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Author Topic: 3 phase generators  (Read 1015 times)
ulaff
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« on: April 29, 2007, 08:27:21 PM »

how much trouble would it be to use a 7kw 3 phase generator in a my bus ? would I need any special equipment? I am just getting started on the electrical system so any help would be appreciated
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TomC
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« Reply #1 on: April 29, 2007, 09:30:09 PM »

You have three legs of 120vac at 2.334kw per leg.  In my opinion, would be a very big pain to try to come close to balancing the load.  The only load I could think that might be balanced, is if you had three roof top airs and ran one off of each leg.

I have a 10 kw single phase wired straight 120vac.  I don't EVER have to think about balancing the load-just if I were to overload it on the total output.  Makes life easier.  Good Luck, TomC
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DrivingMissLazy
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« Reply #2 on: April 30, 2007, 04:52:14 AM »

Most, if not all, three phase alternators can be reconnected for single phase output. 120 volt two wire or 240/120 volt three wire output. Total capacity is reduced by a certain amount depending on what you re-connect for. Check inside the connection housing and see if there are twelve leads, or even six leads connected together in some fashion. If so, you are in luck I think. Let me know exactly what leads are connected together.
Richard
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« Reply #3 on: April 30, 2007, 04:53:21 AM »

There are a number of reasons why a 3 phase generator of that size might not be your best choice, ulaff.
But let's explore them.......

Unless the generator end is built to give 100% of rated power at single phase you will lose 33% of the rated power by using it single phase.  Another question is: Is it a 12 lead generator? If so it probably can be reconnected to 120/240 3 Ph. and you can use 2 legs of the 3 phase but again will only get a bit over 4 KW out of it.

In a word...it's just not practical. You didn't mention who the Mfr of the genset was.  If it was a big Company like Onan or Kohler the chances are good that a single phase generator end might be available for it in the used market.  If it's a Chinese import do yourself a favor and sell it.

You didn't mention the size of your conversion or the type and number of A/C units you plan to run. Even at 7 KW (single phase) a 7 KW is marginally light for a 40'er.

Best of luck with your project.

NCbob
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ulaff
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« Reply #4 on: April 30, 2007, 08:09:43 PM »

This is an older military unit .I had thought of buying it but after closer inspection I believe I am gonna pass on it, Had to many hours,is aircooled and too much trouble too adapt too my needs thanks for the replies
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centrix29
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« Reply #5 on: May 06, 2007, 05:10:18 AM »

Hi,

I use a 12,5kw 3 phase genset in my conversion.  I balanced the load like this:

- Two legs go an electrical panel
     - One leg has one AC and lights
     - Second leg has other AC and other eletrical appliances

- Third leg goes to 12v converter (with 110v breakers)
     - This supplies all 12v lighting and appliances
     - Eletric fridge is on this leg

Hope this helps!

Pat
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DrivingMissLazy
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« Reply #6 on: May 06, 2007, 05:23:06 AM »

The two main problems I found with military surplus gensets was that spare parts were generally unobtainable as the units were built specifically for the military and the manufacturer did not make spares for the civilian marketplace. Also the air cooled units were typically 3600 rpm and extremely loud.
Richard

Hi,

I use a 12,5kw 3 phase genset in my conversion.  I balanced the load like this:

- Two legs go an electrical panel
     - One leg has one AC and lights
     - Second leg has other AC and other eletrical appliances

- Third leg goes to 12v converter (with 110v breakers)
     - This supplies all 12v lighting and appliances
     - Eletric fridge is on this leg

Hope this helps!

Pat
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« Reply #7 on: May 06, 2007, 05:32:25 AM »

As a point of interest, three phase generators that have 12 leads can be re-connected for single phase output.
 
For 240/120 volt three wire output you must derate the unit by 33%.

For 120 volt two wire output you must derate the unit by 66%.

Many military type gensets were manufactured with an alternator large enough so that you could get full rated output even when connected for single phase output. A lot of these units had re-connection boards that made the reconnection very simple.
Richard
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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
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