Disadvantages of 6 wire Bipolar Scheme

[cnc kiwi]

Does anyone know if there are any disadvantages from running a 6 wire stepper motor in the half winding bipolar configuration? They're the only type ofbiplar motors with enough power that i can gat hold of, and I was wondering if using half winding might generate more heat, have less accuracy or anything bad like that as apposed to the standard unipolar wiring scheme or a bipolar full winding configuration (the half winding is supposed to make twice the power of a full winding).

Thanks
cnc kiwi

[Oldmanandhistoy]

The reason to wire a 6 wire stepper motor half winding is to gain more torque at higher rpm’s. It will make no difference to the accuracy of the motor but if memory serves me correctly it will generate more heat.

John

[Richards]

I've run extensive tests with Gecko G202 and G203v stepper drivers with a variety of Oriental Motor stepper motors during the last two years. Almost all of the motors were six-wire motors. What I found was that wiring a motor half-coil gave approximately 70% of the low speed torque of the same motor wired Bipolar Series; however, the half-coil wired motor sustained excellent torque at speeds at least 4X higher than Bipolar Series wound motors. Most of the Bipolar Series wired motors rapidly lost torque at speeds as low as 150 to 200 RPM while half-coil wired motors easily held their torque to speeds of 600 to 800 RPM - and sometimes faster. That fact should be of no surprise to anyone because a half-coil wired motor has 1/4th the inductance of a Bipolar Series wired motor.

I've never had excessive heat with either type of wiring - as long as I use Mariss's formula for determining the maximum allowable voltage for a motor. If I remember it correctly (I'm out of the shop without access to the formula), the formula is:

Maximum voltage < 1000 * SQRT(motor's inductance)

An Oriental Motor PK296A1A-SG3.6 motor has 6mH inductance when wired Bipolar Series and 1.5mH inductance when wired half-coil. So 1000 * SQRT(0.006) = 77.46V maximum if the motor is wired Bipolar Series and 1000 * SQRT(0.0015) = 38.73 maximum if the motor is wired half-coil. I've tested that motor at 70VDC when wired Bipolar Series and at 35VDC when wired half-coil with excellent results and similar heat. Right now, I use that motor wired half-coil with a 27VDC power supply and a Gecko G203v stepper driver regularly. It works perfectly, even at speeds of 750 RPM, which is about maximum for Mach 3 running at 45,000 pulses per second with the steps per inch set at about 1,530.

[cnc kiwi]

Thanks guys that's really helpful, it's just what I needed to know.