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Radiator cooling fan blade removal for training aid

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  • Radiator cooling fan blade removal for training aid

    The automotive instructor brought me a Nissan radiator cooling fan assembly to make into a training aid. The assembly has two fans, which move a LOT of air.

    Making a stand for the assembly was no big deal, but I'm concerned that leaving the blades on the fans is a safety issue and will make the training aid very noisy.

    The motors are pancakes with permanent magnets, which I've never dealt with before. All the DC motors I've seen run wild if not loaded in some manner, so I don't know if just removing the blades is an option.

    Any suggestions on what I could do to make this thing safer and quieter?
    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    IMHO the blades should not be removed so the students can see what they do and also develop an awareness that they need to be extremely careful when working on vehicles with electric radiator fans.

    Consequently it probably needs some sort of safety cage made from hardware cloth, expanded metal, or similar material.

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    • #3
      The motor will not run wild. It will quickly come up to a higher speed than it would with the blades on it, but it will settle there. The rpm will be determined by the voltage feeding it. There isn't a safety issue with the motor itself, unless someone wants to try stopping the shaft, or unless the motor is not secured and jumps out of control when voltage is applied.

      A permanent magnet motor is not like a universal motor, which will want to overspeed without a load on it. The pm motor generates its own back voltage when running, so that opposes the voltage feeding it, effectively capping the rpm.

      A piece of tape as a flag stuck to the shaft is a pretty good and safe indication that the motor is running.

      By the way, there are, or used to be, universal motors in various places in vehicles. Window motors are the last place I have seen them used, although these days every electric motor in a vehicle is a permanent magnet one.
      Last edited by darryl; 11-17-2011, 02:51 AM.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Originally posted by darryl
        By the way, there are, or used to be, universal motors in various places in vehicles. Window motors are the last place I have seen them used, although these days every electric motor in a vehicle is a permanent magnet one.
        Most starter motors are still made with the field coil in series with the armature, otherwise known as a universal motor.

        Any suggestions on what I could do to make this thing safer and quieter?
        A very quick and easy thing to do would be to wire the two motors in series, which will cut the speed in half. If you can then drive them from a lower voltage you can run them even slower.
        Paul Compton
        www.morini-mania.co.uk
        http://www.youtube.com/user/EVguru

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        • #5
          I don't know the specifics for the fans you have but I do know that "brushless DC" motors are becoming more common. They are used for electric power steering motors in automotive applications. Pretty sure they are also used in computer cooling fans. Only reason I point this out is because it means you will need some sort of motor controller (kind of like a VFD for 3phase motors) to run brushless DC motors for the electronics to provide commutation instead of brushes.

          If it has two large wires going in it is probably brushed and can run on 12 volts DC. If it has three large wires and perhaps some other smaller ones it is probably brushless DC and will require a controller.
          Last edited by strokersix; 11-17-2011, 06:27 AM.

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          • #6
            I would just put some mesh over it an leave as is.The students IMHO need to be made aware that those fans do cycle on and off while the engine is running and that they are also capable of removing fingers just as well as the old flex fans.Maybe have the instructor feed a chicken wing into it to demonstrate the effect
            I just need one more tool,just one!

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