VFD dilemma

Hey everyone,

Hoping to tap the collective wisdom on this one:

I've got a 1HP/3ph tool I'm looking to drive from 1ph with a Teco FM50.

Due to the shape of the machine, there's no easily reachable place to mount the VFD, so I plan to use the existing switch wired into the FM50 control terminals.

However, my question is this: the unit has a cooling fan, and constantly pulls air through the housing. In my dusty woodshop, I'd rather not have it operating nonstop - also, the noise would be annoying when I'm doing quiet work.

Does anyone know if the VFD will object to input power being cut while under load? The booklet says the inverter should not be turned on or off using main circuit power - is that just "play it safe" instructions, or will it burn up the drive?

I'd considered putting a 20A toggle switch on the 1ph input, and using that as an "off" switch for the whole system.
It could be mounted right next to the built-in switch - powering up would be a very quick and easy 1 - 2.

Obviously, I'm also trying to avoid having to push multiple switches every time I want to turn the machine on and off. This may be inevitable, but a single off switch would be charming, and the toggle would accomplish that as long as it didn't harm the drive.

Looking forward to everyone's thoughts - thanks in advance!

Best wishes,
Martin Keith
Martin Keith Guitars

Well....

Well, what they really DON'T want you to do, is chop the power while the motor is spinning... first of all, if the drive has a dynamic braking function, it won't work. Second issue, is that when you've got a spinning motor, you have the potential (oh, bad pun) of generating electricity.

Unconnected generators... coils of wire with unknown, uncontrolled whirling magnetic fields can cause some pretty bad things to happen on wire leads.

Typically, VFDs have snubbing circuitry to calm this down, but the wisest method, is to stop the machine, then shut down the VFD.

Don't think you'll find the VFD's cooling fan to be very offensive... they're typically darned-near silent... and most of 'em only run when above a certain temperature.

Suffice to say, if the fan is running, you'd be wiser to let it run 'till it shuts off, before cutting power to the VFD.

As for dust... well, you can solve that, AND any sound issues, by exercising your woodworking prowess- make a little cabinet on the wall somewhere... preferably close to the machine. Make the cabinet about 4x the size of the VFD, and install a lining of styrofoam insulation about 1" thick. At the bottom and top, install a piece of furnace-filter, or a piece torn out from an old T-shirt (flannel works great, too)... to keep dust from being drawn in.

( www.identitycrisisqca.com )

I just upgraded a customer with all new VFDs on their production line (I-Line making wooden I-beams) . . . the drives were located adjacent to the line next to the flying saw. Lots of sawdust and the fans have run 24x7 since about 2002.

We opened up one of the drives yesterday to use for a quick dyne test and it was FULL of sawdust - we blew it out and powered it up - no problems.

I remember going into a saw mill about 15 years ago - they had a new maintenance tech that wanted training on the drives so I asked him where the drive cabinet was for the saw line. We went on a tour around the building and finally found the drive cabinet on a lower mezzanine just below the feedrolls into a double arbor gang saw (4 x 250HP drives) . . . we opened the cabinet and it was completely filled with sawdust - and I mean when the door opened, at least 1/2 a cubic yard of sawdust came out onto our boots!

They spent an hour cleaning it / blowing it out and vacuuming it - the drives were happy as can be still running away.

Apparently there was a reason that the maintenance tech was new . . .

DaveKamp said:

As for dust... well, you can solve that, AND any sound issues, by exercising your woodworking prowess- make a little cabinet on the wall somewhere... preferably close to the machine. Make the cabinet about 4x the size of the VFD, and install a lining of styrofoam insulation about 1" thick. At the bottom and top, install a piece of furnace-filter, or a piece torn out from an old T-shirt (flannel works great, too)... to keep dust from being drawn in.

( www.identitycrisisqca.com )

Click to expand...

Jeepers, all that to save a couple bucks. When I first spotted the "4X" in Dave's reply, I figured he was going to tell you what I would tell you... just buy a drive in a NEMA 4X enclosure, like these:

Vector Drive, NEMA 4X, Indoor Duty<br>Standard Input<br>AC Tech SMVector (C) - wolfautomation.com

And mount it wherever it's convenient. These differ in that the heat sink is outside the sealed case, and arranged with vertical fins so the dust just falls through.

I have one on a 3HP mill, and it works for me.

Dennis

Hee hee.... 4x...

