Are you saying brushless motors do not have permanent magnets?
No I'm saying not all brushed motors have permanent magnets
(sep ex motors don't)
Also, comparing these two motors on *just* torque is not sufficient,. That would be like comparing a pickup truck to a Lamborghini on just torque. That 80% greater power rating translates to a much higher RPM maintained at the same torque rating. I struggled to find much documentation, but it would appear those torque ratings are applied at 3000RPM (or less, couldn't find thorough documentation) on the 1000W and 4500RPM on the 1800W. So one could reasonably have an additional 1.5:1 ratio on the 1800W and maintain that same 3000RPM of the littler motor, while ending up with at least 60% higher torque than said smaller motor.
Peak torque on ALL electric motors is STALLING Torque
(ie near 0 rpm)
rated torque is what the motor is able to provide roundabout 70% of it's rev-band
and average torque is whatever the averaged sum over all of those testpoints will yield.
And there's the point.. the average is even WORSE than peak,
since nominal torque for those is identical
True, this BLDC revs more than the PMDC
but far less than what you seem to expect...
unloaded PMDC: 3700, BLDC: 4200
nominal load PMDC: 3200, BLDC 3500
So not even 10% more rpms
(oh and again.. the two motors above.. there might be different wound motors with different characteristics of course.. but most motors are terribly if at all documented so I had to pick two I could find infos on that are halfway decently reliable (which sadly isn't too trivial in the first place
)
And the torque curve drops significantly on top of the rev band (for all motors as well as engines)
so no chance you can cheat that away..
the amount of time it takes for the voltage to build up in the coil to create a magnetic field is a constant (for a fixed voltage and load)
and so is the time it takes for the magnetic field to collapse.
the faster commutated the motor is, the closer the time for one "switching cycle" is to one "build up and collapse period".
Crossing that line prevents a full build up and/or full collapse drastically reducing efficiency and power output until the motor is unable to rev any further.
Any load applied increases the magnetic resistance and thus demands higher currents, slows the build up and collapse down
(that's why simple PMDC motors run quicker at higher voltages and slower under just minimal loads)
The benefit of faster commutation the PMDC motor has on low rpms, now becomes a drawback (hence the BLDC usually is able to rev higher more easily since any coilphase is granted a little more time to build up and collapse it's magnetic field)
Don't get me wrong, I like BLDCs
but they're fancy and easy to make, easy to maintain and all that..
they're NOT the beefier motor; by far not.
it's essentially the comparision between a
200cc four stroke with say 10 hp
and a 100cc two stroke also with ten hp
one has all the torque, the other all the rpms
both can be fun and both can be the wrong tool for a job
Oh and just to be sure,
since you are certainly wondering HOW ON EARTH
with comparable rpms and well comparable torque
one can be a 1kW and the other a 1.8kW motor
simple: they're of decent to good quality from a reliable manufacturer.
and thus they're labelled for their
reliable mechanical power
or what the mfg considers as such.
both output a peak power of roundabout 2.2kW (yes mechanical)
and both draw about a maximum of 3.1kW electrical if they're allowed to;
both will die in a matter of seconds then
the PMDC heats up quicker (arcing and quicker magnetic flux changes),
hence it must not be powered for just as long under high loads as the BLDC,
which is more forgiving in those terms because it runs slightly cooler.
The BLDC has a nominal 1800W (10min rating) and 1200Watts endlessly
(allowed 30s peak is just OVER 2000 Watts [2050])
the PMDC has a nominal 1000W and no 10min rating at all
(allowed 30s peak is just UNDER 2000 Watts [1980])
'sid
