Star vs IRP current capacity

[ChrisOlson]

If you build a generator and wire it star (wye) and the winding has a current capacity of, say, 40 amps continuous on the DC side of the rectifier - does the current capacity of that same windings change if you re-wire this thing IRP (Jerry) or delta?

At first glance it would appear to me that since you have twice as many AC wires supplying the power to the rectifiers (in IRP), or twice as many wires supplying AC current to the line (delta) that the current capacity of the generator windings is effectively doubled.  Or am I thinking wrong here?
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Chris

[bob g]

going from wye to delta, you increase amperage by 173%, you decrease voltage to ~57.6%

i would assume that going from wye to IRP will result in an increase of amperage, and a decrease in voltage
same as going from wye to delta, but i am not sure of the factors, it might be a bit different than 173% and 57.6?

bob g

edit:  it also occurs to me that it will depend on what you do with the resultant power from each of the IRP groups
if you parallel them, or if you series connect them after rectification

i am guessing here, but if you go IRP (jerry rigged) and connect them in series after rectification
then you will have the same amperage as in wye, but the voltage will be approx 1.73 x the wye phase to phase?
somewhere i remember it listed as ~225% of the voltage of  a single phase

got me wondering now if i read that or dreamed  it?



bob g

[Flux]

Yes the rating does change and so do other factors so it can be confusing.

Basically you can consider IRP as being the same as delta as far as rating under normal conditions goes.

Delta or IRP has a terminal voltage equal to that of one phase of the winding. Star has a voltage equal to the vector sum of two phases in series. For 3 phase star volts are root 3 ( 1.73) times the phase volts.

To get a direct comparison you would wind a star machine with 58% less turns to have the same cut in speed. This would let you get thicker wire in and get back to the same rating.

If you make no attempt to compensate for the voltage then the same machine connected delta has 1/3 of the resistance of the star case and will carry considerably more current in delta compared with star but you then change all the characteristics with the change in cut in speed.

Giving very rough figures ( no attempt to be precise) you have nearly double the current rating in delta compared with star. The same blade match would need the delta winding to be connected to a battery of about half volts.

This is why IRC connection lets you use a 24v machine fairly well on 12v.

So to sum up, for a given winding you get nearly twice the current rating in delta or IRC for the same temperature limit. If you wind the star with less turns of thicker wire to maintain the same cut in speed then the star rating goes up to match the delta.

None of this includes blade matching. A star winding that runs heavily stalled may perform very much better in high winds with IRC but you will loose out in low winds. You have to watch the comparison between power generated and the long term current capacity and invariably whatever the winding you trade a lot of high wind current capability by going for a low cut in speed.


If you load the alternator into a resistive balanced load then the current ratio is 1.73 times the star rating in delta but rectifier loads screw this up somewhat when feeding a battery. That is why I wouldn't be very specific about the actual gain in current rating and it is confused even more with harmonic circulation when not using a star winding.

I hope I haven't confused things too much by including the effects of prop loading as well as the simple winding rating but at different speeds.

Flux

[ChrisOlson]

Thanks Flux and Bob,

I guess what prompted the question; some time back I built a 13 foot 12 volt machine to power our lake home.  Our lake home is a 5th wheel RV, which is 12 volt, hence the need for 12 volt power.  When I designed the generator I designed it for 12 volt IRP with the idea that if I ever upgraded to one of these newer RV's with a 24 volt system that all I'd have to do is switch the thing from IRP (which is what I'm using now) to star and I'd have a 24 volt machine without having to change the stator.

I got the tail on it so it flops around like a fish out of water so it doesn't burn it up from too high of amperage.  But when I tested the generator after building it, driving it with a hydraulic motor, I found that I could get 50 amps out of it in IRP continuous and the stator doesn't even warm above room temperature.  And I could push it to 90 amps and run it there as long as the carbon pile in my Sun AVR would take it before even a hint of heat could be felt in the stator.  I know that in star that thing would be sizzling hot at those kind of amps.

I've wondered about that since I built it.  It's probably one of the most successful turbines I've built to-date as it puts out tremendous power at only 12-14 mph wind speed and the Doc Wattson I got on it says it's only ever peaked at 39.81 amps in higher winds.  If I tightened the tail up a bit I know it would push 80 amps without too much problem in a good stiff wind.  But I was afraid to do that based on the "rating" of the windings in star configuration.

Our water heater in the RV is either 12 volt or propane, and if I could tighten up the tail a bit and let it push 70-80 amps when the wind blows decent I could use the power to run the 12 volt water heater instead of burning propane.  If the amp capacity of the windings are effectively about doubled, as compared to the identical windings in star, it appears that I could safely do that without damaging the stator in the turbine.
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Chris

[TomW]

Chris;

Lake Home. I love that!

Does that make my old dead van in the woods rusting a Hunting Cabin? 

Tom

[ChrisOlson]

I suppose it could be if you can fit a TV and couch in there.

Up and down the lake there's quite a few places that use RV's for summer lake homes because it's a tax-beater.  You can own a chunk of lake property with no improvements on it and the taxes aren't too bad.  Build any sort of permanent structure on it, run power to the property, drill a well or put in a septic system and the taxes go up 20x.