Yeah, buying it in a NEMA 4X pre-kit is handy. I was fortunate to stumble on an A-B 1305-AA12A preassembled in a NEMA 4 case... brand new, in an opened-for-photographing box... With the case, it was a big bigger than I wanted, but it bolted to the side of my Bridgie nicely. Think I got that one for $130.00... put me in jail!

Yeah... I think the thing I'd worry about most with the sawdust... is having enough built up around the busbars to start a fire.

Back when I was teaching at the railroads, there was a screen-saver goin' round that had animated pictures of various manufacturers' trains rolling across the screen...

Every so often, one of 'em (and not a specific manufacturer) would be on fire... or dragging an axle... or being towed by a rescue train...

I put a 3HP ABB drive on a Delta belt sander a few years ago. I used the existing start/stop station and contactor for two functions: First, 2 of the 3 poles on the contactor switch the incoming 240V line to the VFD. Second, the remaining pole on the contactor was wired to the VFD's "run" input.

So, hitting the STOP button does two things simultaneously - it cuts line power to the VFD, and it opens the run command input to the VFD.

Not saying, it's the best setup, but so far - so good...

ANY switchgear box has no good place to mount it. Take a look at ebay, at most any machine tool, and there are dorm-fridge-sized enclosures hanging off the back, mounted on top, sitting on the floor with a large 'hose' attached to the machine, etc.


I have a drill press/VFD integration challenging me to come up with a nice mounting. The result won't be pretty. Most likely a metal (not plastic) enclosure u-bolted to the column, sitting on the base, with the control wiring running inside the column to be installed on the drivebelt shroud.

Install a chip deflector over the enclosure, and call it good.


As to controlling a VFD, it has no problem going thru its diagnostics and immediately starting the motor when the power comes on. That behavior isn't always safe, so the VFD allows it to be turned off.

To retain the braking function, a low voltage switch can provide the Stop signal.

I think cutting off power to the drive to get ON/OFF at the machine is a failure waiting for you. I suspect that you'd hit the power and stand there waiting for the drive to boot up before the machine runs. So very inconvenient as well.

If you have not bought the drive yet, look for a model with a remote keypad. I have a couple of the CV7300 drives and run them both using the remote keypad and cable. The drives are well out of the way and protected. I remove power to the drives when not using the machines.

I also do not have a problem with fans running continuously. Mine only come on when the drive heats up from running at low speeds for quite a while.

Somewhere here at PM is a post that shows a drive kinda wrapped/surrounded in mesh air filter material to keep dust and chips out. That might be helpful for you.

Removing input power to the VFD while running shouldn't cause a problem. But applying input power again could cause problems if you don't wait a few minutes for the VFD to cool down.

Most small VFDs have a surge limiting device on the front end that, when cold, has a high resistance to lessen the effect of the in-rush current seen when power is first applied (due to energizing the DC bus caps). As the device heats up, its resistance decreases.

If you shut off power and then apply it again too quickly, the device is still hot and therefore its resistance is very low, allowing too much of the in-rush through. This can cause damage to the VFD.

Do it clean...

Removing the power from the VFD removes all of the features the VFD has to offer for stopping and controlling the motor.

If the fan is a problem then find a quiet one, if the fan is running it is needed, but most fans are not a noise issue unless you are in your living room.

If the VFD has the ability to be controlled remotely then a couple push buttons, toggle and a pot give you start, stop, direction and speed.

The existing barrel can be rewired to provide the direction and start-stop functions and a pot added someplace for speed control, the "look" shoul dbe factory and all voltage to the control are low voltage so small wires can be used for a clean easy install.

The VFD is mounted near the motor or other place, heat should not be much of a problem as the devices are operating in "switch mode", either they are 100% on (low resistance) or 100% off (high resistance), it is the duty cycle that effects the current and voltage output.

Given the 2 states, the switching devices themselves do not dissipate near the heat you would think, so it should be a small fan if any, and mounting it in suc a manner to be not noisy in your shop should not be an issue.

Look up the specs on most units, there may be an ambient noise specification, just have not looked for one...

My Omron 3hp VFD runs the fan constantly when ever it is powered up.

The Toshiba VFS7-2022p I just bought is dead silent when I apply power. When I start my shaper the fan on the Toshiba starts. When I turn the shaper off the fan continues to run for another 30 seconds to a minute and then turns off by itself. I really like this functionality!

I personally would not cut power to a VFD that is running a motor