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Protecting a VFD?

Pelallito

Aluminum
Joined
Jan 10, 2004
Location
Miami, FL , USA
Hi,
I need to get a VFD for a 3 HP #Phase motor that I am going to use on a grinder. I don't want to spend any extra money on a Nema 4 enclosure if I don't have to.
I have been wondering if I made a Plexiglas or Lexan enclosure for it that was sealed, would it be protected from the metal grinding dust? I realize that it would have to be an over sized compartment so it doesn't get overheated.
I would like to have the screen visible and a speed control and Forward-Off-Reverse switch on the outside.
Would this work? A homemade Nema 12 enclosure so to speak. All wiring would be sealed where they go through the wall of the enclosure.
I have tried looking on line and all Nema 12 enclosures seem quite expensive.
I am trying to do this at minimal expense.
Any ideas and help would be welcome.
Thanks for the help.
Regards,
Fred
 
Why do you want the screen visible? I would be inclined to locate the VFD away from the grinder and wire up a remote switch and speed control. The VFD on my milling machine has terminals for remote wiring, and I assume most VFDs do.
 
Mainer,
I don't have much experience with VFDs. I thought that the screen would give me an indication of the speed that I am running the motor. If it does not, I don't need it. The grinder would be used at full speed or slowed down for fine work. I forgot to mention that it is a 3450 RPM motor.
The grinder that I will use this on is a KMG clone that I built. Most people would call it a belt sander. When used on metal they call them grinders, why I don't know.
Here is a link to them-
http://www.beaumontmetalworks.com/index.html
I don't know much about this, so any advice and help would be greatly appreciated. I don't want to fry the VFD with the dust. I think that anwhere in my shop(garage) the VFD would be exposed to that threat. Please tell me about the remote control feature.
Thanks for the reply!
Regards,
Fred
 
"I need to get a VFD for a 3 HP #Phase motor that I am going to use on a grinder. I don't want to spend any extra money on a Nema 4 enclosure if I don't have to."

Mount the VFD inside a common steel pull box (Hoffman, etcetera, available in numerous sizes) which interior volume is at least four times the volume of the VFD itself.

The pull box should be mounted so it has good air circulation around it.

There is no exchange of air between the outside and the inside of the pull box.

VFD cooling will be by conduction from its heat sink to the pull box, and by convection around the VFD, also to the pull box.

Externally, cooling will be by radiation and convection.

This type of installation is most appropriate where you don't need access to or visibility of the VFD's panel.

I would likely install a fusible disconnect on the input side of the VFD, in accordance with manufacturer's instructions, particularly if there was no panel access.

If you need visibility and/or access, consider a remote panel kit.
 
Hi Fred!

Your VFD's display MIGHT have a function to indicate frequency... certainly not shaft speed, unless it has some internal function to calculate that (I've never seen it, but I wouldn't be surprised if it existed).

As for mounting yours in a protective enclosure, it's important to keep dust out of the VFD, and equally important to keep good, clean airflow to cool the heat-sink areas. Newer VFDs have much better dust/dirt control integrated into their design, whereas older VFDs... crap can get everywhere, especially from grinding metal...

My solution would be to put it in a good enclosure of any type, but keep the enclosure air-passable, with a segment of stout air-filter and a cooling fan at one end, and a segment of filter at the other.

The OTHER way to do it, is to make an enclosure that'll rapidly diffuse internal heat to the outside (pronounced Al_you_mini-Umm) and give plenty of airflow space around the outside.

I've yet to see a VFD that didn't have provisions for remote controls... I'd mount the run/direction switch and speed-control pot at a convenient and safe location on the machine, and mount the VFD in some other, protected and clean location.
 
Peterh5322 and DaveKamp,
Thank you for the ideas and explanations.
I will call the different companies to see how I can get remote control over the VFD.
Peterh-5322 I will put the fusible disconnect in line. Originally I was thinking of putting a switch in line to isolate all power to the VFD. I don't know if I need both.
DaveKamp- I will look into using aluminum in the cooling of the VFD.
Monday I will try calling around and get advice from Factorymation and Dealerselectric. If you can recommend anybody else, I would appreciate it. I tried calling one of them today and they were closed. While writing this, I remembered that they will probably be closed on Monday.
Thanks for the help.
Regards,
Fred
 
For a previous project ... a full shop in another state, at a "home away from home" ... my plan was to use FM50s in Hoffman knockout-less pull boxes, pre-building all of them using a "standard design" here in Northern California, for later installation on-site in Southern Nevada.

As there were two FM50 frame sizes, there were two pull box sizes required.

The idea was to do most of the work in my primary shop, and to leave to the very last moment the tasks of drilling of the holes for pull box mounting (mounted to studs using, say, #10 sheet metal screws) and the punching of the line and load knockouts, using a Greenlee, or equal, knockout punck kit (I have an HF kit which cost $17 and change and does a pretty decent job).

