Tripping Breaker Solution?

[Rick Helmig]

Greetings,

I'm in a constant battle of resetting a tripped breaker if I dig just a slightly too hard on a cut. As a result, I find myself taking probably 5x longer to turn a piece than I should.

I use a meager Craftsman Model 351 Variable Speed lathe. The motor is 2HP, 90v, 12Amp, Single Phase.
And its running on it's own 20amp brand new Square D breaker with a 20amp GCFI using 12awg wire. Nothing else is connected to that line. Typically, it's the breaker that trips and occasionally it will be the GCFI.

I'm no electrician and my knowledge is pretty limited in that regards. But else might I try here? Would it be worthwhile to replace that GCFI with a standard "heavy duty" 20amp outlet? Or maybe there is a different type of breaker I should consider?

I appreciate any suggestions. Thanks!
Rick H.

 

[Chris Edwards]

If you lathe has a VFD to control the variable speed, yes you'll probably need to changes the breaker.

I just had to do this with mine. I had an electrician friend install a new sub panel on the opposite side of my garage. He took the feed, for the sub panel, from a 50A GFCI breaker in my main box, which was initially used for a hot tub by the prior house owner.

I could not run my old Oneway 1224 off this sub panel, whiteout tripping the 50A main breaker, but on one of my other garage circuits I had no issue.

With the main 50A GFCI breaker, swapped out for a normal one, I have no issue.

 

[Forrest Forschmiedt]

Although I haven't experienced this myself, I have seen many threads about lathes tripping GFCI outlets. It seems to be a common problem and seems to be mostly problematic with variable speed equipment.
Do a google search for "lathe trips GFCI" and find a ton of discussions.
Most folks probably just do away with the GFCI for the circuit or outlet that's causing problems. If it is a private residence most likely no one will ever know but you will be losing protection for other uses of that outlet/circuit. Also, if/when you go to sell, inspection may reveal the code violation.
It it's a commercial building best go with code compliant workarounds.
I find it interesting that it sometimes trips the breaker and sometimes trips the GFCI. Are you sure the breaker is not also GFCI? If it's a new breaker it may be a GFCI breaker already.
I have found when upgrading wiring in my house that there are varying qualities of GFCI outlets. Note that most 15a GFCI outlets are rated for 20a. Make sure it is indeed a 20a outlet. There are GFCI breakers available that may be more robust than GFCI outlets.
There are ways to get around the code requirement such as hard wiring the equipment to an approved disconnect instead of an outlet.

 

[Richard Coers]

90v is a DC motor and not single phase. Your controller is single phase. I assume the DC controller is not playing well with the GFCI.

 

[Dennis J Gooding]

Greetings,

The motor is 2HP, 90v, 12Amp,.......

I appreciate any suggestions. Thanks!
Rick H.

Looks like typical Craftsman specs. 90 volts at 12 amps and 100% efficiency would yield only 1.4 HP in the real world.

 

[Mike Johnson]

Use a standard breaker to power the lathe instead of the GFCI breaker, your problem should go away.

 

[Rick Helmig]

Thanks, All. Just to reiterate, it is a standard breaker. The outlet is the only gfci.

I think my next step is to replace that 20amp gfci with a regular 20amp outlet. Not sure if that will have any improvements on the breaker trips. We'll see...

 

[Roger Wiegand]

VFDs and GFIs do not play well together. Electrical "noise" from the VFD trips the GFI. Get rid of the GFI and you should have no problem. I fought this problem for years, the blower motor for my big trailer-mounted organ is VFD controlled, many fairgrounds and such are strict in requiring GFI, hence no power for me a lot of the time. I ultimately solved the problem by installing a big isolation transformer in the trailer to separate the VFD and GFI. In my shop I would certainly not go to that trouble and expense.

 

[Gary Beasley]

As stated in previous postings about the subject hospital grade gfis are way better at handling VFD noise. If you are in a workspace that needs gfi look for that option.

