Cabling a CNC Router

I've been lurking here for a while. I finally got round to starting the build of my CNC Router a couple of weeks ago & I'm flying through it much quicker than I anticipated. I have all the parts that I need except the wiring.

What sort of cable is normally used to connect the stepper motors to the controllers - I assume that it is also the norm to have the controllers nearer the PC away from moving parts, then have the longer cable run from the controller to the motors?

(ultimately the machine will run on 24-28 volts I think, with 3x 2.5A controllers)

Thanks

CraftyGeek

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Originally Posted by CraftyGeek

I've been lurking here for a while. I finally got round to starting the build of my CNC Router a couple of weeks ago & I'm flying through it much quicker than I anticipated. I have all the parts that I need except the wiring.

What sort of cable is normally used to connect the stepper motors to the controllers - I assume that it is also the norm to have the controllers nearer the PC away from moving parts, then have the longer cable run from the controller to the motors?

(ultimately the machine will run on 24-28 volts I think, with 3x 2.5A controllers)

Thanks

CraftyGeek

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HI, Thi was discussed at length a week ago on Kingfisher's 4x4 [ame="http://www.mycncuk.com/forums/showthread.php?p=8664#post8664"]thread [/ame]and its worth re-read of that thread, but the particular post in question I have reproduced below:


Each driver should be connected seperately to the power supply, do not daisy chain them. An individual fuse in the feed to each driver is a good idea. It should be rated 50% higher than the driver output current - so for motors with a 2A phase running bipolar (4A per phase, 8A per driver) a 12A fuse is a good idea. It doesnt need to be slow blow on the driver side of the power supply. Either chassis mounted fuse holders, or the in-line automotive types will work well up to 16A.

For a 2A phase motor wired bipolar (4A) you need at least 0.5 mm sq per core (typically 16/0.2 wire) - do not use single core house wiring cable, its not flexible and will crack under the vibration of the motor (in time). Ideally it should be screened wire... often you can find this on eBay listed as 4-core CY. 4-core 16/0.2 wire is good for 4.5amps (9 Amps derated 50%), above this you will need to use 24/0.2 wire which is good for 8A in 4-core form (although they are usually derated below this for indistrial applications). example

That helps a lot thanks, I'll order some cable & other bits later - but it also brings up another issue that I hadn't really thought about too much.

My motors are rated at 2.5A per phase & my controllers are also rated at 2.5A.

So my basic knowledge of electronics tells me that I should wire the motors as serial to match the controllers. But I see some mention in that thread of that having an impact on the torque of the motor.....so should I really be looking at running in parallel with a resistor? (I guess that ohms law applies here)

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Originally Posted by CraftyGeek

That helps a lot thanks, I'll order some cable & other bits later - but it also brings up another issue that I hadn't really thought about too much.

My motors are rated at 2.5A per phase & my controllers are also rated at 2.5A.

So my basic knowledge of electronics tells me that I should wire the motors as serial to match the controllers. But I see some mention in that thread of that having an impact on the torque of the motor.....so should I really be looking at running in parallel with a resistor? (I guess that ohms law applies here)

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Which motors and drivers? And no, ohms law doesnt apply - motors are inductances. Motors can be spec'd as 2.5A/phase "Bipolar parallel" or 2.5A/phase "unipolar" so saying 2.5A/phase without saying how they are wired isn't necessarily meaningful.

Maybe I wasn't clear enough above.

The motors are 4.5v, 2.5A per phase to be wired bipolar.

I was originally thinking of wiring them as serial to match the 2.5A controllers, but after reading the other thread it mentioned that you get greater torque if they are wired in parallel - that would, I presume, double the current being drawn from the controller - thus needing a resistor to limit the current (ohms law).

The motors are from Arc Euro Trade - 180Ncm (can be used bipolar or unipolar)
The controllers are the Routout 2.5A ones

The power supply that I currently have to hand is 12-14V (varies a tad under load) @ 10A.

I will get a better PSU at a later date, probably around the 25v mark.

Quote:

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Originally Posted by CraftyGeek

Maybe I wasn't clear enough above.

The motors are 4.5v, 2.5A per phase to be wired bipolar.

I was originally thinking of wiring them as serial to match the 2.5A controllers, but after reading the other thread it mentioned that you get greater torque if they are wired in parallel - that would, I presume, double the current being drawn from the controller - thus needing a resistor to limit the current (ohms law).

The motors are from Arc Euro Trade - 180Ncm (can be used bipolar or unipolar)
The controllers are the Routout 2.5A ones

The power supply that I currently have to hand is 12-14V (varies a tad under load) @ 10A.

I will get a better PSU at a later date, probably around the 25v mark.

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Its hard to tell as Arc Euro dont say what mode they spec the current in, however the 3.5Nm motor is spec'd as a 4.2A/phase in bipolar parallel and they call that a '4.2A stepper' so I am guessing that yours is a 2.5A bipolar parallel. the way to check this is measure the resistance of one winding e.g. red to yellow - if it's 4ohm then you can run this bipolar parallel at 2.5A.

Whatever the motor spec' if you only have 12v power supply then I'd run this bipolar parallel at 2.5A. Bipolar series on only 12v is going to be very underpowered.

You don't need a current limiting resistor, the Routout drivers are chopper current limiting drivers... they wont let you draw more than the preset current limit (up to a maximum of 2.5A).

Thanks for that.

What about for the 25v scenario?

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Originally Posted by CraftyGeek

Thanks for that.

What about for the 25v scenario?

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Makes no difference, a current limit is a current limit.... would still wire them parallel...