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Thread: Wrong diagnosis and dumb move by me

  1. #1
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    Wrong diagnosis and dumb move by me

    I posted last night about my Craftsman saw motor crapping out. I took some of the advice and started trouble shooting tonight. First step was to make sure the switch was not clogged with sawdust. In taking it apart I noticed a lable that said "The power relay in this switch is gravity sensistive. Never turn on the power until the switch is mounted on the rails and the saw is upright." When I installed the T2 fence I had to relocate the switch and did not notice the label (in my defense, it was on the bottom) and did not put it in the correct position. So I put it in the correct position but saw tries to start but won't run. Did I burn up the relay? How do I check it? I'm going to check the Sears site and see if i can still get a replacement.
    Last edited by Jim Rimmer; 08-04-2009 at 9:41 PM.

  2. #2
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    Can't you just use a regular house type wall switch in a metal box? Why the need for something like the original,which you probably won't get from Sears.

    It could be a standard type of switch which a good electrician would recognize under a different name.

  3. #3
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    Jim, I would bypass the relay and see if the motor will run before I spent more money and find the motor maybe still bad...if the motor runs when you bypass then go buy the relay
    Dave

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  4. #4
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    Quote Originally Posted by george wilson View Post
    Can't you just use a regular house type wall switch in a metal box? Why the need for something like the original,which you probably won't get from Sears.

    It could be a standard type of switch which a good electrician would recognize under a different name.
    I just checked the Sears website and believe it or not, they have the relay in stock. I wondered about using a regular switch, too, but don't know much about motors and relays (my experience is in electronics, not electrical). For some reason they put a power relay on it when it was designed. Can I take it off and just go straight through a switch?

  5. #5
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    Quote Originally Posted by Jim Rimmer View Post
    Can I take it off and just go straight through a switch?
    That would certainly be cheaper than buying the relay. I use a household switch for my 2hp DC, so it should handle that saw motor.
    Never, under any circumstances, consume a laxative and sleeping pill, on the same night

  6. #6
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    There are actual motor switches that look like a household switch that would tolerate the use better then the standard household switch. Might try to find one of them at your borg.

  7. #7
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    IIRC, from high school, the purpose of the relay is to prevent the saw from restarting, if you lose power. A primitive magnetic switch. That would of course depend on the start switch, if it's a push on and release switch, that may be what it is. A no restart saw IMO is a good feature. Using a light switch would work, but will defeat the feature.

    If it's gravity sensitive, did you try and mount it the correct way and try to start the saw? May save you a trip to teh BORG and/or Sears. Every time I go there my checkbook gets lighter.

  8. #8
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    The relay is not to turn the saw motor on and off, it's to turn the starting winding on and off. (There isn't a centrifugal switch in the motor).

    The relay doesn't have a return spring, gravity does that function. Turn it upside down and it runs the starting winding constantly, which can "let the smoke out" of the motor in short order.

    When you turn on the power via the built in toggle switch, the motor isn't rotating. The high starting current pulls in the relay, providing power to the starting winding.

    Once the motor is up to a reasonable speed, the current drops and the starting relay drops out, de-energizing the start winding.

    You can use any suitably rated switch to turn the saw on and off, however you cannot eliminate the starting relay.

    Regards, Rod.

  9. #9
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    I've been using a dpdt household (commercial grade) toggle switch on my Delta CS for 9 years. I have running on 220v. The only thing I don't like is there is no safety paddle on it to turn it off by bumping it with a knee or leg. The oem switch only lasted a year.

    If I really tried, I'm sure I could come up with something though.

  10. #10
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    Yay! Crapsman!!

    What a *jury-rigged* (epithet deleted) way to keep from putting a decent motor on a saw!! Sears saved a few bucks by letting gravity do the work of a spring, and using a cheap motor without centrifugal contacts! But, it cost you in the long run if you fried your motor because of a hidden tag!
    WayToGo! Sears!!
    Last edited by Chip Lindley; 08-05-2009 at 11:55 AM.
    [/SIGPIC]Necessisity is the Mother of Invention, But If it Ain't Broke don't Fix It !!

