MM20/SP500 bandsaw, motor dead?

[Brian Holcombe]

I went to start the MM20 today and it was non-functional.

Single phase 240v setup.

I started investigating the point of failure and have discovered that:

-The switch appears to be functional. Each motor lead shows 120v but the motor does not hum when the switch is pressed.

-The capacitors are good according to my multimeter. For posterity I swapped them to new capacitors and they’re also good.

I’m now wondering if there is an internal overload that requires taking the motor apart to access but I’m unsure.

The motor is a 100L frame euro motor made by Motek.

Resistance across the leads is 0.7 ohms. This seems low compared to other motors I have.

Resistance to ground from the motor leads both show OL which I believe is s good sign.

[Tom Trees]

Presuming you've checked both door switches?

[Brian Holcombe]

I’ve got 120v at each lead inside the motor when I push the start button so I’m assuming they are good.

[Andrew Hughes]

If it has a switch like this. Or similar you can find a replacement at https://controlparts.com/
My went out a couple years ago.
Good Luck

[Brian Holcombe]

I have 120v on all circuits when I press the start button. The button holds and provides 120v to the motor and coils…..yet….nothing happens.

I’m at a loss as to why it doesn’t hum or try to start or smoke or something, just dead.

[Andrew Hughes]

That’s sure is weird.
I’m trying to remember my diagnosis before I spoke to a tech.
His recommendation was remove switch from housing leave all the wires hooked up. Turn it upside down and give it some taps.
I was able to start my saw. In fact I ran it style swich upside down for a long until I found a replacement.
I since learned those single phase switches are notorious for failing.
Good Luck

[Brian Holcombe]

All the single phase equipment on this machine is going flying into orbit soon.

[roger wiegand]

Are you testing voltage with an electronic meter? You might be seeing phantom voltage from a basically failed connection-- eg voltage but minuscule current capacity. An old-fashioned solenoid type circuit tester is a better choice to ensure what you are seeing is real.

Switch is still the most likely culprit. If it really has voltage then a trip to the motor shop for testing is probably in order.

[Brian Holcombe]

When I shut the switch off the 120v goes to zero, as it should.

[Richard Coers]

Is there a centrifugal start switch in the motor?

[Brian Holcombe]

Spoke with SCM, there are no internal overloads, so he thinks if the motor doesn’t do anything with power supplied that it is dead.

[Brian Holcombe]

Richard, I’m not sure.

[Jim Becker]

May be a good idea to have a local motor shop look at it...since all the switches appear to be cooperating and the capacitor(s) are good, probably something in the windings...maybe something came loose internally. Maybe see if Sam Blasco has any ideas, too.

[Brian Holcombe]

Spoke to Sam, he thought it might be the switches.

Both local motor shops are a booked for a month.

Between cost of replacement switches, downtime and cost of repair, I decided just to replace it. The single phase motors are a giant headache.

I bought a Lafert 5.5hp motor and sourcing a hitachi vfd for it.

[Holmes Anderson]

I would test the centrifugal switch like somebody else mentioned. If the centrifugal switch is stuck open then the motor will not be able to generate enough electromagnetic force to overcome inertia to start rotating. If that is the case then it might start with no load if you manually give it a spin but it would be safer to check the centrifugal switch for continuity. The centrifugal switch should be closed during the motor start phase so you should find continuity. If not, then the centrifugal switch is bad or needs to be cleaned out.

[Barry Versteegh]

After you push start control check for voltage on t1 and t2 on load side of contactor. You should see 240 volt , if you check neutral to t1 and t2 you will see 120 volt the same leg of the power, if one side of your contactor is open you will not 240 volt going to motor, but you will have 120 volt to neutral on both load side of the contactor.

[Bill Dufour]

It should at least hum if either run or start windings are getting power. I suspect terminal wire or screws inside motor are loose. Pass enough current for meter to move not near enough for power.
Tighten/wiggle every connection on the motor board. If no luck remove board and check solder connections to back of the board.
Bill D

[Brian Holcombe]

Connections are all tight. I’m getting 120v because I’m checking one leg to neutral at a time.

I’ll check to see if the switch is stuck open.

[Bill Dufour]

You need to check leg to leg and verify 240 volts. Maybe something changed and you are using the same phase on both legs. To be honest I do not see anyway that could happen downstream of the meter.
Bill D

[Tom M King]

If the motor is getting 240, it ought to say something.

