how to build an engine speed regulator

Discussion in 'The Projects Forum' started by pyager1, May 15, 2013.

  1. pyager1

    Thread Starter New Member

    May 14, 2013
    Hi, I have a generator that used to run on gasoline, but I converted it to propane. but it has no governor. I would like to use a servo from an old r/c to control the engine speed using the throttle on the carb. I was hoping to use the frequency out to maintain the proper rpm. Can anyone help with a circuit for this?
    Thank you
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    That is an interesting way to control the engine speed at (I presume) 3600 rpm. I don't have a circuit to sense the alternator frequency and use that to control a servo, but it seems possible. Of course, you could also use the ignition timing for the same purpose.

    Usually, there is a governor built in the engine; what engine does your generator use?

    ETA: After a little thought, I would probably use a microcontroller. This would make it relatively easy to read the frequency using a circuit such as is shown here and use the PWM function of the μC to control the servo. One could also use the output from the transformer as input to a power supply for the PIC. It should be very doable.
    Last edited: May 15, 2013
  3. Wendy


    Mar 24, 2008
    My bad, I misread the post. Sorry about that.
  4. wayneh


    Sep 9, 2010
    I'd be very nervous using anything that isn't very robust, and fails to low rpm instead of runaway. I guess that could be as simple as using the servo to pull against a dead-man's spring. You just need to be very mindful of what happens with electrical failure, heat-related component failure and so on.
  5. crutschow


    Mar 14, 2008
    If it's a standard type motor-generator for household use it has to have some sort of governor to maintain the speed with a varying load. Why do you say it has no governor? Is it because the governor was disconnected when it was converted to propane?
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    You could put a 12v transformer on the AC output of the generator, that will power your circuit and also let you safely sense the AC frequency from the low voltage side of the transformer.

    Then you could use a freq to voltage converter to turn that freq into a reference voltage.

    Then you need another circuit to generate the pulses to control an RC servo, you can buy that along with the servo from an RC hobby store.

    And probably some opamp circuit between the two to calibrate the ref voltage and use it to operate the servo controller.

    Or you could use an 8-pin PIC micro, and some code.
  7. crutschow


    Mar 14, 2008
    And beware that the feedback loop will likely require some form of PID compensation to avoid oscillations or hunting of the motor speed. The compensation values will likely need to be determined empirically after the governor is built.