Fireball from motor

Matt Rochester

Matt Rochester

Joined
Nov 28, 2014
Messages
1,864
I'm not sure if I posted this in the right spot so move it if I didn't. Thanks. Well I was doing a little grinding when I had a flash from the rear of my motor. I pulled the back cover off the motor and found a burnt spot. I don't know a too much about AC wiring but I was wondering if anyone could help me out. The burnt spot is between the hot wire and what looks like a switch or contact. I'm not sure what caused it or how to fix it. The motor still works but I need to fix it before I burn it up. I don't see any bare or chaffed wires.

 
Can't help you with the motor burnout, but did notice it runs some pretty high RPM's. Much higher than mine, anyway. What current are you running it on?
 
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I can't understand that circuit from the pics but it looks like that burnt spot is something that shorted those two terminals, not a component that fried. I would clean it out and see if it works.
 
I was thinking that maybe it was dust build up that could have shorted it. The bottom pic is the cover just rolled down, so it's upside down to the 2nd pic if that makes since. The white wire in the 2nd pic is connected to the blue wire in the 3rd pic. It still works. How often should I clean the motor out? Shop air?

zhyla said:
I can't understand that circuit from the pics but it looks like that burnt spot is something that shorted those two terminals, not a component that fried. I would clean it out and see if it works.
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Your motor is an open frame motor and is not designed for use in a dirty environment. In fact, the label says that it is for use on a Craftsman 10" saw, which I presume is a wood saw.

You should use a sealed enclosed frame motor for metal grinding equipment.

It is very likely that metal dust built up to where electricity arced between those two terminals. You may be able to clean up the terminals and get it working again, but you should start shopping for a fan-cooled enclosed frame motor for the future.

Mike L.
 
I am not a single phase motor expert by any means, but I do think Mike hit on the problem. Metal dust built up around those terminals (centrifugal switch for starting winding) and shorted causing the fire ball. Most likely, just clean the area good, blow motor out with air really good, from both sides. Most likely be good to go again. Put a filter across the inlet side of open frame to prevent so much metal dust from building up again. Is this a true cure? Naw, not by any means, but it will make the motor last a good bit longer. Also, make a point to blow metal dust out from time to time. You might be surprised how long that open frame motor will last. I used open frame motor for over a yr on my 2X72 grinder and never had a problem. Did blow dust out from time to time. Location of motor to grinding belts will also enter into how much dust is collected by motor. How much grinder is used each day.

edit: is this a capacitor start motor? I see the motor is a 56C frame, got it mounted for direct drive? If so, that puts it collecting more dust than a pulley setup with motor well off to side.

Good luck.

Ken H>
 
It is a capacitor start motor and is direct drive. I am eventually going to buy or build a variable setup. I cleaned it up and just used it finishing up another knife. It worked like normal. We will see what happens from here.

Ken H> said:
I am not a single phase motor expert by any means, but I do think Mike hit on the problem. Metal dust built up around those terminals (centrifugal switch for starting winding) and shorted causing the fire ball. Most likely, just clean the area good, blow motor out with air really good, from both sides. Most likely be good to go again. Put a filter across the inlet side of open frame to prevent so much metal dust from building up again. Is this a true cure? Naw, not by any means, but it will make the motor last a good bit longer. Also, make a point to blow metal dust out from time to time. You might be surprised how long that open frame motor will last. I used open frame motor for over a yr on my 2X72 grinder and never had a problem. Did blow dust out from time to time. Location of motor to grinding belts will also enter into how much dust is collected by motor. How much grinder is used each day.

edit: is this a capacitor start motor? I see the motor is a 56C frame, got it mounted for direct drive? If so, that puts it collecting more dust than a pulley setup with motor well off to side.

Good luck.

Ken H>
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Yup, looks like you let the magic smoke out. metal dust will do it, had a fire in a wall socket in my shop from it, it is dangerous
 
Yea, but with a little work he was able to put the smoke back and and is now back in business! You will be VERY happy with a VFD/3 ph motor setup. I used a 2 hp IronHorse 3 ph TEFC motor ($127 shipped) and a Chinese VFD ($117 shipped). Put filters over air inlets on VFD to prevent metal dust from getting inside. So far, it's working like a champ!

BTW, what size drive pulley do you have? If it's about 4", then your SFPM belt speed is very close to motor RPM in a direct drive setup. Smaller would be better with that 3450 RPM motor, but you're going to be IMPRESSED when you get a VFD so you can have slower speeds.