[Dan Friedrichs]

Brian, you said you have 240V across the motor (or, at least you suspect you do because you have 120V between each leg and ground).
You also said you have 0.7ohm across windings.
If both of those things were true, you'd have 340amps flowing. Clearly you don't, so one of those things is wrong.

I'd investigate further. I think you're going to spend more time and money swapping to 3phase than if you just find the loose wire or whatever.

My guess is that you have one leg open on the contactor or overload. This is connecting 120V to one side of the motor, but leaving the other side floating. Since the motor is just a coil of wire, you're measuring the "same" 120V on both sides, but if you measured across both leads, you'd have 0V (not 240V).

[Erik Loza]

Of all the bizillion MM’s I sold, cannot ever recall a bad motor. Not saying it’s impossible, but would be extremely unexpected. Hope you get ot sorted out quickly.

Erik

[Brian Holcombe]

Dan, just measured as you suggested and you are correct it shows 0v across the terminals but 120v at each individually.

[Tom M King]

How about on the power in lugs on the switch?

[Dan Friedrichs]

Dan, just measured as you suggested and you are correct it shows 0v across the terminals but 120v at each individually.

So you don't have a motor problem. You have a problem in the switch or overload. Somehow you aren't getting power through to the motor.

Unplug, manually hold the contactor down, and check continuity through.

[Brian Holcombe]

I checked the centrifugal switch and it appears to be functional.

[Dan Friedrichs]

It is one of these switches? http://www.solowoodworker.com/mm/switch.html

My guess it that you have 240V on the input to the switch, but 0V on the output (only one leg of the 120V is getting through). I don't think it has anything to do with the motor.

[Tom M King]

That's why I suggested to test the power in to the switch (on/off switch). You have already determined 240 is not getting out. To test the switch, all that's left is to see what's getting in to it.

[Brian Holcombe]

I checked the switch and it was showing 120v at both legs on the output. Is this a faulty testing method?

[Brian Holcombe]

Dan, that page won’t load for me, it’s an Eaton starter/switch.

[John Lanciani]

I checked the switch and it was showing 120v at both legs on the output. Is this a faulty testing method?

In short, yes. You need to test for 240 volts between the two legs and let us know the results.

[Brian Holcombe]

I’ll test that later tonight.

[Dan Friedrichs]

The link was describing problems with an AEG starter common to Minimax, but sounds like you have something else.

Check that you have 240V between the line inputs coming into the top of the contactor.
Check that you have 240V coming out of the contactor (going into the overload relay).
Check that you have 240V coming out of the overload relay.
497730

Sounds like you have either a bad contactor or a bad overload relay. While you could troubleshoot it to determine which (and just replace that part), you could also just replace the whole starter.

[Brian Holcombe]

Looking more and more like the switch…

240v coming in, but not going out. Thanks, Dan for setting me straight on this. In the past for 3ph equipment I have simple checked across each terminal at the switch.

I think I’ll go ahead and buy a new switch to try that before I swap any equipment to 3ph.

[Jim Becker]

Brian, if you think about it, this is a situation where a technical corollary of the old "is it plugged in" is at play. :) In this case, the answer might be, "Yes, but..." 'Hope the switch swap gets you back and running immediately as that's less involved (and less costly) than the motor swap and VFD setup.

[Kevin Jenness]

Some of the switch gear on MM bandsaws has been problematic. Rather than try to replace my on/off switch with the oem item I bought a standard magnetic starter and surface mounted it to the saw frame. Not as low profile but easy to source.

[Brian Holcombe]

Thanks Kevin and Jim! All things to consider.

The 100L frame motor is fairly common in my shop so I don’t mind having a spare 3ph motor and VFD handy.

[Edwin Santos]

Bumping this thread, just wondering what the final resolution turned out to be.
Was it the on/off switch that turned out to be the root cause of the problem?

[Brian Holcombe]

It was the switch. I bought an identical factory replacement for now but may still either change the motor starter and switch systems.

[Edwin Santos]

It was the switch. I bought an identical factory replacement for now but may still either change the motor starter and switch systems.

Thanks for the update Brian. I have the same saw and I'll keep a mental note of this in case I encounter the same issue.

[Bill Dufour]

Where is the factory switch located. I see them down low or up high on the vertical arm. is any location better for some operations?
I am in the process of moving my tablesaw switch forward about 4 inches so I can see it under the table overhang.
Bill D