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Discussion Starter · #1 ·
I have been enjoying my rebuilt and repainted Powermatic model 65 table saw for the past well over a year. All of a sudden in the last couple of days the circuit breaker has begun tripping. As well, I have discovered a sound that wasn't there before. It has worsened and now, after coming to speed, it will trip the breaker within 10 to 15 seconds. I'm not an electrician or a mechanic. This is a 3 horsepower single phase Robbins & Myers motor.
I read something that might indicate that the centrifical switch could be sticking? Or a start capacitor problem?

Thanks, any who are savvy about these things, and yes, you all were right -- I LOVE this saw! :)
 

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There are several things that could be going on but it's not the start capacitor if you have it up and running. Circuit breakers don't last forever especially if you are pushing the limit with that saw. They get soft and start tripping at a lower amperage than they are rated for. What is the size of the breaker and the voltage draw of the saw? If the wiring is too small for the saw that can cause it. Is there anything else but the saw on the same circuit? You shouldn't be drawing more than 80% of what the breaker is rated for. It could also be the centrifical switch sticking. Is it a GFCI breaker? A lot of times they trip too easily even when there is nothing wrong.
 

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Discussion Starter · #3 ·
Thanks, Steve.

I am the only one working in there. And although I can have other tools running, the saw is run by itself. I have it wired for 240 volt with 20 amp breakers at the box. The metal tag on the motor says it draws 15 amps at 230 volts. The wiring I put in is pretty hefty. I'm leaning toward either the breakers suddenly got weak, or it might be the centrifical switch. I do not know how that affects a motor but I will try to figure that out. What I thought was that once the motor is turning up to speed the centrifugal switch cuts out the start capacitor circuit.
 

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Discussion Starter · #5 ·
I have opened up a couple of motors and put them back together safely. I just feel pretty ignorant what I'm looking at so don't want to do that unless I know I'm going for something that I can figure out. Plus getting this Beast in and out of there is a little work. Got any ideas?
 

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Discussion Starter · #9 ·
Yes. It is quite substantial. Good tip!
I ran the saw using the extension cord and it did well. So I plugged it into the original circuit and it worked well! It was pretty warm the past few days. Does heat make a difference?
 

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Yes. It is quite substantial. Good tip!
I ran the saw using the extension cord and it did well. So I plugged it into the original circuit and it worked well! It was pretty warm the past few days. Does heat make a difference?
The motor getting hot could be a issue with connections being loose. Double check everything including where the wire goes into the breaker and see if everything is tight.
 

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. . . . Does heat make a difference?

yes, major big time "difference"

first - a thorough cleaning. check all / any openings of the motor, shine a light into the windings, etc. if there are no openings in the motor housing, remove any plates to examine the inside. the other obvious: is airflow around the motor being blocked from the 'original design'?

I'm not familiar with that specific saw so I can't offer anything highly specific - but overheating will increase the current draw and worse, continued overheating breaks down the insulation on the windings and other wiring inside the motor. that eventually creates the possibility of arc/sparking/fire.

my initial reaction was similar to Steve's - a 'tired' breaker - running 15 amps (near) continuous load on a 20 amp break is cutting it close. 3 hp = roughly 2500 watts, at 220v = approx 12 amps. short surges can drive that up significantly.
 

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Chuck - yes, high ambient temps will aggravate any marginal / borderline conditions.

for example, a motor that is all clogged up with sawdust might work fine in the winter but overheat and trip out in the summer - the restricted air flow /etc/etc/yadda/yadda . . . .

decent designed equipment will have a motor that is sealed/semi-sealed to prevent the accumulation of sawdust (heh, it _is_ a known dusty atmosphere.....) but do have a "fan" which directs cooling air around the motor.

that theory works most excellently until it encounters my uncle, who decided to "box in" his table saw so it was prettier and he had someplace to hang things. he fried the motor.

cabinet type designs have some provision to keep the motor from overheating. when those provisions are interfered with, that typically results in an 'oops'

overheating is not going to happen in situations where it's on-snip-snip-off. extended run times and heavy load/cuts would trigger it.
 

