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Sizing generator

  1. Nov 5, 2008 #1
    Hi All,

    I have a 10hp Petter diesel engine that i want to drive an AC Alternator--Generator 240v AC.

    Is there an online calculator for this or can somebody help me size the correct KVA Alternator for it, i want to produce the maximum power i can with this engine to keep it loaded.

    Thank You
  2. jcsd
  3. Nov 5, 2008 #2
    Looking at the specs for a few generators on-line the HP seems to 1.7 to 1.8 x the kVa.

    e.g... 8.5hp diesel engine - maximum rated 5.0 kva
  4. Nov 5, 2008 #3

    Yeah i also noticed online that some 10hp engines had around 5.0 KVA, then some have more & some less?

    I need to keep this 10hp engine fully loaded & produce as much power as i can with it.
  5. Nov 5, 2008 #4
    I have found an alternator that is much bigger than required by the engine but it is at a give away price.

    If i was to connect this to the 10hp engine & load it just enough for the engine hp would this be ok?
    This way i can get a good load on the engine & let it run at the required rpm.

    Any problems with this?
  6. Nov 6, 2008 #5


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    Gold Member

    What speed is your 10hp engine rated at?

    How big is the alternator?

    Running an alternator at much below its rating decreases efficiency. You may also have problems mounting the engine to the alternator, and with torsional vibration.
  7. Nov 6, 2008 #6

    The engine is rated at 3000rpm but i would like to operate it at 2500rpm max for reliabillity.

    The Alternator is rated at 15KVA, i get what your saying about the efficiency.

  8. Nov 6, 2008 #7
    You have to run at the correct speed and keep it fairly constant in order to produce the right frequency.
  9. Nov 6, 2008 #8
    Yes your correct, Frequency is something i neglected to think about--good point!

    Thank You
  10. Nov 10, 2008 #9
    1 hp = 746 watts. calculate in efficiency and you get the max watts supported by your engine. As far as running it at a lower speed, you can do that with a pulley system to overdrive your generator. In your case 3000/2500 = a 1:1.2 overdrive ratio. Another thing you need to remember is that your engine is rated for 10 Hp at 3000 RPM, It will produce less at 2500 RPM, so be sure to factor this in as well. You may be suprised to learn that you may only be able to power 3000 watts or so.
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