I have a 3hp lawnmower engine. My engine hypothetical rpm range from 3k to 6k.

If I was to connect it to a generator or motor with similar power rating at similar top rpm, lets say a 2000 watts 6000rpm dc motor.

If 1hp is 0.7kw, would I then be able to directly power four smaller 500 watt motors without having a battery?

Looking at building a AWD go kart where the gas engine rpm regulate the speed..

  • \$\begingroup\$ It's worth mentioning that this is similar to how some hybrid electric vehicles work; you might find it helpful to look up details on those. \$\endgroup\$
    – Hearth
    Commented Feb 11, 2019 at 13:35

1 Answer 1


You seem to be describing a system with an engine that can provide 2 kW at the proper speed to drive a generator. The output of the generator would go to four power conversion speed controllers that would provide power to four wheel motors. For estimating purposes, the generator might have a 90% efficiency. The speed control units might have 95% efficiency. The wheel motors might have 85% efficiency. The system efficiency would then be 0.9 X 0.95 X o.85 = 0.73. The full-speed efficiency would then be about 73%. You could drive the wheel motors at about 3/4 of their rated power.

The speed of the engine can not really control the speed. It would be best to operate that at the most efficient operating speed, presumably close to full speed. The wheel motor controllers must control the speed. The power actually used to drive the cart will be reflected in the torque load on the engine.

  • \$\begingroup\$ Thanks for taking the time. i read a little bit last night, and from what i understand if i was to run a dc motor as a generator, it will produce a variable power depending on the gas engine rpm. Therefor if the petrole engine rpm increases then i get increase in electrical power out of the generator. ... then if that power is applied to the wheels motor, would i not get them turning accordingly.... \$\endgroup\$
    – Mat Matik
    Commented Feb 11, 2019 at 17:45
  • \$\begingroup\$ I believe that the first diesel-electric locomotives worked something like that, but one wheel motor had a wheel on each end. As the engine throttle was moved there was a simultaneous adjustment made to the generator field current. There may also have been manual adjustments made to balance the torque of the traction motors. Modern locomotives and hybrid road vehicles work more like I described. However there are quite a few design variations. \$\endgroup\$
    – user80875
    Commented Feb 11, 2019 at 18:16
  • \$\begingroup\$ Lawnmower engines tend to be fitted with mechanical governors. If you control the power with the motor controllers, the throttle should adjust automatically to keep the engine speed constant. \$\endgroup\$
    – William
    Commented Jan 6, 2023 at 15:55

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