Stielz wrote:Im wondering how fast the motor would have to be going for it to switch to sensorless operation.. like if someone were to give a little push off before giving it some throttle would that be enough to get it straight into sensorless commutation?
This is actually the best way to start a small EV with a brushless motor and a sensorless controller! The minimum speed depends on the Kv of the motor (the lower the better) and the sensitivity of the zero-crossing detection circuit but 10% of the maximum speed should be more than enough. I have actually implemented this starting strategy in my controller http://endless-sphere.com/forums/viewtopic.php?f=35&t=27538
and 1% of the max speed is enough to synchronise the motor (I called it the "Windmill" strategy if you look in the code)
Stielz wrote:I am just having problems with my home made motor controller when I run it on the 10S lipo pack as it keeps blowing transistors. I have just had my fist go on it today just running it on 5S and it goes well, not overly fast but it has plenty of torque and acceleration.
They are many many ways to blow transistors, so you need to 1st find what is the trigger. Can you observe voltage or current or temperature peak? it is the same transistors on your board? Do you compensate for hall sensor timing delay with the speed of the motor? what transistors are you using?
Stielz wrote:Obviously the best braking method is regenerative braking as it is the only method that doesnt just convert the kinetic energy into heat in the motor and the controller. However I need a second method of braking for when the battery is fully charged so that I dont have my $250 (NZD) battery pack go up in smoke when the lipo batteries get over charged.
The only way this could be a problem is if you start from the top of a high hill with a freshly fully charged battery pack and continuously brake in regen mode. In real life, regen braking recovers much less energy than what it was required to start moving in the fist place, so you won't overcharge.