Electronics > Beginners
Mysterious things while hacking a Makita BLDC motor trigger
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xavier60:
I think I have figured it out. It is a simple handshake between the battery and controller.
The controller expects the 3rd contact to switch off every few minutes. The controller then responds by pulsing the 3rd contact, causing the battery to turn it on again.
I guess that if the battery feels stressed, it will hold the 3rd contact in the off state.
xavier60:
There is actually a 4th contact on the battery that is in line with the 3rd contact. the 4th contact has permanent 18v on it.
When the battery is slid into the tool's battery holder, a blade momentarily connects the 3rd and 4th contacts together.
This seems to be needed to initially wake up the battery. 
steveinfrance:
How very devious.
All I wanted was to make the controller think it was connected to a genuine Makita battery.
I'd assumed the controller took a look at the third contact once and, if OK, forgot about it.
I suppose it makes sense (literally) for the controller to check if the battery's getting red hot but-assuming it's a thermistor in there- I would have expected it to shut things down if the third contact went high or O/C rather than giving it a tickle (technical term) from time to time.
I know there's a lot of processor in the battery pack hence a lot of complaints about it 'bricking' the battery on deep discharge so perhaps, as you suggest, the third contact is via the battery processor rather than directly connected to the sensor.
Maybe I've got to spoof the third wire input to the controller along the lines you suggest.
That would be good because it would be better, in my application, to keep the motor running for as long as I want rather than as long as the controller decides.
This will keep me quiet for a while !
Was your controller for a brushed motor ?
If you managed to build a BLDC controller I'd be mighty impressed.
Just out of interest it costs about £500 for a commercial BLDC motor and controller with less performance than the Makita which I can buy for £75 without battery, also programming these controllers is a right old game,  so it's worth spending some time on a one-off hack for a potentially quite large production run.
xavier60:
I made the controller for a BLDC model, DHP481. It was a very challenging project and not really worth the time I spent on it.
When I did actually need to use a drill to drive a chemical applicator, I used a brushed model.
Much simpler to control the power directly to the brushes with a buck converter.
https://www.eevblog.com/forum/projects/cordless-drill-hacking/msg1579870/#msg1579870
steveinfrance:
I'm impressed.
The reason for a BLDC is that the equipment will have to work in some possibly difficult atmospheres.
The drill itself is, of course, not ATEX approved nor could be because of the power switching contacts in the trigger.
There's an electrolytic in the controller which produces a nice fat spark on power-on.
I can't just put the whole thing in a sealed box because of air cooling for the motor so I can't use a brushed motor.
If you're right about the handshake to the third contact I'd have to detect that and send something comforting back to the controller.
I'll probably start by interrupting the red lead for a few ms every couple of minutes which seems to reset the controller timer and won't have much effect on performance.
I'll have an optoisolator or reed in there anyway driven by the PLC so less programming to do and I/O to handle.
As you say, it's still easier than building a bespoke controller.
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