Q: Help debug or replace my RF45 clone motor

crcarlson

crcarlson

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Hi Guys,

I am looking for some advice debugging or replacing the motor for my RF45 clone milling machine.

The motor on this mill has started stalling and popping my 20A, 110AV breaker upon startup. I have already replaced the start and run capacitor with no change in behavior. I have taken the motor apart and the start circuit clutch looks fine and nothing looks obviously shorted internally. The motor ran fine for about 40 hours of light use, but now stalls and blows the breaker 90% of the time. With the motor power circuit disconnected the magnetic switch circuit does not overheat or pop the breaker.

The electrical circuit for motor power shows melted insulation and very discolored clear insulation which makes me think the current is much higher than expected.

IMG_2393.JPG


I am out of ideas for things to test and I would like to get running again soon to finish a few projects. I am open to more testing suggestions or suggestions for where to get a replacement motor.

I would like to stick with 110AC so I can using my existing shop power. I am open to the idea of using a 3 phase motor with a VFD if it is not cost prohibitive.

These are the critical motor dimensions in mm (AFIK)

IMG_2398.jpgIMG_2399.JPG

And this is the motor plate
IMG_2396.jpg

Any comments / suggestions appreciated.

IMG_2393.JPG IMG_2398.jpg IMG_2399.JPG IMG_2396.jpg
 
That motor is going to be much happery on 220. A 20A breaker is to small for that motor on 120. How old is it.
 
Have you checked with a multimeter? I would be checking the current running to the motor since those wires don't melt themselves. Does the motor spin freely?. What about the mill spindle? If you have a bearing on it's way out that is seizing then you may be stalling the motor causing the the start current to be much higher than usual.

I believe that you may be barking up the wrong tree and the problem could be more mechanical than electrical.

Paul.
 
That motor is going to be much happery on 220. A 20A breaker is to small for that motor on 120. How old is it.
Click to expand...

I have had the mill about 3 years, but it has had light use. I would guess around 40 hours. The strange thing is that it has worked fine up until about a few weeks ago. I did not change any of the wiring or load on the circuit.

Have you checked with a multimeter? I would be checking the current running to the motor since those wires don't melt themselves. Does the motor spin freely?. What about the mill spindle? If you have a bearing on it's way out that is seizing then you may be stalling the motor causing the the start current to be much higher than usual.

I believe that you may be barking up the wrong tree and the problem could be more mechanical than electrical.
Click to expand...

The spindle spins freely. I was hoping for an obvious mechanical solution. I tried to start the mill in each of the different gear options and I can spin the spindle (with some effort) with my bare hand.

I have powered up the system with the motor wires open and the switch, and other accessories all work fine. No current overload and no heating. Things only get hot when the motor is in the circuit.

I encountered the very same problem with my HF Mill Drill. Although its rated "19" amps it too would pop a 20 Amp breaker. The HF didn't have the 220 Volt option. My local Home Depot had a fairly inexpensive solution. Ask for 10 ga wire, a 30 Amp breaker, and a 30 Amp outlet and Plug. They are very commonly used on small Travel Trailers.
Click to expand...

The breaker does not pop immediately. The motor kind of groans for a good second before it goes. It used to just start right up with a flip of the switch. It is funny to me that it just started failing recently.

The only other symptom of note is that it continued to run fine in reverse for a while, but would always stall forward. I replaced the magnetic switch with no change in behavior. I have tried turning the spindle by hand to see if it would start depending on the position of the rotor, but I did not notice any correlation there.
 
You might want to contact Matt at Precision Matthews (http://www.machinetoolonline.com/PMMillingMachines.html) . He usually has 1-2 of those motor in stock and in general, knows a lot about that style machine.

That's a strange problem that I've never heard of before...


Ray

- - - Updated - - -

BTW: Checking the resistance of the windings (start, run and field), will tell you a lot provided you know the specs. It's possible Matt knows what the resistances should be.


Ray
 
I had the same issue with my mill. The motor would start very slow and with a different sound. After about 3 seconds it would run fine. About half the time it would trip the breaker. While checking the capacitor I noticed the centrifugal start switch looked like it MAY HAVE had lost it's original position on the armature shaft. I cleaned the contacts and returned it to what appeared to be the original position. I think it may have just been slow to release as works fine now. I do know from previous experience that a shorted capacitor or a stuck switch can fry your start winding thus making the motor dumpster filler. Those pesky dirt dobbers built a rock solid nest in a friends air compressor motor around the switch so it wouldn't release and the motor fried on start up.

EDIT: I actually took 2 semesters of electrical engineering in college but it was a loooong time ago and I have drank lots of beer since then, thus killing those brain cells. I was incorrect in calling it an armature. It is a rotor.
 
I would buy or borrow an Amprobe type current meter , clamp on amp meter, and measure the current during startup. Based on what you've already tried, I would move to a different breaker in your panel or replace it. The internal contacts can get pitted and the contact resistance goes up when heated. Heat is what actually trips the breaker if you have a typical breaker panel. An alternate test is to measure the voltage at the breaker when someone else turns on the machine. If it goes low like below 50 volts until it trips, I'd replace it. I need to say if you are not comfortable inside your power panel, find someone who is. It can be lethal for mistakes made.
 
I just thought of another test. Safe and low tech. Plug in some resistive heaters into the same circuit as the mill. Like a toaster, toaster oven and coffee pot with water and add up about 2400 watts of load and see what your breaker does. Device nameplates are not very accurate but they should represent the high value. Feel the face of breaker (black plastic part next to the toggle reset switch) . It will be warm before it trips. Your 20 amp breaker should not trip on 20 amps but take about 2-4 minutes on 21 amps. Using resistive load will avoid any startup inrush current.
 
Guys, I don't think it's the breaker tripping prematurely. In the picture, you can see some smokey connectors -and there's one wire with what looks like a melt-hole in the insulation.

I'm curious about the outcome of this...


Ray
 
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