every day, 14.4V is mighty aggressive (can I say harsh?)

 

[ski3pin]

Yes, you can say harsh. I'm a novice and working on my learning curve.

And yes, the BMS says 99% full and 13.6V.................................but at the terminals that will supply power to my camper the voltage reads 11.9V. This is low and the original problem I posted about. Why?

 

[acdoctor]

Q: I can’t charge or discharge after I used the Android app
A: Avoid pressing the giant padlock on the Android app main screen. If you touch it, it engages the “mosfet software lock” without confirmation. Then it disappears. To find it again, you must switch the app mode from driving mode to monitor mode and back. Avoid clicking it. If you’ve inadvertently pressed it, switch the modes and see if that fixes it.

 

[Gazoo]

Q: I can’t charge or discharge after I used the Android app
A: Avoid pressing the giant padlock on the Android app main screen. If you touch it, it engages the “mosfet software lock” without confirmation. Then it disappears. To find it again, you must switch the app mode from driving mode to monitor mode and back. Avoid clicking it. If you’ve inadvertently pressed it, switch the modes and see if that fixes it.

I have posted twice in this thread, and now three times, the lock you refer to does not exist if using the latest version of the app.

 

[Gazoo]

Here is what the BMS app shows -

The "Switch Function" is turned on in my app. Not sure that will make a difference but it's worth a try.

 

[MisterSandals]

but at the terminals that will supply power to my camper the voltage reads 11.9V.

In post #11, are the red and blue terminals on your battery pack where you are seeing 11.9V? This is the only thing that I think i may be misunderstanding. Or are you referring to a location in your camper?


I went thru this thread from the beginning, reading everything and going thru your setting pix twice, i don't see anything different from what i have on my 2x Overkill 4S systems.

Right now (if Gazoo's Switch ideas does not help), I'd strongly suspect the BMS is faulty.

Sorry, I've really gone thru this as well as I could (extra effort for a fellow telemarker).

 

[ski3pin]

Sorry, I've really gone thru this as well as I could (extra effort for a fellow telemarker).

That one made me smile, thank you! Yes, back in the days of skinny skis and voile mountaineering 3 pin bindings, not so long ago. And the peaks we skiied on that gear! We do have wide boards and cable bindings these days but still embrace the noble telemark.

 

[ski3pin]

I appreciate everyone's help with attempting to sort out this problem. This is my first time on this forum and it has been a very positive experience. Thank you. Here are two photos from this morning that, I hope, clarify the issue.

The voltage reads 13.55V and is right at what the BMS app indicates.

And here at the terminals the voltage is 11.82V

 

[Gazoo]

Only other thing I can suggest, if you haven't tried, is to reinstall the app. If that doesn't work then your BMS is most likely faulty.

 

[MisterSandals]

Only other thing I can suggest, if you haven't tried, is to reinstall the app. If that doesn't work then your BMS is most likely faulty.

Yep. You could start working your way back to the battery on the negative side.
Underneath the top board.
BMS leads at P-
BMS leads at B-
Bolt at end of B- (blue lead)
Bolt on battery side of board

If your issue is between P- and B- leads, it has to be the BMS.

 

[jamiko]

Only other thing I can suggest, if you haven't tried, is to reinstall the app. If that doesn't work then your BMS is most likely faulty.

It has to be related to the BMS because that's the only thing between the battery and those terminals. Are all wires tight? Are the balance leads in the correct order?

 

[ski3pin]

Here is another discovery this morning as I attempted to use Will's capacity tester from aliexpress.

Here is the tester connected to my old AGM battery. The voltage reads 12.7V

And here it is connected to the DIY battery. It reads 1.94V. What is going on? Across the terminals with the multi meter it reads 11.82V as it did in the prior post.

 

[Gazoo]

I bet the capacity tester is putting enough of a load on the BMS to draw the voltage down. A light bulb would do the same thing. Your BMS is behaving the same way as mine did with the older app and the lock was on.

I can suggest a few other things to try but they probably won't work. But try in the following order.

Try turning discharge off and on on the main screen...you probably tried this.

Try unplugging the BMS and plug it back in to reset it. If that doesn't work then reinstall the app.

Find the older app with the lock function and see if that app will unlock the BMS.

If none of these suggestions work then I will be 99.9% certain the BMS is bad. I am not trying to run you around in circles. It doesn't hurt to try everything before coming to a solid conclusion even though you should not have to go through this.

 

[acdoctor]

I don’t see the switch config in the screenshots but if it is enabled and the connector is open it will present just like yours is. Q: What does the optional switch do? (The SW connector and 2-wire pigtail)
A: This connection allows a remote switch to disable discharging of the battery pack. Charging is unaffected. Useful as a remote battery shut-off switch. Connect only to an isolated switch contact. This feature can also be disabled in software.

 

[acdoctor]

I will start by saying I can’t remember from sure but I think this was the procedure.I purchased 2 of the CE models Radio tech. There was a little paper slip that said if you connected it completely and it was not passing voltage to short from B- to P- with a jumper momentarily. My first one worked but the second one was 10.5 volts like the paper said. I did this and it worked. I can’t find the paper now nor can I find it on the web. You would not think that it would do anything but it did.

 

[ski3pin]

I bet the capacity tester is putting enough of a load on the BMS to draw the voltage down. A light bulb would do the same thing. Your BMS is behaving the same way as mine did with the older app and the lock was on.

I can suggest a few other things to try but they probably won't work. But try in the following order.

Try turning discharge off and on on the main screen...you probably tried this.

Try unplugging the BMS and plug it back in to reset it. If that doesn't work then reinstall the app.

Find the older app with the lock function and see if that app will unlock the BMS.

If none of these suggestions work then I will be 99.9% certain the BMS is bad. I am not trying to run you around in circles. It doesn't hurt to try everything before coming to a solid conclusion even though you should not have to go through this.

I did these most of these except for finding an older app. The one result that was changed is that after unplugging the balance leads push connector and then reconnecting the BMS app now has both the charging and discharge off and will not allowing turning them on. Under protection it now reads "locking" and balance is now closed. Here's a photo -

 

[ski3pin]

A quick update, an acquaintance is sending me another BMS. I will hook it up and report on results.

 

[ski3pin]

A quick update, an acquaintance is sending me another BMS. I will hook it up and report on results.

I received the replacement BMS. I installed it and the battery and BMS now function confirming the BMS was at fault. I performed a capacity test of my 120 cells and the result was 111 amp hours. The results -

And the BMS app readout