Variable Speed Drives: What I’ve learned about VFDs

[J. MacDonald]

I have a Beaumont Metalworks KMG-10 package with the small wheel attachment, a base plate and a couple extra tool arms. I bought it with no drive as I had scored two Toshiba NEMA1 (remember this designation) 2HP rated VFDs some time earlier. A VDF is an electrical controller that will take single phase household power in like 115V or 220V and turn it into 230V three phase power and allow you to drive a three phase motor with variable speed. I had also arranged a nice Leeson 2 HP three phase motor (thanks Michael Kanter) so with the appropriately rated Toshiba VFDs I was convinced that I had a really solid drive setup arranged. When the grinder came and I mounted and wired everything I was floored at what a cool setup I suddenly had! The KMG was so solid and with the variable speed drive, I had so much more control that I finally started to enjoy grinding some blades 

A few months later, I found a deal I couldn’t pass up on a low mileage KMG nearby and added a second grinder to my shop. This machine was powered by a single speed Leeson motor and was equipped with stepped pulleys for speed change. I quickly got used to having two grinders and was starting to really have some fun, but I did always prefer the variable speed KMG to the belt change one. It was just a lot nicer to have the fine speed control.

Then, the night just before the recent So Cal Blades Knife Expo in Pasadena I was working my butt off trying to finish a few knives to take to the show and show to a few friends (nothing for sale). Then suddenly my nice Toshiba NEMA1 VFD died with a flash and a loud BANG! I was really pissed. Knowing what I know now, it is obvious that it died because I was using a NEMA1 rated VFD to power a knife grinder. NEMA is the National Electrical Manufacturer’s Association. NEMA sets the standards for all electrical fixtures. NEMA1 rated enclosures are well vented by design and so an environment rich in steel dust is exactly the wrong application for a device like that so my machine was destined to fail by design NEMA4 rated enclosures, on the other hand, are rated dustproof and wash down safe with a hose! Unfortunately NEMA4 VFDs are a lot more expensive than NEMA1 rated VFDs.

In a weird twist of fate, the same day I blew up my Toshiba NEMA1 VFD, I had also arranged to trade off the single phase Leeson that was powering my 2nd machine for a similar three phase motor (Thanks Charlie May). My intent was to install that 2nd Toshiba VFD that had been sitting on the shelf for a while with the incoming Leeson motor and make my 2nd machine variable speed like my first one It was a great plan.

What this really means is that I suddenly had two KMGs, both with three phase motors and only one VFD, and from what I’d learned, one not really suitable to drive EITHER KMG  Arrrggghhh!

After doing a bunch of research I ended up buying a pair of KB Electronics Penta Power VFDs from Rob Frink of Beaumont Metalworks. I researched NEMA4 VFDs for weeks on the net and at local electrical suppliers. I looked at a lot of stuff, but Rob’s prices were very competitive and he’s had good experience with the KB drives running his grinders so was good enough for me.

I had never been happy with the old Toshiba VFD being mounted on the wall behind the grinder, so I’d already determined that I would need to fabricate a new mount to hang the drive directly on the grinder. Once I got the KB VFDs I realized that they were bigger than I was expecting and would need to beef up my plans for mounting the VFD to the machine. I ended up making mounts out of some 1”x2”x5” aluminum bases and some 3/8x5”x17” aluminum uprights milled from some scrap plate I had.

