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Douglas W.

KMG Motor and VFD selections and requirements.

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I've read many different threads from different forums but that only confused me more.

 

I bought a KMG a month ago and am ready to by a motor and VFD.

 

I've been to the local rebuilder once and goofed on pulley size and forgot to mention I prefer a dial for speed control.

 

I'll probably stop by again this week and want to narrow down what I'm looking for.

 

Maybe you can see if I've overlooked a requirement or something thats "just nice to have" I'm aiming for 3 horsepower.

 

I'll start out with a list of what I "think" I know.

 

Before you can pick the motor you want you need to figure out what electricity you have.

 

I have 220 single phase in the garage besides the regular 110.

 

If you want variable speed, without having to switch between pulley selections you need a vfd.

 

You need a 3 phase motor to work with the VFD.

 

So for most people who don't have 3 phase electric you need a 1 phase input 3 phase output vfd.

 

Motor must be a TEFC (Totally enclosed fan cooled motor) or it will be short lived due to grinding contamination.

 

 

When selecting a VFD if budget allows its better to go one hp or more rating then your using because some horsepower is lost in the inversion.

 

Ending speed at belt driven pulley should be around 3450 rpms.

(I have no idea why that just seems to be the consensus of most threads found)

 

So you can either find a motor with 3450 rpms or use a 1725 rpm motor with a larger pulley on the motor side, smaller pulley on the grinder side.

 

You will need to consider how it will be mounted (needs a baseplate/foot/pedestal.

 

You will need a shaft size compatible with the pulleys you select (probably around 5/8)

 

For a 3hp motor you will probably need around a 30 amp cicuit to run it on.

 

Most motors will also need a wiring and plug kit.

 

The VFD will need a nema4 or better enclosure, or a cheaper VFD will need an enclosure built for it or it to can be destroyed by grinding contamination.

 

Most will want a reversing switch on the VFD.

 

When I go to buy mine I will be looking preferably for one with a dial for speed (so far the guy at the local electric motor rebuilder has shown me digital ones with just up and down arrows.) I just think the nob seems like it will be more convenient.

 

 

So does this sum up all the requirements that will need to be met?

 

Does the info I have seem accurate?

 

Feel free to correct my on anything I like to make mistakes and fix them before I spend money instead of after :lol:

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Make sure you get a motor that is rater 220/440 as 440 3 phaze will not run off of a standard vfd . you also need to check that the motor is wired to 220.

most vfd's will show you the amperage that you are using , the last time I installed one I found that my 2 horse motor was drawing way less amps than the VFD was rated for (even when hogged down) I could have gotten away with a much cheaper unit . However its hard to find this out till you have the machine up and running. The vector control units that give constant torque through the range are good .

Also 1725 motors will have better cooling characteristics for low speed applications and most vfds will run them at 2 x speed ( with torque loss at higher speed).

I have run 3 hp and 2hp units from a 13 amp plugged supply on a 30 amp circuit with no problems (we run 240 50hz though) the vfd helps to minimise the current surge needed to start a motor by ramping up the speed slowly.....

speed control on a grinder changes your life!!

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I will try to answer this by inserting my comments in the postl. My comments will be in blue.

I've read many different threads from different forums but that only confused me more.

 

I bought a KMG a month ago and am ready to by a motor and VFD.

You might want to consider removing the pillow blocks and their supports and mount the motor there to make the grinder a direct drive. This helps with a smoother running machine with less loss due to friction and transmission. The KMG comes with a 3/4" bore on the drive wheel and 56C motors have a 5/8" shaft. There are parts made to make a 5/8" compatable with 3/4" (check Grainger or other suppliers.

I've been to the local rebuilder once and goofed on pulley size and forgot to mention I prefer a dial for speed control.

 

I'll probably stop by again this week and want to narrow down what I'm looking for.

 

I sell the KBAC 27D which is the same VFD that KMG uses. I sell these for $448.00 with free shipping CONUS. It is good up to 2 hp. I have a 1.5 hp motor on my grinder and have challanged knifemakers to slow it down. I have had to put my hand on top of the grinder to keep them from turning it over. The way they were trying to bog it down is not consistant with the way they grind blades.

I have not been able to locate a NEMA 4x VFD that will operate on single phase in for a 3 hp motor.

 

Maybe you can see if I've overlooked a requirement or something thats "just nice to have" I'm aiming for 3 horsepower.

