1 coil with 12v, 24v, or 48v option

[etownlax]

Hello all,

I searched but couldn't find it.

What I was thinking was basicly build a 48v coil. But my thought was: "Why not have the option of 12v or 24v or 48v?" So I came up with the idea of making 4 12v coils, all into one coil, made from the thinner wire that a 48 volt coil would use. So you have the option of putting all the leads from the coils in parallel to make a 12v machine or put them all in series to make a 48v machine. Or to make the 24v machine all you have to do is make 2 coils in series then parallel it to the other 2 coils that are in series. If you really wanted to you could make it a 36v machine by leaving out 1 coil and putting the rest in series.

I was wondering has anyone done this? What could be the problems associated with this? I'm getting 20awg wire. I was gonna use 17awg but 20awg was cheaper(thanks Valterra) and 20awg is half the size of 17awg. The only thing I can see being a problem is matching each "inner" coil to the other "inner" coils- Making sure that one doesn't end up being 13v and the next one 11v.

I understand it. But I might have worded it a bit oddly. If you have any questions just ask.

Any suggestions are greatly welcomed. Feel free to pick it apart.

-Randy

[RP]

I think if I was going to do it that way I'd wind each coil "4 in hand" rather than stacking 4 coils.

[etownlax]

I was thinking more along those lines. BUT I would be 8 in hand :-| . Because half #11 is #14 wire(#14 used on a normal 12V machine). So 2 strands of #14 is equal to 1 strand of #11. So 1 strand of #14 would make a 24v machine(2 times the turns). Half of #14 is #17 wire. But Half of #17 is #20. So if you follow what I just said(unlikely :-| ) then for a normal 48v machine you would use 2 in hand of #20 or 1 in hand of #17(4 times the turns than a normal 12v machine). So if I do it my way. I would have to do 8 in hand and the same number of turns for a 12v machine.

Hopefully you got that ;-)

-Randy

[Flux]

The theory is correct and if you were doing a motor conversion it would probably be ok.

With air gap alternators you will have extreme difficulty making everything accurate enough to avoid circulating currents with the parallel connections.

If you insist on using the #20 wire, then as you seem to want a 48v machine, I would reject the 12v option. If you wind 4 stacked sections to a coil as you suggest you will need to be extremely careful with the winding to get even a reasonable voltage balance.

I think the 8 in hand winding will also lead you into a messy winding and again it may not be well enough matched for the 12v case. It may be good enough to use 4 in hand to cover 24 and 48v.

This sounds like a big machine and the 12v option is probably not a sensible choice for other reasons, with line loss, rectifier loss and the problems of the alternator winding.

You don't say what the alternator arrangement is. If it is 12 magnet 9 coils you have little other choice, but if it is 16 magnet 12 coil you have the option of connecting the coils to do your voltage change rather than reconnect each coil. Even then you may still get circulating currents unless you rectify the parallel groups separately.

Far better to decide your system voltage and go for it from the start in the end I suspect.

Flux

[etownlax]

I'm planning it to be a 12 magnet 9 coil alternator. I'm thinking I'm gonna make it 10ft diameter.

Thanks for the input. I guess I will just make it a 48v machine with no option of 12v or 24v.

-Randy

[tecker]

If you build for 48 volts you can regulate for 12 or 24 no problem . Any quad fillar is a mess to do .

[DanB]

In my mind it would be fairly tricky - how would  you 'regulate it' for 12V no problem?  I know that some of the MPPT controllers that will(hopefully) be coming out soon will probably do this but it won't be simple or easy or cheap - and for 12V application they'll need to handle well over 100 amps at times for a 10' diameter wind turbine.

In any event - yes, like Flux said - no matter what you do with an axial flux machine, any parallel connections will cause problems.  Best to keep it all in series and build for the correct voltage to begin with.

[etownlax]

Ok thank you DanB for your input.

