Wind questions concerning voltages

[Yyrkoon]

Hello all, newb here. However I am not exactly an electronics newb(although I probably know just enough to get myself into trouble concerning whether I really know what I think I know ). That aside . . . I am looking for an idea of where I may want to start.

I have some questions concerning 'base' voltage output of any given alternator, for use in charging a 12v battery bank.

 Would using a 48v alternator for charging a 12v system make good sense while using an efficient buck converter ? I know there is more than one aspect to this question so let me explain some of my ideas.

First off I am thinking that while a 48v HAWT/VAWT may need a higher RPM to 'cut-in' at it's intended voltage, that cut-in speed would be lower for a 12v system. I am nearly possitive this is a good thing, however I am expecting some trade off's here, and am not exactly sure what they might be.

Secondly, I have been thinking a lot about using an a/c, PWM controlled/double mosfet designed buck converter. Again, I am not an Electronics genius, but I have found a shcematic or two(thanks to Ed Lenz's link pages). Anyways, from what I think I know, this would be good for converting that extra voltage to amps. SO I guess what my question here is this: does this make sense ? Is there a better way of doing things here ? I know that batteries will 'clamp' the output down, but not sure how high you can go before it can damage the batteries. If reasonable to use, my idea of placement would be just before the DC rectifier, which its self would be in close proximity to the battery bank. Hopefully, this would reduce as much line loss as possible.

This whole idea I have had here started with a conversation I had with a neihbor here that has had plenty of hands on experience with pre-made systems(24v Mallards). These PMA's mounted on a 20' pole burned out within 3 months of use in our area. He now uses a well designed AirX system I believe, and it works good, but does not output as much power as the Mallards when they work. My neighbor is a very experienced electrician, but since these car alternators on what looks similar to a wrought iron frame do not have a furling system, I suspect they ran wild until they burned out. Personally, I would not be adverse to using these if I could find a way to keep them in good working order, as my neighbor says they can put out a good 500W a lot of the time in moderate winds.

The Wind in our area here seems to average at about 5-7mph, but we can get some really good gusts of up to 60+ mph. The cool thing about here(Eastern AZ at ~5700FT above Sea level), is that we get a lot of sun, but when it gets cloudy(like it often does mid-day this time of year), the wind starts blowing. We already have a PV system, a very good one at that, but when the sun goes away . . .

What I am hoping here is making a HAWT/VAWT that can output a decent amount of power in low winds, but be able to live though the high winds here when they do happen. My idea of 'decent' is somewhere between 50W-100W between 7-14mph winds(but of course I would not mind more!). On the dump load end, we are considering designing a controller that will dump into a hydrogen generator. Heating water, or dumping that energy to air through resistors just does not make much sense to us, but I can understand the need for it if nothing else is possible.

Wrapping things up, I hope that I have given enough information for you guys/gals to comment on. Yes, I know I do not have anything very specific here, but please go easy on me as I know several of you are very knowledgeable concerning these things(this would be why I am posting here ) Any comments are welcome of course.

For what it is worth, we are completely off grid, and since the power company wants 10's of thousands of dollars to supply us with power . . . We also have a 30Kw cummings powered diesel generator, but that right now is only used to pump water(until we get a good pumping mill working - for irrigation/consumption), and to power the 220v shop equipment that we have. Eventually we hope to have the hydrogen generator I spoke of above manufactured, and working, as well as a bladder for storage, and possibly even a means for putting that hydrogen to good use  

OH! and hey. Anyone have any ideas on where one could find surplus/used forklift batteries ?!

[Flux]

There's a lot here to think about. It may or may not make sense depending on how you tackle things.

Firstly if it is VAWT I don't want to know. I also have a feeling that you are dealing with HAWTs with no control or furling. If your ideas are to save having to have some form of furling then you may or may not have some luck. I don't think other than tiny machines will survive all conditions without some form of power limiting.

What you propose can work very well if you go about it properly, I just don't know at this stage how much you understand the problems.

It's rather confusing when you talk about using a 48v machine to charge 12v but when you are considering buck converters then you have the potential to make things work if you understand all the problems of loading to match the blades.

Basically the advantage of using a 48v machine to charge 12v is that the line loss becomes less of a problem. If that is indeed a problem then yes you gain, otherwise you would make life easier to use a nominal 12v machine with cut in at the lowest wind speed you hope to use. Rather than clamp the thing down to 12v then the buck converter lets you raise the alternator volts with speed so that in a reasonable wind then your nominal 12v machine will be producing perhaps 48v which you will convert to 12v.

