View Full Version : Two quick 3~/VFD questions:

Doc Nickel
10-09-2008, 02:56 AM
I just got in an AD GS2 VFD for my big Queen City Grinder (http://bbs.homeshopmachinist.net/showthread.php?t=30883&page=2), and I'm in the middle of trying to figure out how and where I can mount it where it won't be in the way or exposed to grinding grit, but can still get cooling air.

There's lots of room inside the column, and the front cover/switchplate has a factory hole easily big enough to pass the VFD.

Anyway, two questions:

There's three sets of wires coming out of the motor- pretty normal- with no labelling or color differentiation. The VFD book just calls them T1, T2, and T3. Is there a specific order they need to be connected to, or is it simply a matter of connecting any set of three to any VFD output terminal?

The book says if it's rotating the wrong way, to swap any two inputs, to I'm assuming that's the case.

Second question: Just as a check before hooking up the VFD, I wanted to check the windings; as I recall, someone pointed out that, if a given winding had electrical continuity to both ends of the wire, was isolated from all the other wires, and a relatively low resistance, then it's probably good. Is that correct?

Bonus question about these Automation Direct VFDs- I see it has a cooling fan. My AC Tech doesn't, but has a far larger heat sink. Does the AD's fan run constantly, as long as there's power to the drive, or does it only come on when the temperature hits a certain setpoint?


10-09-2008, 04:17 AM
Dosnt matter which wire goes where. T1, T2, T3 all go to the motor. Swapping any two of three will reverse the motor, but you can also reverse it by using the fwd/rev inputs.

Make sure there is no switch between the VFD and motor. Direct connection here.

The vfd should have short circuit protection. My main worry would be a short to ground. check each lead to ground and make sure it does not read anything.

Usually the fans on VFDs will come on as soon as you hit fwd or reverse. Then turn off at a programmed time after the input is turned off.

Now one thing more. If you look in your manual it shows how it should be mounted and there may not be enough air space to mount the VFD in the column and keep it cool.

Doc Nickel
10-09-2008, 04:48 AM
That's what I thought, but I needed to be sure, since I'm still new to 3-phase stuff.

If you look in your manual it shows how it should be mounted and there may not be enough air space to mount the VFD in the column and keep it cool.

-Yep. 6" above and below, and 2" to the sides. The column, however, is huge, and this VFD is surprisingly tiny. The column is an easy 10" or 11" square at the top, and the controller is 4" x 5" by about 6" tall. Plenty of room for air and cabling.

Also, this will tend to be a fairly short-use machine. While we can stand at a mill or lathe for several hours, unless I'm trying to manufacture iron filings, I can't see many times I'd have this grinder on for more that a few minutes, total.

In that light, I may sacrifice a bit of airflow in favor of extra dust control to keep the iron grit out of the controller.


10-09-2008, 08:01 AM
Direct mounting on the grinder might impose vibrations on the VFD. Larger DE grinders are not always the smoothest of machines. If the grinder is located near a wall, perhaps a horizontal pedestal mount to the wall, making the controls accessable to the opertaor, but avoiding direct mounting to the grinder.

Many of the newer VFDs will tolerate switching of the output for on/off, check with the manufacturer to see if that is the case, or is a remoteS/S station available?

Doc Nickel
10-09-2008, 08:19 AM
Good point. I do have some rubber isolation mounts from those old tradmills that might not be a bad idea... Though I'll tell you what, if it's anything like the big Baldors the college has, if the wheels are properly dressed, they have about as much vibration as a coffeemaker. :)

As for the internal mounting, I keep coming back to that for two reasons- one, for grit protection, not just from the grinder itself, but also from the rest of the welding area, and second, I'd hoped to have the thing relatively self-contained, so that it can be moved if necessary.

It's a monster, and probably won't be moved much, but I'd still prefer it as an option.

The only external controls will be a set of start and stop buttons like I put on my lathe. According to the manual, a disconnect between the motor and VFD itself, should only be used in an emergency. It can "withstand" such a cutoff, but the book says it significantly reduces the controllers' service life.

There's a "panel" on the front of the column, behind the switchbox in the picture, that is more than ample to accomodate the VFD. So even when it's all assembled, the controller and it's controls can still be accessed. Though the panel is screwed on, it's not a true door, but needing to access the on-box controls should be rare.


10-09-2008, 08:30 AM
You don't need continuous air flow to the VFD, as long as there is enough volume inside it's enclosure, the cabinet (or in this case, the column) acts like a heat sink drawing heat out of the air - just as the circulating air draws the heat off the vfd.

I would recomend making up a heavy sheetmetal panel to fit inside your column. layout your wiring and mount your VFD to that, then mount the panel inside your machine. That makes wiring a hell of a lot easier and neater (which you will appreciate if you run into any problems)

The GS2 drives have a fan that goes on while the drive is operating the motor and goes off a few seconds after you shut the motor off. It does not run the whole time there is power to the drive.

The GS2's are a nice drive and offer a lot of flexability. read through the manual, especially the chapters on setting the parameters and you'll be surprised what you can do with them.

10-09-2008, 08:37 AM
One more thing... the GS2's don't need a seperate breaking resistor module, just a big resistor. The AD website lists the required resistance and wattage for each model.

On my mill with a 2 HP GS2, I needed about 100 Ohms and 1500 watts (IIRC). So I went to home depot with my meter and started checking resistance values for different heating elements - hot water heaters, stove elements and so on. All those were pretty low, 15 to 30 Ohms. The I went to a junk yard and checked the heating elements from a smoothe top electric range... Bingo - 47 ohms! I put two of these in series and wired them to the DBR lugs on the drive and the mill can now come to a nice, controlled stop in less than .7 seconds. Without the resistors it took 2 seconds or so.

Doc Nickel
10-09-2008, 02:36 PM
Yeah, I think you or someone mentioned that heating-element idea before, which I thought was really clever.

I'm definitely not worried about trying to stop this thing in under a second- I can definitely see the utility of an emergency stop if I happen to jam something in the guard, but for day to day use, heck, if it spools down within a minute, that's not too much of a problem. I may just let it coast off, see how long that takes.

The big Baldors at the college take a solid thirty seconds to come to a stop, no braking at all besides friction and eddy currents.


10-09-2008, 03:53 PM
The big Baldors at the college take a solid thirty seconds to come to a stop, no braking at all besides friction and eddy currents.

30 seconds?! The Baldors at Austin Community College take 5 minutes to come to a stop. Hell, half the time I didn't even bother turning it on if I was grinding tungsten electrodes :)

10-09-2008, 08:53 PM
As for the bonus question, yes, the fan on every AD VFD I have used runs any time there is power applied to it, irrespective of whether or not the drive is running the motor. They are great drives, I've used a bunch of them in my work as well in my machines at home.

The stove heating element as a braking resistor is a good one. Where I work, we have a smallish HAAS CNC bed mill that has two spiral stovetop elements in a perforated metal enclosure for that. I was surprised when I saw that. I felt a bit vindicated, that is not just some cheapskate home shop hack anymore!!

10-09-2008, 09:07 PM
Same experience on the fans running constantly on the AD drives.

Braking,on that big grinder I would let it coast too.I had a customer who programed a faster stop on his jump saw(5sec down to .5 sec).It stopped quick alright,so quick it spun the nut off the arbor and launched the blade:D