More Stepper Questions
January 04, 2009 04:46AM
Hi All,

I have a question about the Stepper Driver 1.2 and different steppers. Since Zach and his supplier are out of the recommended stepper, I have been looking for others. I found a six wire, but can't figure out how to make it work (the board only has four connections). Does anyone know how to wire up a six wire to the controller board? My board appears to be working fine (flashing the orangish red/greed LEDs during the exerciser).

The specs on my stepper show two coils with a center tap on each coil. ie:

in tap in in tap in
1 2 3 4 5 6

I hope that makes sense. Any ideas? Thanks.

Re: More Stepper Questions
January 04, 2009 06:35AM
Just use half of each coil. I.e. one connection to the one end of the coil and the other to the centre tap, leave the other end open circuit. Run the motor at its rated current and you will get the same performance as you would get if it were driven from a unipolar drive circuit.

You can also connect to the ends of the coils and leave the centre tap unconnected. In that case you have to drop the current by a factor of 1.4 to avoid exceeding the power rating. You may get up to 1.4 times more torque but your maximum speed will be up to four times less.

Re: More Stepper Questions
January 04, 2009 04:05PM
Thanks Nophead. Looking closer at this stepper, it's rated at 3.6v at 2.4a . Does it look like I'll burn it up because of the voltage problem? If not, it looks like I'll need to use the high torque/low speed option. Does this sound right? I don't really know too much about stepper's so I'm in new territory.

Thanks again
Re: More Stepper Questions
January 04, 2009 04:20PM
No the stepper driver is a constant current chopper so it won't exceed the current rating of the motor regardless of the voltage.

Having said that 2.4A is more than it can supply, 2A is the max, and it gets hot at full current. Most people turn the current down to the point it has enough torque for reliable operation.

If it is NEMA23 I doubt it will be lacking in torque, so I would recommend using half of the coil for the best speed.

If you do use both halves of the coil make sure you don't set the current more than 2.4/1.4 = 1.7A to avoid overheating the motor.

The current is the voltage on the vRef test point divided by the sense resistor value, 0.5 ohm.

Re: More Stepper Questions
January 04, 2009 04:53PM
That helps a lot. It is NEMA23, with more rated torque than the Darwin steppers, so I'm sure it'll have plenty of room to spare. I'll use half coil like you recommend and adjust the pot for minimum current.

Thanks again.

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