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  • Dc motor question

    I tried to find out what I have via google. Really I tried. I have read all about DC motors from brushless to brushes to step to servo and controllers and and and and.....

    I have a small squirrel cage fan on my coffee machine. It is 24v DC. It consists of a coil that is connected to a bunch of thin plates all stuck together. There is a hole in the middle that the armature goes through. There are no brushes. It gets hot and stops turning after about two hours. This fan is continuous duty so long as the machine is switched on which is always except for cleaning. It has just some type of metal bushings for bearings. I replaced on bushing with a ball bearing and it helped but after 6 hours it stopped and was very hot. My next step is to replace the other bushing with a ball bearing also. From my very eloquent description can you tell me what type of motor this can be? The armature looks like it has windings on it also.
    Location: The Black Forest in Germany

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

  • #2
    Are you certain that it runs on DC? If the armature looks like it has windings what are they connected to?
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    • #3
      They aren't connected to anything. Could there be permanent magnets in the armature?
      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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      • #4
        Are you sure it's DC?
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          Originally posted by Evan View Post
          Are you sure it's DC?
          I wouldn't bet my life.
          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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          • #6
            Sounds like AC to me.
            One way of testing for P.M. on the rotor is to short the stator wires together and try and spin the fan, if there is significant difference in resistance between shorted and not, it has P.M. rotor.
            It could be a split phase AC motor using a shading ring to obtain the split ph, if the rotor looks like it has copper conductors on it, they could be the rotor conductor bars natural to an induction motor?
            Max.
            Last edited by MaxHeadRoom; 12-02-2012, 02:51 PM.

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            • #7
              It is 24 volt dc. The same transformer that powers the 24volt dc magnetic valves runs this motor. I just went and looked.
              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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              • #8
                Are you sure the motor is hooked into a DC supply side?
                IOW, after a bridge rectifier etc, often now 24v DC solenoids have a small bridge in them in order that they can be supplied with AC or DC.
                Max.

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                • #9
                  It is probably connected to the unrectified output of the transformer. It would be done that way for safety reasons. Better than having 220 floating around in the machine. In that case it is most likely just the remaining bearing. That kind of motor has practically no starting torque and if overloaded slows way down. It will then get very hot. However, they are usually impedance protected so they will not burn out even if stalled, just get hot. Fix the bearing and see what happens.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Originally posted by MaxHeadRoom View Post
                    Are you sure the motor is hooked into a DC supply side?
                    IOW, after a bridge rectifier etc, often now 24v DC solenoids have a small bridge in them in order that they can be supplied with AC or DC.
                    Max.
                    OK, Is there a way for me to check whether it is 24 DC or AC? My extensive electrical testing devices consist of two digital multimeters!
                    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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                    • #11
                      If you test it on the DC setting it should read near zero.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        Thanks Evan. I will put it on my list of things to do.
                        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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                        • #13
                          What you're describing is an ac motor. They can be wound to run on any voltage, so it's not surprising that it's a 24 volt motor, probably done for safety reasons as suggested. By far the most common failure mode is the bushings seizing up. If one goes bad, it's almost a certainty that the other will be bad as well. In many cases, you can oil them and all will be fine for a year or two, but often enough you have to get all the old oil residue out so it doesn't turn the fresh oil into goo and seize it up again. There's also often some kind of felt washer in there which is supposed to hold oil, and it's often sealed in by swaging part of the bearing retainer. A metal working enthusiast would probably get rid of both bushings and put in ball bearings.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Essentially THIS THREAD IS WORTHLESS WITH NO PICTURE

                            Might easily be a DC motor, driven by what amounts to a tiny inverter...... many millions of small cheap computer cooling type fans are made that way. See if there is any little circuit board associated, it only takes one IC and a sensor or two to run it.

                            if you cannot provide a picture, then at least determine if the 24V is supplied to it as AC or DC.

                            Regardless, if it is running, odds are that the other bearing gave out, and replacing it will likely do the trick.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #15
                              It sounds like a common shaded pole AC motor. What's not common is the voltage.
                              What's the coffee maker brand and model number? It may be easier to go from that angle. If it's UL listed, there should be a diagram inside somewhere.

                              Most will look like this:

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