So you've got yourself a good understanding of a three phase bridge, controll methods and electronics 101 - but when trying to get a reasonable shunt feedback from your high-powered system at high speed, you only meet problems.
Because of their inductance and very low resistance - getting high bandwidth (for high electrical rpm operation) from a normal high powered shunt is troublesome. Take a 1000A 50mV shunt (50W dissapation at rated I). Even if the shunt was only 5 cm's long (~2inch): the inductance would already be 50nH. The L/R time constant would be 1ms. The -3db frequency would be ~160Hz. If I'm not mistaken a normal hubbie reaches around 140Hz running 24inch wheels and 40mph. Maybe ok for hubbies in other words, but a RC motor? Not a chance.
So, how do you overcome this?
Hall effect feedback. You've heard that this is expencive, subject to sorrounding electrical fields and generally hard to work with - but all those are blown out of proportions.
Allegro carries a line of 200A bidirectional IC's with built in hall effect sensor and amplification stage. These are plug and play.
Allegro also carries 'SIP' hall effect sensors. I'll do a write up once I've fully tamed them. You need shielding, a toroid to focus the field and a basic understanding of physics. I plan to calibrate them using the 200A ic's.
-Stork
Because of their inductance and very low resistance - getting high bandwidth (for high electrical rpm operation) from a normal high powered shunt is troublesome. Take a 1000A 50mV shunt (50W dissapation at rated I). Even if the shunt was only 5 cm's long (~2inch): the inductance would already be 50nH. The L/R time constant would be 1ms. The -3db frequency would be ~160Hz. If I'm not mistaken a normal hubbie reaches around 140Hz running 24inch wheels and 40mph. Maybe ok for hubbies in other words, but a RC motor? Not a chance.
So, how do you overcome this?
Hall effect feedback. You've heard that this is expencive, subject to sorrounding electrical fields and generally hard to work with - but all those are blown out of proportions.
Allegro carries a line of 200A bidirectional IC's with built in hall effect sensor and amplification stage. These are plug and play.
Allegro also carries 'SIP' hall effect sensors. I'll do a write up once I've fully tamed them. You need shielding, a toroid to focus the field and a basic understanding of physics. I plan to calibrate them using the 200A ic's.
-Stork