[ausev] Motor dyno, was: GE 11.5 inch motor

[Chris Robison]

Here's a totally different thought, one that's pretty obvious but I 
hadn't quite put the specific pieces together.

I sent the Netgain folks an email asking if it would be possible to have 
Warfield do a one-off Warp 13 motor with a shunt field winding, to use 
it as a generator. With a shaft-to-shaft hookup, I think this would be 
an ideal way to test any motor they sell to its limits.

Measure current via a shunt (a big one like my 3000A shunt perhaps) and 
voltage drop across a load. (Wow, what a load that would be, might be 
good for heating a warehouse in the winter.) Use that to figure power 
dissipation from the generator. With that power figure and RPM data from 
a simple pickup, you'd be able to calculate torque without an expensive 
sensor. Figures would be kinda rough and you'd have to estimate the 
losses on the generator side, but I think with some tweaking and 
experimenting you could get close enough to quote along with caveats 
about the testing method. The good news is that they'd be able to test 
any of their motors even to the extreme limits of their capabilities.

This would relieve them of the tens of thousands of dollars they'd have 
to spend for a commercial dyno capable of that level of horsepower.

Maybe my logic is off here, but I think it would work...

   --chris



Willie McKemie wrote:
> On Tue, Jan 01, 2008 at 11:39:20AM -0600, Chris Robison wrote:
>>> A big centrifugal water pump with a choke valve on it's outlet would 
>>> certainly make a good load.  It might be possible to make some power 
>>> estimate by measuring the flow and the temperature difference between 
>>> inlet and outlet.
>>>
>> Cool idea, if you could achieve something approaching accuracy. I'm 
>> concerned that it wouldn't be able to build up enough pressure though. 
>> Centrifugal pumps or fans are good at pushing against backpressure, but 
>> not really at the pressures I'd think would be necessary. Something like 
>> a gear, scroll or piston pump might make a better load against an 
>> adjustable orifice. Maybe with a pressure sensor, and some way to 
>> measure output flow (and probably temperature as you mentioned). Maybe 
>> if you blocked the centrifugal pump completely, you could make the 
>> device measurement exclusively thermal.
> 
> Alright, you got me going on this.  It's been 40 years since I've had 
> engineering mechanics and such; I'm CERTAINLY no expert.  But, here are 
> my thoughts.  First, I think we can consider that all energy is being 
> converted to heat.  Using a no flow pump would mean that heat would be 
> continuously rising (no steady state) and you would have a hard time 
> determining how much heat was being generated per unit time.  I think 
> the goal would be to have the pump reach a steady state temperature and 
> then measure both the flow rate of water and the temperature rise of the 
> water.  There would be some heat flow from the pump to air (which would 
> be difficult to measure), but I think most of it would be in the water 
> (which should be relatively easy to measure).
>  
>> Torque curves are really important too, though ... and my searches so 
>> far have found that shaft-to-shaft torque sensors are really expensive, 
>> on the order of many thousands of dollars. Maybe we could wait for a 
>> cast-off on eBay, maybe one that's lost its super-accurate calibration 
>> or something.
> 
> I would think that torque (on the above hydraulic dynometer) would be 
> pretty easy: a lever arm restraining rotation on the pump and a scale 
> or other linear force measurer.
>