What I learned about the VFDs themselves for all you curious other knife makers is that while NEMA1 VFDs have really come down in price making them very attractive as an option for variable speed drive for your grinders. Unfortunately, using a NEMA1 VFD in a knife shop is asking for trouble and is why so many people seem to have issues with their VFDs. The pictures below show the difference in sheer mass between a 2HP rated NEMA1 Toshiba VFS7S and a KB Electronics KBAC-27D. Both devices are rated to deliver full HP from a 220V single phase line like you’d find for a dryer in an everyday garage. It’s obvious from the pictures how much beefier the KB VFD is when compared to the similarly spec’d Toshiba. The Toshiba has a digital display and all the parameters are programmed via a membrane keypad on the front of the VFD. It is lightweight and fan cooled with a minimum sized heatsink. The KB in stark comparison is large, beefy, wash down rated and all the controls are analogue trim pots sealed well away from any contaminants. Having worked in the audio business for a couple decades, the difference reminds me of the difference between a cheap Japanese receiver and a beefy American made power amplifier. The KB just has a lot more to it. The KB is mostly discrete components where the power section on the toshiba is integrated circiuts.

Regarding purchasing drive components from Rob Frink, I have to say, you couldn’t hope to deal with a better man. After I’d already done my homework and decided his price was fair and his offerings suitable, when I was placing the order, Rob mentioned that he’d include a couple of power switches and other parts in the purchase price. When I got the box, there were a couple KB Main power cut off switches and a bag full of these really cool wash down rated European fittings that help make the whole adventure totally dustproof! What I’ve learned is that if you believe in him enough to buy his grinder, you can trust him to supply the right drive as well. Highly recommended!

So remember:

Variable Speed is Good!

NEMA1 is BAD

NEMA4 is your friend

Beaumont Metalworks ROCKS!

 

[J. MacDonald]

The mount under construction

 

[J. MacDonald]

Here's the KMG after all the surgery in what I hope to be it's final form. Canb't wait to grind on it this weekend The second shot is to give you an idea as to placement.

To complete the project, today I received a 2nd base plate that I'll paint tomorrow so I can reconfigure the second machine and return it to service. It'll have the same drive and mount as the machine pictured, but will only have a 1 1/2 HP Leeson motor instead of the 2HP shown on this machine. It will also be bench mounted instead of pedestal mounted like my 2hp machine. Otherwise they'll be twins

I should never need to upgrade my grinders again

 

[Chant]

Being a bit of a dunce in the shop arena, I ordered a complete package from Rob -- the KMG, the Leeson motor, the same VFD you got, the base plate, and the VFD mounting arm he sells. The whole thing went together like clockwork, and I couldn't be happier. The mounting arm he sells is much like the one you made.

One of the nice things about the design of the KMG is that you can start to play with making your own attachments. I'm working on a platten attachment that will allow me to more easily true the flat grind on a blade by running the belt along the length of the blade. My design would be safer with the motor running in reverse, which I can do by getting a new switch for the VFD. The open design of the KMG allows for a lot of playing around :thumbup:

 

[h2ostx]

John,

I have to agree wholeheartily with your findings. I too bought a KBAC-27D after much research on the internet, the nema 1 controllers just didn't add up to a good fit in a metal working shop. Then I started to see the posts that the open VFD's were burning out, and this confirmed my decision.

The KB controllers are well worth the money. IMHO

I made a mount for my control using 2"x3"x3/16" thk. angle iron, welded to a 3/8" thk piece of plate steel. Attached the controller to the 2" wide leg, fit perfectly and allows cooling on the fins. Looks somewhat similar to your setup, but mine is really simple. Not nearly a nice.

Kelly

 

[alexmin]

I'm working on a platten attachment that will allow me to more easily true the flat grind on a blade by running the belt along the length of the blade. My design would be safer with the motor running in reverse, which I can do by getting a new switch for the VFD. The open design of the KMG allows for a lot of playing around :thumbup:

Jeff,

do you mind sharing your design with us? I was also thinking about making similar attachment.

Thanks,
Alex

 

[alexmin]

I'm working on a platten attachment that will allow me to more easily true the flat grind on a blade by running the belt along the length of the blade. My design would be safer with the motor running in reverse, which I can do by getting a new switch for the VFD. The open design of the KMG allows for a lot of playing around :thumbup:

Jeff,

It must be extremely useful attachment. Do you mind sharing your design with us?

