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Stepper wiring scenarios
« on: April 05, 2008, 07:50:49 PM »
In addition to the other thread could someone shed some further light on the situation, as I'm always keen to get a better system.

So could someone give a Pro' N' Cons answer with wiring description for each method of wiring Steppers, 8 wire in my case.


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Offline Sam

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Re: Stepper wiring scenarios
« Reply #1 on: April 05, 2008, 09:51:14 PM »
Definitely read the whole thing, but for what your asking, you can skip down to page 7.
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Offline jimpinder

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Re: Stepper wiring scenarios
« Reply #2 on: April 06, 2008, 05:39:19 AM »
I started all this off - and we are now on "Hot  Thread" status.

Basically with 8 wire motors (assuming you are going to wire these to 4 output drivers) there are three ways.

My problem was my motors would not accelerate up to anything like full speed, using the drivers that I had. The motors were 7.5v, rated at 2.5 amps per winding (there are four windings A.B.C.D) . The resistance for each winding was 3 ohms. My cards are rated at 30volts (actually I use 24 volts) and 2.5 amps max.

I first connected these in series - A to C - and B to D. Electrical circuits in series add the resistance so the motor became a 2 pole motor with 6 ohms resistance on each winding.

Power from an electric motor is dependent on the amount of current going through it, and by connecting the windings in series I had doubled the resistance, which cut the current (and therefore the pwoer) by half. There is one way of rectifying that problem - increase the voltage which will force more current through, giving more power - but unfortunately my drives were limited to 30 volts, so I was not going to get much increase there.

My second effort was to rewire the motors - this time in parrallel - A and C together, B and D together. In parrallel, resistance is, for the sake f this post, halved.  The same 24 volts would force additional current through the windings, giving me more power - in theory 4 times the power.

It did work, and I got the motors spining at up to 30 ins per minutes ( a massive increase over the 4 ins per minute I had before).

I had measured the current drawn whilst doing this - and this is where I went wrong. Because these are stepper motor driven electronically by chopper circuits, the current shown on a meter is not an accurate reflection of the current drawn by the windings. The very conservative 0.9 amps reading I got is apparently way off the mark. The agreement is I am lucky still to have my driver board in one piece, or at least not fried. I am not sure but they may by current limiting.

To sustain that performance, I would need a set of drivers able to carry twice the current.

The compromise was to only use two of the windings -  A and B. Wired singly they have 3 ohms resistance, which means they carry 2.5 amps. This still gives me the OMPH I am looking for at 24 volts, and they succesfully run the axis at 16 ins per minute. I have dropped this to 12 for the sake of accuracy (and so I do not drop steps) - sinceI do not need tremendous speed on my lathe. (18"" bed).

I now have 3 times the speed for G0 movements, still have more power, at a net cost of zero.

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