 

I'll start out with a list of what I "think" I know.

 

Before you can pick the motor you want you need to figure out what electricity you have.

 

I have 220 single phase in the garage besides the regular 110.

Good

 

If you want variable speed, without having to switch between pulley selections you need a vfd.

Correct or go with DC controler and motor (not as good a choice).

 

You need a 3 phase motor to work with the VFD.

True

 

So for most people who don't have 3 phase electric you need a 1 phase input 3 phase output vfd.

Correct

 

Motor must be a TEFC (Totally enclosed fan cooled motor) or it will be short lived due to grinding contamination.

Correct

 

When selecting a VFD if budget allows its better to go one hp or more rating then your using because some horsepower is lost in the inversion.

Not correct. The KBAC 27D is rated up to two hp motors. The jumper can be set for constant torque and therefore there is no horsepower loss. Also consider that motors have a Service Factor (SF). My motors have a 1.5 SF. To determine the available horsepower add 15 percent. So a 1.5 hp motor is actually closer to 1.72 hp.

 

Ending speed at belt driven pulley should be around 3450 rpms.

(I have no idea why that just seems to be the consensus of most threads found)

3600 rpm is a good speed for working but what you really want to know is the fpm (feet per minute) of the belt.

 

So you can either find a motor with 3450 rpms or use a 1725 rpm motor with a larger pulley on the motor side, smaller pulley on the grinder side.

 

You will need to consider how it will be mounted (needs a baseplate/foot/pedestal.

 

You will need a shaft size compatible with the pulleys you select (probably around 5/8)

 

For a 3hp motor you will probably need around a 30 amp cicuit to run it on.

 

Most motors will also need a wiring and plug kit.

Correct. It is easy enough to fabricate a power cord from the wall to the VFD. Between the VFD and motor you will need stranded 4 conductor cable. This is not something you can just go to the local Home Depot or Lowes and get and probably not your local hardware store. You also need cable glands for the wire penetrations for a dust proof connection. (It doesn't help to get a NEMA 4X enclosure then let the dust in at the wire penetrations). I sell a wiring kit that includes 8' power cable, 2' 4 conductor cable, 3 cable glands and wire nuts. For 115v it is $45.00 and for 230v it is $60.00. Both include free shipping, CONUS.

 

The VFD will need a nema4 or better enclosure, or a cheaper VFD will need an enclosure built for it or it to can be destroyed by grinding contamination.

Correct

 

Most will want a reversing switch on the VFD.

Probabably not but it can be added for $25.00. I tried having reversing on my first grinder and found that I had problems with tracking. You might want the reversing switch if you are going to run a disk grinder using the one VFD to run both machines.

 

When I go to buy mine I will be looking preferably for one with a dial for speed (so far the guy at the local electric motor rebuilder has shown me digital ones with just up and down arrows.) I just think the nob seems like it will be more convenient.

I think that is good. I also like the VFDs that are set up with jumpers rather than programing. Much simpler and once set it will not lose it programing due to power outages etc.

 

So does this sum up all the requirements that will need to be met?

 

Does the info I have seem accurate?

 

Feel free to correct my on anything I like to make mistakes and fix them before I spend money instead of after laugh.gif

 

I hope that this helps. It appears that you have done lots of work on this. Just remember, if you ask 10 knifemakers a question you will probably get 12 answers.

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Hey guys, I'm in the same boat. I'm looking to get a VFD with an input of 220V 30amp single phase, and output to my 4HP three phase motor.

I will email you later wayne to get your opinion on a VFD.

Thanks

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Andy, I'm not trying to keep from visiting but just to let you know, I don't have any information for a VFD for a motor bigger than 2 hp, unless you can use 3 phase, 3 phase out.

Sorry. I have looked but have not come up with anything yet. If anyone else knows of something let me know and I'll see if I can't add it to my list of products.

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You can not see the brand name and it is not listed.

It is in China.

It is programable not set with jumpers.

It is not in a NEMA 4X enclosure so add another hundred or so for an enclosure and don't forget the inconvenience of having to open the enclosure to make adjustments or to turn it on or off.

Seven day return policy, you pay return shipping. Shipping is $45.00, however, that may have some extra profit built in for the seller. That sure isn't much time to get it check it out, decide you can't use it and get it shipped back, and do you have to ship it back to China?

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