If you are running low rpm – and low amps the motor is not making a lot of torque
Torque is high when amps are high
Max amp draw and torque occurs as the motor is loaded toward zero rpm
At low load levels at low rpm motors are inherent inefficient so a very high proportion of the energy going in becomes heat say 90% so the heating effect is surpisingly high. Usually a combination of mass and internal fans deal with the heat. Keep in mind most heating occurs on the brushes in a brushed motor.
Brushless motors have the same issues, however most of the heating occurs in the electronic controller.
An easy way to cool an electric motor is to take a feed from the prop wash. If possible use direct cooling. This is a simple tube around the motor with water inlets at opposite ends and opposite sides of the motor. The lowest point on the motor being the inlet. The highest being the outlet. Seal the end of the cans with rubber ring and sikaflex.
If a pump is needed it can be very low pressure the water flows required are not huge
Yours,
Andrew Gilchrist
fastelectrics.com
Australia
0419 429 201
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Michael Mccomb
Sent: Thursday, 13 September 2012 11:18 PM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] cooling an electric motor?
it seems that the cooling mechanism for electric motors usually consists of a shaft mounted fan of some sort... in one way this is obvious but then again at low rpms there isn't much cooling going on and this is too bad as electric motors have the advantage of delivering high torque at low rpm.... seems like an externally powered fan system that move air at sufficient velocity regardless of the the motor rpm would be much preferable....
interested in comments
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