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Chuck - yes, high ambient temps will aggravate any marginal / borderline conditions.

for example, a motor that is all clogged up with sawdust might work fine in the winter but overheat and trip out in the summer - the restricted air flow /etc/etc/yadda/yadda . . . .

decent designed equipment will have a motor that is sealed/semi-sealed to prevent the accumulation of sawdust (heh, it _is_ a known dusty atmosphere.....) but do have a "fan" which directs cooling air around the motor.

that theory works most excellently until it encounters my uncle, who decided to "box in" his table saw so it was prettier and he had someplace to hang things. he fried the motor.

cabinet type designs have some provision to keep the motor from overheating. when those provisions are interfered with, that typically results in an 'oops'

overheating is not going to happen in situations where it's on-snip-snip-off. extended run times and heavy load/cuts would trigger it.
Great examples and explanations in your posts here... :thumbsup:
 

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Discussion Starter · #15 ·
Sooo... the motor cover concept cannot work? What becomes of dust collection? This question is more for all than aimed at Tom. I'm particularly interested what others with Powermatic 65 saws are doing.
And as I think about it, my shop built cover may not have been in place last Summer.
 

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Discussion Starter · #17 ·
So the "box in" of the motor end is out I guess. (Although I see a motor cover being sold on Ebay and now wonder why that works for some and not for others.)

I'm still trying to solve dust control for this saw. I'm wondering about creating a cover of rubber or ?? that could be clamped around the motor body and fastened to the opening's edges. One could leave slack material at strategic spots to allow for angle changes and raising/lowering the blade. Temporarily I cut a hole in plastic and used rare earth magnets as in the photo.
 

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to clarify....

dust control vs dust collection - do you have anything sucking the sawdust away from the saw?

theory says....the normal dust level in a shop should not be blocking things/creating problems. however if you have no provision to suck away the sawdust when in use, that may be problematic.

looking at the pix, the "bell housing" with the slots - I expect air is being sucked in those slots and blown "out" around the motor to cool it. the plastic sheeting may indeed interfere with that concept - if the "forced" air flow from the fan cannot get around the motor "circumference"

I see "light" spots through the slots in the housing - do the fan blades have caked on dust? fan blades are basically wings - futz with the shape of a wing on an airplane and bad things happen....

the fan blades should be "clean and dry" - don't go cleaning them up and making them shiny with WD-40....

basically I'm a bit puzzled at 'the problem' - the saw is designed such that the motor swings through an arc - the question is the focus on "Where's the Dust?"

if everything is cleaned out and blockages removed, and if you are still having tripping issues, the potentially really bad news could be the motor has been mistreated in a previous life to the point of having some damage....
 

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Discussion Starter · #19 ·
Thanks, Tom.

There is a 4" dust port low on the back side of the cabinet to which I've a dust collector attached.

I haven't had any breaker trips since that hot spell a month back.

It is my assumption that the vacuum will be inadequate if there is a wide open side of the cabinet. (Yes?)

"looking at the pix, the "bell housing" with the slots - I expect air is being sucked in those slots and blown "out" around the motor to cool it. the plastic sheeting may indeed interfere with that concept - if the "forced" air flow from the fan cannot get around the motor "circumference""
It makes sense that the fan is drawing air into and through the motor, and I see no problem created if the plastic were tight on the outside of the motor body. I'm not sure if I'm getting what you're driving at here.
 

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I'm not on a first name basis with this model. however comma.... there is normally some type of shrouding / baffles / covers / whatever so that swarf/sawdust is "contained" and directed to the OEM(?) 4" dust port. it should not simply be blown into the base cabinet and await achieving a high enough pile to get sucked out the port....

"It makes sense that the fan is drawing air into and through the motor,"
it is likely not "through" the motor - me bets the fan exhausts around the gap just past the screws that hold the bell housing on, and blows air over the motor casing. one does not want to block that flow all the way down the motor. when the motor is running, you should plainly feel/detect the airflow in - and out - of the fan.
 
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