# motor parameters determination

#### h.d

Joined Oct 22, 2007
150
hi all
right,,if we have a dc-motor and we dont know any if the parameters
only the terminal voltage
so how to determine the motor parameters????

#### hgmjr

Joined Jan 28, 2005
9,029
My first effort would be to try to take the information marked on the body of the motor and attempt to track down the datasheet from the manufacturer.

Failing that, I would measure the DC resistance. I would then apply the know voltage and measure the current it consumed. I would then stall the motor and measure the stall current it consumed. I would get a tachometer and measure the speed of the motor in RPM.

There are other parameters that would be nice to know but these will do for a starter.

hgmjr

#### h.d

Joined Oct 22, 2007
150
i should determine the maximum and nominal torque and current

#### hgmjr

Joined Jan 28, 2005
9,029
i should determine the maximum and nominal torque and current
Yes, that would be good information to obtain. Calibrated Torque meters are not that easy to come by unfortunately.

hgmjr

#### h.d

Joined Oct 22, 2007
150
yes , for that i ask
the problem that the i havent the nameplate and the kit number

#### hgmjr

Joined Jan 28, 2005
9,029
It is almost cheaper in the long run to put the unknown motor aside and then purchase a motor for which you can obtain a datasheet.

hgmjr

#### h.d

Joined Oct 22, 2007
150
the motor cost is 120 $u think that purchase a new one is more cheaper than test it ?????????????? #### hgmjr Joined Jan 28, 2005 9,029$120 does up the ante in favor of testing over replacement.

If you need to know the torque and you know anybody that can provide access to a torque-meter then maybe you can borrow one.

hgmjr

#### h.d

Joined Oct 22, 2007
150
yes, i will test the motor in the drive laboratory in my university
there we have the needed equipment

#### h.d

Joined Oct 22, 2007
150
i test the motor in noload mode
220 Vdc
0.5 A
4750 rpm
Ra=35.5 ohm
but i kmow that the motor is 2hp ?????

#### h.d

Joined Oct 22, 2007
150
from the last values can i involve the power of the motor?

#### scubasteve_911

Joined Dec 27, 2007
1,203
Power and Voltage will give you operating current.. One horsepower is just over 700W, so you can do the math on that one. It's hard to figure out things like rotor inertia, friction, and torque without the proper equipment.

Steve

#### thingmaker3

Joined May 16, 2005
5,084
746 Watts to the horsepower. (Actually, they were mining ponies, not horses at all...)

Torque (in foot-pounds) = horsepower * 5252 / RPM

I leave it to the reader to convert to SI units if needed.

#### h.d

Joined Oct 22, 2007
150
i ask about if i can calculate the power of the motor from the measured valuse tha i get it (noload curren,noload speed,Ra, & the nominal operating voltage)
i need the torque an dthe power.

#### scubasteve_911

Joined Dec 27, 2007
1,203
Power cannot be determined via no-load conditions. I'm not a motor expert, but I believe the power rating has a lot to do with the ambient temperature rise acceptable.

Steve

#### h.d

Joined Oct 22, 2007
150
Power cannot be determined via no-load conditions. I'm not a motor expert, but I believe the power rating has a lot to do with the ambient temperature rise acceptable.

Steve
i think that too
i should load the motor to determine the torque and power
but the deficcult is how to load it and measure the load..
that what i will search about it.

#### scubasteve_911

Joined Dec 27, 2007
1,203
I guess acceptable temperature level has a lot to do with motor construction. Things like maximum wire temperature, PM demagnetizing temperature, epoxy temperature rating, etc. Sometimes you can gauge the motor power by knowing it's type and size, since that is a pretty consistent thing. Sorry I cannot help anymore than this, I actually still have yet to take my motors course

Steve