Author Topic: Help me Reinvent the wheel for mppt (Read 2255 times)

halfcrazy · « **on:** April 04, 2009, 10:53:32 AM »

Ok first off i have the standard 10ft wind turbine from otherpowers design it has the 1 by 2 rectangle magnets. It is 48 volt. It is controlled by a Midnite solar Classic MPPT controller. what i want to try to accomplish is to use what i have for steel work for this experiment.

So my questions are

-what magnets should i try the 2 inch round?
-what would everyone recommend for coils? i suspect we would want to cut in at say 60volts dc. then it seems we could use a heavier then normal wire as the classic can keep it out of stall?

I currently have very good luck with this turbine as i understand it Dan calls it an 800 watt unit with the rectangle mags? We have seen 2500 watts on a couple good wind events and see 1600 watts very easy.

My thoughts are we could make a couple simple changes to the design of the mags and coils to make this turbine do 2500-3000 watts very comfy with the Classic in control.

Ryan

Placed in the proper section.

halfcrazy · « **Reply #1 on:** April 04, 2009, 07:44:07 AM »

Sorry i thought that magnets and stators where wind? someday i will figure out the proper categories.

Janne · « **Reply #2 on:** April 04, 2009, 09:03:27 AM »

Mayby a good starting point would be the OP's new 10' design, or even the 12' design.. with the 2"*½" round magnets.

You should take the maxium voltage input of your mppt controller, and design the stator so, that you will be about 80% of the maxium voltage when the turbine is outputting it's rated 3000W. Because of the mppt, you can get the best efficiency (and need to lightest possible transfer cable)by designing the stator voltage as high as possible.

Just some pointers that come to my mind.

TomW · « **Reply #3 on:** April 04, 2009, 09:08:45 AM »

Crazy;

The title has "MPPT" in it and that is your stated final use, thus "controls".

Tom

halfcrazy · « **Reply #4 on:** April 04, 2009, 09:33:15 AM »

I kind of was leaning towards the 2 inch discs. my theory for this experiment was to use the stock 10ft machine with no metal work mods. i do realize this will limit me some but i think it would be a good test of what is possible with existing turbines.

My logic was 60vdc cut in would end up giving me about 180 volts at 3000 watts. I could be shooting for say 225 vdc output but i don't know if there is any real benefit there?

I am curious if there would be a better magnet for the job then the 2 inch discs but if i want to stay with the stock rotors then i may not get much more in there anyhow. As i mentioned my goal for this experiment is to keep all the existing metal work.

I am in the process of building a pair of 17 ft turbines and we will be trying for the most efficient design there to but that is another day and another thread.

Flux · « **Reply #5 on:** April 04, 2009, 09:57:58 AM »

I think the 2" magnets would benefit from an increase in magnet rotor diameter. If you want to avoid that then keeping the rectangular magnets but increasing the thickness would seem worth considering. Going up to 3/4 " thick would make a significant difference. Ideally you need a wider gap and thicker stator but I suspect there are no real mechanical issues that would prevent that.

I can't comment on the voltage, you know the controller, I don't. The only thing that will limit you is the controller maximum input voltage. From my experiments I would have thought that if you cut in at 48v in the lightest wind that will do anything ( 5-6mph?) then at full load you would be up to 200V as long as you can keep alternator efficiency right up. I really see no serious issue with 200v and 3kW as far as line loss goes unless it is a long run. If the converter will stand more volts and you can match it at cut in then starting at 60v could be fine and would cut cable costs but once you go to mppt the cable issue becomes relatively trivial compared with direct connection.

You could raise efficiency even more by going to 1" thick magnets but I suspect the benefits will be small. Having made a quantum leap with the mppt you may not find it worth chasing a few more watts if it involves a large increase in cost as a bigger prop always gets you there easier.

Flux

halfcrazy · « **Reply #6 on:** April 04, 2009, 10:17:10 AM »

Thanks flux the 60vdc cut in was just a number i pulled based on my bulk voltage of 59.2. the controller will handle 250vdc.

