[qwertysimo]

Hi,

I made some progress with my build. Machine is alive but lot of work to be done. Anyway, my electronic wiring at the moment is as simple as neccessary for working machine, with E-Stop button implemented only as an input signal for software. I want to make final wiring properly to have a safe machine and environment. I spent few days reading materials and ended up with attached sketch. It is more a logic diagram, definitely not a wiring plan.

I followed basic principles:

• Mushroom latching style E-Stop button is operated directly on 230V line.
• Pressing the E-Stop button powers off stepper motors and spindle, leaving the controller powered.
• Start button (NO) is combined with holding control relay.
• Stop button (NC) used to power down the system, instead of using E-Stop button.

My idea is to communicate as many emergency situations from hardware level to software as possible. At the sketch bottom there is logical AND block that signals existing emergency situation to software. (Some inputs may need inverting.) I wrote some notes to explain my mind:

• AA - Control relay (R) function check. (Why not?)
• BB - Contactor (C) function check. (Why not?)
• CC - If VFD triggers circuit breaker (CB1), it is emergency situation - steppers must stop or the tool breaks.
• DD - If stepper motor branch triggers circuit breaker (CB2), spindle should be stopped not to damage the workpiece.
• EE - If stepper motor driver signals fault, this is emergency. One of indicated faults is stall condition which could damage machine if it happens to dual-motor Y-axis. (Happened to me with my first MDF build.)
• FF - If the control branch dies (CB3 triggered), software should know it.
• GG - NO contact of E-stop button to signal manual E-Stop button press.
• HH - All previous input signals logically multiplied (AND) and sent to software.

Other notes:

• I want to have more E-Stop buttons available. NC contacts will be wired in series, NO contats in paralel.
• That AUX blocks beside circuit breakers are auxiliary contacts that monitor breaker status.
• Meter at the diagram beginning is power meter so I can track power consumption.
• I do not consider a water pump or dust collector to be emergency hazard thus not present in sketch.
• VFD is loud and has no on/off button so I will add a switch between contactor (C) and VFD to power it off in case when I want to use router without spindle.

Few questions:

1. What about fuses between 48VDC power supplies and stepper motor drivers for extra safety? I found here a post explaining why not to do it but I have also seen wirings with fuses included. Which is correct?
2. I drive the contactor (C) coil directly from 230V line. Would it be better to power it from control relay (R) contacts? They would be in series and contactor would not power up if the relay is broken.
3. If circuit breaker CB4 triggers, which means there is absolutely no control of system, would it be reasonable to disengage the CB3 branch? Relay in CB4 branch that would control CB3 branch via NO contacts - to act like automated 2nd Stop button.

I would like to ask you to review it and provide me feedback particularly on design flaws. Any tips for improvement are welcome of course.

Thank you.

[Al_The_Man]

Your schematic is a little incomplete but it is normal to use a low voltage control for such as E-stop relay etc, 12vdc to 24vdc is common,
The control relay would be at the end of the E-stop string and remove power from motor and spindle contactors/relays.
I have answered so many of these typical questions, I think I will put a typical circuit together in PDF form.
The control relay would also advise the controller a E-stop has taken place and a watch dog or charge pump would be in the E-stop relay series string.
Al.

[qwertysimo]

...it is normal to use a low voltage control for such as E-stop relay etc, 12vdc to 24vdc is common,

If 12 VDC or 24 VDC is not actually needed, are there other reasons why not to buy 230 VAC driven relay or not to wire E-stop buttons directly on 230 VAC wire?

[pilotarix]

Hi,
I am not a specialist in this by any means.

However, I currently also try to get my control box together and I found this not so easy because, as I said, I am not a spezialist in this field.
I bet, a lot of people using pretty hair raising solutions, like I do so far. I would assume that only a few, trying to use industry standard like solutions or something that comes pretty close. One reason might be, that the better, safer and closer to industry standard you build the more expensive it will be.

Anyhow, to your question, one reason to use low voltage in the control circuit might be safety, I read something like "no high voltage outside the enclosure" means on switches lights and the like which are mounted "outside" of the enclosure (enclosure door is outside!). One exemption is probably an enclosure door mounted disconnect switch.
In doing so, you will need an extra AC to DC transformer that delivers power to the relays after the start switch was operated. That will probably raise you budget by about 60 $. Maybe other people who know this stuff better than I do, know better supply sources and can get this significantly cheaper.

So far my 2 (lay person) cents

@Al

...I think I will put a typical circuit together in PDF form...

I bet, no I am sure, a huge amount of people, including me, would be very appreciative.

Thanks
Chris

[qwertysimo]

That sounds reasonable! I also found another discusion that states the same principle:

To answer your question about control voltage... If you have the EPO in the same console as the rest of circuits with that voltage, then it can be 240. If it's going to be mounted where it would be needed (remote from that box), run it as 24 volts. As a point of reference, in Europe and many other parts of the world , you can't have more then 24 volts (they define it a little differently) on any circuit at operator accessible controls. Here it's been 120v forever (industrial machines operate on 240 or 480), but the move is toward low voltage.