If you start with a 48v machine then you may be seeing upwards of 200v in a high wind. If you can convert that efficiently to 12v with a converter then ok that's fine.

You will have to devise a way to control the converter so that the load into the battery phases the converter to track the input power of the alternator to the cube of the wind speed. What you are producing is a mppt converter. It will let you extract much more power from a given alternator without burning it out but even so I think anything other than a tiny machine would get out of hand at over 30mph.

If you can go the mppt route then it will perform very well but to just use this approach for survival in very high winds then you have a different issue as the power rises as the cube of wind speed. If you let the prop speed track wind speed then it will get fast and noisy above about 30mph. Once you start limiting the speed  you are relying on prop stall to hold things down, it requires very large alternators or you have to try and brake things to keep in stall. If you loose the load then you have a serious problem without some backup form of power limiting.

Flux

[Yyrkoon]

Hi Flux, thanks for the response. To make things maybe a little easier on you, I can say that my buddy here is/has been an EE for over 30 years now. Having said that he knows very little about the technicalities of electric motors/generators etc. He is brilliant when coming up with designs from scratch, but I guess the motivation for this sort of thing never was there(until now heh). He does know much more about conversion/regulation than I do, and I plan on hitting him up for info when he is back in town.

I have read a lot here, including your diary entry on 'load matching' was it ? I also am very interested in this myself(that is: if I understood what you're talking about, because a lot of it is over my head).

My reasoning for 48v stator into a 12v battery bank was really tri-fold.

1. efficiency.
   
2. survivability.
   
3. Possibility to convert more power.
   
   

Efficiency is pretty basic electrical stuff, and I am pretty sure I have that part nailed. At least within reason.

Survivability I was hoping would be another aspect of using a 48v wound stator. Meaning I was thinking/hoping this could withstand more punishment.

Converting power we pretty much already covered.

I DO want as much power as possible with whatever I end up with, BUT not at the cost of reliability. Pretty much I want a bullet proof alternator, that outputs as much power as possible(to a point). If this means using a HAWT, with a mechanical, or electrical furling/brake system, that is what I will do.

Eventually, I want to get into custom building my own axial flux, with probably dual rotors, and a 48v stator. Going really really big here could be possible also, as we are on 40 acres, no neighbors closer than 1/4 mile away, and I just so happen to have 200-300ft of very solid well casing sitting around doing nothing I am getting the feeling the more I read here however that I do not want to rush into things, and I may just grab a Mallard mounting kit, and an AC Delco alternator from the local bonyard here to play around with. After that, perhaps build the 10' homebrew(the one with the very detailed pages).

There is definitely lots to think of here . . . and everything I need to know is probably going to take a while to figure out.

[Flux]

You have given this a fair bit of thought.

Efficiency is not inherently higher for a 48v alternator than a 12v one, in fact for the same magnets and copper it ought to be the same. A 48v system will come out higher generally because the line losses will be less for the same power and rectifier loss will be less. With conventional loading directly into a battery the only thing that makes much difference is the cost of the line cable at 12v. The 48v system will need to be degraded to 50% at full load to prevent prop stall.

The gain with a 48v alternator converting down to 12v will be almost exclusively from reduction of line loss. The alternator efficiency will be the same as a 12v one when its voltage is allowed to rise with speed.

Survivability will not be different for 48v. This is a function of the heat generated in the stator and that depends on efficiency. Survivability will be much better for mppt operation whatever voltage you start from.

Again the possibility to convert more power comes from mppt not from a higher voltage alternator.

If you can solve the problem of dealing with the much higher voltages from a nominal 48v alternator then you gain a bit on line loss. You may be pushing the limit for a normal buck converter starting at 48v for a 12v system and may be better with a switchmode power supply incorporating a transformer for the large voltage change .

For the power levels that you can handle at 12v I still think that starting at 12v nominal at cut in and running up to perhaps 48v on full load will be an easier solution. The 12v system will be limited to lower power and I can't see the line loss issue being a big one unless you have a very long cable run.

Forget the VAWT go for a HAWT and accept that furling will make your life infinitely easier. If you and your friend can manage the converter then you are really on a winner, the gain in performance is pretty spectacular.

Flux