Stepper Wiring Help

Mostly Printed CNC - MPCNC Advice
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I’ve been working with my MPCNC for a couple of years now. I built it with a 12"x12" area, and it’s served me well.

But I’m working on expanding that now. I’ve built a new table for it, and have cut tubes, and reassembled everything, squared it up, etc.

I’m to the point of wiring things up, but I can’t use the old harnesses I got with my kit, due to the extended area. I have an old spool of 18AWG wire and some molex connectors I’d like to use up. The connectors, unlike the dupont connectors on the original, only fit one way, so I want to make sure I get the stepper motor wiring right.

I have 4 leads coming out of my Nema 17’s. Red, Green, Yellow, Blue. I’ve tested them by cutting the connector off, and holding wires together, so I know that Red and Green are a pair, and Yellow and Blue are a pair. I’ve done some reading, and see that these are usually referred to as A+, A- & B+ B-. Or on my Ramps board it’s 1+, 1- & 2+ 2-.

Does it matter which pair is A or which pair is B? Like, my RG pair could go to A or B, as long as BY goes to the other?

My understanding is that it doesn’t matter if you get the +/- swapped, but it does if you get the A/B (1/2) swapped. Obviously, I don’t want to damage anything. Do the +/- not really matter at all? Are all of these viable arrangements?:
R+G-/B+Y-
R-G+/B+Y-
R-G+/B-Y+
R+G-/B-Y+

Or do I need to be aware of the +/-, and if so, how?

If the motor is moving backwards, what gets swapped? Do As become Bs, and vice versa? or do the +s become -s?

Thanks

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It fits up to a 5’ axis, how big are you going? Why not just slice in extension if you are unsure, it is the easiest way to do it.

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  1. How old? We used to wire them in parallel. The drivers may be set for driving two motors in parallel (1.4V or so). Now, we connect the motors in serial, so the drivers need to be set lower (to about 0.7V).

  2. It doesn’t hurt to reverse + and -. But if you have wires ABCD, these are the different (and safe) ways to reverse the direction:

ABDC
BACD
DCBA
CDAB

It may not be obvious, but if you wire it all up with A+ to 1+, etc. The worst consequence is that you have one or both motors going the wrong way.

  1. If you are using directional connectors, the easiest way to fix it is to swap A+ and A-.

Here are some details on the serial wiring:

https://docs.v1engineering.com/electronics/steppers/

Be very careful with the current settings if your build was parallel.

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Ryan, I had to wait til I got home to check. I had thought that the wires were not long enough to reach through my now 45" tubes. But you are correct, that if I plugged in the middle stepper first, and then pulled the wire, and the stepper’s cord into the tube, I could reach the other side. I would still like to understand the stepper wiring better, if I can.

Jeffe, I think I got the kit in 2018. It’s in Serial, with two wires on each harness going to each stepper end, and then two wires connecting the two stepper ends.

I see your ABCD example, and that jives with my understanding so far. The question is if I should be able to tell + and - somehow on the motor end? The board has each pin labeled. Following your example, and stipulating that wire color is a bad guide, if I know that AB are a pair, and DC are a pair, how can I be sure that I’ve got things running “ABDC” and not “ABCD”, which isn’t among your safe examples? I know I have pairs of wires on the stepper; given AB, which wire is A and which is B?

And if I do not have A+ to 1+, if I end up with A+ to 2-, or whatever else, what are the consequences?

Edit: I checked the back of my steppers, and was able to pull up this page from the manufacturer, which both clears things up, and muddies the waters a bit. On the page, they list the wire colors, and their affiliation, but as “1A”, “1B”, “2A”, and “2B”

https://www.automationtechnologiesinc.com/products-page/3d-printer-machine-parts/nema17-stepper-motor-3/

Then, the manual, listed on that page shows the wires as: A Red, C Grn, B Yel, D Blu.

Given that I know Red & Green are a pair, and Blue & Yellow are a pair, That makes the 1’s a set and the 2’s a set. Or AC and BD.

But I’m still to the point of not knowing if A or B are + or -, so I think I’m in the same spot?

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ABCD and ABDC are both safe, but reversed directions from each other.

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If ABCD goes ‘forward’ then you would have

ABDC: reverse
BACD: reverse
BADC: forward
CDAB: reverse
DCAB: forward
CDBA: forward
DCBA: reverse

If you are going to solder everything and need it to rotate the right way the first time then you have to analyze the data sheet. But if you can experiment then you can try it and flip the connector to DCBA if it’s wrong.

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Cool, thanks for the explanations. I do appreciate it.