 

[Ken Burns]

There may be too much resistance in the circuit — wire too long or bad connection somewhere. Disconnect from breaker, short out one end and check resistance with ohmmeter on the other end. Calculate voltage drop and check in electrical tables for acceptable level. Or, as someone mentioned, your motor controller may be bad.

Ken

 

[Don Wattenhofer]

90v is a DC motor and not single phase. Your controller is single phase. I assume the DC controller is not playing well with the GFCI.

A DC motor controller is not a VFD (Variable Frequency Drives vary the speed by maintaining a frequency to voltage ratio on a 3 phase AC output connected to a 3 phase motor) the output of the DC controller is "direct current" meaning there is no frequency. Teh speed of a DC motor is controlled by varying the voltage to the motor. The GFCI may trip due to electrical noise feedback from the rectifier portion of the DC drive or the high speed switching that is used to vary the voltage output. Note he said that some times the GFCI tripped. The circuit breaker may be tripping due to sudden high overloads or continuous overloads. The amperage in the AC line feeding the drive could be monitored with a low cost clamp on ammeter and would be a good way to diagnose the problem.

 

[Rick Helmig]

UPDATE: so I swapped out the GFCI 20AMP Outlet for a fresh Leviton 20amp Outlet with no success. I loaded up a piece of heavy beechwood to test it out. I could take light scraping cuts but ANY push cut for more than 2-3 seconds and the breaker trips.
I should add that new outlet is only 12 inches from the panel and I plug the lathe directly into that (no extension cords).

I'm afraid adding sub-panels or diagnosing frequency drives is beyond skill sets but I will start researching that. I'm trying to avoid the expense of an electrician but I may have to bite that bullet. In the meantime, is there any other low hanging fruit solutions I might want to consider? In another post, I saw mention about breakers that are made specific for electric motor type applications. But so far I haven't found anything like that.

And again, thanks for the feedback and suggestions. I'm still learning here and this has been a valuable resource.

Cheers!
Rick

 

[Don Wattenhofer]

Rick, The problem appears to be in your drive or the motor so rather then contacting an electrician, who may or may not know anything about DC motors or drives, contact an Electric motor repair company. Google electric motor repair and you should find several near you, the best bet for low cost would be something in a small town or farming community.

 

[Richard Coers]

You don't have a frequency drive, you have a DC controller. As Don said, take it to a motor shop.

 

[Mike Johnson]

You now have it narrowed down to the motor or the controller.
Using a multimeter you can take several measurements to determine if the motor is good or bad.
Odds are it is most likely the controller that has issues, or possibly a wiring issue.
A motor shop or electrician that works on DC drives and motors will know how to troubleshoot the controller.
There are several components that usually fail in a DC controller, which usually can be repaired if you can use a soldering gun.
There are several YouTube videos that cover DC controllers and troubleshooting, you will need to know the proper use of a multimeter to do this safely.

 

[Rick Helmig]

Thank you, All. Much appreciated!

Happy turning....
Rick

 

[Bill Boehme]

Before you begin the more difficult work, have you plugged the lathe into another outlet that is on a different non-GFCI circuit breaker? It's not too uncommon especially for an older breaker to become weak and trip at a much lower current if it has a history of tripping. Also, I presume that you have verified that the breaker in the panel that you have been using is NOT a GFCI. A GFCI will have a test button.

I have some doubts about there being a problem in the motor or controller because the controller usually has its own internal protection, either fuse or breaker. If not that, the driver semiconductor in the controller would become the de facto fuse well before the breaker in the service entrance panel trips.

 

[Rick Helmig]

Before you begin the more difficult work, have you plugged the lathe into another outlet that is on a different non-GFCI circuit breaker? It's not too uncommon especially for an older breaker to become weak and trip at a much lower current if it has a history of tripping. Also, I presume that you have verified that the breaker in the panel that you have been using is NOT a GFCI. A GFCI will have a test button.

