Re: Help! Smoking Motor;

[Bill Dube <billdube@killacycle.com>]

At 03:09 PM 3/31/00 +0100, you wrote:
>
>
>	I have just put a new motor on my e-scooter and when I wired it up
>and took it for a drive and it smoked.  It smelt of Flux and general
>electric burning smell.  The motor is a Bosch 24v 750 watt permanent magnet
>motor and is being powered by two 12 v deep cycle batteries in series,
>through a scoota 24v 120 controller from 4QD.
>
>	The motor is too hot to touch and keeps on smoking for a long period
>when the bike is not moving.  
>
>	Any body know what I can do?

	You have likely geared the motor incorrectly. You need to gear the motor
so that it is spinning at it's full rated RPM when the e-scooter is at it's
design speed (probably 20 mph). 

	If you gear the motor such that it spins too slowly, it will overheat.
When the motor is spinning slowly, it takes in a lot of amps and very few
volts to generate the HP (indeed, watts) needed to propel the vehicle. At
high amps, the resistance of the motor windings causes a lot of watts (I^2
x R) to go into heat. If you spin the motor quickly to generate the same HP
you do it with a lot of volts and just a few amps. Thus, the windings
generate little heat because they are carrying little current.

	I should add that the PWM controller you are using will very nicely put
out big amps and low voltage while taking in high voltage and just a few
amps. If you had used a contactor or a primitive resistance controller of
some sort, it would have been immediately obvious that you had geared the
scooter incorrectly.

	I hope you didn't fry your motor. Does it still spin OK when you apply
power? You may have cooked the field magnets. 


Bill "Wisenheimer" Dube'  billdube@killacycle.com
check my website at:
http://www.killacycle.com