Motor speed controls - store bought and ???

Discussion in 'Burners and their construction' started by dennis, Dec 31, 2020.

  1. KDM

    KDM Copper

    Yes, this rings a bell with me. Different types of motor. I use a variable drill speed controller with my leaf blower and it works a charm. I suspect I got lucky, though. One small quirk someone might be able to clear up for me: My leafblower is much too powerful. I run it with the speed very low. BUT I have to start it with the speed quite high then turn it down: it won't start at "low".
    Is this because it basically just needs to get momentum up, but once it's going it can keep going?

    Blower and Speed Controller.JPG
     
  2. Tobho Mott

    Tobho Mott Gold Banner Member

    I notice the same thing using dimmer switches and router speed controls for my hair dryer, shop vac, and leaf blower, but I never really worried about it. Someone else will have to explain why.

    I start all the way off then dial it up until it starts going, then I can turn it quite a ways down from there. Same thing happens with ceiling lights on dimmer switches in my house.

    Jeff
     
  3. dennis

    dennis Silver

    It might well be due to the output waveform from such controls.

    My reasoning: when testing a few universal motors - one from a rescued vacuum, and the other an old sewing machine - I was able to use a ~ 10 volt nicad battery pack. The motors turned over quite slowly, but did so *steadily.*

    I suspect that going to more sophisticated controls may well solve the herky-jerky-motor-problem - though it will probably cost (a lot!) more.
     
    Last edited: Feb 19, 2021
  4. Mach

    Mach Silver

    Its been a long time but isn't that inrush current? Google says:

    Inrush current, also referred to as “locked rotor current,” is the excessive current flow experienced within a motor and its conductors during the first few moments following the energizing (switching on) of the motor. This current draw is sometimes referred to as “locked rotor current” because the current necessary at startup to begin the rotation of a non-rotating, de-energized motor shaft, is very similar to the extreme current draw experienced for the moments when a motor is overloaded to the point of seizing. In both cases, the current draw is such that is required when the motor is trying to overcome an idle motor shaft.

    https://www.jadelearning.com/blog/understanding-motor-starting-inrush-currents-nec-article-430-52/
     
  5. ddmckee54

    ddmckee54 Silver

    One thing to remember, don't turn the motor speed down too low. When you do, you won't have enough airflow from the motor's fan to cool the motor. 20-25% of full speed is the lowest you want to run the motor for sustained periods.

    Don
     
  6. rocco

    rocco Silver

    Good point. Also, while most blower motors have a separate fan to cool the motor, some like cheaper vacuum cleaner motors, use the air flow through the blower to cool the motor so with those, if you throttle the air flow, you also need to be careful not to overheat the motor.
     
  7. ESC

    ESC Silver Banner Member

    I'm still a big believer in throttling the intake because the velocity of the air from centrifugal fans overcomes furnace back pressure. Controlling the RPM reduces that optimum velocity. So with the fan wheel at full speed restricting the intake side doesn't change the velocity at the point of ignition but does control the oxygen available for combustion. Then you just adjust fuel for maximum temperature.
     

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