some recent observations imply my understanding of induction seems weak.
at first, I used some smaller diodes in a circuit, expecting the current from the inductive flyback to to be small relative to that driving the load (say, one drives 1A into a coil, maybe seeing 50 or 100mA going back up the diode, with the diode existing mostly to limit voltage spikes).
like, I figured it would have been more like a small capacitor, throwing a small amount of current, which then quickly gives out as the coil is satisfied (basically with the coil and diode in parallel).
then I observed some diodes getting rather hot (dunno how much heat is ok for diodes), and observed that the flyback current was equal to the current going in (a little over the rated values for the diodes, I was using 1A diodes and measuring around 3A of flyback, with switching at around 6kHz at 50% duty cycle).
simulators seem to support this, and as well that reducing the duty cycle seems to reduce the voltage but seemingly increases flyback amperage relative to input amperage:
estimated (simulator output implies this, but doesn't give average values, and the graphs are difficult to decipher in this case), say:
12v input at 10% duty cycle gives around 1v across the coil, but if there is 100mA input, there is around 1A of flyback current.
I am guessing as duty cycle goes down, total input current decreases, and at some point this largely goes away (no voltage means no current).
some of this was noticed when trying to run an automotive alternator turned into a 3-phase motor, for example, got it to spin up with these settings (my variable power supply was only able to supply 4.4v 4.5A in this case):
field coil: 50% duty cycle, measured 1.5v across field coil, 1A/1A flyback;
phase coils: 9% duty cycle, about 0.4v across the coils, and apparently around 3A per phase (or around 9A of flyback from the phase coils);
got motor spinning at around 100 RPM, with very little torque (I suspect the lab supply is a bit weak for this, and a motor this size may require a fair bit of power to be, well, powerful).
this seemed like some rather crazy measurements, but I guess they are more sane in retrospect.
I mostly had fiddled with the duty-cycles and similar until I had got it to spin, also determined that I may need to beef some things up before moving to higher-power testing (I prefer to minimize fried components).
side notes:
the field coil was wound with what looks like 20 AWG (as a single big coil with steel teeth wrapping around the sides from the top and bottom);
the phase coils looked like about 5 turns or so of 14AWG wire, with each phase existing as 4 sub-coils wound in series, and then the 3 phases are connected to a central common wire.
thoughts / comments?...
at first, I used some smaller diodes in a circuit, expecting the current from the inductive flyback to to be small relative to that driving the load (say, one drives 1A into a coil, maybe seeing 50 or 100mA going back up the diode, with the diode existing mostly to limit voltage spikes).
like, I figured it would have been more like a small capacitor, throwing a small amount of current, which then quickly gives out as the coil is satisfied (basically with the coil and diode in parallel).
then I observed some diodes getting rather hot (dunno how much heat is ok for diodes), and observed that the flyback current was equal to the current going in (a little over the rated values for the diodes, I was using 1A diodes and measuring around 3A of flyback, with switching at around 6kHz at 50% duty cycle).
simulators seem to support this, and as well that reducing the duty cycle seems to reduce the voltage but seemingly increases flyback amperage relative to input amperage:
estimated (simulator output implies this, but doesn't give average values, and the graphs are difficult to decipher in this case), say:
12v input at 10% duty cycle gives around 1v across the coil, but if there is 100mA input, there is around 1A of flyback current.
I am guessing as duty cycle goes down, total input current decreases, and at some point this largely goes away (no voltage means no current).
some of this was noticed when trying to run an automotive alternator turned into a 3-phase motor, for example, got it to spin up with these settings (my variable power supply was only able to supply 4.4v 4.5A in this case):
field coil: 50% duty cycle, measured 1.5v across field coil, 1A/1A flyback;
phase coils: 9% duty cycle, about 0.4v across the coils, and apparently around 3A per phase (or around 9A of flyback from the phase coils);
got motor spinning at around 100 RPM, with very little torque (I suspect the lab supply is a bit weak for this, and a motor this size may require a fair bit of power to be, well, powerful).
this seemed like some rather crazy measurements, but I guess they are more sane in retrospect.
I mostly had fiddled with the duty-cycles and similar until I had got it to spin, also determined that I may need to beef some things up before moving to higher-power testing (I prefer to minimize fried components).
side notes:
the field coil was wound with what looks like 20 AWG (as a single big coil with steel teeth wrapping around the sides from the top and bottom);
the phase coils looked like about 5 turns or so of 14AWG wire, with each phase existing as 4 sub-coils wound in series, and then the 3 phases are connected to a central common wire.
thoughts / comments?...
