Richard
Controllers are very poor quality amplifier, they sense the position of the rotor in relation ot the windings and fire in 2 of every three windings to get the rotator moving away from the magnetic field it creates – and so it spins
Most controllers are pwm (pulse with modulation) the frequency of operation defines how many times they pulse (higher rates can make for smoother motor operation or cope with high pole counts)) The controllers are in either switching mode – repeated on an off – almost always on at full throttle
When you set the throttle at say 30% what you are setting is the % of time the throttle is on for so if the esc runs at 1500 hz then it switches on and off 1500 times per sec and each pulse is is 30% of 1500 ie or 0.0002 seconds in length. For 70% of the time it is “off”.
The motor will run at the same speed until the load changes. If the load increase the amps will go up but the rpm must go down. If its reduce the speed goes up but the amps fall.
The problem with part throttle operation is this - in brushed motors which have lower efficiency and relatively low power limits the a controller looses only a couple of percent of efficiency at part throttle. In brushless motors at part throttle the efficiency falls by about the same as the percentage of throttle not in use
So in the above example a motor which peaks at 80% will loose 70% at 30% throttle – that is the controller plus motor efficiency will drop to close to 56% .
Usually however the power levels at part throttle are so low that it doesn’t matter. The speed is so low there is still plenty of horsepower reaching the prop. Also the motor still makes about 95% of the torque the current could create and that is what is needed most a low speed
From:
Sent: Tuesday, 22 November 2011 8:22 AM
To: electric boats
Subject: [Electric Boats] Brush less controls
I am curious as to what is set on a brush less motor controller when the throttle is set at a particular setting..
From my observations this first year with the system it seems to set the motor rpm and then take as much current as needed to maintain this rpm when the conditions change..
If this is not so does anyone have a simple explanation.
.Richard
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