Newbie- help on stepper motor voltage rating

[ravikhatri]

hi to all
I am an engineering student and am using a stepper motor for my project . so noway related to CNC but still i need some help from all you guys on Stepper motors .
i am having a sanyo denki stepper motor which i got from my city junkyard at around 50 Rs which is around 1 US dollar .
it has six wires and has following things written on it "DC 3A ,1.8 deg , type:- 103h6707-0741."
I found out that it is a unipolar motor ( am i right?) and was able to find the center tap and the winding connections . the ressistance was 1.2 ohms from winding to centre tap and 2.4 ohm from winding to winding .
the problem is that i want to know that at what voltage i should drive it . i guess it would be around 4V or so but when i saw some driver from some manufacturers the voltage they are using is say 33V, 50vetc , here i am confused ?
i am using a L297 stepper motor controller for motor control and interface it to a 8051 series microcontroller . i also want to know that how to make the driver circuit for this . which switch to use ,a mosfet i guess , then which one ?
i have elaborated the question as this is my first post and i don't want anything missing . also i am a total newbie in this field so any suggestion will be highly welcomed . i am low in finance so i can not purchase those readymade driver boards and also i like to do it myself .
hopeing to here soon from you ,
you can also email me my email id is ravikhatri_789@yahoo.co.in
thanks in advance

[audioandy1762]

Hi

You would normally run a stepper motor between 10 and 20 times it's rated voltage but limit the current, this is the reason the driver manufacturers quote the voltages you have seen.

The above is dependent on the limits of the driver you are using.

Do a search on the site for stepper motor power supplies this is a subject that has been covered plenty of times with some very good explanations.

Hope this helps

Andy

[jeffs555]

If you use the voltage from ohms law(ie V=IR), this will limit the current to the safe rated current.

However, the motor is an inductor, and the current through an inductor can't change instantly. The rate at which current changes is proportional to the applied voltage(di/dt=V/L). Every time you step, the current in the motor coil has to change. The higher the voltage the faster the current can change, and the faster the motor can turn. That is why drivers use higher voltages than the rated voltage of the motor.

Like Andy said, to use higher than the rated motor voltage you need to limit the current. The L297 has current sensing, and will chop the voltage to limit the current.

PS The L297 is normally used with a full bridge as a bipolar drive. It can be used in unipolar mode, and here is one page about that. http://www.pchilton.co.uk/index.php?..._stepperdriver
For unipolar drives, the mosfets must be rated for at least twice the supply voltage.

[ravikhatri]

thanks to all of you for your help .
so i think that now i have to use the chopper feature provided in the L297 to limit the current .
And i have also read that there is another method by using Feedback in mosfets .
Can anyone provide me some links on this or some other help .
and i really liked this site as it has so much of experts, and also very eager to help too .
thanks again