DIY Electric Car Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
Hey,

Is there anybody that knows if it is possible to measure the constant 'k'(T=k*flux*I) of a series DC motor?

It's an old series wounded DC motor of Leroy Somer, T22, 11kW, 150A, 85V. I can't find any specs about it ont the internet and also the company doesn't have the information anymore


Simon
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
Thanks, I know the formula but the problem is that I can't reach the motor, I just have the ends of the wires so I was wondering if it's possible to derive it experimentally :)
 

·
Registered
Joined
·
7,837 Posts
Thanks, I know the formula but the problem is that I can't reach the motor, I just have the ends of the wires so I was wondering if it's possible to derive it experimentally :)
Maybe, but I suspect it would be easier and more accurate to remove the motor. Can you know the torque and magnetization curve for the motor as it sets? Since Kt = Kv (with SI units), I guess you could use the rad/sec, armature voltage at no load and separately excite the field to get a magnetization curve.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #5
Quite difficult because I there is no torquemeter :/ But I'm going to try make a load bank with a DC generator and a gear wheel. So with changing the resistance load of the generator I can draw more or less torque from the motor
 

·
Registered
Joined
·
542 Posts
Member GerhardRP did quite a bit of work on modeling. Maybe that would help you: http://www.diyelectriccar.com/forums/showthread.php?t=39931
As you try to understand my modelling, start with this formula:
field(I)=(V-IR-Vb)/Speed.
If you make a bunch of measurements with various currents obtained by varying voltage and load, measuring motor voltage, current and speed using SI units, you will get the motor "constant" which is a function of I. Notice that you don't need to know the torque for this procedure.
Measuring the resistance is a little tricky, because it is so small, and the brush voltage confuses things. Accurately measuring the starting surge current and voltage or using a briefly stalled motor can do the trick.
For starters, use maybe 2 volts for the brush drop.
After you have the field as a function of current, you can predict torque (ignoring magnetic losses such a eddy currents) using
torque(I)=Field(I)* I, again in SI units.
Good luck,
Gerhard
 
1 - 7 of 7 Posts
Top