Ken H>
 
That is an open motor that is not conducive to metal grinding environments. I used one when I first started also and just had to keep it blown out or it would short out. When you buy a new one make sure it is TEFC (totally enclosed fan cooled) It will last a lot longer with limited maintenance. Then if you go 3 phase and put in a VFD then you will have the cat's meow.
 
It's a 4 3/4 drive pulley. It is running a little fast! I need to find a 3 inch or so until I build another grinder.

Ken H> said:
Yea, but with a little work he was able to put the smoke back and and is now back in business! You will be VERY happy with a VFD/3 ph motor setup. I used a 2 hp IronHorse 3 ph TEFC motor ($127 shipped) and a Chinese VFD ($117 shipped). Put filters over air inlets on VFD to prevent metal dust from getting inside. So far, it's working like a champ!

BTW, what size drive pulley do you have? If it's about 4", then your SFPM belt speed is very close to motor RPM in a direct drive setup. Smaller would be better with that 3450 RPM motor, but you're going to be IMPRESSED when you get a VFD so you can have slower speeds.

Ken H>
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4-3/4" drive pulley with a 3450 RPM motor? You are humming that belt at almost 4300 SFPM - good for profiling, but I don't have the skill to do any bevel work at that speed. Even with a 3" drive pulley you'll still have 2700 SFPM. That's about what I use for 36/80 grit belts for starting bevels on heavy blades, but for a thin blade, I'm moving to 1200 SFPM with 300 to 400 grit belts.

As Richards said, VFD is the "cat's meow". With fine grit belts (400 to 600) I find myself using 800 SFPM speeds more than I ever expected to.

Ken H>
 
Ken H> said:
4-3/4" drive pulley with a 3450 RPM motor? You are humming that belt at almost 4300 SFPM - good for profiling, but I don't have the skill to do any bevel work at that speed. Even with a 3" drive pulley you'll still have 2700 SFPM. That's about what I use for 36/80 grit belts for starting bevels on heavy blades, but for a thin blade, I'm moving to 1200 SFPM with 300 to 400 grit belts.

As Richards said, VFD is the "cat's meow". With fine grit belts (400 to 600) I find myself using 800 SFPM speeds more than I ever expected to.

Ken H>
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Well, when 4300 sfpm is all you know then it is what it is!!! I just thought that's how everybody did it without a vfd! Anyway I am going to look into a new motor and vfd. Come to think of it shaping the handle at those speeds is tough. Just gotta be easy. I may try the setup that you have if I can get it around 300 or so. That may explain why I have so many burn marks on my fingertips.
 
Rookie25 said:
Well, when 4300 sfpm is all you know then it is what it is!!! I just thought that's how everybody did it without a vfd! Anyway I am going to look into a new motor and vfd. Come to think of it shaping the handle at those speeds is tough. Just gotta be easy. I may try the setup that you have if I can get it around 300 or so. That may explain why I have so many burn marks on my fingertips.
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Lol., You are lucky you even have fingertips:D
 
Let's see, "IF" you're willing to work with an open frame VFD and protect it will installation in a NEMA 4 type box, OR, take the cheap way (my way?) and put filters over the inlet, you can do it for less than $300 for VFD and 2 hp TEFC motor. I think I gave links above, if they are broken, drop me an email or PM and I'll fix links.

Ken >
 
For some reason I can't figure out the whole PM thing so can you post a link to the motor and vfd? Thanks bud.
Ken H> said:
Let's see, "IF" you're willing to work with an open frame VFD and protect it will installation in a NEMA 4 type box, OR, take the cheap way (my way?) and put filters over the inlet, you can do it for less than $300 for VFD and 2 hp TEFC motor. I think I gave links above, if they are broken, drop me an email or PM and I'll fix links.

Ken >
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For PM or email, you should be able to click on my name and there would be a dropdown, click on "See profile" and there should be a place to PM or email.

Here's a link to a thread where I posted some photos of grinder and talk about it some. On post #3 are a couple of links - they are still valid.

http://www.bladeforums.com/forums/showthread.php/1234634-New-Grinder-for-me

I just checked the ebay link - they have a typo there listing VFD at $1,128! I'll bet a msg to them would get the correct price - I think they're $128 now shipped. That's for a 3 hp, I saw a 2hp drive for $116 shipped.

Any questions I can help with, give me a holler.

Ken H>
 
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