killing ML 1400s

Don't know if anyone has had something like this happen before, but I'm out of ideas...
Micrologix 1400, no i/o being used, only 24v from a rhino power supply and a patch cable from a stride switch, a panelview 800 and a powerflex 525. Everything is great until I power on the VFD breaker then it fries the plc. looks like maybe a triac inside has burned up? No continuity that I can find between any high and low voltage wiring. Any ideas what would cause this?

stupid question but did you measure the voltage and does it match the voltage spec of ml?

chud said:

stupid question but did you measure the voltage and does it match the voltage spec of ml?

Click to expand...

It's right at 24vdc.

br4axton357:

I am more a communication kind of guy, neither hardware nor software specialist, and have mostly learned by doing. I am not an expert in motion, but I have experience helping customers diagnose Profibus DP networks, as I sell one such tool from a German manufacturer. You may find my advice empiric and lacking formal terminology, but I hope it might help your search for ideas.

Years ago I was hired to diagnose what I was told was a Profibus DP communication issue. All the information was provided by purchasing people without technical background.

When I finally arrived at the plant, a steel-sheet cold-rolling workshop, I got into discussions with the customer and it turned out that the Profibus communication boards of the drives were being fried, not unlike what you seem to describe. Of course a fried Profibus board cannot communicate, hence they wanted support for Profibus diagnostics.

But my diagnosis did help because we found out with the oscilloscope function that the grounding of the whole machine was incorrect. I am unable to describe how they figured this out.

Forgive me for my lack of technical lingo but I can tell you they brought in their electricians, confirmed the machine builder's wring and the industrial codes, then fixed the grounding and communication started working normally.

Hope this helps.

When you have distributed control panels, that are networked together, it is very important that there is an equipotential bonding between the panels.
If not, stray noise will find a path to ground for example via the networking cables, causing all kind of problems.

JesperMP said:

When you have distributed control panels, that are networked together, it is very important that there is an equipotential bonding between the panels.
If not, stray noise will find a path to ground for example via the networking cables, causing all kind of problems.

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wow, this and the previous answer have a real "Fool Me Once" flavor.


It's like wiring the lights on a boat trailer from your car: it's almost always a bad ground.

what is the communication from the vfd?
ethernet, dh485?
what comms port are you plugging the vfd cable into?
you may have 2 different types of comms cables creating the issue.


james

Jesper is spot on, it's is very likely a ground issue at least that's where I'd start looking. If the VFD is mounted to the same panel that the PLC is I.E. they share a chassis ground, and that panel isn't grounded to earth ground (at all or adequately), any stray voltage will raise the ground floor which will create a voltage differential between the chassis ground of the PLC and anything connected to it that is not tied to the chassis ground, like the Ethernet and serial port. In North America Neutral is tied to ground on the 120 power source which depending on how the panel is wired also runs the risk of feeding high levels of AC voltage into the chassis ground. I'm not very familiar with how a VFD handles braking but if it does so my dumping the motor's current onto the ground that also can cause problems on a panel without proper grounding.

James Mcquade said:

what is the communication from the vfd?
ethernet, dh485?
what comms port are you plugging the vfd cable into?
you may have 2 different types of comms cables creating the issue.


james

Click to expand...

Using straight through patch cables/ethernet for communication. Connected to the left side ethernet adapter on the drive, then to the switch, then into the plc.

We used PF525's and we kept frying the enet switches, even with the 24VDC power off the enet switch would smoke. Wrong Connector on 525 !!


Check that the comm cable (RJ45) is in the right connector in the drive. AB put two RJ45's side by side, one is for Ethernet, the other actually has voltage on a couple of pin, for RS485 comms.... And will fry anything connected as Ethernet...

Trying to attach the page from manual but having trouble..


View attachment Embedded Ethernet525.pdf

JesperMP said:

When you have distributed control panels, that are networked together, it is very important that there is an equipotential bonding between the panels.
If not, stray noise will find a path to ground for example via the networking cables, causing all kind of problems.

Click to expand...

If I had a dollar every time I found bad grounding/bonding I could probably buy a nice house, maybe even retire.

It's amazing how many folks don't even hook the ground wires up.