Disabling servo amps.

I have AMC 30A8 amps that I drive from a 5i25/7i77. Now I'm trying to disable the amps when the machine isn't enabled. The amps are normally enabled and disabled by connecting a pin to ground. From the manual: "TTL level (+5 V) inhibit/enable input. Leave open to enable drive. Pull to ground to inhibit drive. Inhibit turns off all power devices."

From conversations with PCW, I believe I have to use a relay to invert the enable logic but I'm not entirely sure how to do that. I have this 24V reed relay:



If I'm understanding the other posts I've read, I need to send 24V to the ena0+, ena0- to trigger the relay, and connect the inhibit+ to the ground through the NC contacts of the relay?

I have these two lines in hal:
net x-enable axis.0.amp-enable-out
net x-enable hm2_5i25.0.7i77.0.1.analogena

Am I in the right ballpark? I suck at electronics so thanks in advance for using small words and/or colorful pictures.

That looks like a single Normally Open (NO)
contact, you will need a normally closed contact
relay for this purpose

Of course.

I've replaced it with NC relay which I've wired up. Powering the coil enables the amps as expected.

Now I've got 24V from field power to ENA0+. Connecting the coil to ENA0- / GND does nothing.
Connecting to ENA0- and GND on the field power flips the relay but toggling hm2_5125.0.7i77.0.1.analogena doesn't change the state.

Where am I messed up in my wiring and config?

You need to be a bit careful here or you can damage the ENA outputs
The relay needs to draw 50 mA or less and the relay coil must have a flyback diode

Wiring should be:

+24V --> Relay coil 1 and flyback diode cathode --> relay coil 2 and flyback diode anode --> ENA+ --> ENA-
24V GND

PCW wrote:

You need to be a bit careful here or you can damage the ENA outputs
The relay needs to draw 50 mA or less and the relay coil must have a flyback diode

Wiring should be:

+24V --> Relay coil 1 and flyback diode cathode --> relay coil 2 and flyback diode anode --> ENA+ --> ENA-
24V GND

O.k. The diode makes sense to me but I don't understand the connection from ENA+ to ENA-.

The ENA+ and ENA- path is made when the switch is on (the list shows the entire current path)

As a side note, the reason I would wire it this way instead of connecting ENA+ to +24V and ENA- to the relay
is that if ENA+ is connected to +24V, an accidental short of ENA- to ground will destroy the optocoupler

If I'm reading the snippets from your instruction manuals correctly you need a 5v relay, not a 24v relay. Your 5i25 will output a 5v signal to enable the drive, so you'll need a relay with a 5v coil right? The relay will switch the enable to ground to inhibit the drive. You'll put a diode across the coil terminals. Roughly as shown in this diagram, I show a SPDT relay because they're more common than SPST relays, and more versatile, you could use a NC SPST relay though. If you wanted to go one step further you could put your E-stop in series with the relay coil using a NC contact.



I know they cost a few dollars more than mechanical relays, but if it were me I'd use a solid state relay in this application because they draw a fraction of the current a mechanical relay will and at TTL levels you're pretty limited by the amount of current available already, plus you won't need a flyback diode.

I missed the part about the 7I77, you can use a 24v relay and not worry as much about the available current as much as you would if you were using an output on your 5I25 card, nevertheless I would still prefer a solid state relay. The wiring diagram would look roughly like this

o.k. I'm about 95% confident that my (dis)able circuit is right now and connected correctly but it still doesn't enable/disable with the linuxcnc 'toggle machine power' button. So either I fried the opto coupler or I still have something wrong in software config.

What would be the symptoms of the former and what else can I do to verify hal config?