Recommendation? VFD Help!

Mitchell Knives

Mitchell Knives

Knifemaker
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Knifemaker / Craftsman / Service Provider
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I have an AMK Knifemaking disk grinder that has about 2 hours of use on it. It seemed to work fine up until recently. I was using it to sharpen a blade and it simply lost power.

I can't recall if it tripped a breaker or not, but it hasn't worked since. When I plug it in and turn on the VFD (Model KMBA-24D), the disk moves maybe .25", then immediately stops.

I removed the VFD cover and everything seems to be in place. However, the "Overload" LED flashes constantly.

I've done some Googling, but can't seem to figure out what the issue might be.

Any ideas?
 

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Are you plugged into a GFCI circuit or power strip by chance? Are you using an extension cord? What are the specs of the circuit and wiring that you’re powering the VFD with?
 
Drew Riley said:
Are you plugged into a GFCI circuit or power strip by chance? Are you using an extension cord? What are the specs of the circuit and wiring that you’re powering the VFD with?
Click to expand...

I'm not using a GFCI or a power strip, although I was using an extension cord when it stopped working. I had used an extension cord previously, but am just using the cord attached to the motor now.

The circuit is standard 120V with the wiring that came with the unit when I purchased it.

The overload LED is flashing red slowly, which seems to indicate a short circuit per the manual.

I have 3 other VFDs and have never seen this happen. Very strange. Hope the VFD isn't fried!
 
Try it without the extension cord and see if it trips. I’d also pull the motor cover and make sure all of your connections are tight. Same with the VFD.

Do you have a multimeter? Are you getting 110-120vac at your outlet?
 
Drew Riley said:
Try it without the extension cord and see if it trips. I’d also pull the motor cover and make sure all of your connections are tight. Same with the VFD.

Do you have a multimeter? Are you getting 110-120vac at your outlet?
Click to expand...

Same result with or without the extension cord.

I checked all the connection and everything looks good. There is nothing I can see that would cause a short circuit. It seems unlikely that it would be the motor.

I'm getting 121V at the outlet.
 
I think I may have isolated the issue.

I connected the motor another VFD and it works, so it's not the motor.

Something apparently killed the original VFD.

Power surge maybe? IDK.
 
Yes, it still flashes red with only the power connected.

I even removed the jumper and wired it for 220v to make sure it wasn't just an issue with the 110v circuit. Same result.

Seems like I'll need to order a VFD, but I'm not sure. I can't really see how it could be anything else.
 
Last edited:
If all of your jumpers and connections look right, I'd give AMK a call. If if let the magic smoke out after only 2 hours, it could be a bad VFD from the get go. I'd think they should warranty the VFD. Alternatively, you might give KB Electronics a call and talk to one of their service techs. They might have a little better insight on that particular model and what might cause the OL error you're seeing.
 
Drew Riley said:
If all of your jumpers and connections look right, I'd give AMK a call. If if let the magic smoke out after only 2 hours, it could be a bad VFD from the get go. I'd think they should warranty the VFD. Alternatively, you might give KB Electronics a call and talk to one of their service techs. They might have a little better insight on that particular model and what might cause the OL error you're seeing.
Click to expand...

I called AMK and there is no warranty because even though I just started using it recently, I purchased it probably 2 years ago.

I may call KB, but I have a feeling they will just tell me to send it in.

I went ahead and ordered a replacement VFD. If I can get the original working again, I'll turn it into a buffer or something.
 
Mitchell Knives said:
I called AMK and there is no warranty because even though I just started using it recently, I purchased it probably 2 years ago.

I may call KB, but I have a feeling they will just tell me to send it in.

I went ahead and ordered a replacement VFD. If I can get the original working again, I'll turn it into a buffer or something.
Click to expand...

Did you recharge the capacitors ?
Plug it in for a day or two before trying to use it.
That stuff is in the manual too.
 
Two hours of use sounds like a heat thing....

Are your conductors sized accordingly? How long of an extension cord?

If it wasn't wired correctly, it probably wouldn't of even turned on. :/
 
Just an idea for you to consider, but you can run multiple equipment on one VFD by installing a socket on the VFD output. Plug the needed machine in when you want o use it.
A switch and two or three sockets can also be used to make changing machines faster. Use three pole switches rated at 25% more that the highest draw tool. 10 amp switches are usually more than enough.
 
Crag the Brewer said:
Two hours of use sounds like a heat thing....

Are your conductors sized accordingly? How long of an extension cord?

If it wasn't wired correctly, it probably wouldn't of even turned on. :/
Click to expand...

I believe it came with 16 gauge wire, which should be OK for 110v. I get the same results even without an extension cord.

The weird thing is that it worked just fine for 2 hours or so.
 
Stacy E. Apelt - Bladesmith said:
Just an idea for you to consider, but you can run multiple equipment on one VFD by installing a socket on the VFD output. Plug the needed machine in when you want o use it.
A switch and two or three sockets can also be used to make changing machines faster. Use three pole switches rated at 25% more that the highest draw tool. 10 amp switches are usually more than enough.
Click to expand...

That's a great idea and I may do just that until the replacement VFD arrives.
 
The KMBA is not a Nema4 enclosure. Could be you got 2 hours worth of metal dust in there and fried the VFD. Especially if it was sitting around in the shop for a couple years.
 
J. Hoffman said:
The KMBA is not a Nema4 enclosure. Could be you got 2 hours worth of metal dust in there and fried the VFD. Especially if it was sitting around in the shop for a couple years.
Click to expand...

Possibly. Who knows.
 
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