I have some doubts about there being a problem in the motor or controller because the controller usually has its own internal protection, either fuse or breaker. If not that, the driver semiconductor in the controller would become the de facto fuse well before the breaker in the service entrance panel trips.

Yep, i've had it on several outlets and non-gfci breakers now. All had the same result. Given the current pandemic, I'm trying to self-educate myself a bit more about motors and controllers before I take any new costly steps.
Tks!!
Rick

 

[Richard Coers]

If we knew the brand of controller and brand of motor we might be able to help. Could be the motor has brushes. Did you check that? Lots of pictures would help.

 

[Rick Helmig]

If we knew the brand of controller and brand of motor we might be able to help. Could be the motor has brushes. Did you check that? Lots of pictures would help.

Thanks, Richard! I'll pull the cover and motor away this afternoon to get some pics to post. It's got brand new brushes and bearings. I just replaced those but the tripping problems were present before.

 

[Bill Boehme]

I'm not familiar with the Craftsman lathe, but something that is usually easy to check on a DC motor are the motor brushes. Getting into more complex troubleshooting, a loss of torque on a DC motor is often caused by open windings on the rotor. A good place to look first is at the commutator ring where you would see the ends of wires that should be connected to the commutator ring that are instead sticking up into the air like whiskers on a cat.

 

[Rick Helmig]

I'm not familiar with the Craftsman lathe, but something that is usually easy to check on a DC motor are the motor brushes. Getting into more complex troubleshooting, a loss of torque on a DC motor is often caused by open windings on the rotor. A good place to look first is at the commutator ring where you would see the ends of wires that should be connected to the commutator ring that are instead sticking up into the air like whiskers on a cat.

Thanks, Bill. I had taken some pics when I had replaced the bearings and carbon brushes. But I'm not seeing any 'whiskers'. See attached.









Something else I just noticed, the power cord on this model, which I assume is original, is 14 AWG. I'm wondering if it would be better suited with a 12 AWG???

I'll get some better full pics of the circuit board this evening.

Regards,
Rick

 

[Don Wattenhofer]

I'm not familiar with the Craftsman lathe, but something that is usually easy to check on a DC motor are the motor brushes. Getting into more complex troubleshooting, a loss of torque on a DC motor is often caused by open windings on the rotor. A good place to look first is at the commutator ring where you would see the ends of wires that should be connected to the commutator ring that are instead sticking up into the air like whiskers on a cat.

I was also thinking of shorted windings on the armature that would cause arching as the brush passes the commutator bar connected to that particular winding, which may be visable on the brush as burned away edges.

 

[Richard Coers]

All that grease is odd. What is that for? That commutator looks a little sketchy. Is that an arcing pattern behind the wear?

 

[Bill Boehme]

I'm in a constant battle of resetting a tripped breaker if I dig just a slightly too hard on a cut.

I don't know your experience level, but if you are a self taught beginner it could be that you are staling the motor on the lathe. The comment about "digging slightly too hard" make me think that tool technique might possibly be a factor. Also, as Dennis Gooding hinted at earlier don't believe any horsepower claims on Sears tools. At best, I would say that the motor could output ¾ HP and that would only occur at full speed and for a short period of time, At slower speeds the power would be proportionally reduced. If the controller uses speed estimating feedback it's possible that a stall (locked rotor condition) could result in the motor drawing enough current to trip the breaker.

 

[Don Wattenhofer]

All that grease is odd. What is that for? That commutator looks a little sketchy. Is that an arcing pattern behind the wear?

Good call Richard I went back and looked at the picture and I would guess more than 1 coil is shorted. Another good bet would be that the motor has a zerk fitting for greasing the bearing, which would account for "all that grease" as in one pump is enough why not be sure and give it a few more pumps. That may be the cause of the problem with the armature.
If it is the armature then the motor is toast, since I don't think there is anyone left that rewind an armature and if there was it would cost more than the motor is worth.

