Ok, there's an awful lot of miss-information about the various axial flux
motors, Eteks, Perms, Lemcos, and Agni motors on this list.
These motors have a high power to weight ratio; they're LIGHT and therefore
have low themal mass. That means that they will heat up FAST. The continuous
current rating of the motor is ONLY when running at it's rated rpm. If the
current rating is 100 amp at 48 volt (3500 rpm) then the rating might only
be 65 amp at 24 volt (1750 rpm). The armature acts as its own fan well
enough to justify the continuous rating, but even propper shaft mounted fan
is less effective at lower rpm. Banding the armature will REDUCE the current
rating since it blocks some of the cooling air. If you are getting the
solder close to it's transition temperature then banding will be no help
whatsoever, the solder will fail because it is weak at that temperature.
Even if it doesn't get spat out, it's going to be causing bad joints. You
need at least one temperature sensor, probably on the brush gear. This
should at the very least illuminate a prominant warning light, if not
actually pulling the throttle back in the event of an overheat. Where
banding does help is in increasing the burst speed of the armature. If you
could double the burst speed, you could double the voltage, double the
reduction ratio and therefore halve the current needed for a given torque at
the rear wheel, whilst keeping the top speed the same. You would then halve
the heating in the motor.
The Etek is being given the toughest job. It's an inferior version of the
Lemco, built down to a cost. For it's intended applications it's fine, but a
lot more is being asked from it, often without understanding of its
limitations. For one thing the efficiency drops off a cliff over about 350
amp.
Any motor needs to be guarded aginst forrien bodies passing through it, so
some thought needs to be given to mounting position and screens/shields.
Thought should also be given to their effect on cooling. For many
applications an external cooling fan is a requirement or at least advisable.
A centrifugal type is going to be best as they produce much more flow
against back pressure. If you search for Nidec Gamma fans on ebay, you'll
come up with some bargains. If you can fine the right value NTC thermistor,
you can put it in series with the fan and place it in the exit air, so you
have a temperature controlled fan.
Paul Compton
www.evguru.co.uk
www.sciroccoev.co.uk
www.bvs.org.uk
www.morini-mania.co.uk
www.compton.vispa.com/the_named