And actually, our 5th wheel RV is bigger than some people's houses, we live there about 90% of the time in the summer, and we can be found out on the lake most evenings catching a few walleyes for supper, so we call it our summer "lake home".
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Chris

[jlt]

What are the specs of the 12ft turbine . and also what does the irp stand for .Why not jd jerry delta or something like it.

[TomW]

What are the specs of the 12ft turbine . and also what does the irp stand for .Why not jd jerry delta or something like it.

IRP ::: Individually Rectified Phases. The connection formerly known as Jerry Rigged.

A more descriptive term some of us have started to use for clarity..

Not to take anything away from Jerry as he was the one who started using it here.

Tom

[ChrisOlson]

What are the specs of the 12ft turbine . and also what does the irp stand for .Why not jd jerry delta or something like it.

It's a 13 footer, not a 12.  Tom already explained the IRP thing.  Using IRP vs delta seems to yield some slight advantages in performance.  There's one downside with IRP - you have to run 6 wires down the tower instead of 3.

The generator in my machine is a 12 pole 9 coil, wound with dual strands of AWG 13 wire.  I wanted to build a 16 pole 12 coil but when I layed it out I couldn't fit dual strands of AWG 13 in it.  That big wire is pretty hard to work with and get good tight coils.  I tried winding two different test coils and just couldn't get it to fit unless I increased the diameter a full inch - and I already had the generator rotors cut out so decided to go with the 12 pole 9 coil configuration instead, which I could make fit in the allotted space.

So, in IRP it's a good 12 volt machine that should push 80 amps without hurting it too badly - in star it's a very heavy-duty 24 volt machine.  Don't know how it works in delta - I've never tried that.  After following ghurd's suggestion on experimenting with IRP, and finding out it works better than delta, I've never messed with delta generators.
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Chris

[ChrisOlson]

That is why I wouldn't be very specific about the actual gain in current rating and it is confused even more with harmonic circulation when not using a star winding.

Flux,
Here's how I usually figure this; the formula I use for the maximum continuous current capacity of magnet wire in a coil is given by the diameter of the wire in inches squared times 4869.48.  I got this formula from one of the magnet wire manufacturers - I think it was Essex that told me that. In free air cooling the wire will carry considerably more amps than in a coil, however, and they told me that formula yields a conservative result.

So this generator has dual AWG 13 windings in it and AWG 13 is .072" wire.

• .072² * 4869.48 = 25.2 amps continuous per strand of wire
• Since there's dual strands you can multiply this times 2 for 50.4 amps per phase
• n star each phase only carries the current for 2/3's of the time, so you can divide that 50.4 by .67 to get a continuous rating of ~75 amps in star
• In delta or IRP there's four winding wires carrying the total sum of the current, so you can multiply the 25.2 times 4 for ~100 amps continuous

So it would appear that the current rating in IRP or delta, in this case, is more than in star but maybe not double.  Or is my math off here?
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Chris

[jlt]

The reason I was asking about the specs  i have a  12ft mill that   i made with 15" rotors 16 2x1x1/2 mags and 120 turns of 14 wire. It is connected irp . I had to open the air gap a bit to keep out of stall. mine is for 48 volt.I really had a tough time getting the coils to fit.  

[ChrisOlson]

The reason I was asking about the specs  i have a  12ft mill that   i made with 15" rotors 16 2x1x1/2 mags and 120 turns of 14 wire. It is connected irp . I had to open the air gap a bit to keep out of stall. mine is for 48 volt.I really had a tough time getting the coils to fit.

I also have 15" rotors with the same mags but a 13 foot rotor (actually it measures 13.4 feet). If I would've used a 12 coil stator I figured I would've needed 51 turns.  I tried it but I couldn't make AWG 13 wire form tight enough coils to get them to fit.  So I tried the 9 coil arrangement with 77 turns and by eliminating the space used up by the holes in 3 coils, the 9 coil arrangement would fit.  I actually ended up with a small amount of space between the coils.

Mine doesn't stall at all with the air gap at .750"  If I would've used AWG 14 wire I think I could've gotten 12 coils to fit.  But AWG 14 scared me a little bit for 12 volt IRP as I figured it was a big light.  If I would've known what I learned here in this thread, I maybe could've gotten by with it.
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Chris

[jlt]

I have a set Of 14 ft blade blanks . That i have hesitant to try ,but after reading about your  i think i may try them and  then i can tighten up the air gap. I only short out 1 phase to stop it .Shorting all 3 makes it stop very violently.Almost like throwing a rod in the spokes of a bicycle.

[ChrisOlson]

I have a set Of 14 ft blade blanks . That i have hesitant to try ,but after reading about your  i think i may try them and  then i can tighten up the air gap. I only short out 1 phase to stop it .Shorting all 3 makes it stop very violently.Almost like throwing a rod in the spokes of a bicycle.

I think that's a characteristic of IRP because mine does the same thing if I short all three at once.  I think with star or delta it's a bit gentler when shorting it because of circulating currents in the stator or something.  With IRP it's like somebody threw a board in the fan - so I only short one phase to stop mine too.
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Chris