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????

 

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

 

i should determine the maximum and nominal torque and current

 

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

 

yes , for that i ask
the problem that the i havent the nameplate and the kit number

 

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

 

the motor cost is 120 $
u think that purchase a new one is more cheaper than test it ??????????????

 

$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

 

yes, i will test the motor in the drive laboratory in my university
there we have the needed equipment

 

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 ?????

 

is their answer?????
from the last values can i involve the power of the motor?

 

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

 

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.

 

ok am dont ask about the units
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.

 

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

 

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.

 

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