Electric Motor for Table Saw

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  #1  
Old 02-23-04, 11:24 PM
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Thumbs down Electric Motor for Table Saw

I bought a 2HP motor to replace an ancient 3/4 motor on a table saw that was given to us years ago.

Its a old one, sturdy, and has old world charm about it. But anyway, the motor finally died over the last cold spell and with all the dust this motor has sucked into it and wood it is cut, needed replacement.


I bought this new 2HP motor expecting no problems. The old one was wired 220 with a unsafe toggle switch mounted inside the saw. I redirected the new wiring with flexible conduit to a single gang metal box with 20 amp commercial switch. The load at max is 7.5 on a total of 15 amp rating. Naturally, I used 14 gauge solid.


Hooked it up, rewired the motor to work off of 220, turn it on,,,,,,find out that the motor is spinning the wrong way.


Somewhere I read either on the spec tag or the box it came in was that the motor was one direction turning,,,,,,with no reversing of the turning of motor.



Total surprise to me, but not taken well either. I have $85 dollars in a motor turning the wrong way and I am sure that I cannot return the motor unless it is not working.


The design of motor will not allow me to change on the support brackets, let alone no arbor sticking out of the other side of motor to switch pulley to other side.


So, I am sure that this motor cannot be wired to go another direction, it has 6 posts, and 2 capacitors (no relevance to operation) where the motor is wired to operate at high or low voltage.


If this motor does not apply to this operation, what do I ask for when I call up to order a motor that works for this application???



Rebuilding the old motor is out of the question. It is ancient, and I heard that the locals around here charge a fortune to rebuild one, and no guaranties even if they do.


I'm just a plumber trying to cut some wood, and now I am 4 hours and $85 with a pile of wood with no way to cut it.


All thought are appreciated.
 
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Old 02-24-04, 06:22 AM
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Most motors are bi-directional. There should be a wiring diagram on the motor that shows the voltage connections and rotation connections. It ususally only requires changing 2 wires.
 
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Old 02-24-04, 09:06 AM
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Any motor can made to turn the opposite direction. Some of them are designed to do it via connections in the junction box. Some of them have to be dismantled and the wiring connections changed internally.
If you go to ECN Contractor Technical Reference Section you should be able to find a motor similar to yours and reverse it. Look at the posts titled split phase motors.
 
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Old 02-24-04, 09:09 AM
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If you take the motor apart, you may void the warranty.
 
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Old 02-24-04, 09:12 AM
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Here are the connection diagrams for changing the rotation of single phase motors.
http://www.electricmotorwarehouse.co...n_diagrams.htm
 
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Old 02-24-04, 09:33 AM
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If the motor is a single-phase "split-phase" induction-motor, it's designed with a "Starting-winding(s)" and a "Running-winding(s)".

AS an example---If you connect S1 and R1 to Line 1 and S2 and R2 to Line 2 , the motor will rotate C-W.

If you connect S2 to Line 1 and S1 to Line 2 the motor will rotate C-C-W- note that you simply "reverse" the connections of the Starting-winding leads to the Line-leads to reverse the rotation.

A dual-voltage motor is equipped with 2 Running and 2 Starting windings------ for 220-volt operation, the windings are connected in series. You probably have two winding-leads connected to Line-terminal 1 and two winding-leads connected to Line-terminal 2. The problem is correct identification of the 4 leads--- --2 Running and 2 Starting.

There is a capacitor in series with the Starting- winding--this is a "Open-circuit" for Direct-Current. The Running-winding is a "Closed-circuit" for both D.C. & A.C. You MAY be able to determine the winding-circuits using a Battery-powered multi-tester.

Aother option is to take the motor to a motor-repair shop where they may assist you in identifying the connections.

Good Luck & Enjoy the Experience!!!!!!!!!!!
 
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Old 02-24-04, 10:30 AM
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Changing the rotation is an easy job. The motors are designed to allow you to change them.
 
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Old 02-24-04, 11:19 AM
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I see the dilema. This is a compressor motor. This means it has a specific purpose. I may be perminently wired for CCW rotation as the nameplate says. This doesn't mean it can't be changed though. Check your area for a motor repair shop and have them take a look at it. They may not charge you anything.
Sorry.
 
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Old 02-24-04, 06:25 PM
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Okay. Thank you for the responses. I called a local motor repair shop, and the same knowledge was given about the compressor motor ( I sent this thread link to the companies email ).

