Hi All,
I have a new Li-ion battery pack rated at 12.6V, which includes its own built-in protection circuit. I've attached the datasheet for reference.

As an experiment, I wanted to test how long the battery would last in my application and whether the charger could recover the battery once it reached a very low voltage—specifically around 8.1V (approximately 2.7V per cell).

However, during this test, something seems to have gone wrong. The battery now appears to be stuck at around 5.5V and is not recovering. This makes me suspect that either the protection circuit has failed or the balancing circuitry for the cells has been damaged. Based on the 5.5V reading, it's possible that only two cells are functioning at 2.7V each, or that something else in the protection circuit has malfunctioned.

I’m unsure if this is the root cause, but I have my doubts and would like to know if this sounds plausible.

My application controls several 12V DC solenoids. On startup, it initiates a process that forces the solenoids into their closed positions, drawing a surge of current. It’s possible that as the battery voltage dropped very low, the microcontroller’s brownout protection triggered a reset. Upon restarting, the system would again attempt to drive the solenoids, potentially creating a loop that repeatedly drew high current from an already weak battery.

We are driving the solenoids with DRV8847. Can it be possible that there could have been an inductive spike of some sort fed back into the battery pack?

I had assumed the protection circuit would guard against this kind of behaviour, but it seems something has gone wrong. Does this explanation sound reasonable or has anyone experienced something similar?

 

Hi DJ,
I would say that 2.7V is a little too low. Looking through that datasheet, I cannot find the recommended cut-off Voltage.?
Look at the calculator in this link.
Locate your 18650 cell type and refer to the discharge graph.

E
https://lygte-info.dk/review/batteries2012/Common18650comparator.php

My type:

 

Hi DJ,
I would say that 2.7V is a little too low. Looking through that datasheet, I cannot find the recommended cut-off Voltage.?
Look at the calculator in this link.
Locate your 18650 cell type and refer to the discharge graph.

E
https://lygte-info.dk/review/batteries2012/Common18650comparator.php

My type:
View attachment 353393

Yes, I am testing how the system and battery perform and recover once they are fully discharged. During this test, I suspect that something may have damaged a component in the protection circuit—possibly related to the solenoids.

 

Hi DJ,
What methods are you considering getting all the cells back up to 3V?
Are they connected as 3, pairs?

E

 

Usually, even if the battery were to go very low, I am able to recover it via the charger. But in this case, there seems to be some damage that I am trying to understand the reason for.

 

Hi DJ,
I guess the solenoid/inductor loads being powered have suppression diodes fitted?
E

 

The driver includes the protections

 

It certainly is possible to damage a battery pack that has inadequate protection.

 

It certainly is possible to damage a battery pack that has inadequate protection.

At moment I only have the protection as per the battery pack. I am thinking the circuit protects the cells, but nothing to protect it.

 

The battery has three LiPo cells. It seems plausible that in addition to the BMS for the pack, the individual cells have standard DW01-style protection boards. If this is the case, it is possible that one of the cells discharged to the point it's individual protection board has disconnected it's output an so it can't be charged.

Unfortunately it requires disassembling the pack, but if you can:

1. Determine If protection boards are in place; and, if so...
2. Locate the cell in protection; and,
3. Charge it directly until to the cell terminals until it us above the OD limit; then,
4. Charge each cell to as close to 3.7V (or some other value under 4.2V) as possible; then,
5. Charge the cells as a battery through the BMS until they are fully charged—
   

You might be able to recover the pack.

If strikes me that 15A max and 0.2C discharge rate may be underspeced for something using solenoids.

 

Hi

The battery has three LiPo cells. It seems plausible that in addition to the BMS for the pack, the individual cells have standard DW01-style protection boards. If this is the case, it is possible that one of the cells discharged to the point it's individual protection board has disconnected it's output an so it can't be charged.

Unfortunately it requires disassembling the pack, but if you can:

1. Determine If protection boards are in place; and, if so...
2. Locate the cell in protection; and,
3. Charge it directly until to the cell terminals until it us above the OD limit; then,
4. Charge each cell to as close to 3.7V (or some other value under 4.2V) as possible; then,
5. Charge the cells as a battery through the BMS until they are fully charged—

You might be able to recover the pack.

If strikes me that 15A max and 0.2C discharge rate may be underspeced for something using solenoids.

I purposely discharged my battery over time to test how long it would take to fully discharge. Once it reached around 8.1V, I wanted to observe how my system would shut down completely, and then how it would behave as the battery charged up again. Since my charger provides a 10mA recovery charge, I simply wanted to test how long it takes for the battery pack to return to normal operating voltage.

However, I suspect that during this low-voltage phase, the solenoid may have been triggered—possibly due to a PCB reset—and I’m concerned whether a solenoid could damage the circuit under such conditions. Since the solenoid is an inductive load, could this have caused an issue when the battery voltage was critically low?

I am using the following driver for my solenoids:

DRV8847PWPR Texas Instruments | Mouser Europe

But I am now thinking I should place this diode across the + - terminal of my battery, please advice?

mouser.com/c/?q=621-SMBJ36CA-13-F&sn=Diodes+Incorporated&utm_source=octopart&utm_medium=aggregator&utm_campaign=621-SMBJ36CA-13-F&utm_content=Diodes+Incorporated&exact=true