Re: SRSG motor power

["Greg Leyh" <lod-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

"Gomez ADDams" wrote:

> I am in the process of building a massive multiple-series SRSG for 
>my next big coil project. (24" secondary, ~24kW in)
>
> I haven't been able to come up with much information for calculating 
>the "wind" loading of the rotor, or the recommended motor starting 
>torque for a given mass/moment arm.


Hey Gomez, how's things?

One important point to remember about wind loading on rotating
armatures is that the required power increases with the *cube*
of the speed.  It's probably easiest to just measure empirically
the drag resistance of an irregular armature at some low speed, 
and extrapolate from there.

I have only a couple of data points on RSG motor power.  My 
small coil has 2 aluminum rotors with fairly aerodynamic
electrodes on a 14" circle.  The rotors are only half-shrouded.
The DC drive motor consumes about 2.5HP at 3500 RPM.  Electrum
uses 4 aluminum rotors with eight 3" wide electrodes per rotor, 
on a 28" electrode circle.  The electrodes are shrouded on both 
sides.  The DC motor takes about 28.5 HP at 3200 RPM.

My "guess" on your application would be about 1 to 1.5 HP at 
3600 RPM... perhaps 10% to 20% less with good shrouding.

I'm not sure what starting torque you should expect, as I ramp
both of my RSG's in a controlled current fashion.  But typically 
for a motor starting something like a pump, the start currents 
can be 5 to 10 times the running current, for several seconds.
-- 


-GL
www.lod-dot-org