Thanks,
Alex

 

[micad]

Just a thought for those of you with NEMA 1 type drive enclosures.....

Why not mount the drive in a protected area away from your grinding and run a set leads to the motor and a remote (from the drive) push button station and speed pot at the grinder?

Got to be cheaper than blowing the drive.

-Mike-

 

[J. MacDonald]

Mike, I thought seriously about that approach, but that would only move it from the immediate grinding area out to where the mill, lathe, bandsaw and drill press are. Still not a friendly place for a NEMA1 drive. There are 3rd party enclosures that are filtered, but add a lot of bulk and they're so expensive it's easier to just go NEMA4 at least in my shop. Trust me, I had to think long and hard about this as these things are near $500.00 each so it's not pocket change, at least not to me.

 

[Chant]

Jeff,

It must be extremely useful attachment. Do you mind sharing your design with us?

Thanks,
Alex

I'll post some pics when it is done (provided it works!). Should be done next week.

 

[DAMNENG]

Just a thought for those of you with NEMA 1 type drive enclosures.....

Why not mount the drive in a protected area away from your grinding and run a set leads to the motor and a remote (from the drive) push button station and speed pot at the grinder?

Got to be cheaper than blowing the drive.

-Mike-

Mike

I agree with you. I have been running a TECO mounted in a remote location on my KMG for over two years with no troubles at all. And for those who want to have variable speen on more than one grinder, you can wire up a switch box so you can choose which gringer the output of the VAC drive feeds. This shouldn't be too much of an inconvenience unless you tend to grind on two grinders at once.

Jim A.:thumbup:

 

[C L Wilkins]

Mike

This shouldn't be too much of an inconvenience unless you tend to grind on two grinders at once.

Jim A.:thumbup:

I'd pay to see that!

Craig

 

[pabradford2]

John,

I guess great minds think alike. No only do we have the same grinder and motor setup, but it looks like we even painted ours the same color. I choose the easy way out for mounting the VFD via the mount Rob sells. I purchased my 2HP KB VFD and motor at last years Blade Show. It works like a dream. I also have a 1 1/2 hp KB powering his 2X72 horizontal grinder. Both have performed flawlessly. He gave me the same type of fittings you described but I couldn't get my wires through them. I carefully filled it up with clear silicon. Not a speck of dust has gotten through.

Happy Grinding.

Philip

 

[pso]

John

I am glad that you are up and running again. The set up with the KB's looks really well made. It should last forever, just like the grinder. Also, thanks for posting the pictures of the KB. It is interesting to compare it with the old MTE and the PDL brand VFD's that I have (both NEMA 4 or IP 54). Were the special fittings installed where the two rubber plugs go on the KB?


MICAD suggested "Why not mount the drive in a protected area away from your grinding and run a set leads to the motor and a remote (from the drive) push button station and speed pot at the grinder?" That is what a lot of the industrial users of VFD's do. I have seen electrical rooms with the wall covered with VFD's, each connected to a motor several hundred feet away. Often the motor is mounted in a location that is too inaccessible and/or too hazardous to mount the VFD near it and expect someone to operate it.


The following is not meant to put down the KB nor to defend the Toshiba VFD's. I have no financial interest in either. I would just like to clear up some misconceptions from the viewpoint of someone who was on the VFD R&D and manufacturing side.

Probably less than 5% of the VFD's made, worldwide, are intended to run from a single-phase 220 - 240 Volt or a single-phase 110 Volt input without derating it's output power. Check the specification tables in the manual before making a purchase or you may be dissapointed when your VFD trips out under load.

One needs to make sure that one is comparing apples with apples and using products as they were intended to be used. The manuals for all the NEMA 1 rated VFD's will warn you NOT to install them where there is the possibility of exposure to dust, especially conductive dust. Fortunately, or unfortunately, it seems that some people have managed to be able to use their NEMA 1 rated VFD's for many years, creating an illusion that they are OK for use next to a grinder.