So i have 2 choices go with the Round discs and make larger rotors. what would be the minimum rotor size you would go with?

or go to the 3/4" thick 1 by 2 mags and rewind my stator with the heavier wire.

right now i have 140 turns of #17 so if i went with round discs i presume i could do something like 130 tuns of #15 provided it would fit? that should give me a cut in voltage of 60ish?

but if i go with the 3/4 thick mags what would you wind for a coil?

halfcrazy · « **Reply #7 on:** April 04, 2009, 10:49:21 AM »

oh i botched that math i think i meant 175 turns to get 60vdc

Flux · « **Reply #8 on:** April 04, 2009, 12:24:18 PM »

I have not used round magnets and I have not drawn out anything to see how much you would need to increase disc size but you should be able to use about #15 wire and you may be able to reduce turns a bit.

If you go to 3/4 thick magnets you should be able to keep a similar gap flux with a stator about 1" thick. With the same flux you are looking at similar turns ( 140) but you should be able to get #15 wire in. This will get you about 2/3 of the resistance of the original stator.

If your converter can boost then the cut in volts is not too critical. If it can't boost then for best low wind results you will need 60v for a fully charged battery.

There is probably not too much logic in optimising low wind performance for a battery at dump volts, if you can get your cut in at 50v then that should be fine.

If anything it is still probably still safer to go for a few more volts than strictly necessary at cut in so the converter can do the correction for differing states of charge. If you can go up to 250v then starting at 60 is fine.

I suspect 3/4" rectangular magnets of reasonable grade should be a good way to go. N42 or above should be fine, the highest grades may not be cost effective but the old N35 stuff is now old technology and better avoided as you should be able to get N42 at a similar price. If N48/50 is cost effective then you may be able to cut turns a bit more and cut even more resistance. You may even be able to get even thicker wire in but #15 may be your lot.

Just as a matter of interest, if you can get the converter input volts up to 200v your stator loss is still lower at 3kw out than the conventional machine at 1kW and the new winding will let you run a lot cooler at 3kW than the conventional machine at about 800W.

Flux

halfcrazy · « **Reply #9 on:** April 04, 2009, 01:08:38 PM »

Thanks flux thats about what i was looking or hoping for a Semi simple remodel. I will look at getting the 3/4 rectangles they do have them in higher grade N50

so if i went with #15 wire for 140 turns per coil with N50 1 by 2 by 3/4 mags what do you estimate the cut in voltage? would it be mid to upper 50's or should i drop the turns down?

bobfandango · « **Reply #10 on:** April 07, 2009, 03:13:40 PM »

Well, the answer to that hinges on the estimate of the flux gap density. Most estimates of flux gap density for the 2x1x.5 N40's is around .7T. You didn't say what RPM you'd like to cutin, but assuming 140 rpm, you'd hit 60 volts with 140 turns if the flux gap density is around .8T. With those much stronger and thicker magnets, this seems pretty easy to do. In fact, I'd guess you are past that (but that is just a guess). Others no doubt could provide a better estimate.

bobfandango · « **Reply #11 on:** April 07, 2009, 03:30:07 PM »

I looked at the specs for the heavy duty stator Dan sells. Based on its specs and working backwards, the magnets that are called for must have a flux of about .85T. So yeah, I guess the N50's you are talking about should be in the range of .8 to .85 and hitting 60 volts at 140 rpm could be had with 140 turns. Unless of course I screwed up the math.....

Sly · « **Reply #12 on:** April 07, 2009, 05:19:35 PM »

Hi,

For what it is worth this is the details of my machine might help with your

decision(s):

Otherpower 10'

N42's, 1"x2"x1/2"

127 turns of 15 gauge (1 in hand) for a stator that ended up 5/8" thick.

cut in 155-160 RPM (48VDC)

1/8" gap between magnets and stator for an overall gap of approx. 7/8"

Keep in mind that from day one my intent was sacrifice a bit of output for long term durability and in discussion with Flux this is my final configuration.

It has taken a pounding since November and I am extremely please with it.

I follow your pioneer/research work with great enthusiasm and hope that the veterans on this site will continue to provide assisstance so one day we can all benefit from your MPPT research. Keep us posted good or bad!!

sly

halfcrazy · « **Reply #13 on:** April 07, 2009, 05:39:10 PM »

ok i think what we are going to do is get the 1 by 2 by 3/4 mags and make a stator that is 5/8 to 3/4 thick with #15 wire turns to be determined

bobfandango · « **Reply #14 on:** April 07, 2009, 06:26:30 PM »

halfcrazy,

FWIW, these figures above would correspond to a flux of .65T which makes perfect sense given the relatively wide gap... I'm getting more confident that the 2x1x.75 N50's would be in the .8+ range maintaining your existing stator width.

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