They told me that the motor that was on it is valuable. Here it is when I took it apart. This motor, I have no idea how it never caught on fire like this.

http://img23.photobucket.com/albums/...UNBAR_ELEC.jpg


So what I did was air clean it, inspected it and found a wire that looks like it was recently rubbed and the jacket was broken.


http://img23.photobucket.com/albums/..._Internals.jpg

I used electrical tape on the cut and used a small torch to melt the tape so it wouldn't move. Kind of like that shrinking heat tubes used in underwater connections for 3 wire submersible pumps.


I put the motor back together once it was clean, and the same result: It will sit and hum, then the armature will rotate and actually start moving slowly,,,,,,,and eventually will start to run full force like it was hanging up for some reason.

It will sometimes turn in the wrong direction, but if you have it turning the direction you want it initially, it will follow the direction you turn it.


I went ahead and used liquid graphite at the sealed bearings at each end of motor case, and then followed up with a couple shots of powdered graphite.


The motor operates so quietly now that the lubricant is used and takes I know 3 minutes to stop turning once the current is off.


So, the motor repair shop said it would take about $85 approximately to fix it, and he said that this type of motor being cast iron with the 4 rods and capacitor inside of it is better than the motors they make today.

I would almost imagine that 40 years of sawdust played a part in the wear of this motor, but I have no idea what they would fix, replace, tighten, or rebuild.

I would like to know so that if I ever run into this again which I am sure, I would like to know the way it works, in simple form.



Any input would be nice to confirm my go ahead with having this rebuilt. The guy said for the exact same motor, 1 HP with 3450 RPM would run around $190 new.


I would do that,,,,,,,and use the compressor motor for a failing grinder in the other part of the garage, but that brand new motor will be sucking dust into it on the first cut, no way around it. Would rather keep the old one if I could.


Thanks,

Steve
 
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Old 02-25-04, 04:41 AM
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What do you mean, "the way it works"? Do you mean the way single phase motors opperate?

The reason it doesn't start could be 3 things.
1. Bad capacitor.
2. Bad centrifugal switch. (Burnt contacts)
3. Too much end play in the shaft and the switch isn't engaged at rest. You can chek this by pulling and pushing on the shaft (end to end). If there is play, this could mean the contacts aren't engaged by the rotor.

In any case, I doubt you could do this repair yourself with the exception of the capacitor. You can get them through Grainger.

$85 doesn't seem too much for the repair. They may try and talk you into new bearings when they get it apart. (Industry standard procedure)
 
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Old 02-25-04, 09:59 AM
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Thanks for replying.


The shaft end to end play is tight, so the movement of shaft is correct.

The bearings seem to be fine, along with the graphite i used will probably give me years more use but I agree with your statement.

The capacitor I have no idea how to detect if it was bad or not. If it was defective, does the motor not run period? Or is this something that slowly over time goes bad and gets weaker as time moves on?

Bad centrifugal switch.....I have no idea what that is.....but would that make the motor just sit and hum until you manually start to push the armature one way or another to get it started?

Sorry about the questions, but this is a learning process for me and the more I ask, the more I will know about these motors.

I won't work on it myself other than cleaning contacts or what have you. I just don't want to spend another $85.....to find out that parts to rebuild this one will put me in the 3 digit range dealing with old product.

Kinda like plumbing. Sometimes it is just easier to start over.
 
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Old 02-25-04, 10:20 AM
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The capacitor is the can looking thing. That sounds like what the problem is. If you turn the shaft, it will start.
The switch is in the picture you took. If the contacts are fused closed, it will start but not get up to speed.
What a happens is;
The motor starts with the switch closed. This keeps the capcitor in the circuit. The capacitor gives the motor the jump start needed to start a heavy load. i.e. loaded compressor.
Once it starts to rotate, the centrifugal device on the shaft opens the switch and it goes into full speed.
If the capacitor is bad, and they do go bad, it won't get the jump start needed, hence rotating the shaft manually is sometimes enough to get the motor past the speed of the switch.
The rotation of the motor, in this case is in the wiring from the switch to the motor windings.
The motor can be reconnected for a different rotation (expert needed). Tell them this when you bring it in for repair.

The rotation direction is determine by facing the shaft from the end. CW or CCW. You need to determine this for your saw.

I had 15 years fixing these and motors up to 7,000 HP and 4,000 volts.
 
