Peakfoto Digital Photo Still n Video wrote:
When pressing lightly on the throtle the bike wheel Buzzes, it turns fine, stop
buzzing from 1/2 to full power.
Do I need to put a motor start cap on it? to smooth out the pulsing?
Your bike's controller is switching on/off to control its speed. The
controller depends on the motor's inductance to smooth the rapid on/off
voltage pulses into a (more or less) smooth current.
Your bike probably also has a permanent magnet DC motor with brushes
(it's the cheapest kind). But this type of motor has low inductance.
Thus it does a poor job of smoothing out the voltage pulses. The result
is the noise you hear (and corresponding pulses in the torque the motor
produces.
You can't add a capacitor; that would make things worse! But you can add
inductance in series with the motor. This will do a better job of
filtering the current and reducing the noise.
Jay Summit wrote:
> I know that on my controller (from Curtis), from 0-10% load the
> switching frequency is low enough to be in human hearing range
> (1500 Hz) and my motor "whines". After the controller goes to
> more than 10% load it switches to a higher frequency and becomes
> silent.
Yes; this is a feature (some would say a "bug") in the -C model Curtis
controllers. At very low throttle settings, the earlier -A and -B series
controller's on-time got so short that it couldn't properly control
motor current. This allowed too much peak motor current, resulting in a
"lurch" when starting a big low-inductance motor.
Instead of shortening the on-time, Curtis fixed this problem in the -C
controllers by lengthening the off-time. This gets you down to a very
low percent on-time for smooth starts; but also makes the audible
"whine" you hear.
--
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
-- Leonard Cohen, from "Anthem"
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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