Lagunmatic 3516-SX Retrofit

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)

andypugh wrote: 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)

You may be right about that and I'll have to look into how to do that. Good thought on the operating current - I couldn't find that exact spec but I did find the DC coil consumption which is 1.2 Watts = 50mA at 24v. I'm fairly sure this is the right spec but not 100% certain.

There is indeed a diode between the input wire [20] and common [1] at the relay. Thanks for watching out Andy.

Here are the photos I posted in larger format. Click for original size:

Original Wiring:

After changing transformer, spindle vfd, and connecting power:

How the 7i77 is currently wired:

Failed 7i77 wiring attempts: