VFD's and dust

Britt_Askew

Britt_Askew

Knifemaker / Craftsman / Service Provider
Joined
Dec 9, 2010
Messages
1,218
I ended up going with the teco fm50 vfd. I know it is not dust proof but for me just starting out 175.00 vs 450.00 for one thats dust proof is a huge difference. I have read alot about the lifespan can be real short though if the unit is not sealed from dust and my question is , is "dust" dust a killer or is it just metal dust I should be concerned with ? I am thinking it is just metal dust I should be worried with ?? as the metal dust on a circuit board I am guessing is what could short it out. What about radio's and such in the shop? For 20 years my sawdust has never caused a problem but should I think about filtering my radio from metal dust?
 
i dont reckon your radio should be an issue there a pretty sealed unit with no way of anything being sucked inside them, with your vsd the general rule is it should be in a dust proof box atleast 3-4 times the size of the actualy vsd (vfd)......

So saying that i would seal it in box that is placed under your bench and wire a on and off switch and a potentiometer for speed control which they can be wired out to be ontop of the bench or next to the grinder,the vfd's there sensitive to both metal and wood dust so make sure its sealed well and placing it under the workbench keeps it already away from alot of dust. You can buy sealed boxes from places like i would assume in the states radio shack, or just build a wooden box yourself, seal all the corners with a gap sealer of some sort and you'll be sweet as!


edit-just to add the box that i was thinking of that would work i think they call them junction boxes or distribution boxes or just electrical boxes, you can find dust proof ones of them and there a very professional looking way also to house your vsd
 
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Yes, you will need to build a box. Regular dust and sawdust are not as big of a deal but metal dust will kill the VFD. There should be dimensions given in the owners manual for the VFD for what size of box to make, depending on whether the box will be ventilated or not.
 
Well so far its 1 and 1 for regular dust making a difference. Here is a picture of my radio ( one of the most important tools in the shop) thats been in my shop for about 15 years now, the sawdust has been thick at times and every once and a while I take a deep breath and blow it off.

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OK...maybe I didn't understand your question. Is the VFD going to be powering a knife grinder or some other tool that creates metal dust? Or a wood saw?

I don't see what sawdust and your radio have to do with the VFD needing an enclosure?

If your radio is located a bit away from your grinder I don't think it will be a huge deal. In any case it's not really practical to enclose the radio. If it dies, it dies. 15 years is a lot of life from a radio, dust or not.
 
Wire in remote on off switch and speed pot the vfd's manual will state the max distance allowed. Place the vfd in a place far and away from migrating dust. Or make an enclosure that can allow it to breathe that has filters on it. I think there is a maker on here that did this do a search on vfd enclosure.
 
DSC00048.jpg Here is one of mine with the cover off this is a clean box from depot or bellows electric supply.
 
There are several reasons I am wondering about the dust issue. If metal dust is the only thing I really have to worry about I can put the VFD in another room away from the metal dust , if "dust" dust would be a problem I will build an enclosure. But my main concern is my other electronics. I stay in my shop 7 days a week. along with the radio there is computer and monitor, tv and sat. box. yes I have a tv in the shop.... football games, car races, hockey games, and the big bang theory.

"dust" dust has never been a problem for my other electronics but I wonder if I need to take steps to keep my other stuff safe now that my dust is metal instead of wood ( the radio is old but I could buy quite a few VFD's for what it cost)
 
I have had the same electronics just like you do in my shop with no issues so far including a speaker above my main grinder. I went to the trouble to safegaurd the vfd's because they are costly the other electric gizmos were not.
 
My mentor has 2 15+ year old burr kings that we use every weekend and they are open. One with the VFD the other without. He says he has never had an issue but he does run a squirrel cage fan to suck the grinding dust out of the shop.
 
If the VFD is located in another room then it should be fine. The problem with that is you need a long run of that heavy gauge 4 conductor power cable, which is not cheap.

As for general dust, I work for a mechanical contractor and the current project we're doing has about 300 VFDs (ABB $$$) total and none are sealed enclosures.
During construction they are exposed to concrete dust and drywall sanding dust and god knows what, but they don't have many issues. The enclosures, although not sealed, do a decent job of keeping most crap off of the guts.

I think you can manage ok with all of your electronics. Just keep the shop clean, and ideally you should use floor sweep compound when you sweep up to keep the amount of airborne dust low. You can arrange the stuff so that the vents are blocked from direct access to the dust (but still allow airflow). I would imagine the concentration of metal dust would be exponentially greater the closer you get to the grinder (i.e. some thing twice as far away as another will get far less than half the dust exposure). So the best case is the grinder is on one side of the shop and all the electronics on the other.
 
For my Teco, which is mounted in a location that experiences a LOT of metal dust, I made this enclosure for it:

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I patterned it after pictures that another member posted on here years ago. After grinding for months, I opened the box, and it was entirely dust free.

--nathan
 
VFDs generate quite a lot of heat; usually it's around 100W, as a very rough ballpark figure, for VFDs in "our" sort of sizes. Dry, non-conductive dust mainly becomes a problem when it interferes with the VFDs ability to keep cool.

Metallic dust is obviously conductive and can (will) short out either the control electronics or the power section components. Either results in a dead VFD, but on the power side, it's much more exciting.

I'd expect the magnetic fields, generated by the switching of the larger currents in the power components, to attract ferrous dust. Most of the grinder-related VFD failures I've heard about have been on the power side.

The separate room may be the easiest way to go for you. If you end up enclosing the VFD, it's the heat removal that tends to be the problem. Heat transfer from the air inside an enclosure, through the walls, and to the ambient air outside, is a pretty inefficient process at best. Metal enclosures are generally better at it than plastic, and you need lots of enclosure surface area, preferably vertical.

Regards

Tim
 
timgunn has most of the situation. For a more detailed "WHY", read on:

The VFD creates heat, and that creates convection. So the VFD will draw in some fine dust that would not otherwise enter a device like a radio.

A radio gets warm at most, and some produce no heat at all. They carry just a few millivolts of current through the circuitry, and they are have simple oscillator and PLL circuits. Because they produce little heat, and have no high power or adjustable circuits, most PC boards are either potted or heavily coated with protectant.

A VFD carries many amps of current. This can easily bridge two points in the complex Diode and IC circuitry if any path is provided. Even non-metallic dust can conduct some current at these levels, and can also change capacitance. Because there are so many adjustment and connection points on the PC board, it is mainly unprotected, and thus quite vulnerable to short circuits.

Keeping dust out of the VFD will be the way to keep an expensive VFD running for a long time.
If the radio fails due to dust ( unlikely), you buy another $15 radio.
 
I patterned mine on Nathan's. ;)

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Of course I have a decent dust extraction system and I have a Shopvac addiction :o so my shop is not that dusty but the VFD has been working fine for more than 3 years.
 
Thanks for all the input, I really appreciate it. I feel like I have a much better understanding now.
 
Heres an action shot of a friend of mine using one monster of a surface grinder, we did some turkish twist damascus that day! Anyhow take a close look and u can sneak a peek at the teco that has ran that machine unenclosed for he couldnt remember how long, i about crapped when i noticed the teco but has had no issues????
knives464.jpg
 
I could walk through the West Texas prairie holding a golf club up in a lightening storm without getting struck, but I'd hate to push my luck.

--nathan
 
I have decided I will build a box :)
Nathan I also want to tell you thanks for your forge build thread... I read other threads on the subject but when I found your thread the light bulb finally turned on, Thanks
 
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