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mini roubo #4: testing the switch on the planer

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Blog entry by kaaahl posted 888 days ago 3646 reads 0 times favorited 8 comments Add to Favorites Watch
« Part 3: the death of a jointer -- help troubleshoot? Part 4 of mini roubo series Part 5: lots of yak shaving this past week. »

This will be my last post today, I swear. I just figured I would document this out in case other people run into power tool failures in the future.

First things first, I put the machine back together, except for the switch. I originally planned on using a voltage tester with live current, but I was nervous about that. The voltage tests that I had (read, that I stole from my dad’s tool box) looked old or cheap or both. But I found a video online to explain how to check circuits for resistance to see whether they are opened or closed.

The basic concept is you use an multi-meter and measure the resistance. If the two points aren’t connected, you get a “1” or an open message—there is a high level of resistance. If the two points you touch are connected, you get a “0” or closed message—there is virtually no resistance.

First, find multimeter.

Next, switch to measuring ohms and test multi-meter. When the two leads are touching, ohms (the green scale at the top) gets buried on the right—no resistance. When it’s open, it’s buried on the left—high resistance.

Unplug the machine from all equipment, we just want to test which circuits are connected, not the power in those circuits. I balled tinfoil around the plug end of the machine to complete the circuit on the plug side.

Examine switch. Black, white, and green come into the switch—black is usually hot, white neutral, green ground. Two yellows come out from the motor—one connects with white / neutral and the other connects to the other side of the power switch.

Now the testing.

Switch set to “off”, touch black and white wires with probes—> “0”—> so the plug isn’t shorted anywhere.
Switch set to “on”, touch black and white wires with probes—> “0”—> doesn’t really tell me any new information
Switch set to “off”, touch white neutral from power cord and yellow hot coming out of the switch—> “1”—> no power is making it through the switch, as it should be.
Switch set to “on”, touch white neutral from power cord and yellow hot coming out of the switch—> “0”—> switch did it’s job and power can flow through it.

I don’t know what it will tell me, but then I did the following two:

Switch set to “off”, touch yellow wire at switch and other yellow (normally connected to neutral)—“1”—> there isn’t a completed circuit.
Switch set to “on”, touch yellow wire at switch and other yellow (normally connected to neutral)—“1”—> there still isn’t a completed circuit.

I don’t know if their should be a completed circuit on the motor side when it is not running.

Anyway, it looks like I should investigate the brushes and see if I can find a screw extractor.



8 comments so far

View hhhopks's profile

hhhopks

563 posts in 1001 days


#1 posted 888 days ago

the 115 Vac is not plug in. Right? Unplug it.

Meter resistance test:
Set meter to read ohm value.

Short/close contact/switch close; you should able to get a tone (beep if the meeter has that feature) or have a very low resistance value reading.

Open/open contact/switch open; you should have no tone or have a very high resistance reading.

The name plate shows 115 Vac, so it is a single phase. Your switch should switch the “Hot” leg (black typical). The White wire should be the neutral and green is ground.

When the switches close the two wire should tone out or no resistance across the switch. If the switch is open, then the resistance is infinite. So when the switch is close there should be power all the way to the motor. With power disconnected, you should able to tone out from the source side of the swith to the leads going to the motor. If nothing you have something that interrupts the power flow like an overload (near the switch?).

It it tones out (near no resistance) then it is in the motor area. Does the motor has an overload? Reset as necessary.
Check the brushes. Replace as necessary.

Your connections at the motor Junction Box are good. Right?

You should take a reading of your motor. With the motor leads disconnected take a reading of each lead to ground (motor casing). If it tones out, you need a new motor. No tone is a good thing here. The two motor leads may or may not tone out. That will depend on the motor design. However, if you have a very low resistance value, that may be a bad thing.

If you do reset the overload, you should do some cleaning….........lube….......sharpen the blade.
All that stuff makes it easier for your motor run cooler so it won’t trip the overload.

Hope this helps.

-- I'll be a woodworker when I grow up. HHHOPKS

View kaaahl's profile

kaaahl

14 posts in 889 days


#2 posted 888 days ago

hhhopks, thanks for all the specific help. new brushes and a screw extractor set are in the mail. I also pulled the blades and am sending them away to be sharpened—will be sure to lube up the appropriate parts when I get it going again.

I don’t know if there is another overload switch closer into the motor, I can’t get the cover off until that screw extractor comes. Well, i could drill it out by hand, but I would rather not. But looking closely at the engineering diagrams, I don’t see anything between the switch and the motor, perhaps you see something else.

I tone out across the two poles of the switch. I don’t tone out if I connect the two yellows (ie the hot going to the motor and the neutral completing the circuit) whether or not the switch is on or off. There must be an overload in their somewhere, will see if I can find it.

View kaaahl's profile

kaaahl

14 posts in 889 days


#3 posted 888 days ago

connections at junction box are solid

View Tim Dahn's profile

Tim Dahn

1467 posts in 2189 days


#4 posted 888 days ago

These work great and are usually available at hardware stores

-- Good judgement comes from experience and experience comes from poor judgement.

View hhhopks's profile

hhhopks

563 posts in 1001 days


#5 posted 888 days ago

If the two leads coming out of the motor doesn’t have a lot of resistance as in almost infinite, then the motor wire or the the windings have burnt open. If so the motor, will need to be replaced (unless the motor has an overload). If the motor has an overload it should be a button of some sort like the motor on your garbage disposal. It shouldn’t be hard to find.

If the motor is burnt out, you should able to smell it.

-- I'll be a woodworker when I grow up. HHHOPKS

View kaaahl's profile

kaaahl

14 posts in 889 days


#6 posted 888 days ago

Tim, thanks for the advice. I bought something similar on amazon and it’s in the mail. I try to avoid shopping in person—it always takes longer and I spend more.

hhhopks, it is the case that the two leads coming out from the motor don’t seem to connect a circuit (ie, i get an open circuit reading—the “toning out” thing wasnt registering at first b/c mine multimeter doesn’t have a speaker.). I’m hoping that the motor itself isn’t damaged.

I found how to change the brushes—you don’t have to take the assembly apart, there are two access holes. One of the brushes was burned through. Maybe that could be the source of the problem? I really don’t want to buy a new motor and am hoping I can get by with a cheap fix. Will wait for them to come in the mail and then re-check things.

View kaaahl's profile

kaaahl

14 posts in 889 days


#7 posted 888 days ago

and maybe i can find that overload switch as well.

View hhhopks's profile

hhhopks

563 posts in 1001 days


#8 posted 888 days ago

After replacing the brushes the motor leads should have low resistance that is if the brushes are seated properly. Often they brushes should dressed such that the ends should match curvature. I can’t remember what that call that. Basically you file it down (sand paper may work) so you have a curvature to maximize the surface contact.

-- I'll be a woodworker when I grow up. HHHOPKS

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