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Thread: Generators

  1. #1

    Default Generators

    I'm hoping to tap into the very wide knowledge base here; I am looking for a single phase 25kva generator, but 3 phase machines seem in the majority (at a reasonable price).
    I am told that a 3 phase generator can be reconfigured to single phase. In the case of, say a 10 ova three phase machine being reconfigured to a single phase, what is the final output? Is it 10kva single phase, or 30 kva, or somewhere in-between? If it somewhere in-between, how would I work out what the final output would be on any generator?

    Thanks for reading.

  2. #2
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    Default Re: Generators

    A 3 phase machine gives you 3 phases of 220v. so you don't really have to reconfigure it to get 220v as it gives 3 supplies of 220v
    Problem is that each Phase is 60deg off set for each phase.
    If you only use one phase your load would be unbalanced and you would get really poor efficiency.
    And that is as much as I can remember...

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    Default Re: Generators

    Quote Originally Posted by The Beast View Post
    A 3 phase machine gives you 3 phases of 220v. so you don't really have to reconfigure it to get 220v as it gives 3 supplies of 220v
    Problem is that each Phase is 60deg off set for each phase.
    If you only use one phase your load would be unbalanced and you would get really poor efficiency.
    And that is as much as I can remember...
    Not necessarily100% correct. A three phase outlet is not always three cables with a common neutral but can just be the three live phases only with 380V between them. This would require a transformer to convert it to a single phase 240v.


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    Default Re: Generators

    What is it you are doing with it? Why the need to rewire a commercial generator that is configured to the proper output and national safety regulations etc? Not being snarky at all. I'm truly curious.

    Edit: Oh and can this be done by way of an external power distribution box? Is there anything available that is configured to do that?

    For example......it's a much easier thing to do, but I'm looking for an affordable (read less expensive...not cheap) box to plug into my 220V/30A outlet.....a box that will have both a 220V/30A outlet in it but also some 110 outlets. I have a 60Gal/6HP compressor that runs on 220V so I have a cord just long enough on it to get to the 220V outlet....which used to be for the old style water heater. Now it's a 120V external tankless. I wish I could have a box plugged in all the time so the compressor is connected 24/7 but I also have 110V outlets to use if needed. These boxes are very expensive.....around $300-$500.

    But if they exist, surely there'd be something for your application?

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    Default Generators

    Lots of older farm houses have a 3 phase (380v) supply with the distribution split. Neutral (NOT EARTH)+ 1ph (220v)supplies one set of breakers and so on. The trick is to balance the phases so that the load is distributed evenly.

    Alternatively get a 3ph 380v to 1ph 220v transformer.


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    Default Re: Generators

    Trevorm...While a 3phase jenny can be re-configured to single phase,it is not the route i would attempt to take.
    Also,on the rating of 25KVA...An output expressed in KW is more 'real world'
    On a single phase system you have 220V between L and N. On a 3phase system you have 220V between each of the phases and N...so you have,in effect,3 single phase supplies. You must however,remember that you will have 380V between phases.
    On a conventional 3 phase installation,the single phase loads are balanced over the 3 phases.
    If you are looking at a new installation,the wireing in the distribution board fed from the Jenny is no different to conventional wireing from a mains supply.
    If you are looking to use the jenny as a back up to an existing single phase supply then the easiest route would probably be to wire the jenny to a smaller sub board feeding out to required circuits,with a 3 phase change over switch between mains and jenny supply.

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    Default Re: Generators

    25 KVA Single Phase would be scarce and expensive. Up to 7,5 KVA Single Phase is easily obtainable.

    If it is for your house and your wiring is for single phase I can understand the use of single phase. For other uses, why not go 3 Phase?

    For a normal home a single phase 7,5 Kva unit should be more than enough. Not needed that both geysers and the oven and the hair dryer be used at the same time.

  8. #8

    Default Re: Generators

    the gen is needed for my daughter's shop; she has a lot of fridges/freezers. David, if I use a 3 ph to single ph transformer, what output would I get?

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    Default Re: Generators

    For a shop, that means probably a landlord and also single phase wiring. Get a single phase. To redo the building to accommodate single phase from ESKOM and 3 Phase from the generator is not worth it and would need the landlords approval and a lot of electrician time etc.

    Maybe figure out if a 7,5 single phase unit might run halve of the fridges and then alternate between them during loadshedding or downtime? A fridge or freezer is in any case not running permanently, so just do internal "load shedding" in the shop.

  10. #10

    Default Re: Generators

    Thank you all; I have some options to explore

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