Burnt Panel View

Damaged

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Join Date
Oct 2008
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Alabama
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Guys, I maybe out of line on this post but, I feel you guys can lead me in th right direction.

I recently had a panelview 1250 plus, burn up. It was powered up by 24VDC along with other 24vdc equipment and devicenet. All were fused under a 7 amp CB. (This was put together before I came in by a foriegner)

When the panel view "went" it must have jolted the Devicenet master. After clearing the circuit of the burnt panel view that was tripping the 7 amp breaker, we finally got the devicenet network to respond after several attempts of downloading the network and pulling the card and resetting (Control Logix chassis).

When we installed the new panel view, it booted fine but as we were wrapping up, putting J-boxes back together blah,blah,blah, the new panel view began to smoke. Only after 15 minutes, no communication had been made, it was only powered up to the run application screen.

We pulled the wire from the new panel view, and had to install our last PV on an isolated 24VDC power supply being to scared to install it back on the 24VDC supply we used prior.

I checked the voltage with a fluke volt meter, and had 24.1 vdc and checked AC voltage getting a 0.78 vac.

Can anyone explain to me what I have missed and why other devices are running fine on this circuit but the panel view burns on it?

We shut a customer down and owe a large sum of compensation and these guys want answers. Running out of head scratches.

Could someone point me in the right direction or offer some items I could check?
 
Verify: Units 1&2 smoked with the old supply. Unit 3 is working with an isolated 24 supply?

.78 AC noise is a little high, but not the cause of failure.
1) Measure the voltage on each lead to frame ground. I suspect one of your leads got in contact with a hot line. Other 24DC devices might be isolated enough to tolerate it.
2) Check all other leads going to the HMI. Something is high with respect to ground. If the high voltage is coming in on another connector, then your isolated supply will also be high with respect to ground. Measure it there.
For example, one of the communication wires is shorted to 120VAC hot. The path to ground is through the return leg of your grounded 24DC supply. Now that you have an isolated supply, the return leg can float at 120VAC. This scenario isn't likely (120VAC on Comms),just an example of where I'm going with this.
3) If you can't find it that way, then open up one of the burned HMI's to see what's burned inside. The blackened area will be close to the offending connector.
 
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Units 1 and 2 did smoke with old power supply and and ethernet cable plugged in. Unit 3 is currently running and operating on an isolated power supply with the same ethernet cable attached.

The burning connector was the VDC in connector. I have asked the HMI repair company to recommend a root cause of failure, but I just dont think they will be able to provide me with enough information.

Thanks for your input. I will do some further testing with the leads and chassis tomorrow.
 
My first line of thought would be improper grounding of the panel itself.

Check voltage between V+ and V- and also between V+ and ground.

Grounding of panel ( or the lack of it) is the most common cause for such problems.

cheers.
 
I've seen 50V potential in a cabinet using separate 24V power supplies. Ground the supplies together, and forget "earth ground" as a reference. That seems to be an issue here, measuring to the metal cabinet. as long as the supplies are sharing a common ground, they will not give you a false voltage, barring induction from another source.
 
Thanks for the replies..... Update!
The chassis was not grounded, I thought maybe the frame would at least have some grounding y the mounting screws, I was wrong. The mounting screws have nylon balls on the end, no metal to metal.

So....I proceeded to check voltage and here is what I got:

+V to -V = 22.59 VDC 0.05 VAC
+V to Cab= 12.12 VDC 0.05 VAC
-V to Cab= 0.074 VDC 0.083 VAC

These measurements were all taken while the equipment was not in production. I will take them again when production is in full blast in the morning.

I will update further.

Tom - there is just one source coming in on 2 wires, no other wires are entering the cabinet. What is your thought on grounding the negative? As when to and when not to?
 
