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what typically causes a thermal overload to trip

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  • what typically causes a thermal overload to trip

    The coolant pump on my bandsaw will run for about 15 seconds and then it trips the thermal overload on the coolant circuit. I though maybe the pump part was full of gunk. I took the pump out and disassembled it completely. The armature "looks" good and smooth. No smell of any kind such as burnt.
    One bearing feels just a little rough. Would that be enough. It is a three phase motor running on 380 volts.

    Any suggestions?

    I also hooked the motor up to the saw without the pump attached and it does the same thing.
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    Try a new thermal overload.
    Location: Saskatoon, Saskatchewan, Canada

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    • #3
      "what typically causes a thermal overload to trip"

      Heat.

      Phil

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      • #4
        "Heat. "

        Funny guy!
        Location: The Black Forest in Germany

        How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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        • #5
          If it stays on long enough before tripping, measure the amps - should agree with name plate. Meg motor and check connections. If amps are good OL is weak. Alternately bypass the overload and see if it lets the smoke out.

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          • #6
            Maybe the windings are soaked with water causing a grounded condition.

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            • #7
              Is the overload adjustable? Check the amps the pump is drawing against the nameplate and make sure the overload is set a little higher.

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              • #8
                Quote: It is a three-phase motor running on 380 volts.


                I also hooked the motor up to the saw without the pump attached and it does the same thing.
                .................................................. .....

                Be sure that you have the correct heater. They are voltage specific. If it trips without the pump attached something is definitely wrong. If the incoming wiring is not in the correct sequence. ie Balanced one leg can be carrying more than its share of the load. That is exactly what the heater is designed to detect and prevent damage from. Since the power is a function of the square of the current. Slight imbalance becomes important. Measure the current in each leg and record. The difference between legs is what you are looking for. There is a procedure to minimize this but you are still dependant on the balance of the incoming power. This gets into the old wye vs delta transformer connection problem. Don’t remove the heater and run the motor unless you monitor the current or you will let the smoke out! That comment may have been tong in cheek but it is akin to putting pennies in the old round fuse boxes.
                Byron Boucher
                Burnet, TX

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                • #9
                  I am now a member of Magic Blue Smoke Club!

                  I took the motor out and hooked it up to power. This time I let it run for more than a few seconds. After about 15 seconds it started to smoke! I unplugged it and waited a few minutes and plugged it back in again. This time lots of blue smoke came out and then BANG! The breaker blew and the motor is now officially dead!

                  The first time smoke came out I couldn't smell anything so I thought it might just be moisture. That is why I plugged it back in to power. At least now I know it is the motor.

                  Do I get a paper or anything to show membership?
                  Location: The Black Forest in Germany

                  How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                  • #10
                    Thermal overloads allso have a tendecy to deteriorate with age and the frequency they have been tripped. The originals on my (1972) Bridgeport got so bad they would trip even under light load after only a few minutes. I finally got tired of it happening and replaced them. Since the replacement 3 years ago they haven't tripped even under the heaviest loads.

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                    • #11
                      Originally posted by Black Forest
                      Do I get a paper or anything to show membership?
                      You get a LUCAS sticker for your toolbox
                      Peter - novice home machinist, modern motorcycle enthusiast.

                      Denford Viceroy 280 Synchro (11 x 24)
                      Herbert 0V adapted to R8 by 'Sir John'.
                      Monarch 10EE 1942

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                      • #12
                        You answered your own question anyway!
                        It (O/L) was trying to tell you something.
                        Max.

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                        • #13
                          Many men have been where you are now and failed to get the secret smoke back in.......succeed and fame and wealth will follow.
                          Opportunity knocks once, temptation leans on the doorbell.....

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                          • #14
                            sorry double post Alistair
                            Please excuse my typing as I have a form of parkinsons disease

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                            • #15
                              No motors but a similar tale. I or Bron and I lived on an island in Scotland without electricity. We bought an expensive sony twelve inch black and white tv this was in 1972 and I used to hook it up to a car battery and we got a few days out of it.Anyway one day I inadvertently switched the polarity clips and there was a bang with a room full of thick smake I though thats it all that dough down the drain it cost more than one hundred and fifty pounds for a smal tv that was a lot when the average wage was around twenty a week anyway I reswitched the polarity when the smoke dissipated and it went back to work for many more years. I must have blown a safety device or something,but I couldn't believe it when it worked fine right away. Alistair
                              Please excuse my typing as I have a form of parkinsons disease

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