NEMA 4 VFD's will always be bigger than a NEMA 1 VFD with the same rating. This is NOT related to the quality of the product but are a result of the intended end use. Some of my co-workers are repackaging some of VFD's for arctic oil field applications where they sit outside. They are about 3 to 4 times the exact same VFD with a NEMA 1 rated enclosure. So a bigger VFD is not really better, just different.

Having had the opportunity to open up and compare different brands of VFD's, I have found they all use similar components, no matter whether they are made in America, Europe or Asia. The transistors in the KB look like they would have ratings similar to those used in any number of NEMA 1 VFD's with the same output rating.

The main reason for the large size of the KB is that it does not use a fan whereas virtually all NEMA1 VFD's do. The fan increases the effectiveness of the heatsink several-fold. The cost of a small fan is less than the extra heatsink size required by the KB.

The use of chips that integrate many functions increases the reliability of the product. It is a well proven fact that solder joints are potential failure points, especially in a high vibration environment. A discrete version of a VFD will have more solder joints than one using a few chips and will perform no better.

Having had to crunch the numbers before, I can tell you that it does cost much more to design and manufacture a NEMA 4 rated VFD than one with a NEMA 1 rating.

The few NEMA 4/IP54 rated VFD's that are available will most likely serve a knifmaker equally well. The various NEMA 1 rated VFD's are all just as likely to work well if installed in a clean environment and they are all just as likely to blow up if metal dust is allowed to get into them.

Phil

 

[rtj1981]

I picked up a NEMA 1 VFD off ebay and used a old ammo can to put it in. It included a remote key pad with it that controls the speed. So far it has run great with no problems and no dust that i can detect inside the can. I checked on the company's website about mounting it in an enclosure and the only stipulations were that it neede one inch on the sides and 2 inches of clearance on the top and bottom.

closed

open

key pad

 

[pso]

rtj

The clearance specifications in the manual are to allow free air circulation for cooling the VFD. It assumes that the air will circulate into the room. The $500 box that John refers to would suck outside air in through a filter to provide fresh, cool air for the VFD. The heat generated by the VFD is carried away when the air leaves the box. I have heard of industrial applications where a VFD is mounted in a totally sealed box that is much larger than the VFD. The VFD's fan circulates the air inside the box. The heat generated by the VFD escapes through the large surface area of the box. This approach is tricky since it is difficult to calculate the heat flow through the walls of the box and testing is required. If your VFD is not tripping out on over-temperature after running at full load for extended periods, then your set-up has "passed the test". If it does trip out, then, use a larger box.

The one other area to check is the keypad. Not all are completely dustproof. You will have to check in your manual. Metal dust getting into the keypad will probably not cause a "big bang" but will likely cause some sort of erratic malfunction that will drive you crazy over time. A simple improvement would be to wrap the keypad in a thick plastic bag. Also, the opening for the wires from the VFD should be sealed up with some caulking.

By the way, what brand/model of VFD did you get?

Phil

 

[rtj1981]

The brand is ac tech SM230S, its the 3hp model. I got everything with shipping for $300. The keypad appeared to be a totaly sealled unit, there is a gasket on the back and i used one of those project boxes from radio shack to mount it on. I was concerned with the heat build up inside the box and for the first couple times i used it would open the ammo can to feel if the inverter was getting hot. So far its run like a champ. If this summer it starts getting too hot i was considering getting drilling a hole through the back and putting a dryer vent over it on the outside. I am no expert on this stuff so if anyone can see any potential problems please let me know. Thanks

 

[pso]

rtj

Check the VFD after it has been running for 15 -20 minutes of running under load. A rough rule of thumb in electronics is if you cannot hold your hand on it, it is probably too hot.

Use two dryer vents, one at the top of the ammo can and one at the bottom. You want the outside air to flow in then carry the heat out.

Phil