  11. #11
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    I have had a 20 amp household switch on my 3/4 H.P. drill press since 1964. The original motor went bad last week,but the switch is still good. it depends upon how large your motor is,and if 20 amps can handle it. Magnetic is better,of course,so your machine won't start back up after the power comes back on.

    Chip,that Sears motor from back then ran for long enough,don't you think? Probably an Emerson rebadged.

  12. #12
    Quote Originally Posted by Chip Lindley View Post
    What a *jury-rigged* (epithet deleted) way to keep from putting a decent motor on a saw!! Sears saved a few bucks by letting gravity do the work of a spring, and using a cheap motor without centrifugal contacts! But, it cost you in the long run if you fried your motor because of a hidden tag!
    WayToGo! Sears!!
    I guess Franklin ( they make submersible pump motors, more than anybody else in the WORLD) is also cheap. Most if not all three wire well pumps have a current sensing relay for the start windings, along with the compressor in your AC, and refrigerator. I have a 30+ year old Skill bench grinder that uses a current relay to operate the start windings. Delta uses same set up on some of their disk/ belt sanders. How would YOU service a relay in a hermatic compressor? You can't take it apart. Being exterally mounted isn't a sign of cheapness, but of quality engineering, IMHO. I don't havve to disassemble a motor to replace relay (aka start switch.) Imagine if a submersible pump, 200'+ down in a well had to be pulled to sevice start switch. We charge around $350 to pull pump, but only $65 labor to replace control box. located at top of well. Just because you aren't familar with a system, doesn't make it bad. Just different from what you have delt with before.

  13. #13
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    Latest in the saga: Took the relay apart and cleaned contacts and reassembled. Saw just buzzes. Turned it off, gave the blade a spin and then hit the switch (I know, not safe. It did take several tries because of my inability to get to the switch quickly and my fear) and the saw started up. Bypassed the relay and went directly through the switch and same results. If I turn it off and let the blade coast for awhile and then hit the switch it starts back up as long as I don't wait until it stops. That tells me the motor and bearings are OK.

    So I guess I have to have the relay. I checked it out and there's really not much to it. I read zero ohms across the coil and I would think there should be some very low resistance. If I put an ohmeter on the contacts and rotate the relay in my hand, it goes from open to closed but apparently does not pull in when power is applied. So I guess while I had the relay horizontal I burned up the coil maybe accounting for the smell that I thought was the motor.

    One thing that has me puzzled. What/how does the relay drop out after the saw starts?
    Last edited by Jim Rimmer; 08-06-2009 at 2:20 PM.

  14. #14
    The fact that the motor runs when you spin it to get it started means that the run winding is OK, but the starting winding may still be burned out. The function of the starting winding is to give the motor it's initial rotation, and then the run winding keeps it going. Once the motor is spinning, the starting winding is then taken out of the circuit either by a centrifical switch or as in your case a relay. If you have an ohm meter you could check the starting winding for continuity; if it is good, it will probably read close to 0 ohms, if it has no continuity, the winding is open and is bad. When the relay was not mounted vertically, and you started the motor, it probably kept the starting winding energized and may have burned up the winding, resulting in the smell you noticed. Under normal operation the starting winding is energized for just the first second that power is applied to the motor, therefor it is usually a fine gauge wire that will burn up if left energized too long. The relay is pulled in by the high starting current of the run winding on initial power up, and the relay contacts energize the starting winding; once the motor is spinning the run winding current drops to its normal value, and the relay drops out as the lower current isn't enough to keep it energized.
    Last edited by Dave Lash; 08-06-2009 at 6:08 PM.

  15. #15
    Quote Originally Posted by Chip Lindley View Post
    What a *jury-rigged* (epithet deleted) way to keep from putting a decent motor on a saw!! Sears saved a few bucks by letting gravity do the work of a spring, and using a cheap motor without centrifugal contacts! But, it cost you in the long run if you fried your motor because of a hidden tag!
    WayToGo! Sears!!
    Springs break, but gravity doesn't. Works 24/7/365 without a break. It simply a case of reading the directions, which most of us (myself included) don't do. Directions, what directions?

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