Gen head efficiency - big vs small?

[Lloyd]

I sure wish someone had an off the shelf system that even I could hook up to my 8 HP Witte and produce about 350 VDC to feed the Sunny Boy.  Its getting close to crunch time as the back hoe is coming in next week to start the generator building hole.  If I get right on it I'll be producing electricity after dark in about two years.   

Casey

Casey,

Are you sure the 350 is the Vmin, and not the Vmax? Is it required DC or AC?

If it is Vmin a rectified 240 almost gets you there 3 phase 240 = 345.6 Vdc add a 1..25-1 step up transformer before before rectification, and you'll be 518 Vmax

I think there are many ways to skin your cat, if you know what type cat it is? Do You?

Ya got  an owners manual with V requirements, what amps out are you looking for and at what voltage?

Lloyd

[LowGear]

Lloyd,

Ask and you shall receive.  I don't why I settled on that 350 VDC but it should work as my attachment shows (I hope).  Your review would be appreciated.  Three phase generators are very plentiful and not really that more expensive.

Casey

[BioHazard]

As always when I ask a question here I get information I never even vaugely thought of before. 

I guess if you only plan on running 120v stuff from your generator it seems like a 3 phase generator has advantages over a single phase, and no disadvantages...am I wrong?

[LowGear]

Oops,

I should have shown you the output as well on the SMA 6000US.  As you can see this is a 240 VAC, in my case, inverter.

Casey

[deeiche]

rm /

[rcavictim]

Here's one way to look at the issue of efficiency of a three phase generator vs single phase.  A certain amount of power is lost in the field winding, this power is heat generator by current flowing thru the resistance of the wire.  If this is DC (see the thread on ST waveforms for what happens when it's not) then the power is constantly being wasted.  In a single phase generator, you have a part of the time when the waveform goes thru zero that the generator is not generating any power, but power is still being wasted in the field.  In the three phase setup, due to staggering the power windings, there is always some winding generating power.  So slightly less waste.

In the case of using 3 single phase generators to make 3 phase, you have 3 field windings, each one wasting power, so you wouldn't get this advantage.

Very clever and astute observation!

[LowGear]

Perhaps related is the advantage of running a motor at 240 Volts rather than 120 Volts.  Half the Amps means less heat and less heat mean greater efficiency.  You guys know you're way over my head but sometimes simple is good too.

Casey