Lagunmatic 3516-SX Retrofit

I would wire it like this:

+24V --> 7I77 field power= vfield = TB2 pins 1,2,3,4
24V common --> 7i77 field common = TB2 pin 8 --> relay(s) common

Note that neither of these connect to chassis gnd or 5V gnd

Also you mentioned the 120 neutral line. I hope you mean the chassis/Earth gnd
You should NEVER connect 120V neutral to any low voltage side signal or power

PCW wrote: I would wire it like this:

+24V --> 7I77 field power= vfield = TB2 pins 1,2,3,4
24V common --> 7i77 field common = TB2 pin 8 --> relay(s) common

Note that neither of these connect to chassis gnd or 5V gnd

Also you mentioned the 120 neutral line. I hope you mean the chassis/Earth gnd
You should NEVER connect 120V neutral to any low voltage side signal or power

Thanks for correcting me, neutral was the wrong word. Everything on this machine is being powered by 4-wire 3 phase without a neutral.

If I am interpreting you correctly, you are saying I should move the connection at pin 5 to somewhere between pins 1-4 and add a jumper from TB2 pin 8 to the relay common?

I'm not sure I am reading that right because it seems like this should give the same result as my last photo? The 24v power supply didn't seem to like that.

Unfortunately I won't be able to test until Friday because of work travel. It's overrated!

I seriously appreciate your help here. I've got two more machines to convert after this and I'm a Mesa customer for life

You are scaring me now.

Connect the wires to the _right_ places. Don't just guess and see what happens.

Maybe you need to connect the other side of the relay direct to field 0V rather than tie field 0V to random points on an electrical system you don't seem to have fully mapped out.

I get that - if I knew the right place I'd happily make that connection

I'm fairly confident this one relay would activate if I disconnected it from the common ground and directly to the 7i77 field ground. But every relay on this machine is connected to wire [1] common ground so that doesn't help me much. I really need to complete the circuit between the 7i77 outputs and the machine's common ground and it is just perplexing why this won't work.

I have the schematics and I've studied them for hours. When I hit a wall I ask for advice and luckily people are willing to lend it. I try to follow it the best I can but sometimes I don't understand why I am doing something.

Are you saying that the relay common is frame ground?

PCW wrote: Are you saying that the relay common is frame ground?

I can see fault conditions in various components causing that, even if it was not design intent.

Yes I think it is setup that way. Is that unusual? I only have a couple photos handy, but if you look at the output side side of the 120v transformer (top center) hopefully you can see the common wire and ground are tied together.

First photo is when I first received the machine:



Second photo is more recent. I had to swap the transformer because the machine was setup for 208v and I have 240v. The old control worked fine with this wiring:

giz

Get a friend with some practical electrical knowledge to help you.

The connection of one side of the 120V transformer secondary to chassis ground was very common for US machines in the '80s ( our normal domestic power connection is 120V to neutral which is tied to ground at the service entrance) . Also many had the return sides of the DC power supplies tied to chassis ground. All of this was done to ensure that a fault to chassis ground will cause a fuse or circuit breaker to open. It can get tricky when retro fitting these older machines if all the new hardware isn't opto or relay isolated to keep the new hardware happy. Sorry it is impossible to tell you how to fix this without drawings of the old and new circuits.

John

None of my images the last few posts are coming in as large as I thought they were - sorry about that.

I think it's pretty clear there is an issue with the ground so I'll research that. I'm not new to electronics by any means but this is the first project I've done with mixed AC/DC and complex controls. I've wired my house, my car, and tons of various DC projects. In a past life when I designed semi-automated stations I only did the mechanical portion and our Controls Engineer handled the electronics. I should have hovered over his shoulder more often.

Thanks for the insight into older machine tools John. I have all the electronic schematics available back at home.

It might be worth creating a new 0V / Common for anything controlled by LinuxCNC.
Do you know what the operating current of that relay is? Is it within the current limits of the 7i77 outputs? (And it probably needs a protection diode, unless there is one in the relay)