Earthing?

[Neale]

Electric current through a wire creates a magnetic field around it. Current flowing in opposite direction creates an equal and opposite field. Keep the wires close, ideally twisted together, and the magnetic fields cancel out, don't transmit interference, and are resistant to outside magnetic fields for the same reason (rather simplified but the principle is true). Pass wires through separate holes and not only do you lose that "cancellation" effect because the wires are further apart, but you now create a magnetic field between the two wires that can induce (= create) a current in the metal box between them, which is exactly what you don't want to do. I can bang on about differential signalling and common-mode rejection, but the simple model is pretty sound to understand what's happening.

[Edward]

I can't see why anyone would want to separate wires of a circuit through different holes or not....

A practical question about wiring the 8 wires of a stepper in parallel:

For short run desk tests I normally join and solder each pair length as supplied to go to the respective A+,A-,B+,B- twisting it together along the way, as Neale mentioned above. But now I have to do it properly using 4 core screened CY cable, 1.5mm2. which I think is rated at a whopping 18A. Should I cut the motor cables as close to the motor source as possible, solder each pair to one of the four cores of the CY cable and use heatshrink on each joint, and then a bigger dia heatshrink to hold together the lot? This bulky point where all the cables join at the motor side, and the screening ends, isn't it a possible source of interference?

If so, is there a recommended best way to do this?

In terms of magnetic fields and interference, is it better to instead use 8 core CY cable all the way to the driver but of a smaller cross sectional area?

Edward

[Robin Hewitt]

But now I have to do it properly using 4 core screened CY cable, 1.5mm2.

Why is that "properly"? I like big fat wires, as big as will fit in the screw terminals on the driver. I run my big fat wires through flexi-plastic conduit to keep it tidy.

Why would you want screened? Armoured would be more understandable.

If you are worried about interfering with your high speed computer connections, you could screen those perhaps.

[Edward]

Robin, now you are confusing me:)

As far as I understand, "armoured" hardly offers any electromagnetic containment. All signal cables will be screened. I will use flexi conduit for the motor wires too. Do you mean you run 8 separate fat wires inside the conduit?

Edward

[Clive S]

Robin, now you are confusing me:)

As far as I understand, "armoured" hardly offers any electromagnetic containment. All signal cables will be screened. I will use flexi conduit for the motor wires too. Do you mean you run 8 separate fat wires inside the conduit?

Edward

Edward just do as you suggested chop the wires off about 250mm from the motor and then join them to the CY cable personally for the motors you are using I would go with 1mm size. If you want to be posh you can get an end cover for the motors and take the cy cable into that.

[Edward]

Thanks Clive.

The 3.1Nm motor would draw a maximum of 4.2A, but we all know that in reality it's probably about half of that anyway.

So a cable of 1mm2 (normally rated for at least 10A) will more than cover this. However, I wonder if there is any benefit in using a thicker cable, other than robustness...or obsession:)


I like the motor covers with the glands. Is this something you printed yourself, or are they readily available for the Nema23 frame? BTW, my Z motor is to the side of the column, just like in your picture.

Edward

[Clive S]

Thanks Clive.

The 3.1Nm motor would draw a maximum of 4.2A, but we all know that in reality it's probably about half of that anyway.

So a cable of 1mm2 (normally rated for at least 10A) will more than cover this. However, I wonder if there is any benefit in using a thicker cable, other than robustness...or obsession:)


I like the motor covers with the glands. Is this something you printed yourself, or are they readily available for the Nema23 frame? BTW, my Z motor is to the side of the column, just like in your picture.

Edward

I printed these a few years ago but since then I have milled them from various blocks of plastic including those fencing posts made from car tires. If you do a search for hem I have seen them in Europe somewhere

https://www.hardware-cnc.nl/en/winke...nema-23-detail

http://www.thingiverse.com/thing:243126

[Robin Hewitt]

I wonder if there is any benefit in using a thicker cable, other than robustness...or obsession:)

Now't wrong with a bit of healthy obsession

Thin cable is fine and dandy if you were lighting a bulb or charging your iPhone with a bit of AC but this cable has more to do than that.

On the other end of it is a hefty inductive load, it may have tuned itself a bit to reduce the peak but sooner or later it is going to want to reverse the current in a coil winding PDQ. It will try to control that current using a chopper circuit which depends on measuring the current flowing some way away. Did you fit the optional braking resistors?

Fat, low resistance cable takes the strain off more expensive components.

[Edward]

I notice that Robocutters do sell similar motor covers


https://robocutters.co.uk/proddetail...CoverKitNema23