hello everyone,
here's a photo of a BLDC controller for a power tool. It looks like a typical controller, except there are 3 leads input from the battery, red black and yellow. Don't know what the yellow is for, and when i hooked up dc voltage to the red and black (like i do on brushed power tools) the motor did not run. I hotwired plenty of scooters with BLDC, none of em had 3 battery leads. What gives?
PS. there's an extra gray and black wire comin off the controller. its for an led.

 

In most cases the third connection is for a temperature sensor (usually a thermistor) so the tool can choose to shut down instead of overheating the battery. Sometimes it is (also/only) a way for the BMS to sense that a tool is present and turn on the output; or, it can be for a data connection allowing the battery and tool to exchange information about state digitally.

It depends on the brand. If it is a thermistor, you will need to simulate its presence by putting an appropriate resistor between that pin and 0V otherwise the tool will think there is a fault condition and not run.

 

In most cases the third connection is for a temperature sensor (usually a thermistor) so the tool can choose to shut down instead of overheating the battery. Sometimes it is (also/only) a way for the BMS to sense that a tool is present and turn on the output; or, it can be for a data connection allowing the battery and tool to exchange information about state digitally.

It depends on the brand. If it is a thermistor, you will need to simulate its presence by putting an appropriate resistor between that pin and 0V otherwise the tool will think there is a fault condition and not run.

hmmm.... well if it's (almost certainly) a thermistor, it could be connected 2 possible ways inside a battery pack:
either G--thermistor--yellow or +--thermistor--yellow. Either way, there would have to be another resistor inside the controller to complete the voltage divider. So i'll just find a pot and try both ways n see which way works.
If it's a connected sensor for the BMS, then the yellow lead don't matter because i'm not using a BMS, just connecting a voltage to the black n red. So if that's the case, then it should be working normally this way.
If it's a data lead like in phone batteries, i'm screwed. But i really doubt that they would do that. This is a Harbor Freight tool. A BMS with a uC is overkill for a company (Bauer, a Harbor Freight brand) that specializes in low end tools.
So i'm gonna get a pot and give it a try.
thanx, we'll see....

 

https://www.vsec.top/connection-circuit-diagram-of-ntc-thermistor-used-in-lithium-battery/

 

Certainly making random connections without a clue is great way to convert useful equipment into scrap metal. The yellow wire may well be for a temperature sensor, OR it might be a tap to get a lower voltage for some control logic. After you burn out the module it will not matter.

 

https://www.vsec.top/connection-circuit-diagram-of-ntc-thermistor-used-in-lithium-battery/

thanx that was quite helpful

 

Certainly making random connections without a clue is great way to convert useful equipment into scrap metal. The yellow wire may well be for a temperature sensor, OR it might be a tap to get a lower voltage for some control logic. After you burn out the module it will not matter.

Then i guess i better not make any random connections without a clue, right? Kinda goes without sayin, don't it?
Anyway, i couldn't find a pot so i just took a 10k and put it between yellow and ground and BINGO, i have a cordless router. Seems it IS for a thermistor, after all. Job done.
Not that you don't have a valid point. It's entirely possible, but i just can't see it happenin. Put an 1117 IN the battery pack? for the controller? I seen alot of shit, but that would grossly violate standard practice. The 7805 is ALWAYS part of the same board, for several reasons. There would have to be some REALLY compelling (and really bizarre) reason to do something like that.
But yeah, if they did that and i connected 18v--10k--Vdd, then OOOOOOO NOOOOOOOOO Mister Bill, there's a good chance i'd have a $45 paperweight.