DC motor help

S

sparrow75

Joined
Mar 22, 2009
Messages
328
So I'm grinding some micarta scales today on my homemade treadmill motor grinder, around half the speed. And all of a sudden, It started going full speed, sparking from the rear end of the motor.. VFD controls are not working, I can't slow it down, I can't stop it on the stop button. There is some sort of emergency switch, and that worked.

Now, as soon as I click that main switch, motor starts full speed, sparkin' and all

I tried running VFD on it's own, motor detached.. it's behaving as it should, display working all controls responding. But when I attach motor, display not working and motor going full speed. I should mention, VFD is from the treadmill too, so it should (and did before this) start from the lowest speed and then i would adjust desired speed

Anyone of you guys have the slightest idea what is going on, I am f###ed up.. grinder gone crazy on me :confused: :(
 
I'm afraid that's not an option right now.. where i live, treadmills are not so common nor there are bunch of used ones for cheap..
I just want to try to find out what should I ( not me, but some sort of qualified person for that ) have to look into first.. motor or VFD?
judging by the symptoms, what could it be?
please, this is very important for me right now
 
Thinking here..................

Definitely a short and my guess is that it's from metallic grinder dust. I'm assuming this treadmill motor isn't sealed well (mine aren't) and it's vulnerable to airborne gunk. Hopefully it's not the windings that are shorting out.

I'd blow it out with high pressure air first and pray.

If that doesn't work I'd take it apart, carefully, the spring assembly tensioning the carbon brushes is touchy (you don't want to have to find brush, or spring, replacements either I bet) and examine it looking for blackened spots. If you find some clean those up as best you can (maybe someone else can tell you exactly how to do that I've had access to technical help when I had DC motor issues) and pray some more.

Show us pictures of what you're doing and you might get some pointers.

Also post the measurements of your motor and maybe some pictures of the wiring. Someone here might have a motor lying around gathering dust.

It would be a shame for that dandy grinder of yours to be laid up for want of a motor.

Good luck

Corey "synthesist" Gimbel
 
Thank you Corey
Sparks are coming of the brushes as far as I was able to see.. I will try to find someone more specialized in these sort of things and see what he can tell me. If nothing, I will take it apart and clean it well. I do have a filter on the back of the motor, but some miniscule particles might gone through and messing with the brushes? But still, (to me) that doesn't explain why the motor is not responding at all to VFD.. I said "to me" as in I am a dum dum when it comes to these sort of things
Can micarta dust do this? I was grinding micarta for the first time on this grinder when this happened
Again, thank you very much for taking interest in my problem
Vladimir
 
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Just for fun I looked into what the shipping costs for a treadmill motor the size of mine would be to Serbia. It was interesting.



Not as bad as I expected actually. So if the motor was cheap enough this might be a doable option. Find the right size motor on eBay and send it over. Probably take a couple of (anxious) weeks I'm afraid, but possible.
 
That could be an option.. I will try to salvage this one first, 'cause I lost my job recently and must try to be an even bigger cheapskate than before :D
thanks man :thumbup:
 
Because the motor is an open frame type, even if you get it to run right again the problem will soon return. Also, your treadmill motor was not made to take the load of running a grinder. Treadmill powered grinder setups look like a good idea on YouTube, but don't last long.

Things that may help with this motor:
Unplug the power and vacuum it well. Then blow out everything with compressed air. Don't forget the controller board and switches.
Inspect all wires and connections. You may have something loose or shorted.
Remove and clean the brushes and armature ..... making sure to re-install them properly. ( don't do this if you are not sure how it is done.)
If you get it running right, rig up some sort of system to suck away the grit in grinding.
Build a shield and filter to protect the motor. This may be as simple as building a box with a furnace filter in the end and a cooling fan inside.

Things to do to permanently solve the problem -
Look for a closed frame AC or DC motor. They will be labeled TEFC ( totally enclosed fan cooled). A single speed motor with a step pulley will allow multiple speeds and last a long time. If you can get a sealed AC or DC motor and a proper electronic speed controller, that would be great. With the right motor type, you can expect to have a long life out of the setup.
 
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I ran my treadmill motor for about 18 months and then it did the same thing....just a matter of time. I bought a 1.5hp with a three speed pulley and am pretty happy with it.
 
I was aware of all of the negatives with treadmill motors, but had to use it.. didn't had anything else. I tried to avoid the dust problem by making a filter out of kitchen aspirator fabric



And it was working fine.. but when started grinding micarta (seems to have much finer dust then metal grit) problem occurred. I really don't know if that was coincidence..? If I get this thing to work again, I will try two layers of aspirator fabric, maybe will help some more
Let me say this, I'm not trying to diminish anyone's advices, and am very grateful for them.. matter of fact, I'm in the process of finding closed frame motor. I thought that the damn filter will be enough :grumpy:
Anyways, I will try to fix this and maybe post results
Thank you :thumbup:
 
The problem is that the filter blocks some of the cooling air flow and the motor fails quicker. Fine dust from grinding will just clog it up and make it fail faster.

The short and long of it is that a tread mill motor isn't made to be on a grinder...and won't last long if used.
 
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