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70 Posts
Discussion Starter #1
I went to my EV Club meeting today in Tempe AZ. At the meeting this young m=
an told me about a motor adventure at his old school BGSU in 2002. Google:B=
GSU EDI FALCON ELECTRIC RACE CAR
He stated that a 10HP Lincon AC motor was converted to liquid cooling with =
transmission fluid. The internal rotor was immersed in the fluid requiring =
seals to be installed in a custom light weight case. =

=

He said the motor developed 100hp continuos but lost about 5% eff in the pr=
ocess. They used it at high RPMs and at higher voltages than the motor was =
spec'd for. When I googled the keywords above I found that the motor was no=
ted as 10times the specd HP at 145HP, giving the motor an original 14HP rat=
ing. =

=

Given that a vehicle requires at least 2-3lbs of vehicle for every lb of en=
gine/motor, and since a 145 HP continuous motor must weigh over 200lbs (I'm=
guessing) and a 14HP is mybe 65lbs, I'ld say that 500lbs less gross weight=
is worth the 5% loss. Since a lighter EVehicle saves some more for needing=
less battery storage, so much the better. =

=

I'ld have to add some estimate for the external fluid cooler and possible s=
econdary pump, but still sounds like a good tradeoff. BTW, the lighter moto=
r frame saves some weight as well.
=

What do you all think about the related issues of this modification? Will t=
he seals be reliable? How common are fluid cooled AC motors anyway?
=




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Registered
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70 Posts
Discussion Starter #2
This can only apply if you start with a good 10hp AC motor to begin
with. Let me try and explain.

While all motors are a balance between the power you put in and the heat
you can dissipate, the less heat you generate, the more you can push this.
In a dc motor the majority is resistive losses in an AC motor the
reactive losses are a big concern.


A little theory:
The fundamental rpm of an AC motor is 3600/ (# of pole pairs) - slip so
a 4 pole AC Syncronous* motor motor at 60 Hz (3600cycles/minute) is 1800 rpm

*Induction Ac motors have slip a percentage the rotor lags behind that
creates the magnetic field needed for torque production. This is why you
see 1725rpm.

The more poles, the more torque at the expense of rpm. So a motor that
is designed for 60hz is huge for it's torque. A typical 30hp 60hz motor
is 18" around by 20" long and weights 100's of pounds. But it can be
made with unsophisticated materials because 60hz is such a low
frequency, that the reactive losses are low. Now take the traditional 4
pole motor and turn it into a 12 pole motor, same amount of windings and
iron and the torque triples, but 600rpm and you can't drive very fast.
The solution is simple, crank the frequency up and gear down the result.
Now a 100lb 10" diameter motor 10" long can do the deed. The issue
becomes the added heat generated as the ac field in the laminations
changes polarity more times per second, the cheap laminations don't like
changing magnetic polarity and resist giving off heat. The currents are
stronger and the cheap oxidation layer between the laminations is
insuffient to stop eddy currents from spiraling between laminations
forming even more loss. The windings vibrate more and self destruct in
less time.

If you have an inverter grade 10hp ac motor, like say from a CNC mill,
Then you can push the hz higher and cool the losses you have and do
well. They are often water cooled already.

something like this(a little big) which gives 1500/6000 rpm means it
was made for VFD. 15hp cont,20hp 30min means a lot more! for 10seconds
ebay

130158862063
or 130158876810

or a pair of these 170152432843

I have seen better on ebay, things seem a little dry right now.


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