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. :blush:

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

Of course. :blush:

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

kornphlake79 wrote: nevertheless I would still prefer a solid state relay.

Normally-closed Solid-state relays exist, but are uncommon.

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?