Hi Guys,
This is my first post to the group... but the experience in regard to this subject is important.
All Permanent Magnet motors have less inductance than series wound motor, ie no field windings to help run interference. The chopper drives we all use for traction drives really do pulse the electricity, only straight DC with no pulses like a relay across a battery is without pulses. These pulses generate torque pulses mechanical and these are real and very fast, same rate as the chopper drive, these will rattle all mechanical connections in a drive train, gears being noisier than belts.
To lower noise we must acknowledge that source is the rapid rise in current when the chopper drive turns ON resulting in a mechanical torque signiture in sync with the applied electricity.
Thus there are several ways to mitigate this real noise,
a.) Increase the inductance of the motor by including an extra inductor in series with the motor, wire in between the motor and the controller. Do not install between battery and controller, this is a no-no. The inductor can be as simple as an aircore inductor, consisting of multiple turns of power wire all bundled into a circular winding, more the better for more uH. The inductance will lower the rate of current rise and increase the current available in the OFF phase of each chopper cycle.
b.) Provide a torsional compliance damper coupling between the motor and the driveline/load to keep from banging the clearances between gears... A rubber damper dounut is a typical solution, but should not be too stiff, it must be torsionally compliant.
c.) If the chopper drive has variable frequency adjustment, increase it to the mazimum available. Best to use this feature in conjuction with the two above.
d.) If the above is not something you can implement, due to lack of materials then your left to simply enclose the motor in a box with a ventilation path the is surpentine to allow airflow yet block sound waves, the interior of the box is lined with sound absorbing materials.
Sincerely,
Ron
Black Sheep Technology
www.black-sheep.us
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