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Juniper80
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Join Date: Oct 2010
Location: Denmark
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Torque on PM DC Motor Without Load

11/30/2010 10:20 AM

Hi folks. I was wondering if the torque on a PM DC motor is constant, when turning it(using it as a generator) without any loads(wires not connected)? Also, is it possible to measure this torque? The reason why i want to do this is: I measured rpm on the motor, when i was using it as a generator. It was turned by a simple home build turbine, without the wires connected to anything. doing this, i was hoping that i could calculate the power generated by the turbine(even though it will be approximately). I know i should have used a Prony brake, and i also tried. Unfortunately it broke 30 sec. into the experiment. I don't have any data on the motor. Thanks :)

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PWSlack
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#1

Re: Torque on PM DC Motor Without Load

11/30/2010 11:39 AM

Er, if it isn't connected to anything then it isn't generating any power.

If it is connected to something, the power is the terminal volts times the terminal amps.

Torque experienced by the prime mover is proportional to the current generated.

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Juniper80
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#2
In reply to #1

Re: Torque on PM DC Motor Without Load

11/30/2010 12:02 PM

Hi. You are right. I should have put it differently. I wanted to measure the power generated by the turbine alone, by using: P=W*M, Where M is the torque and W is 2*phi*n, n being rounds per second. I have n, and thougth i could measure M on the motor with out load!

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Tornado
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#3
In reply to #2

Re: Torque on PM DC Motor Without Load

11/30/2010 5:46 PM

Measuring torque M consists precisely of applying a load....so this quest is in vain.

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Juniper80
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#4
In reply to #3

Re: Torque on PM DC Motor Without Load

11/30/2010 6:10 PM

You are right, but still. Wouldn't the Motor induce a load, because of the internal magnetic resistance, that one should be able to measure? :/

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PWSlack
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#5
In reply to #4

Re: Torque on PM DC Motor Without Load

11/30/2010 6:43 PM

<sigh> Yes, though it wouldn't be generating anything at that time....

The quest is pointless.

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Juniper80
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Location: Denmark
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#6
In reply to #5

Re: Torque on PM DC Motor Without Load

12/01/2010 3:19 AM

Ok. So the motor doesn't generate any power, i know that. But the turbine blade makes the motor turn at a given rpm, with a specific torque(the magnetic resistance), thereby inducing power, which i should be able to measure(if i knew the torque). Its the power of the turbine i'm trying to measure, not the power induced by the motor/generator.

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