help on hacking a powertool to run on off-brand battery
Bene wrote 03/01/2023 at 21:34 • 0 pointsHi all,
I got my hands on a Scheppach branded weed wacker without battery and charger. Its a 40v lithium system. I already own a 40v lawn mower so I thought I'd just use this battery, similat to how I use Makita batterieys on Parkside tools (with a 3d printed adapter).
Here comes the problem: Running the tool off the Güde-branded battery with only the power connected works only for three seconds after starting the machine. There is a third contact in the battery bay which I hoped would be for the thermistor of the original battery (which I never had in my hands).
Anyways, connecting a 12k resistor between negative and this pin did not work, nor did any value that I dialed in with a 8k potentiometer. Opening the housing shows that there is only a 25A 36V switch on the handle and a controller bard for the low voltage cutoff between Motor - and battery -. This board also has the third battery connector connected to a point labelled "COM".
So I suspect there is some communication between battery and tool that I cannot replicate because I don't have the original battery and also no oscilloscope.
I dont want to simply bridge the board as this would also disable the low voltage cutoff which is not included in the battery.
the board mainly has a shunt, a mosfet and a MCU (Holtek HT66F018).
So do you have any good advise in which direction to proceed?
Pictures: https://imgur.com/a/rLDJzKY
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In theory, you could set up a comparator in place of the MCU that uses the MOSFET to disconnect the power if the battery voltage goes under some threshold. You could use another to monitor current with the shunt and do the same for overcurrent.
Are you sure? yes | no
I had to deal with that for one of my jobs, when it comes to brands they either have "smart" tools and "dumb" batteries or the inverse. anyways, I was curious what the connections are off of your battery, if it's just the 2 power pins then there is almost certainly internal low voltage protection (a smart battery) what brand is the 40V battery?
Are you sure? yes | no