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Motor Brushes - again again..

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  • rowifi
    Is it solved? Do we have a source? Is there a spec for them - can we get them made? Is there a spec for the motor ( before I take it apart )? Mine has stopped
    Message 1 of 7 , Jan 3, 2011
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      Is it solved? Do we have a source?
      Is there a spec for them - can we get them made?
      Is there a spec for the motor ( before I take it apart )?

      Mine has stopped .. I measure nothing across the motor terminals .. the brushes are about 11mm or so .. I would have thought it would be intermittent rather than being just dead!

      I will investigate further...

      Rob
    • tecfacet
      I have a new set here.  If you want, I will measure them.   In my experience, replacing brushes on this type of motor just requires brushes of the same
      Message 2 of 7 , Jan 3, 2011
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        I have a new set here.  If you want, I will measure them.
         
        In my experience, replacing brushes on this type of motor just requires brushes of the same physical size and style.
         
        Roger

        --- On Mon, 1/3/11, rowifi <alphamode@...> wrote:

        From: rowifi <alphamode@...>
        Subject: [CAMM-3] Motor Brushes - again again..
        To: CAMM-3@yahoogroups.com
        Date: Monday, January 3, 2011, 3:26 PM

         
        Is it solved? Do we have a source?
        Is there a spec for them - can we get them made?
        Is there a spec for the motor ( before I take it apart )?

        Mine has stopped .. I measure nothing across the motor terminals .. the brushes are about 11mm or so .. I would have thought it would be intermittent rather than being just dead!

        I will investigate further...

        Rob

      • rowifi
        I ve discovered that it isn t the brushes! The motor runs if I connect it separately to an AC suply so I need to fix the Speed controller. No need to measure
        Message 3 of 7 , Jan 4, 2011
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          I've discovered that it isn't the brushes! The motor runs if I connect it separately to an AC suply so I need to fix the Speed controller.

          No need to measure the brushes - but thanks for the offer :)
          Rob

          --- In CAMM-3@yahoogroups.com, tecfacet <tecfacet@...> wrote:
          >
          > I have a new set here.  If you want, I will measure them.
          >  
          > In my experience, replacing brushes on this type of motor just requires brushes of the same physical size and style.
          >  
          > Roger
          >
          > --- On Mon, 1/3/11, rowifi <alphamode@...> wrote:
          >
          >
          > From: rowifi <alphamode@...>
          > Subject: [CAMM-3] Motor Brushes - again again..
          > To: CAMM-3@yahoogroups.com
          > Date: Monday, January 3, 2011, 3:26 PM
          >
          >
          >  
          >
          >
          >
          > Is it solved? Do we have a source?
          > Is there a spec for them - can we get them made?
          > Is there a spec for the motor ( before I take it apart )?
          >
          > Mine has stopped .. I measure nothing across the motor terminals .. the brushes are about 11mm or so .. I would have thought it would be intermittent rather than being just dead!
          >
          > I will investigate further...
          >
          > Rob
          >
        • robinghewitt
          Hi Rob The motor pcb does look like it grew from humble beginnings. Judging by it s footprint I think the SSR has to be an opto isolated triac with a built in
          Message 4 of 7 , Jan 4, 2011
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            Hi Rob

            The motor pcb does look like it grew from humble beginnings. Judging by it's footprint I think the SSR has to be an opto isolated triac with a built in dropping resistor. An odd choice, unless they started by simply hard wiring the motor on/off.

            You sound confident but as I've been buried in the 3000 circuit diagrams for the past week it is fresh in my mind and may help someone if I run through it. It is a bit weird :o)

            Either the motor or spindle must have an encoder on it somewhere because it produces pulses as it spins. The pulses come in on the Counter Board plug J102 where they are converted to a voltage that increases with the revs. The line FV carries those volts to the main board plug J301 and straight out again to the motor board J304. It also lights the speed LED's sequentially on the counter board.

            The motor board compares FV to the volts coming from variable resistor VR1 and decides whether the motor should be on or off. They must be using single rail op-amps rather than comparators because there is no pull up resistor on the output. Another odd choice which they pay for further on.