[qwertysimo]

I am working on my control circuit. Looking at localy available products, I need advice.

I can choose control relay with 24 V AC -or- 24 V DC coil.
I can choose contactor with 230 V AC coil -or- 24 V AC coil.
I can choose 230 V AC to 24 V DC power supply -or- 230 V AC to 24 V AC transformer.

I prefer 24 V DC power supply driving control relay with 24 V DC coil; contactor with 230 V AC coil connected to control relay poles.
I can utilize 24 V DC for enclosure fans as well.

Would 24 V AC scenario provide some advantages?

[Al_The_Man]

A couple of thoughts, I prefer DC inductive devices, relay coils, solenoids anytime, as they do not burn out if the armature does not shift, or someone pokes a solenoid armature over etc.
If you can go with relay and contactor DC coils then I would personnaly go for it, ensure you place a BEMF diode across the coils, in the event of using AC coils, use a RC snubber.
120vac power contactor coils are often more common and available, but for the operator control circuitry as mentioned it is now manadory in some jurisdictions to use low voltage for the control circuitry, E-Stop etc, either 24vdc or 12v is acceptable.
A contact on the control relay can be used to switch the 120vac/240vac coils if needed.
Al.

[qwertysimo]

Thanks Al.

OK, 24 V DC for relay coil with flyback diode, contactor 230 V AC coil switched by relay contact.

[Al_The_Man]

OK, ensure a RC snubber across the AC coil.
Al.

[lloydsp]

"OK, ensure a RC snubber across the AC coil."
---
Yep... or use an SSR with built-in snubber componentry.
LS

[qwertysimo]

AC coil will be the only device on control relay contacts. What is the purpose of RC snubber in this case? To minimize interference when switching off the coil or to protect relay contacts? The coil itself should withstand the surge, shouldnt it?

[lloydsp]

The snubber circuitry is to reduce arcing erosion of the relay contacts. Any large electromagnet produces a strong "reverse EMF" pulse upon breaking the circuit. That pulse can often be of a much greater voltage than the 'applied' voltage, and of significant current capability; and it can cause serious arcing of the driving relay's contacts -- ultimately causing failure.

Snubbers are standard on this sort of circuit, and dirt-cheap. You don't want to avoid using one "just because it's inconvenient".

Lloyd

[qwertysimo]

Datasheet for contactor that I will receive tomorrow specifies only the coil driving voltage. I will measure the coil and do some math to get basic idea on RC values. Thanks to both of you.

[Al_The_Man]

The main reason I use them is for BEMF reduction, I have had machines that whenever a motor contactor picked up the control went haywire, the snubber fixed it.
I tend to wire them across coils than contacts.
Some manuf. supply a custom one to clip directly across the contactor coil
Al.

[lloydsp]

I agree, if your wires from relay to contactor are long or twisted, or run very close to other wiring. But if the leads are short, it doesn't matter much which end you put them on.

Since there are usually robust connections available at the contactor, it always seems easier to do it there.

Lloyd

[Al_The_Man]

The Electrocube pdf shows the two, either across the coil or across a contact, either way the snubber should be located right on either one being suppressed.
Al.

[qwertysimo]

If the electronics box will be attached to base table frame and never relocated, are there any reasons to place panel connectors on the box?
I mean, are there advantages if I connect cables from limit switches or stepper motors to connectors on the box or simply connect them inside the box to screw terminals?

Once the table/router dimensions are fixed, cable lengths are fixed, how often is it needed to disconnect cables during maintanance? Do I miss something?

[RCaffin]

Once the table/router dimensions are fixed, cable lengths are fixed, how often is it needed to disconnect cables during maintanance? Do I miss something?
In theory, you do not need connectors. Quite superfluous.
In practice ... you NEED connectors, because Murphy will give you hell if you do not have them.
At the very least, undoing a cable from terminals is a pain, and putting every wire back into the RIGHT terminal hole afterwards is highly unlikely in practice.
Yes, I use connectors everywhere - and good connectrors at that.
Then I connect the backpanel connectors to the PCBs via terminal strips.
Attachment 333894
(The main PCB here is optical isolation between X, Y & Z encoders and Gecko DC drivers.)

Cheers
Roger

[qwertysimo]

Thanks, idea of pulling out cables from fully populated box and routing them back is not really tempting!

What about the spindle cable? I want to keep it in one piece directly connected to terminals in VFD - no join in between, not to break the shielding braid.

[RCaffin]

Spindle cables are a pain - or perhaps I should say that the RFI emitted by the VFD is a pain.
I don't have any trouble putting a connector in the spindle cable. I use a 9-pin D connector for all the power connections. 4 pins on one side are V+, 4 pins on the other side are V-, and pin 3 in the middle is the link for the cable shielding. As you can see, pin 3 on each connector is also tied to the solid aluminium base plate. This is the equivalent of star point grounding. It works.
Attachment 333900

Cheers
Roger