benjamin wrote:What exactly are you trying to achieve? Was it not acceleration that feels even? I get the feeling that you are completely ignoring what I'm writing...
@Benjamin I learned something new from what you said about the current being recycled through the motor during the duty cycle off time, and also the operating frequency is a lot higher than I expected so thank you for clarifying these points! I learned a great deal.
To answer what am I trying to achieve:
The operating RPM range under it's own electrical power for a BLDC motor is from 0 RPM to no load RPM.
Considering No Load RPM as 100% RPM and 0 RPM as 0% RPM...
There are a range of RPM %'s that 10 battery amps @ 50V DC can be theoretically "fed" into the motor.Above
a certain % RPM
, 10 battery amps @ 50V pack voltage is no longer possible because of Back EMF and therefore above a certain % RPM, 500 watts electrical is simply not possible.
Close to 100% RPM (No Load RPM), very close to 0 battery amps is the most battery amps possible to be "fed" into the motor, even full throttle.
From 0% RPM until a below a certain % RPM at which Duty Cycle = 95% @ 500W @ 50V Pack Volts electrical, it is possible to "feed" 10 battery amps or more into the motor, because it is not prohibited by Back EMF from 0rpm until this certain %rpm determined by kv and motor physics.
My goal is this:
During full throttle acceleration, all the way from as close as possible to 0rpm... all the way through the RPM at which Duty Cycle = 95% @ 500w electrical, I want to "feed" precisely 10 battery amps into motor whenever the throttle is fully depressed. I know fully that due to back EMF, above a certain RPM, 10 battery amps is not possible.
There are 2 AMP limits... this means NEITHER LIMIT CAN EVER BE EXCEEDED according to the programming.
If I want 10 battery amps, and 10 battery amps is 500w, then the motor amp limit must also be high enough that it permits at least 500w
electrical at all possible rpms, including very close to 0rpm during full throttle acceleration from very close to standstill.
If the motor amp LIMIT
when multiplied by the PWM effective motor voltage
at 20 RPM is equivalent to ONLY 200w at 20 RPM
, then the true battery amp limit at 20 RPM is equivalent to ONLY 200w
/ 50v pack V = ONLY 4a battery amps... ONLY 200w... not 10A battery amps
and not enough for 500W at 20rpm because wattage is limited to 200w by the motor amp limit
So to recap, my goal is 10 battery amps & 500w full throttle at all physically possible RPMS, but if the motor amp limit = 200w @ 20rpm, then at 20 rpm, the BATTERY LIMIT IS EFFECTIVELY 4A NOT 10A. If the battery limit is 4A, then my goal of 10A battery amps is certainly prevented
at 20rpm and below, by a large margin.
Assuming a 0.0415ohm VESC detected motor ( 0.0415ohm x 2 = 0.0830ohm lead to lead ) and 50V Pure DC Supply:
10A Battery Amps = 500W / 50V DC <-battery amps LIMIT must be 10 amps
77.61A Motor Amps x 6.44V Effective PWM Volts = 500W <-motor amps LIMIT must be 77.61A motor amps to allow full 10A battery amps (500w) very close to 0rpm, full throttle
77.61A Motor Amps x 0.0830ohm Winding Resistance = 6.44V Effective PWM Volts
10 Battery Amps x 50V DC =
(77.61A Motor Amps x 0.0830ohm Winding Resistance) x 77.61A Motor Amps [I^2R] =
77.61A Motor Amps x 6.44V Effective PWM Volts
In simple terms it's physically possible to choose "10 battery amps" and "feed" exactly that into the motor at full throttle while accelerating from ~0% rpm until X% rpm @ 95% duty @ 500w... above X% rpm, less than 500w electrical and less than 10 battery amps is the most possible.
Simpler stated my goal is full throttle = 10 battery amps from the lowest possible rpm, through the highest possible rpm allowed by Back EMF, but no more than 10 battery amps at any RPM full throttle.
To do this I think it would be necessary to use the following amp LIMITS:10A/77.61A/100A
battery / motor / absolute amp LIMIT
assuming 0.0830ohm winding lead-to lead, 50v dc supply, 10 battery amps and therefore 500w electrical desired at full throttle for all physically possible rpms (0%RPM-X%RPM) not prevented by back emf.