 

[Bill Boehme]

I was also thinking of shorted windings on the armature that would cause arching as the brush passes the commutator bar connected to that particular winding, which may be visable on the brush as burned away edges.

There doesn't appear to be any open windings as I suspected, but as you noticed it looks like there might be metal smearing between commutation segments which indeed could be a problem by reducing torque and increasing current. There is an abrasive tool for dressing the commutator. I believe that it can be found at MSC.

I agree with Richard about the huge amount of grease. That seems like way more grease than necessary. More isn't always better and this is probably one of those cases where just a dab of grease would be enough. I see two possible problems:

• The grease is restricting the flow of cooling air through the motor.
• The fluid drag at high RPM could be considerable.

Just a thought from personal experience ... these days motor repair shops are only interested in industrial jobs because the cost of repairing a consumer product motor is a deal breaker.

 

[Rick Helmig]

Good stuff, guys. Thank you! I'm guessing I'm probably the 3rd or 4th owner of this lathe. However, when I bought it a few months ago, it still looked new. And for the 150 bucks I spent for it, I'd say I got some excellent value and an new life long hobby out of it.

I have no idea where all the grease came from and too be honest, i'm not really sure what's required. The commutator does seems a little rough to the touch. I can hear and see what seems like a bit too much sparking on the brushes but again, i'm no expert at such things.

So tomorrow I plan to:
- Clean out most of that grease. Manually turning the spindle did always seems a bit more sluggish than expected.
- Do a bit of dressing of the commutator. Might a light sandpaper suffice?

Not sure if all this will fully address my tripping breakers issues but I hope it helps!!

Also attaching a pic of the board as requested.

Regards,
Rick

 

[Mike Johnson]

Over lubrication of motors is a common failure, too many people tend to add an extra "shot" of grease every time they add lubrication, over time you end up with a mess inside the motor affecting the mechanical and electrical functions of the equipment.

 

[Don Wattenhofer]

Good stuff, guys. Thank you! I'm guessing I'm probably the 3rd or 4th owner of this lathe. However, when I bought it a few months ago, it still looked new. And for the 150 bucks I spent for it, I'd say I got some excellent value and an new life long hobby out of it.

I have no idea where all the grease came from and too be honest, i'm not really sure what's required. The commutator does seems a little rough to the touch. I can hear and see what seems like a bit too much sparking on the brushes but again, i'm no expert at such things.

So tomorrow I plan to:
- Clean out most of that grease. Manually turning the spindle did always seems a bit more sluggish than expected.
- Do a bit of dressing of the commutator. Might a light sandpaper suffice?

Not sure if all this will fully address my tripping breakers issues but I hope it helps!!

Also attaching a pic of the board as requested.

Regards,
Rick

The circuit board does not show any signs of burnt components plus the fact that the motor still starts and runs likely points to the motor as the problem. Many years ago ( about 1964) I worked for an industrial motor repair company and it was common to get motors in for rewind that had burned out winding's due to being over greased like that. The motor produces heat as it runs and the grease insulates, which interrupt the convection of that heat out of the motor, then it over heats and the varnish insulation on the winding's breaks down. The brushes on a DC motor continually make contact with individual coils, which magnetizes the coil and causes a repelling action with the permanent magnet field so the armature rotates and thus connects to the next coil etc. The black marks on the commutator bars plus the arching sounds are a very strong indication that the armature is partially shorted or should I say toast.

 

[Joe Kaufman]

The grease is probably from the gear reduction section. It is advertised as a direct drive lathe and the max motor speed is listed as 10,000 rpm. It is probably a planetary reduction and if it is filled with too much grease the drag could be a problem.

