This is the PCB from a Ferrex 40V angle grinder from Aldi. I did the mechanical teardown in another video, so now it's time for its control PCB.
One slight correction to make. The battery thermistor input is pulled up to the positive rail and not the zero volt rail. It appears to be used for actual thermistor monitoring as well as control.
This PCB has two main functions. It gives a ramped soft start to the tool and also detects the control signal from the 20/40V battery to indicate when it is low on charge or overheating. I don't think the battery itself has any ability to switch power off to the tool. It will be explored in its own video.
The bulk of the circuitry is for internal voltage regulation and MOSFET driving, with other simpler sections detecting the switch being turned on or off to facilitate doing another soft start reliably with each switch operation.
Reverse engineering this was made a lot harder by the way the PCB is soldered to the battery blades in situ and the fact that a section of it was covered in an unusually resinous silicone-like coating that was very hard to remove cleanly.
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