Hmm.. I have had simular problems with PV+'s and a funny thing is that these are all american machines.
Now, I find that in your country there seems to be a reluctance to ground the -ve of dc supplies & a lack of circuit protection.
The systems involved only have one 110v fuse & one 24vdc fuse. this has caused us many problems the machine is in a wet area & the lack of individual fusing makes faultfinding very time consuming.
I don't know why but a 6 amp fuse on the 110v does not blow in the event of solenoid coil failure but instead it drags it down & re-boots or blows the relay in the output card.
I have grounded the 24vdc -ve, fitted a fuse for each output card (blown a couple of these cards as only one supply fuse for whole of 110v supply), a fuse for each input card & a fuse for each instrument requiring a seperate supply, not had a pv+ go down since (although heard a few tales of the psu in these failing regulary).
engineers find it easier to faultfind so why do you not fit more protection, we have a number of machines from the states & these all have a distinct lack of fuse or mcb protection.
Here in the UK (and in the rest of europe) I find that most machine manufacturers do split the supplies with protection for each card/ instrument.
 
Parky,

thanks for your reply. Personally, I have adopted various forms of panel design from several different countries. I have worked with machinery and OEM's from Germany, Spain, Czech Rep, and here recently Korea. I fuse every piece of 24VDC that comes out of the Power Supply. Each Output card has a fuse, all inputs have a fuse, control circuit has a fuse, all periphials have a fuse and I will land a 24VDC "General" fused @ 5 amps on a terminal block for anyone who wants to add some form of 24VDC energy consuming device and looks for the easiest source to apply it. I will also add a smaller power supply and power the bus for Devicenet if it is used in the particular project.

The piece of equipment that is mentioned in this Thread was designed and maintained for the last four years by a Korean. The system has been plugged and plugged for the past 4 years also. Not that the guy maintaining the system is not capable, but the guy maintaining the system has been under management pressure, and I am sure we all know how that goes.

Parky could you give me your outlook on grounding the 0VDC on a power supply?

Thanks again for your post.
 
normaly the ground of the 24dc are connected to the generall ground of the electrics. dont doing this can couse the damage of a device by the fault of another device that could also work properly without any faulty behavior. measuring 12volts from ground of the dc converter to the cabine indicates something like this. or do i understand you wrong and you have a symetrical
-12 , 0 , +12 dc powersuply like its used in device electronics with amplifiers? if not and its a normal ac/dc 24 volt converter you have some faulty device. disconect everything from the converter and measure to ground. if its still 12 volts the converter is faulty. if not put back every connection seperated and measure again. you should find the faulty device by doing so.
i would do so in this situation. could be a lot of work but as i readed about this it looks like a double error where the hmi died as the second fault came up. the first fault could be present for years if you dont have ground monitoring on the circuit without leading to an error.
 
Well Damaged, I was an electronics engineer for years & my grounding in that field made me realise that not only earth loops cause a problem on screened cables but it also applies to power.

As AB is very popular in your country I'm sure many of the engineers over there have suffered problems with remote analog I/O on a rio scanner module if the 24v dc -ve is not grounded.

It makes sense as any -ve potential that is not grounded can pick up spurious spikes from other power sources in the cable trunking etc.

power supplies if grounded will absorb a cetain amount of spikes relative to ground by their design with capacitors etc.

An ungrounded dc supply can carry negative spikes at such a magnitude to create an effective potential of say 50 volts from 24v +e to negative i.e. the -ve terminal will for a time (length of spike) have say -25v giving a potential across the 24v instrument of 50v.

I have seen these spikes on a 24v psu that is not grounded with a scope & it's frightening.

We also ground the 110v neutral leg on all of our panels as these have isolating transformers.
Oe other thing to note is that I tend to use 110v for power rather than 240v off one of the phases, many panel builders fit neutral removable links if the plc, instuments etc. are powered from the phases to neutral i.e. plc off 1 phase & other instrument on another phase, removal of the neutral link can cause A POTENTIAL OF 415 VOLTS ACROSS THE PLC OR INSTRUMENT.
I have seen this happen a number of times when a neutral link has been removed when the main isolator is switched off, then they have forgotten to replace the link before switching on.
only takes a few seconds & bang goes a number of pieces of equipment.
 

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