 

[Joe Kaufman]

I found the manual online. Doesn't look like a planetary gear reduction is used so excess grease shouldn't be that big of a problem. Are you sure the brush end cap is in the correct position for minimum commutation current. Did you mark the position before you disassembled the motor? Are their index marks or a keying position for the correct position? The commutator bar arching looks like it is similar on the segments I can see. Is it uniform on all segments? If so then it is doubtful there are open winding segments on the armature. The commutator should be cleaned up with sandpaper or trued up on a lathe and the insulation between copper segments should be slightly below the surface. Do you know an "old timer" auto mechanic, he could help with the commutator clean-up. Sometime permanent magnet motors (ceramic magnets) are difficult to remove and reinsert the armature w/o damaging the field magnets. Is that a possibility?

 

[Richard Coers]

I zoomed in on the picture. Sure looks like a few gear teeth showing way down at the bottom of all that grease near the center.

 

[Joe Kaufman]

There is definitely a gear reduction. There are 2 of the same part # of gears + the end of the armature has a gear teeth machined on it. My earlier comment about the possibility of a planetary gear set is not the case so what looks like "excess grease" should not be a significant drag. If the gear section was not disassembled or thrust washers misplaced and the spindle turns relatively freely w/o motor section attached it is unlikely a problem exists there. That Craftsman lathe was also marketed by Palmgrem. Only metal working equipment is currently listed on their website. After you clean-up the commutator and seat the brushes with sandpaper (emery cloth can leave conductive particles), reassemble and let it run free at about half speed for 10 minutes or so. Check parts for significant temperature rise. It would be helpful to monitor the line current with it running free, then under load and max current when breaker trips.

 

[Bill Boehme]

I wouldn't use sandpaper to dress the commutator because sanding will lead to it not being a perfect circle around the motor axis which will lead to the brushes bouncing which will further aggravate the situation. Also, don't "seat" the brushes. New ones already have the right curvature. The brushes are quite hard, but any sanding will roughen the surface and cause poorer electrical contact with the commutator.

Some DC motors and universal motors have an adjustment that allows the brushes to be rotated several degrees each way about the motor axis. The purpose of this adjustment is to "tune" the brush angle for a null point in the arcing. Other brushed motors have the brushes set at a fixed point which was determined to the the correct angle ... hopefully.

 

[Rick Helmig]

Thank you all for the tips and advice.

The bad news:
I'm afraid she's a lost cause....
I stripped the motor down again for probably the 10th time. Checked and cleaned everything and tested the commutator bars. The ohm's were pretty consistent at around .08 ohm's but 2 of them dipped down to .04-.05. I'm not sure if that's a wild enough swing to suggest a short but i assume it's not good.
Regardless, I put it all back together and spent a good bit of time trying to get the brushes seated just right. That took a while but I eventually got it to not spark as much and sound 'smooth' when running. However, after a few test cuts it was apparent that the problem was still there and possibly even worse. So I repeated everything one last time and got the same result. She still runs but any load greater than simply sanding, and it will trip.

The good news:
- I guess now I got a dedicated disc sander???
- The wife just gave me the thumbs on a buying a new lathe and April is the National Woodworking Month so there are some good sales going on! ...I'm thinking either a grizzly g0766 or the laguna 18-36.

Again, thanks the comments and help. Much appreciated!
Rick

 

[Mark Jundanian]

A new lathe, well there's a happy ending.

 

[Russell Nugent]

Guess I'd better start blowing breakers.

 

[Robert D Evans]

I give a thumbs up on the Grizz G0766. I got mine last year and it's been great. Just make sure you put it together where you want it cause it's not going to move after that. My old lathe is now the Beale buffing station.

 

[Rick Helmig]

I give a thumbs up on the Grizz G0766. I got mine last year and it's been great. Just make sure you put it together where you want it cause it's not going to move after that. My old lathe is now the Beale buffing station.

Thanks, Robert. I see you're just up the road in Hoschton. I'm in Dacula. Good to know I got some local turners around!
Cheers!
Rick