Want to upgrade grinder motor to variable speed--best option?

J

JoshEarl

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Sep 30, 2007
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From what I've been able to glean, the least expensive way to upgrade from a single-speed to a variable speed grinder is to get a cheap 3-phase motor and a VFD.

Could someone give me an overview of what I should be thinking about in pursing a setup like this? I've done some searching, but most of the VFD-related questions are very specific, and I'm looking to understand the big picture.

I'm currently running a 1-hp 1750 rpm motor from Grizzly at 220v. I'd like to get some more horsepower (mainly for platen grinding while removing forge scale from razor blanks), but what I'm most interested in is the adjustable speed. I'm hoping to spend $200-$300, which seems doable.

What are some good options as far as VFDs? What is involved in hooking this up? I'd be comfortable doing basic wiring, but some of the posts mentioned capacitors and such.

From what I've read so far, it sounds like I should be looking for a 3-phase TEFC AC motor in the 3-5 hp range, and a VFD that is rated for the (current? horsepower?) motor. It sounds like I'll get a little more than half of the rated horsepower by running it on single phase juice. Would a 1750 rpm or 3500 rpm model be better?

Are there other avenues that I should explore as well?

Thanks,
Josh
 
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One of the problems with going for a 5hp motor is increased cost for both the VFD (variable frequency drive) and the motor. Many makers will tell you that 2hp should be sufficient even with the minor power loss from the VFD. You drive should be rated for at least the same horsepower as the motor. Make sure your VFD you choose takes 220V singe phase input and outputs 3phase. You should get a motor of your desired horsepower and it should be TEFC 3phase.

Another thing to look at is the rating of the VFD case. If it is NEMA 4, that means it is pretty much dust and washdown rated. Unfortunately, these are also pretty pricey. I got a VFD with an open case and built a clean box for it (TECO FM50). You can see it in my website's shop tour page. If you don't protect an open VFD, you run the risk of metalic dust build-up over time which will eventually short out your VFD.

Hopefully that gives you some idea.

--nathan
 
I found this. Is an IP20 enclosure an open box design?

I thought I read that the HP would drop to 5/8s of rated output. Is that overstating the impact? I would be fine with 1.5 HP, so maybe a 2HP motor would be the way to go. The 5HP motors look like they're huge, anyway.

Thanks, this is very helpful so far...

Josh
 
Josh, watch ebay for VFDs and motors. There are some really good deals there is you have enough time and patience. I got my 1 HP variable speed setup from ebay for under $150 shipped, all components were brand new and top quality - NEMA 4 enclosed VFD and TEFC Baldor motor.
 
JoshEarl said:
I found this. Is an IP20 enclosure an open box design?

I thought I read that the HP would drop to 5/8s of rated output. Is that overstating the impact? I would be fine with 1.5 HP, so maybe a 2HP motor would be the way to go. The 5HP motors look like they're huge, anyway.

Thanks, this is very helpful so far...

Josh
Click to expand...

That is the one I was looking at. I was interested in it over the Teco FM50 for 3 reasons.
1 it is cheaper
2 it is smaller by a little
3 it has the speed knob right on the front. It just seems a little easier to change speed by turning the knob instead of the buttons.

I got my vfd components for just a little over $215. Now I just need to set it up correctly.
 
I've no experience with that particular VFD, but many VFD's in this price range are very similar as far as internals. IP20 is the same as NEMA 1, so it WILL need to be protected from dust.

As for the speed control on the front, the easiest and best thing to do is to wire remote mounted controls with a stop/start/reverse and speed pot. That way you don't have to access the VFD and it can stay clean. No need to worry about the buttons. Constantly opening the box to get to the speed pot or even mounting it in the open will be a problem when it comes to dust. A simple pot at radioshack and some wire is all you need, and there should be ports to wire it into the VFD.

--nathan
 
silver_pilate said:
I've no experience with that particular VFD, but many VFD's in this price range are very similar as far as internals. IP20 is the same as NEMA 1, so it WILL need to be protected from dust.

As for the speed control on the front, the easiest and best thing to do is to wire remote mounted controls with a stop/start/reverse and speed pot. That way you don't have to access the VFD and it can stay clean. No need to worry about the buttons. Constantly opening the box to get to the speed pot or even mounting it in the open will be a problem when it comes to dust. A simple pot at radioshack and some wire is all you need, and there should be ports to wire it into the VFD.

--nathan
Click to expand...

Wow, it seems these days I am learning new stuff every hour. Sounds like just the thing I was looking to do. I will have to keep that in mind when I actually start hooking things up. I had seen your pictures of the remote buttons but didn't realize it was an easy hookup.
 
See if you can find an electronic copy of the owner's manual. Then you can look through it and check out the basic wiring setup. Bookmark this thread, and maybe the following pictures can help you when you get around to setting it up. Here's some pics of how I did mine:

The wiring diagram for the TECO FM50:

VFD2.jpg



The basic wiring to and from the VFD:

IMG_0552copy.jpg



And the control box:

IMG_0546.jpg


You should be able to follow how I did everything with the diagram and the labels on the pics, and you can see how I wired the switch and pot by matching up the colors.

--nathan
 
This has been really helpful, guys. A few lingering questions:

1.) Approximately how much power would I lose off of 1.5 HP and 2 HP motors during the 3-phase conversion?
2.) Is 3500 rpm or 1750 rpm preferable? Or doesn't it matter?

I really appreciate the info...

Josh
 
I can't tell you exactly how much power loss there is. Maybe someone else can answer that one. However, I can tell you that with my KMG's 2hp motor run off my 2hp VFD, I haven't stalled it yet. I'd say go for 2hp minimum. More power is always a plus, but you have to weigh it against more expense. 2hp should be sufficient for most people even with the loss through the VFD. I flat grind almost exclusively which puts a great deal of load on a motor, and even when grinding on a big bowie, the 2hp KMG has never had trouble.

As for rpm range, if you're setting up a grinder similar to the KMG with a pulley and belt drive, you can go for either speed range as you match the sheaves on the motor and drive shaft to get the rpm you want through the drive shaft to the drive wheel. If you're going for direct drive, it depends on your drive wheel size. For a grinder running a 4" drive wheel, you definitely want 3600 rpm motor. Even with a 6" drive wheel, a 3600 rpm motor will probably be pretty good, though fast at the upper end.

--nathan
 
I have been looking into a 2 or 3 hp motor and vfd and youll be looking at 500 bucks min. a 2 hp vfd is 200 bucks and a 3hp vfd 250 buck now the motors can run from 2 to 4 hundred depends on manufacturer and hp Im looking for a 2 hp so if you get a great deal send me a private email.. Just remember you get what you pay for. kellyw
 
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