Electric motor advice/sourcing help needed.

[69427]

Looking for help finding an affordable variable speed motor for a test setup I'd like to build over the winter. I'm trying to do some horsepower (via wattage) measurements of differing engine mechanical fans. I've always distrusted the results I've seen in hot rodding type magazines, as the tests were always done on a static engine dyno (where the fan has to pump a lot of ambient air), whereas in the real world there is varying "wind" speeds entering and exiting the radiator due to the vehicle speed, and this varying wind exit speed should affect the instantaneous angle of attack (for lack of the correct phrase) that the fan blade sees in the moving air. I'd like to vary both the fan RPM (up to about 5000) and the (radiator exit) air speed hitting the fan blades, and measure the electric motor current (and then convert to horsepower) to see what the horsepower requirements are in a somewhat real environment. I don't know at this point what the motor horsepower requirements would need to be, so that's just one of the many unknowns. (I've got another aspect of mechanical fans I'd like to measure, but you'll think I'm crazy if I go into detail on that at the moment, so I'll leave that discussion for later.)

I'm not an electric motor expert, so any helpful suggestions of what might work, and where to get a motor (used and cheaper is preferred) to do this experiment is appreciated.

Thanks.

[Sam Cogley]

Find a cheap or free treadmill on Craigslist, the type that has a knob on the control panel attached to a potentiometer to vary speed.

[BBShark]

Obviously, a DC motor would be the easiest way to do the conversion at varying speeds. Any idea of the peak HP required (in order to "size" the motor - X watts at 5000rpm)?

[mrvette]

All I know is the Dual Spals I have are supposed to spike to near 40 amps on startup, running in direct parallel with each other, no single fan operating setup....and ~25 amps running......my FI computer will turn off the spals when reaching about 40 mph for a few seconds.....a/c running or not......

IMO, any fan at ~45 mph+ is just blocking airflow.....

[69427]

Originally Posted by Sam Cogley

Find a cheap or free treadmill on Craigslist, the type that has a knob on the control panel attached to a potentiometer to vary speed.

I like that! Thanks.

[69427]

Originally Posted by BBShark

Obviously, a DC motor would be the easiest way to do the conversion at varying speeds. Any idea of the peak HP required (in order to "size" the motor - X watts at 5000rpm)?

I don't have a good idea of what the hp requirements are yet, and unfortunately I won't really know until after the test. I've heard some outrageous numbers from some people for the fan drain, but I don't buy it. At the moment I'm just shooting for the most motor I can find at a reasonable price.

[69427]

Originally Posted by mrvette

All I know is the Dual Spals I have are supposed to spike to near 40 amps on startup, running in direct parallel with each other, no single fan operating setup....and ~25 amps running......my FI computer will turn off the spals when reaching about 40 mph for a few seconds.....a/c running or not......

IMO, any fan at ~45 mph+ is just blocking airflow.....

I agree, but it just seems to me that a turning mechanical fan is going to block less air than a non-turning electric fan. (I can't easily prove it at the moment though.)

[mrvette]

Originally Posted by 69427

I agree, but it just seems to me that a turning mechanical fan is going to block less air than a non-turning electric fan. (I can't easily prove it at the moment though.)

INteresting point, got NO clue, but I have to ASSume that the fans of any type are being forced to turn at ~45 mph no matter what type they are.....would be curious to know about the mechanical fans and what you are exploring, must be about your racing/class requirements......I"m just an old street racer.....

[BBShark]

Originally Posted by 69427

I don't have a good idea of what the hp requirements are yet, and unfortunately I won't really know until after the test. I've heard some outrageous numbers from some people for the fan drain, but I don't buy it. At the moment I'm just shooting for the most motor I can find at a reasonable price.

Gene said the fans are @ 25 amps running and I have heard that number before. That's 300 watts. 300 watts @ 5000rpm is a big motor.

[69427]

Originally Posted by BBShark

Gene said the fans are @ 25 amps running and I have heard that number before. That's 300 watts. 300 watts @ 5000rpm is a big motor.

Okay, this is where I'm a bit foggy. Three hundred watts is less than half a horsepower (.4 hp). I don't have a good feel for what RPM that electric fan is at when consuming that four tenths of a horsepower (and then trying to somehow extrapolate the power draw at 5000 RPM).

Meanwhile, I'm trying a simple experiment until I can get back to my favorite scrap yard where there's usually a treadmill or two thrown in the pile. Dug around in my dad's shop while recently visiting my mom. Found a one horse motor (3450 RPM) with a 5/8" shaft, the same size as the w/p shaft on the Corvette. I tried out a spare fan spacer I had, and it looks like I can bolt up my flex fan to this setup to do an initial test. Here's the motor and spacer:

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The only question yet is transferring the torque and retaining the spacer on the shaft. The shaft has a keyway, while obviously the fan spacer doesn't. I was kicking around putting a couple set screws into the keyway unless there's better options available (and I'm all ears). Also, I've got a AC breakout cord to allow me to measure the motor current. I don't have a strobe tachometer, so I'm still trying to figure out how to measure the motor/fan speed.