            They now have a line that goes to the top of the page on the circuit diagram, low turns the motor on, high turns it off. The motor on/off input pulls it high to kill the motor after getting it's level shifted.

            Now it gets really odd. The wonderful thing about an opto isolated triac is that you light the LED to turn it on, kill the LED to turn it off, no need to to produce a pulse train on the gate to retrigger it everytime the mains crosses zero volts. But on the motor PCB the mains is rectified and converted in to just such a pulse train. Are they trying to clip the mains wave rather than just switching on when below speed, off when above? Technically a good effort but probably over complicated and more to go wrong. Why the expensive opto triac if they have the pulse train and a humble 20p triac would suffice?

            Robin
          • rowifi
            Hi Robin Thanks - I havn t analysed it in depth yet, but it s similar to a light dimmmer. The Pulse counter VF signal didn t seem to generate logic pulses as
            Message 5 of 7 , Jan 4, 2011
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              Hi Robin

              Thanks - I havn't analysed it in depth yet, but it's similar to a light dimmmer.

              The Pulse counter VF signal didn't seem to generate logic pulses as such - in fact the voltage was 5 volt ( using a meter ) until the small non reflective part of the pully was in view of the sensor, then it seemed to drop to 4 or so volts. Seems weirdly analog as there is no adjustment for changes in reflectivity or sensitivity on the sensor board itself.

              I'll need a scope on the signals to be sure whats going on..

              I haven't got the circuit with me at the moment but it's going to be this weeks project I think.
              Rob








              --- In CAMM-3@yahoogroups.com, "robinghewitt" <zen112891@...> wrote:
              >
              >
              >
              >
              >
              >
              > Hi Rob
              >
              > The motor pcb does look like it grew from humble beginnings. Judging by it's footprint I think the SSR has to be an opto isolated triac with a built in dropping resistor. An odd choice, unless they started by simply hard wiring the motor on/off.
              >
              > You sound confident but as I've been buried in the 3000 circuit diagrams for the past week it is fresh in my mind and may help someone if I run through it. It is a bit weird :o)
              >
              > Either the motor or spindle must have an encoder on it somewhere because it produces pulses as it spins. The pulses come in on the Counter Board plug J102 where they are converted to a voltage that increases with the revs. The line FV carries those volts to the main board plug J301 and straight out again to the motor board J304. It also lights the speed LED's sequentially on the counter board.
              >
              > The motor board compares FV to the volts coming from variable resistor VR1 and decides whether the motor should be on or off. They must be using single rail op-amps rather than comparators because there is no pull up resistor on the output. Another odd choice which they pay for further on.
              >
              > They now have a line that goes to the top of the page on the circuit diagram, low turns the motor on, high turns it off. The motor on/off input pulls it high to kill the motor after getting it's level shifted.
              >
              > Now it gets really odd. The wonderful thing about an opto isolated triac is that you light the LED to turn it on, kill the LED to turn it off, no need to to produce a pulse train on the gate to retrigger it everytime the mains crosses zero volts. But on the motor PCB the mains is rectified and converted in to just such a pulse train. Are they trying to clip the mains wave rather than just switching on when below speed, off when above? Technically a good effort but probably over complicated and more to go wrong. Why the expensive opto triac if they have the pulse train and a humble 20p triac would suffice?
              >
              > Robin
              >
            • robinghewitt
              Hi Rob It doesn t really care what volts come off the actual sensor because it feeds in through capacitor C18 on the counter board which creates FV, all you
              Message 6 of 7 , Jan 4, 2011
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                Hi Rob

                It doesn't really care what volts come off the actual sensor because it feeds in through capacitor C18 on the counter board which creates FV, all you need from the sensor is edges.

                best

                Robin
              • tecfacet
                Hello. I have a set of new brushes here that I can measure if you like. In my experience, replacing brushes like these are only a function of replacing them
                Message 7 of 7 , Jan 4, 2011
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                  Hello.

                  I have a set of new brushes here that I can measure if you like.

                  In my experience, replacing brushes like these are only a function of replacing them with brushes of the same size and type. Nothing really special about a brush unless you are talking metalized.

                  The brushes in the CAMM-3 appear to be ordinary brushes.

                  Roger
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