Hey guys, I recently installed a drive on a 40 hp fan on a large grain dryer. We started testing the dryer a couple days ago and there has been a problem with the ingnition sequence on the burner (the flame sensing probe is not showing a flame). A service tech from the manufacturer came out, replaced the ignition board and the thing worked fine all day yesterday. He did suggest to me that the problem could be VFD noise and reccommended installing a load reactor after the drive. Now, I do have a line reactor in front of the drive, but I thought that load side reactors are specifically for softening the peaks of the voltage to the motor to avoid insulation breakdown? Today i was out there for hours trying different things. First i I tried isolating the ground to the ignition board, isolating the motor ground, isolating the vfd ground (all directly to a ground rod) but had no positive results. Anybody have any thoughts on the situation??? The motor leads were ran by a previous electrician from the dryer controller inside a building about 40 feet away through a pvc conduit with a few other 120 volt control wires. They are routed through a large termination cabinet at the dryer as well (the leads are all at least three inches away from any other data wires and all are shielded cables) . Tomorrow Im thinking about removing the motor feeder from its pvc conduit and totally isolating from the rest of the wires. Any insight would be appreciated!
vfd noise problems???
- Thread starter Rsteenson
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kwired
Electron manager
- Location
- NE Nebraska
I don't mean to be a smarty pants, but is the flame sensor rod clean and burner surfaces clean? These flame sensors detect a small voltage that develops between the sensor rod and grounded surfaces of the burner assembly. Corrosion and other build up on these surfaces will effect detection of that voltage. If you suspect the drive is cause of problems can you temporarily run the blower across the line and see if the problems go away? If they don't then you know it is not the drive.
I will not take offense to any suggestion at this point haha! I am using the vfd for phase conversion as well as speed control so across the line is not an option unfortunately. I cleaned and drilled out the burner holes and the probe myself....also the dryer tech replaced the probe the other night. I read in the troubleshooting guide for the igition board about grounding the burner directly to the chassis but havent done that just yet.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Din ding ding... I think we have a winner!
VFD output conductors are MARVELOUS local radio transmitters, unless their signal is dampened by... grounded metal. You MUST run VFD output cables in metal conduit or use "VFD Cable" that has metallic shields. You will find that information in the installation manuals of all VFDs (from reputable suppliers).
You should also NEVER run other control wires in the output conduits of a VFD, in fact I don't recommend running them in the same conduits as power leads of any sort.
mike_kilroy
Senior Member
- Location
- United States
Rsteenson;1425684The motor leads were ran by a previous electrician from the dryer controller inside a building about 40 feet away through a pvc conduit with a few other 120 volt control wires. .....Tomorrow Im thinking about removing the motor feeder from its pvc conduit and totally isolating from the rest of the wires.[/QUOTE said:
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Equally importantly or possibly more so is the steel conduit or screened/armoured cable as Jraef has pointed out.
Running the conductors in PVC conduit is like running them in air. I'm a bit surprised that anyone would have done that.
And I don't think an output reactor would do a lot to fix the problem.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
Jraef, I really get perturbed by smart people confusing damp with dampen ... the latter gets it wet. You meant (I assume) unless their signal is damped by... grounded metal.
I know, sorry to vent ... just so many control theory courses where the instructor threw a glass of water on those of us who forgot ...
weressl
Esteemed Member
All the shielding of the motor feeders are valid, but before you do that, you may try to change the carrier frequency to see if it makes any difference. Cheapest and may just be 'good enough', not necessary the right one though and before you run the speed up/down through the range you wouldn't nkow if you 'got it' or not.
I don?t often comment on spelling unless it is funny or alters the meaning in an odd/amusing way. If I did, I'd be fair game for reciprocal posts.
The use and abuse of the English language is prevalent on the internet. Sometimes I see phonetic spelling that takes a little thought to interpret.
Asan example, something I posted in another forum earlier today:
You have to hear it with a local accent........
My take is that, as long as the meaning of the post is clear, it conveys the message.
Taking a pop at the poster isn't constructive.
Admittedly quick and cheap. But I wouldn't bet the farm on it.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I had this argument, in reverse (meaning I took your position), with a prof a long time ago when I was so bold as to have challenged his use as well. I was put in my place by virtue of the fact that Merriam Webster begs to differ;
So as he put it; "You are making a case for the #2 definition to be the first and only. Please take that up with the fine folks at Webster's, not me."
The dictionary people include words that have been created through usage even when improperly used.
Damp - n. Slightly Wet
Dampen - v. to be made slightly wet
Dampened - past v. - was made slightly wet
Damp - v. to reduce or to deaden
Dampen - ?. to be made to reduce? or to be made to deaden?
Dampened - ?. - was made to reduce? or was made to deaden?
Damped - past v. - was reduced or deadened.
-en adds "to be made" to convert a noun to a verb. Not used to convert a verb to a different verb. But usage trumps proper construction.
Did you have any difficulty in understanding the point Jraef was making?
weressl
Esteemed Member
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Agree, but worth a try since it hardly cost a penny....
other than your time. but in general, I agree it is probably a good first shot at the problem.
load reactors would be my second shot at it.
redoing the conduit is a pricey thing to do and would take me a while to get to. might be cheaper to just leave the conduit as is and disconnect the VFD wires and run VFD cable seperately.
mike_kilroy
Senior Member
- Location
- United States
pulling the vfd wires and running separate would tell the story though, so worth the effort. but perhaps it would be easier to remove the 120v control wires instead? or just disconnect both ends so vfd cables are alone for the test?
If this solves the issue, perhaps rather than buying shielded vfd cable or metal conduit change, just twisting the 4 motor cables with drill for the whole length and stick in separate pvc might be enough.....
anyway, I do not recall hearing if the vfd motor leads included a 4rth ground wire to motor case or not? If not, it too needs to be added. even shielded vfd wire has 4 wires (if you dont put it in metal conduit, altho here I would run a ground wire too)
If this solves the issue, perhaps rather than buying shielded vfd cable or metal conduit change, just twisting the 4 motor cables with drill for the whole length and stick in separate pvc might be enough.....
anyway, I do not recall hearing if the vfd motor leads included a 4rth ground wire to motor case or not? If not, it too needs to be added. even shielded vfd wire has 4 wires (if you dont put it in metal conduit, altho here I would run a ground wire too)
Big drill bit?
mike_kilroy
Senior Member
- Location
- United States
Ha! Actually, this was/is common with some experienced machine tool rebuilders. They just stick the 4 wires into the end of the drill and turn it on while their buddy walks back along the wire and lets it twist itself. They even have standards for how many twists per foot type thing.... makes a really neat looking cable assembly. I've watched in awe while they twist a 50' long set of #6 wires.....
Wouldn't you need a fairly large chuck to accommodate four #6 conductors?
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