I think I'll stick to making it just a 48v alternator. But I'm gonning to use 2 strands of #20 not because #17 is too thick but because I can get #20 for like 50bucks.lol So at this point 2 #20's is in my best interests. But I do understand your reasoning about parallel lines. I will try my best. I'll probably run the wire out of 2 spools. Then run it out like 100 feet and tape them togather every 5-10 feet(time consuming but might be worth it). Then when I wind up to the tape I simply remove the tape before continueing. This way I can keep the lines perfectly in sync.

-Randy

[tecker]

I don't think this guy is building for 100 amp output DB  but lets say he has 48v X 50 amps you basicly set up a 48 volt series string and 4 12 volt battery banks and switch between the four 12 volt banks as needed.

[finnsawyer]

You're ignoring the effect on resistance and power.  Going to (in effect) the 24 volts at 2 in hand he would get 1/4 the resistance.  At 12 volts the resistance would be 1/16 as much.  In each case the power generating capability would theoretically be the same (into a matched load resistance).  The power out will be reduced severely by regulating down from the (high) resistance 48 volt version.  Perhaps, if he really wants to have the different voltages available, he should consider a single phase alternator using step down transformers.  I realize this flies in the face of the infatuation shown here with the three phase design, but it is up to him to define what he wants to do and then consider all the options.  

[DanB]

To me making compromises in the stator (single phase) and dealing with transformers etc.. etc..  is a lot more complicated than just building 1 good stator for the voltage you need to begin with, and if he decides on a different voltage at some point, it would be easier to build another stator.  I don't see any advantage to building a machine with all these options - pick a battery voltage and stick with with it!

[finnsawyer]

I don't know if the users of this site are aware that a transformer also transforms impedance.  That is, a step down transformer to half the output voltage and twice the output current will present 1/4 of the input impedance at the output looking back toward the source.  So, while transformers do introduce losses, their ability to match a high input impedance to a lower output impedance means they probably would give better results than 'regulating' down in voltage.  I suggested single phase because that would require only two wires from the alternator at the pole to the single transformer at the batteries.  He might also consider a single phase design having a natural higher frequency output, such as the one I presented in my diary.  There are cases where the windmill must be a considerable distance from the point of use, and in such a case this kind of system would make sense.  

[TomW]

Dan;

Good analysis. Complexity just adds to the failure potential, IMHO.

I still think perfection is not achieved when nothing more can be added but can be achieved when nothing more can be removed and still do the intended job.

The elegance of simplicity has a great appeal

Having said that, I say the poster should do what they desire, report back on the results and learn something first hand.

Personal opinions, of course.

Cheers.

TomW

[etownlax]

I'm gonna have a couple pounds of copper that will be extra. So I was thinking I might give my idea a try. But just on 1 coil. See how its works.

I do have a few more questions. If I have 2 coils basicly stacked togather. And each has exactly the same number of TURNS. Is there anyway that the voltage would be different assuming that they are on the stator receiving the same flux? What would happen if 1 has same number of turns BUT is just a bit longer due to being wound more on the outside and therefor having a different resistance? Also I'm assuming that RPM vs. Voltage is not linear. So if you did get 2 coils at the same voltage at the same RPM there is still that chance that at a different RPM they will be different. Am I correct at assuming that?

Ok thanks for all the replies and thoughts.

-Randy

[DanB]

yes - you'll definitely get currents circulating between any parallel connections especially with the axial flux design I think.  I even notice it when we wind with multiple strands in hand on larger machines - there is definitely noticable drag in the stator and I expect its currents running between the parallel strands within each coil (though I don't think it's that significant in that case).  You could do it as you describe - there will be losses at lower voltages and you'll have tons of little connections to change each time you want to change voltage (and Im not sure why you'd ever want to).  Again - if it were me, I'd keep it all simple and make the stator that suits your needs.  I expect for the extra work involved in making something so adaptable - and considering the added inefficiency... it would be easier to build 3 stators.