Safe Current Capacity Confusion

[Pete the Meat]

Hi all. I'm building a wind turbine with dual stators, It all started when someone gave me 2 identical 45Amp car alternators, I chopped the casing up on one to enable me to house both sets of laminated coil rings seperately in the other casing. I've replaced the original bearings with Linear bearings, this will allow the rotor to move from one coil set to the other.

The plan is (hopefuly), @ low wind speed the rotor will run inside a ring of very fine wire coils, @ high wind speed the wind will move the prop/rotor back into the second set of heavier guage wire.

I Downloaded a small program called "Wiretron" it converts wire size & gives info on Safe Current Capacity for each guage wire.

Well, i made some calculations to get 12v 11Amps @ approx 300rpm (on paper), 1st i doubled the poles, then halfed the wire size & doubled the turns twice, if i'm right that would take me to 30AWG but this has a Safe Current Capacity of 477mA I'm supposed to be knocking out 11Amps.

Then i measured the original stripped coil wire it was about 1.15mm thick, converted & compared this with my "Wiretron" program the result was = #17Guage wire with a Safe Current Capacity of 9.8Amps.

How could my alternator produce 45 amps safely?

If any one has any idea of what size wire i should be using on both of my stators and maybe a prop diameter to drive this baby, I'd realy appreciate some advice.

Thanks.....Pete

[scoraigwind]

You can get magnet wire in different grades.  The stuff I get is OK up to 200 degrees C.  If you run it hotter than that then its life expectancy is not great.  There is a very good link for insulation life and temperature at http://www.motorsanddrives.com/cowern/motorterms4.html

It also gives you a way to find out how hot the stator is getting, but only after you have built it and you measure the resistance.  And of course it depends on how much wind is blowing over the thing as well as the surface area and stuff as well as the current in the wire.

[commanda]

Car alternators are 3 phase.

Amanda

[Flux]

Pete,

Your wiretron program probably relates to transformers or similar.

The actual rating of wire depends on so many factors that I wouldn't trust any formula for current rating.

As Amanda said the car alternator is 3 phase so that any particular wire does not carry current the whole time and this allows a greater rating. Also car alternators have small coils and there is little build up of temperature at the centre of the coil, heat transfer to the stator is good and also the thing runs in a gale from the large cooling fan.

For your use you can roughly base the wire size on the existing wire, your cooling will not be nearly as good but wind power has lower average power levels, you will only see peak rating for short periods.

Use 180 or 200 degree grade wire and assume the original wire size is good for about 40A. The current of other wires will be proportional to their cross sectional area

so that if you use wire of half the area, only expect it to be good for 20A.

This should get you in the right area, when you have built it then you can measure its temperature rise by resistance using the formula in Hugh's very useful reference.

Love to know if you can get that sliding rotor to work.

Flux

[commanda]

Love to know if you can get that sliding rotor to work.

A star/delta switch will achieve much the same thing.

Amanda

[Norm]

  Got that right! Sounds much easier and Quicker!

   2 cents

   (Ah...Well...back to my 2ft.bladed stepper motor project)

                      ( :>) Norm.      

[Pete the Meat]

Thanks 4 your replies guys & gals, before i start winding all these coils, where can i find these "Star Delta" switches for sale?..."2 cents" i'm interested.

I saw Amanda was making some on another posting, these included other functions that are way over my head and i think i only need a basic one, if i can get one i will double up my coil rings doubling the length each coil, just to make use of it.

Pop in for tea if you come to Cornwall Hugh.

Cheers....Pete

[commanda]

You need a tacho first to give a voltage signal proportional to rpm for the star/delta to switch on.

Both of these are described seperately in my diary if you're handy with electronics.

Amanda

[Pete the Meat]

eek, I wish i was.

Your (Ammeter, Voltmeter, Tacho, Star-Delta switch) is that what i need? do you do a version without the Ammeter & Voltmeter, although i can see the benifits, i'm just trying to get costs down on my first turbine

Cheers......Pete

[commanda]

RobD does one as a kit, based on a pic micro. He doesn't appear to have any prices for it on his website, however. http://www.dsgnspec.com/

If putting a kit together is beyond your skill level, I could put one of mine together with just the tacho & star/delta switch. Really though, the extra parts aren't much. Better would be a fully assembled board, with just the meter for the tacho. Then the rest is there for when you want to add them later, just plug in the meters. The panel meters run about $20 Australian each.

Email me directly to continue this.

Amanda