Help Needed

[The Gresley Luthier]

Hi All.

After many many days scratching my head, trying to put together a control circuit for my SELF BUILD cnc router I have to conclude I need help.

I am not an amateur with electronics, but an advanced beginner. I am trying to put a wiring schematic together which includes at least an E Stop & Fault Trips. My CNC consists of 3, DM556T Stepper Drivers, 3 NEMA 23 Stepper Motors, a 240 vac > 36 vdc transformer, my spindle is 240 vac. I hope to be using ARDUINO UNO as controller.

Can anyone offer help and advice please.?

Regards.

Ray.

[m_c]

I've not got time to draw a diagram, but break it down into key sections.

Start with the mains.
Mains power in -> isolator switch.

Then it needs to split.
Via a Control (Enable) relay for the stepper power supply.
Power for the spindle (if VFD, then you can keep them permanently powered, and rely on the control wiring to start/stop things. If a standard router, then for safety you probably want an additional big relay for cutting power to it, that is controlled at the same time as the stepper power supply relay)
Power for the controller/control circuits, which should be permanently on.

Then think about the control wiring.
E-stop loop should directly control the enable relay, with a suitable signal fed to the controller.
Stepper drivers need the step/dir signals fed to the controller, but you'll need to check voltage levels, as the UNO might only output 3.3V, and most drivers need at least 5V, so you might need a buffer board.
Stepper driver enable signals would typically be controlled by the controller, but you can set them so they're permanently enabled and rely on the E-stop.

[The Gresley Luthier]

Thanks m-c.

I get it a bit better now, can i be a pain and ask what type of relay you would recommend, i have only used the small type powered and controlled by ARDUINO?

Regards and Thank You.

Ray

[EddyCurrent]

Ray,

Forget the electrics for now, I would like to see some mechanical drawings of your proposed build.

[m_c]

I generally use RS part 488-2610 (24VDC coil, but other coil voltages are available), along with the holder 803-376

You'll likely get equivalents far cheaper on AliExpress, but there are lots more types depending on what you're doing.
I find that DPDT a useful size for what I tend to do, so keep a few in my stock, but have also used much smaller versions, along with bigger versions.
Using DIN rail makes cabinets far neater, and makes later changes a bit easier than just a jumble of wires going directly between things.

If you need something for bigger loads, a contactor usually makes more sense, or a SSR (Solid State Relay), however a caution is SSR relays can fail short circuit.
For something like controlling the power to a router on a homemade machine, I'd probably go for an SSR, as they can be had quite cheap, and the risk of failure isn't that high, and should the worst happen, the rest of the machine should still stop.
However on an industrial machine if I wasn't using a VFD controlled spindle, and need power disconnected reliably, I'd use a contactor, as the chances of one welding completely shut is very slim.

For example my ongoing big mill retrofit, power to the servo drives is handled via two contactors (each powered up with a 1 second time delay to reduce the power up surge).

Key thing you need to work out is how big the load is, and what power you have available to power the relay coil.
An Arduino will only allow loads of around 10mA (IIRC they can handle 20mA, but 10mA gives a good safety margin), so you'll likely need to use interface/signal relays to power bigger relays.

You'll also probably want to use differential line drivers to interface the stepper drivers, and some form of buffer/opto-isolator inputs to an Arduino.
The low voltage of the Arduino means they can be prone to noise and false triggers, which can cause a whole world of pain if your shielding and wiring isn't perfect.

I'd strongly recommend you make all the control wiring 24VDC, then have suitable interfaces to the arduino, as it will make things much more noise resistance.
The interfaces can be done pretty easily on strip board with suitable chips, provided you don't mind a bit soldering.

[The Gresley Luthier]

Hi EddyCurrent,

I would like to upload some drawings probably in PDF format, but i have learnt how to do that yet on this forum. Cannot seem to find the Help button for advice.

Regards.

Ray

[The Gresley Luthier]

Many Thanks m_c,
.
Please slow down a bit, I really appreciate all your help, but you are forgetting I said I was above a beginner in electrics, but now you are talking in terms which are a foreign language to me, so my learning curve is massive not slow. Words like SSR, Different Line Drivers, what are they??

Regards and Thank you.
Ray