What is this?

[jcdammeyer]

I've set up to use two SSRs to control the heating elements on my kiln. Project #42. Way down on the list because I really don't have anything for the kiln to do at the moment.

You can use something as simple as a 5VDC wall wart to make 5V that you run through the ESTOP and Power Switch to the SSR which switches on the main DC motor power etc.

There are other safety considerations too BTW. If you hit ESTOP everything should stop. If you then twist the button and undo the ESTOP those motors that were running must not be able to restart until commanded to by the system.

My mill had relay logic set up so that if the Single Phase 2HP spindle motor was ON and ESTOP was hit the relay controlling power to the 'system', including the spindle, could not be re-energized until the spindle control switch was set to OFF.

In other words the Spindle Switch had a NC contact that was in series with the signal to the Master Power relay. Once the relay was ON there were contacts on it that latched it on. The relay control was also in series with the NC ESTOP switch. So hit ESTOP and Master Power relay drops out. It can't come on until both the Spindle switch is OFF and the ESTOP is released.

You can't do that with an SSR since it's a single contact. So ultimately you still need at least a DPDT relay which can then run the SSR for master power.

 

[DavidR8]

I've set up to use two SSRs to control the heating elements on my kiln. Project #42. Way down on the list because I really don't have anything for the kiln to do at the moment.

You can use something as simple as a 5VDC wall wart to make 5V that you run through the ESTOP and Power Switch to the SSR which switches on the main DC motor power etc.

There are other safety considerations too BTW. If you hit ESTOP everything should stop. If you then twist the button and undo the ESTOP those motors that were running must not be able to restart until commanded to by the system.

My mill had relay logic set up so that if the Single Phase 2HP spindle motor was ON and ESTOP was hit the relay controlling power to the 'system', including the spindle, could not be re-energized until the spindle control switch was set to OFF.

In other words the Spindle Switch had a NC contact that was in series with the signal to the Master Power relay. Once the relay was ON there were contacts on it that latched it on. The relay control was also in series with the NC ESTOP switch. So hit ESTOP and Master Power relay drops out. It can't come on until both the Spindle switch is OFF and the ESTOP is released.

You can't do that with an SSR since it's a single contact. So ultimately you still need at least a DPDT relay which can then run the SSR for master power.

That makes total sense. I need to put some thought into my electronics and wiring everything for safety.

 

[jcdammeyer]

That makes total sense. I need to put some thought into my electronics and wiring everything for safety.

Here's the original circuit for my manual mill. The key contactor (KM Relay) is a 4PDT relay. If you follow the 24V you can see the ESTOP has to be OFF (NC so current flows through it). Also the Coolant Pump switch and Spindle control switch need to be OFF (NC so current flows through them) that allows the KM Relay to switch on which provides power to the various devices.

With the KM ON one of the contacts continues to provide power to the KM relay supplied by the ESTOP switch. That's so the KM contactor stays ON even if the spindle and coolant switches are turned on (The NC switch becomes OPEN).

But if ESTOP hits power to that KM bypass relay contact is lost, the KM drops out and power is gone and motors stop. And you can't enable the KM relay again until ESTOP, Coolant and Spindle are all switched OFF closing the NC contacts in each switch.

If you want real safety add an NO momentary switch in series with the motor and cooland NC contacts. Now even if everything is OFF and the ESTOP is reset you still need to momentarily press this 'ON' Switch.

 

[jcdammeyer]

And just to add to the confusion. If you want your CNC system to be able to shut down your system you need to put something in series with the ESTOP. And your CNC system may well need to know when you have pressed the ESTOP. So here's the same drawing as above for the original machine but with the changes to allow the PMDX-126 to shut down the system.

And the PMDX relay that does that is enabled when the CNC system is running and tickling the ChargePump pin. If the PC goes away so does the ChargePump and therefore off goes the relay on the PMDX which removes control of the new relay in this diagram.

Bingo, machine stops if CNC control system hangs.

 

[jcdammeyer]

This is what sits between my PC running LinuxCNC with the Ethernet connected MESA 7i92H and the hardware. The PMDX-126 is set up to expect the charge pump on Parallel Port #1 Pin 17. If it vanishes then the outputs all switch off including the ESTOP stuff.