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Anyone know how much torque a 550kva generator will make?

  1. Jul 9, 2016 #1
    im working on making a diesel/electric semi conversion on one of the trucks at work. does anyone know how much torque a 550kva generator will make, top rpm rating is 1200 and 50hz, engine is a c15 caterpillar running 410kw. having a really hard time finding the answer, any help would greatly be appreciated
  2. jcsd
  3. Jul 9, 2016 #2


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    I'm a bit rusty but in the absence of a better answer...

    Your generator cannot produce 550Kva if the engine driving it can only manage 410kW.

    Lets assume the generator is 90% efficient. If the engine delivers 410kW the max power the generator could make is 410kW*0.9 = 369kW.

    Here is one approach to work out the torque...

    Power (in W) = torque (in Nm) * angular velocity (in Rads/S)
    Torque = Power/angular velocity

    1200rpm is equivalent to 1200*2Pi/60 = 126 Rads/S

    So the torque at 410kW and 1200 rpm is going to be about..

    Torque = 410,000/126 = 3,253Nm or about 2,400 ft.lbs

    Lower rpm would imply a higher torque.

    The torque will also depend on the actual electrical load.
    Last edited: Jul 9, 2016
  4. Jul 9, 2016 #3

    jim hardy

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    In English units
    Horsepower = 2 X pi X Torquefoot-pounds X RPM / 33,000

    33000 of course is 550 ft-lbs per second per horsepower X 60 sec/minute sense you have angular velocity in RPM
    and at 0.746 kw/horsepower, 410kw = 549.6 hp

    top speed is 1200 but to make 50 hz at 1200 rpm requires an odd number of poles(5) and generators have even numbers of poles
    so surely it's a 6 pole generator running at 1000 RPM ? Does it have a tachometer ? What does it show ?

    if 549.6 hp = 2pi X Torque X 1000 rpm/33000
    then Torque = 2886.5 ft lbs ?
    Is that close to what CWatters got when corrected for lower RPM as he suggested ?

    old jim
  5. Jul 9, 2016 #4
    oh ok thanks, just wondering, i see some electric trucks out there that use electric motors with the diesel engine to produce over 3k pounds of torque and i really wanna do this with the freightliner i got but i have no idea where to get the motor, how to adapt it to the engine, and how to mount the transmission to it. my plan was to put on a big turbo, bigger injectors, bigger cam, and injector pump but i see the electric motor is way more efficient. do you guys know if id be able to some how connect a transmission to a cat c15 generator set?
  6. Jul 9, 2016 #5


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    But Torque is not Power. You need to multiply torque by angular velocity to get Power. Only then can you make proper comparisons.
  7. Jul 9, 2016 #6

    jim hardy

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    You mean take off the generator and mount a clutch & transmission ? That's a question for mechanical engineers forum.
    Is it a SAE bellhousing ?
  8. Jul 9, 2016 #7


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    Just to clarify.. The figure I calculated above was for the torque that the diesel engine would have to produce to turn the generator (when the generator is delivering max power to some unspecified load).

    It sounds like you are proposing..

    Diesel engine -> Generator -> Electric motor -> Wheels

    That's the set up used in some trains...

    The main advantage is they can produce high torque at zero rpm unlike a diesel engine alone.

    As for the details I think you are going to have to find a forum dedicated to building these trucks?
  9. Jul 9, 2016 #8


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    kVa and kW aren't the same thing and aren't closely related. The load determines both the power and power factor of the generator and this one apparently was rated for a relatively poor (conservative) 75% power factor, which is pretty reasonable.
  10. Jul 9, 2016 #9
    its a how trains get all their torque, they have it on a few trucks out there right now. a company called nikola one is making a really nice truck that runs 2000 hp off electric motors driven by a diesel engine with a 320kw battery pack. if you guys want to check it out heres the link https://nikolamotor.com/one i wanna do the similar design but without battery packs, just use the diesel engine constantly to run the motor, the new truck is $375,000 and i dont really have the money for
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