With a full charge on my coreless's two batteries, I could install all the boxes/VFDs in an afternoon, even at a "dark" (that is, powered-off) site.

This concept was made all the more economical, and functional, as I was able to buy five used, but in excellent condition, Square D three-phase fusible disconnects for scrap value.


Here's my concept for a single-/three-phase VFD installation, considering the line side, only (the load side would be wired as usual):

1) wire all VFDs for three-phase input,

2) three appropriately-sized conductors for L1, L2 and L3, to the safety switch's load side,

3) three-phase safety switches mounted as required for visibility and distance from the machine, but

4) no fuse in the B-phase switch, and

5) no feeder conductor connected to the B-phase line side terminal, then

should the site later be converted to utility three-phase, only the line side needs to be changed, and the fuses updated as to number and rating.


I am wiring my VFDs this way, particularly those which are connected to the line with a cordset.

For a cordset-connected machine, only the cordset needs to be changed to convert it from single-phase input to three-phase input, as everything on the load side of the disconnect switch is already wired for three-phase.
 
Last edited:
Peterh,
I read your reply a coupe of times and ended confused. It is my fault because I am not an electrician and do not know the correct technical vocabulary.
In here-

Here's my concept for a single-/three-phase VFD installation, considering the line side, only (the load side would be wired as usual): Line side being 1ph or 3ph?

1) wire all VFDs for three-phase input, I have 1 phase input only at home, if I M SAYING IT RIGHT.

2) three appropriately-sized conductors for L1, L2 and L3, to the safety switch's load side,
lOAD SIDE BEING 3 PHASE?

3) three-phase safety switches mounted as required for visibility and distance from the machine, but

4) no fuse in the B-phase switch, and b phase swich?

5) no feeder conductor connected to the B-phase line side terminal, then

should the site later be converted to utility three-phase, only the line side needs to be changed, and the fuses updated as to number and rating.


I am wiring my VFDs this way, particularly those which are connected to the line with a cordset.

With a cordset connection, only the cordset needs to be changed to convert a machine from single-phase input to three-phase input as everything on the load side of the disconnect switch is wired for three-phase.

I will never have 3 phase in the shop because it would be prohibively expensive to run it there.
Thanks again for your help, and sorry that I am not understanding this better.
Regard,
Fred
 
As too the remote control: Shop the drive around, many of the older Mitsubishi's have a "removable" keypad interface, that also happens to be fairly well sealed on the face. The REALLY great part of the deal, is that it is connected via a RJ-45. These are EASY to mount remotely. I don't get out much any more so I'm not sure how all the drive interfaces connect up any more, but I'll bet you'll find more than 1 brand using connectorization that is commonly available.

Other options use a digital ( or analog ) out put from your drive and send it to a little (red lion) led display. These can be had cheap on flea-bay. Mount the display in a box (hoffman 8x8x4 ?) with your drive controls.

Wanna get fancy? Buy a 4x HMI from flea-bay. =)


peterh5322 said:
Mount the VFD inside a common steel pull box (Hoffman, etcetera, available in numerous sizes) which interior volume is at least four times the volume of the VFD itself.

I agree with that statement. Remember --> AT LEAST! :)

Doug S.
 
"I read your reply a coupe of times and ended confused."

Sorry ... I presented several concepts in one post, each separated from the others by double spacing.


(Like this).


(And this).


If you know ahead of time that you will never have three-phase in your shop, then by all means implement the associated economies.

If, however, you could have three-phase in your shop, or in a subsequent buyer's shop, then do consider the wiring scheme I detailed, above.
 
Peter,
I thought that they went together. I will read them now with that in mind.
I would follow your recommendation in the wiring scheme to the letter if I get a chance to set up a 3 phase shop.
I would love to have 3 phase, it would make my life much easier.

Doug S,
What is a 4x HMI? I will google it now. I found it, your right about it being fancy and $$$. I will get a box 4 x or larger to house the unit after I buy it.
Thanks again for the help and explanations.
Regards,
Fred
 
Guys,
I was able to get a 12 X 18? X 7.5 aluminum box and have been working on wiring both of my VFds in there. I will never run them at the same time. One is a 1 HP Delta and the other is a 3 HP Teco Westinghouse.
I did the calculations and I thought that I had more than enough room in there for my units. What do you think? I may have made a mistake and mounted the box to a wall rather than off the wall leaving an air space between them.
Do you think that I still need to add some form of ventilation?
I will be adding a remote control to this as soon as I buy the parts.
Thanks for the help
Regards,
Fred
 
Protecting a VFD

Pelallito,
I have attached a chart that gives the size of Enclosure and Size of Fan for VFD installations, use this as a guide for your enclosure construction. Some VFD now have removable control pads so that can be mounted on the lid of youe enclosure, if not you can remotely wire Speed Pot (10k) and your Stop/Start Buttons.

Regards,
Keith.
 

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