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  • Biax motor overheating

    What causes universal brush motors to overheat??

    I got a new second hand motor out of a mechanically damaged biax and installed it in mine.... It runs quite well and the mechanism turns over freely...

    However the motor runs very hot within a few minutes of starting up...

    If I run it for four minutes then dissassemble the motor the commutator is over 100C..This does not sound right to me...

    Any ideas other then restricted air flow (the motor fan is working)
    Precision takes time.

  • #2
    I would suspect dirty commutators, or weak springs for the brushes? Do you get a lot of arcing as it runs around the brushes?
    Eric Sanders in Brighton, Michigan
    www.scope-werks.com
    www.compufoil.com

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    • #3
      What cycles per second is your power supply and is it the same on the motor ? Had this problem on a vertical mill once. The motor was for 50 cps and my power supply was 60 cps. Got very hot in a short time. I had to change out the motor.

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      • #4
        the cycles is right 50/60 cycles..It is a DC motor like an electric drill motor not an induction motor...

        You cannot see the brushes as it is all enclosed... The ventalation slots are right back in the handpiece..
        Precision takes time.

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        • #5
          Overheating when everything else seems normal can be caused by partially shorted coils. A motor shop generally has equipment to test for shorted coils but they may not be detected by ohmmeter tests.

          Do carefully check the brushes and commutator for good connections.
          Don Young

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          • #6
            Originally posted by Terry L
            What cycles per second is your power supply and is it the same on the motor ? Had this problem on a vertical mill once. The motor was for 50 cps and my power supply was 60 cps. Got very hot in a short time. I had to change out the motor.
            The overheating problem with the 50Hz motor could have been due to low voltage, as I understand it when you switch to a 60Hz power supply you need to increase the voltage by 20% as well.

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            • #7
              Not on a "univeral motor". You can run them on DC if you like.


              You may have shorted segments on your commutator or bad windings. Take it apart and look at the armature windings. If one set is discolored or shows heat stress at the connection, you may have a winding problem. A motor shop will have a "growler" - that will check you armature.

              Probe the brushes - they should move easily (spring loaded).

              You may have a mechanical problem loading the motor. If you can, take off the "load" - i.e. the scraper mechanism. Run the motor and see if it gets hot under "no load".

              Comment


              • #8
                I've had a problem recently with built-in vac motors. If the brushes aren't seated properly, they will arc and heat up the commutator pretty quickly. In turn the comm gets burned and the problem becomes runaway. If the comm is not perfectly concentric and round, the brushes will bounce and the same problem arises.

                Many brushes are designed to stop when worn to a certain point. If this happens, the contact fairly quickly becomes too light, and burning will occur.

                Of course, in general, series motors like to run fast and they generate lots of heat. Most cases I've seen the cooling is barely adequate with the built-in fan, and if you slow the motor down you lose some of that. Sometimes the cooling air depends somewhat on the case, and removing the motor from the case results in less cooling air being forced through the motor, even if the fan is left intact.

                Sometimes there's a shroud on the brush end that helps keep the air flowing through the motor. I've had some cases where the shroud has been removed, and the whole bush area looks like it's overheated.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  Short brushes?

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                  • #10
                    Originally posted by Ringer
                    the cycles is right 50/60 cycles..It is a DC motor like an electric drill motor not an induction motor...

                    I got a new second hand motor out of a mechanically damaged biax and installed it in mine

                    I’m wondering where you found a new second hand motor in this country, they must be like rocking horse poo.

                    How does it create that DC voltage? Simple rectifier. I’m wondering if you might have ended up with a US specification motor - 110VAC, and it doesn’t like running on our 240V.

                    I think we talked about Johny Lasco. Best scraping guy down here by a long shot, buried him a few years back. 4 of his 5 wives were at the funeral.

                    He always had US Biax’s. But he had a 240 – 110 step down transformer made.

                    If it came into the country via Hettler Trading, its probably 240.

                    Regards Phil.

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                    • #11
                      Hi Phil, it was a ebay buy from the US, I got it cheap as the motor was shot.. I was going to get the motor rewound and converted to 240V but a US PM member sold me the motor out of his damaged biax....

                      I have been running it out of the 110V output that my milling machine has to run the power feed unit.. I initially suspected the milling transformer may have been not big enough as it is only 200vA in size so I connected it to my Miller welder generator as it has both 110V and 240V outlets and puts out 6.5KvA.. It still had the same problem, heating up withion a few minutes..

                      The brushes appear fine, the commutator is not showing any burn marks from arcing, but something is amiss....I am wondering if the housing is not aligning up the motor correctly as the bearing housings are in each section of the machine..

                      I may have to take it to town and get it checked out, and possibly rewound to 240V, but before I do I will play around with it some more...
                      Precision takes time.

                      Comment


                      • #12
                        I would first clean the brushes and comutator, Q-tips & alcohol is good, use toothpics to scrape between comutator segments,wipe down with alcohol, don't forget inside of brush holders.

                        Carbon build up will bridge the segments causing shorts and mutch powre loss while drawing higher amerage. It is not uncomon to see a ring of fire part or all the way around comutator.

                        Cookie

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                        • #13
                          Anyone know what the brushes are supposed to look like, seeing they are not available from Biax???

                          I know Black and Decker used the same size brushed in some of their equipment... 3/16X1/4 brushes.. http://www.graphitestore.com/itemDet...d=43&curPage=1
                          Precision takes time.

                          Comment


                          • #14
                            Originally posted by Ringer
                            Anyone know what the brushes are supposed to look like, seeing they are not available from Biax???

                            I know Black and Decker used the same size brushed in some of their equipment... 3/16X1/4 brushes.. http://www.graphitestore.com/itemDet...d=43&curPage=1
                            Who made the motor? If it wasn't Biax, I reckon there's a fair chance they were made by Scintilla, who make or did make the pro Bosch jigsaws. I'd look at Bosch jigsaw brushes for a start. You can always file down oversize brushes, if you can find some with similar terminations.

                            Tim

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                            • #15
                              Originally posted by Timleech
                              Who made the motor? If it wasn't Biax, I reckon there's a fair chance they were made by Scintilla, who make or did make the pro Bosch jigsaws. I'd look at Bosch jigsaw brushes for a start. You can always file down oversize brushes, if you can find some with similar terminations.

                              Tim
                              Well I originally thought it would be a Bosch motor seeing the machine is made in Switzerland.. However the brush size is clearly imperial, not metric as you would expect from a Euro machine... It also dates back to the seventies..
                              Precision takes time.

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