Service - Ni-cd-to li-ion screwdriver conversion. CF-4S30A-A balancer with charg

Hello
Some facts:
- Black & Decker 14.4V Ni-Cd screwdriver
- 18650 cells from another screwdriver that still worked, used 8 pieces, two pieces in parallel. This gives a total of around 16.8V.
- 18650 cell protection ordered from China CF-4S30A-A, having a charger, balancer and various security features. Continuous current like 30A, temporary like 70A.
s-l100..jpg Download (142.32 kB)
The case is that after plugging everything in and quickly pressing the trigger, the screwdrivers cut off the power. First, I gave 4 cells 18650. Then I gave two cells in parallel and the problem decreased but still occurs. When the trigger is squeezed slower, the screwdriver normally turns and holds power.

Can it be fixed somehow?

You have written, after all, that this is a controller for LiFePo and not Li-ion. For Li-ion, the voltage on 4 cells is 14.4 (max 16.8V) ... Probably the battery controller stupid from too high voltage after charging the battery or you plowed the cells discharging them below 2.5V and then they are tubes and do not hold capacity ...

Or maybe the controller does not charge more than 14.4 instead of 16.8V and therefore you have undercharged cells and hence no power when overloaded.

I gave the photo of the driver for illustration. I have the same for li-ion. The auction even says that for li-ion 18650.
A strange situation, because without load they now have 16.5V. In addition, as I wrote, after unscrewing the screwdriver has power. This sudden impulse from the engine causes the cut-off.

After running the screwdriver at full speed, it shows 16.2 V.

Well, since you gave an illustrative photo, I gave an illustrative reason

You can try to put some ceramic capacitors at the input of the screwdriver, around 50-100uF / 25V. Their low series resistance should compensate for the current jerks caused by the motor.

Or the used rechargeable batteries from the screwdriver are already used up. Although they normally charge to 4.2 volts, the current probably is not so much.

Added after 4 [hours] 17 [minutes]:

Case solved. It's nice on new batteries (4S1P).

Hi.
The problem will probably come back as the batteries wear out a bit.
For all those struggling with the problem of voltage cut-off with a quick start in CF-4S30A-A and similar BMSs, the solution can be found here:

In the comments, a lot of diagrams and solutions for other BMSs.
As if someone had a problem with diagrams and was afraid of the Cyrillic alphabet, it is pictured here:


Have fun
Greetings.