Thread: Low voltage E-Stop ideas

Hi Geoff,

On my G540 controller I have the controller box on/off power switch turn on a small 12V switch mode power supply. This 12V supplies an Estop circuit that consists of the EStop button, a start and stop push button.

A small 12v relay is used in conjunction with the above switches to create a safety estop setup. The contacts of this relay switch a terminals of 240V contactor (or larger relay) that switches 240Vac to the power components such as the G540 supply, 240V output relays etc.

I'll see if I can dig up a circuit.

Cheers,

Peter

Thanks Peter.

I've been browsing cnczone.com and I've come up with quite a few variations, some of which are down right dangerous!
The plan so far sounds like your design, a separate 12/24V power supply to control switching of the G540 supply and the spindle/VFD via relays.
I'm sure as rodm has said, there's not a big advantage in having multiple e-stops on a small CNC device but I figure build it in now in case one day I do have need.



Don't interrupt the camping just for this.

The circuit below is a sample EStop I snatched of the net.

The DC (power supply) is 12Vdc. Control relay (CR) is a 12V relay such as the link below, but you could use any small 12V relay as the contacts carry very little current.

12V 20A Panel Mount Relay [RL-03] - US$10.00 : Homann Designs!, The preferred CNC Component SupplierE-STOP Circuit.jpg

The normally Open (N/O) Start push button is wired in parallel with the relay contacts so that when the start button is pushed it supplys 12V to the relay coil activating it and closing its contacts so that the 12V is supplied to the relay coil when the start button is released.

The 12V is also supplied to the Master Control Relay (MCR) that is switching the 240V mains through it's contacts. The MCR contacts need to be rated well above the normal current expected to flow through it. For a 10A system, I'd use a 20A rated relay. Al;so use a double pole relay and switch the Active and Neutral.

The Normally closed (N/C) Stop button (and 1 or more EStop buttons) are wired in series as shown. When any of these are pushed, the 12V is removed from the relay coils the MCR cuts the Mains power.

Even when the EStop is released, the start button needs to be pressed to re-activate the mains.




Cheers,

Peter

Excellent! Nice and simple, I like that.

I've got a small PC type power supply that I was planning to install in the enclosure in case 5V or 12V was required for some other purpose, this will do for the relay supply.

I'm assuming that the 240V switched by the relay is for all items that run off 240V i.e. power supply, VFD, etc? I can't see any advantage of just shutting down the VFD and disabling the G540 via pin 10 - although a few of the circuits I found on cnczone did just that..

What mains components you shut off with the relay is up to you. Think of the reasons that you need to push the Estop.

If the VFD fails and suddenly starts the spindle by itself the only way to shut it down is to remove the mains power.

If the G540 output fails and won't turn off an output, just removing the enable input won't guarantee that it will turn off the output.

Personally, I'd have the estop remove 240V from the G540 power supply. the VFD and any other switched outputs. After all it is an "Emergency Stop" not a "cycle pause".

Cheers,

Peter

I agree with that so current plan is to turn of power to everything except the computer.
I looked the idea of pause/resume switches as is done with the Mechmate but as someone pointed out, the 6040 is not that big that I can't just do that from the keyboard and still reach anything I need to.

Now to source an aquarium pump ...

Only thing I would add is to use a solid state relay if you can, they are much quieter (electrically speaking) as they usually switch when the AC is at zero voltage level, they have quite reasonable current ratings, and will operate with a wide range of switching voltages (3-32 voltsDC).

Cheers.

Russell.

Hi Russell,

I have to respectfully disagree. When a solid state relay fails, it mostly fails in the "ON" state, which is the last thing you want for an ESTOP. This is the reason that safety contactors are not solid state.

Use solid state relays to swich you 240V outputs, but have the estop relay a mechanical one.


Yes, a relay is electrically noisy but in my opinion it is much safer. That is why I suggested a relay that is spec'd at twice the max current you will be drawing

Ideally you want to use a "contactor" but for a small machine that is not drawing more that 10A a relay is sufficient.

Cheers,

Peter

Well there you go, ya learn something new every day, I didn't know that they stayed on in a failure situation. In this case then a relay would be a better option. Like you mention at least doubling the rating of the relay would be a good idea, I have seen plenty of relay contacts welded together, especially with inductive loads such as transformers.

Cheers.

Russell.

Hi Russell,

Yes, that's why I suggested a relay with double the current capacity, for a 10A system, a 20A or 30A rated relay.

I've been using a 20A relay on my G540 controller for about 4 years now.

For high inductive and high current loads a contactor is required. They are designed to combat arcing and welding.

Cheers,

Peter

I had been considering solid state relays (due to arcing and noise) so thanks for the timely post.

TO help reduce noise effects, I have some ferrite toroids that I was going to use on the data cables and a couple of mains filters for the computer power connection at least.

No planning today though, too hot!