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faroun
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Joined: 18/09/2008
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Posts: 62

Posted: 09:35pm 15 Oct 2009

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hi there guys, i come accross this hobby motor, i am not sure why it said it is 7000watt??!!, so much power from so little motor.
is this thing for real or am i missing somthing?!?
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idP roduct=5139
.
a watt is a watt correct?? if that is the case is there an explanation to this kind of motor?

thanks

best regards
http://www.greenenergywindturbine.com/fawts/preview.html

Many Ideas One Brain.
http://www.wrapwind.com

Dinges
Senior Member

Joined: 04/01/2008
Location: Albania
Posts: 510

Posted: 01:29pm 17 Oct 2009

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[quote=Faroun]so much power from so little motor. is this thing for real or am i missing somthing?!? [/quote]
Yes, it could be for real. The technical information doesn't show at what RPM that power is delivered, and what the duty cycle of the motor is.

If it's used for model a/c purposes, it will normally run for only 5-10 minutes and be stopped for 20-30 minutes. So it's likely rated with that kind of use in mind, and may not be rated for 7kW at 100% duty cycle. Also, it's probably rated at that power when forced-air cooled, as when installed in the nose of a R/C aircraft.

Also, the motor will probably be running at 10.000-15.000 RPM (unloaded). P=T*omega, where omega = angular velocity (rad/s); (omega = 2*pi*RPM/60); P=power (Watt); T=torque. If RPM increases, power will increase (assuming torque remains constant)

Because the RPM is so insanely high, power output will be high. Which is why that motor can deliver a lot of power in a very small package.

It's also why windturbine generators tend to be very large for the amount of power they put out: they are running at very low RPMs. So they *need* to be physically large to get a decent amount of power out. As RPM goes up, power output goes up (or, size of the genny can decrease for the same amount of power).

The motor is useless (as-is) for windturbine applications. A rewind with many more turns of thinner wire could make it more useful at lower RPMs. But if you decrease the number of RPM by a factor of, say, 10, the availabe power will go down by that same factor too. So only 700W (roughly speaking). By the looks of it it isn't brushless either. Still, I wouldn't mind playing around with such a motor. Looks to be a fun toy.

Peter.Edited by Dinges 2009-10-18

GreenD88

Senior Member

Joined: 19/05/2009
Location: United States
Posts: 104

Posted: 03:36pm 17 Oct 2009

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It is a brushless motor, and it's rpm/v rating is as follows: 180 rpm/V So 48v = 8640rpms, 24v = 4320rpms, 12v = 2160rpms. Would be pretty cool to play with I agree.

Licensed Master Plumber / EPA 608 Universal License / 410a Safety Certified / Medical Gas Brazer/Installer

faroun
Regular Member

Joined: 18/09/2008
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Posts: 62

Posted: 10:53pm 17 Oct 2009

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wow.. thanks for the explanation..well done.

u r correct, it looks like fun to tincker with.

regards

Many Ideas One Brain.
http://www.wrapwind.com

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 11:53pm 17 Oct 2009

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I think I would tinker with it in the intended purpose. This would be an impressive performer in a decent model plane. One of my own electric planes has a single blade carbon fibre prop, spinning at approx 20000rpm max. I can fly it around for approx an hour at level flight, or about 15mins having fun with aerobatics.

Gordon.

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