Question of Voltage vs. Torque/Speed

[ullbergm]

A friend and i have two different ideas of what increasing the voltage from 5V to 12V and adding a power resistor does to the torque and speed of the stepper.

Does increasing the voltage actually speed up the motor?
Does it increase the torque?

Thanks,
Magnus Ullberg

[balsaman]

It speeds up the motor and increases the torque at higher speeds. It does nothing for the holding torque, assuming you use the correct resistors. If you incorrect resistors, it could either increase or decrease the holding torque, depending on the actual current.

Eric

[bunalmis]

Ok we can look from other dimentions.

Lets exam the simple Serial Resistor, Inductor and DC voltage circuits.(This is not real stepper motor model)

I = (V/R)(1-exp(-Rt/L)) current wave form equations. (Eq.1) (State 1)

Imax = V/R

Imax dont changes If you increase the value of V and R 2 times.

Imax = 2V/2R

but current waveform changes

I = Imax*(1-exp(-2Rt/L)) (Eq.2) (State 2)

Eq.2 Current waveform change faster than eq.1


You can see the second graphics area bigger than firs area.

That mean average current of second equations (state 2) higher than state 1.

Now we can said If you increase the voltage and Resistors same ratio

Average current increase, torque and speed increase power lost increase. (These are proportional by current)



Bulent UNALMIS

[ullbergm]

Originally posted by balsaman It speeds up the motor and increases the torque at higher speeds. It does nothing for the holding torque, assuming you use the correct resistors. If you incorrect resistors, it could either increase or decrease the holding torque, depending on the actual current.

So it increases the speed that the motor goes from one step to another?
if the computer sends the commands at the same interval it will still move at basically the same speed?
And since the motor moves quicker between steps it allows you to lower the interval on the computer without getting stuck in between two steps in the motor?

Did i get that right?

[balsaman]

No,

It gives the motors the ABILITY to turn faster. The motor will still go the rate it's told based on the feed rate you specify. The motor will have more torque at speed, and your rapid moves (tool up) will be faster. The rapid is setup for your machine in the software setup. With 12 volts and resistors you can set it up for a higher speed then if you use 5 volts on a 5 volt motor.

So for example on a machine, if on 5 volts lets say you can go 6" per minute before the motors lose torque and miss steps, perhaps on 12 volts the motors won't lose steps until you reach 12" per minute.

Eric

[balsaman]

Go here : http://209.41.165.153/stepper/Tutorials/UniTutor.htm

for a good tutorial on steppers.

Eric

[ullbergm]

Originally posted by balsaman No, It gives the motors the ABILITY to turn faster. The motor will still go the rate it's told based on the feed rate you specify. The motor will have more torque at speed, and your rapid moves (tool up) will be faster. The rapid is setup for your machine in the software setup. With 12 volts and resistors you can set it up for a higher speed then if you use 5 volts on a 5 volt motor. So for example on a machine, if on 5 volts lets say you can go 6" per minute before the motors lose torque and miss steps, perhaps on 12 volts the motors won't lose steps until you reach 12" per minute. Eric

I see.
Thanks a bunch