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Old 02-25-04, 11:51 AM
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Good description, I can understand what you just mentioned.


It sounds like the capacitor is the problem then. If I manually move the armature and get it rolling, this motor instantly clicks and kicks on like there was nothing wrong to begin with. It will run full force till you cut the juice off. Like nothing was wrong with it.

SO, can I buy a capacitor and install it myself to save a buck?

I wouldn't know where to buy it, but it sounds from what you described, that is the culprit of my problems.
 
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Old 02-25-04, 12:10 PM
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You can buy them at Grainger.com or locally. You need all the info from the capacitor. This still doesn't solve the rotation issue.
 
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Old 02-25-04, 02:09 PM
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Originally posted by dogman1953
You can buy them at Grainger.com or locally. You need all the info from the capacitor. This still doesn't solve the rotation issue.
I don't believe there is any rotation issue with the old motor in this case, just the new one he was trying to replace it with. Repairing the old motor should leave you with a saw that runs just like it always has before now.
 
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Old 02-25-04, 02:54 PM
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Okay. New motor is out of the picture now.


Old motor, has no end shaft play, runs if you help turn the direction of shaft until it clicks and kicks on, if not, it hums and slowly starts to turn and then eventually takes off.


Runs great once past this point.



So, a new capacitor fixes this problem and the old motor is repaired, right?


Most of the capacitors on the grainger.com website are under $30 and that would be my next line of defense if all is okay with the rest of the motor. Which from the way you all describe it, it is.
 
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Old 02-26-04, 05:09 AM
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That sounds about right.
If the capacitor was good and switch was fused shut, the motor would start but never get up to speed. It would hum loudly and draw a lot of current.

Remember this. A new 1 HP motor should run about $115. Once you start investing in an old motor, you may start to reach this point. Buy the new one.
If for some reason you have to bring the old one in for repair at least they won't have to charge you for the capacitor.

Remember to mark the parts do that they go back together correctly. The last thing you want to do now is drive the fan into the windings. Also, take a look at the contacts on the switch to see if they are still intact while you have this apart. Make sure you don't bend it in any way.

Good luck and let me know if this worked out for you.
 
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Old 02-27-04, 05:04 PM
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The guy is right about old motors being better than new ones. They were designed with slide rules and enough iron to do the job. New ones are designed with computers with an eye to cutting costs.
That said, a single phase motor has no torque to start the shaft turning. Since a motor at rest is not developing any impedance from the rotating magnetic field, it is essentially a short circuit and leaving it on that way may have caused the burning you saw. The capacitor ( or start winding or shaded pole) creates a phase shift within the motor that gives it this torque. When it reaches sufficient speed to run on its own, there is a centrifigal (or centripetal if you're an engineer) throw out switch that takes it out of the circuit. On some motors, there is no switch and the capacitor is designed to run right along with the motor. If you've had the motor apart, the switch is obvious on the end of the shaft.
If it takes 3 minutes for the thing to spin down, then bearings aren't the problem. I'm surprised the capacitors in Grainger are under $30. I'd expect them to be under $10.
Often the capacitor will be mounted on the side under their own cover. Take it out (don't put your tongue across it, they hold a charge) and take it to your re-wind guy to match it up with a new one. It will have a voltage rating and a farad (or microfarad )rating.
I'm betting that's all that's wrong with it.
 
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Old 03-01-04, 05:28 PM
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Thanks for all the replies. I tried searching for this thread in the fourm by date, and to no avail, it is invisible?


I found this by looking up an old email in order to locate it.


As soon as I get a little free time, I will buy a capacitor and let you all know the results.



Thanks again.


Have you all noticed threads just disappear?



 
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Old 04-02-04, 02:56 PM
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Thumbs up

It worked! Total Cost: $4.38

Finally took the time to put the motor back together before the parts dissappeared.


Soldered the connections to the new capacitor, put it all back together and the motor kicks on instantly.

All I have to do now is remount the motor to the table saw and I will be cutting wood soon enough.


Even though I ended up with a $80 motor, I will replace my failing wire wheel motor that has a tremendous amount of end play in the shaft.


Good thing is, I learned an important bit of knowledge of motors now, and will give me an edge on things next time I hear a water pump or sump pump imitating the same problems. I will at least know that there are a few possibilities to consider, other than just junking the motor because it is not working.


Thanks again!
 
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