Author Topic: Alternator Efficiency  (Read 5023 times)

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Warrior

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Alternator Efficiency
« on: September 30, 2005, 11:36:01 AM »
Note: I'm not trying to prove anything, just checking on my numbers


I've been doing some number crunching with the info from the moded hornet. I used these numbers just as an example.


Efficiency was calculated at each speed. Blade power versus alternator power output.


The basic formula to find the blade's power at a certain wind speed is


Power [watts ]= 0.00508 [air dens] x area [sq ft] x windspeed³ [mph] x eff %


This is from Windstuff Ed's site with some conversions to imperial units


Assuming a 49" blade @ an efficiency of 40%, it gives me some wild numbers at low speeds


Alternator Efficiency was calculated as generator output divided by blade output x 100%


Moded  Hornet


Wind Speed     Calculated Blade Output    Generator Output    Generator Efficiency    Total Efficiency



  1. mph                         90W                        95 W                      105%                       42%
  2. mph                       215W                       153 W                      71%                         29%    
  3. mph                       420W                       260 W                      62%                         25%
  4. mph                       724W                       338 W                      47%                         14%


I wonder if I'm doing something wrong. Benz law says you can't get more the 40-50% (ballpark) from the most efficient blades so the first 3 results are really strange...specially 105%!!!

Anyone want to check these numbers?


Thx,


Warrior

« Last Edit: September 30, 2005, 11:36:01 AM by (unknown) »
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Warrior

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Re: Alternator Efficiency
« Reply #1 on: September 30, 2005, 05:46:20 AM »
The number alignment doesn't seem right on my screen, preview was OK though. Hope this fixes it:


Wind Speed  Blade Output  Gen Output Gen Eff.  Total Eff



  1. mph            90W        95 W      105%       42%
  2. mph           215W       153 W       71%       29%    
  3. mph           420W       260 W       62%       25%
  4. mph           724W       338 W       47%       14%

« Last Edit: September 30, 2005, 05:46:20 AM by Warrior »
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ghurd

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Re: Alternator Efficiency
« Reply #2 on: September 30, 2005, 06:16:13 AM »
Maybe try assuming a 49.5" blade efficiency is 42.5%, and the truck speedometer is off by 1.5 MPH, with a small head wind of 1 MPH, and the areodynamics of the truch making a small air stream up to the blades.  If you know what I mean.


Chart shows fine here.

G-

« Last Edit: September 30, 2005, 06:16:13 AM by ghurd »
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DanB

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Re: Alternator Efficiency
« Reply #3 on: September 30, 2005, 07:04:08 AM »
I don't believe truck testing is very accurate at all, especially at lower speeds.  If the machine is in front of the truck I expect youll have air piling up in front of the truck possibly lowering the readings, if its above/behind the cab of the truck I expect itll be seeing lots of extra wind thats going over the cab possibly giving optimistic readings.


It also gets very tricky I think, since power in the wind is related to the cube of windspeed, a small error in measurment could easily throw your output/windspeed ratings off by 50 - 100% I think.  We have twice the power at a bit over 12mph that we do at 10mph.


I've just about given up trying to get accurate output/windspeed measurments, I think the equipment required is fairly involved.

« Last Edit: September 30, 2005, 07:04:08 AM by DanB »
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inode buddha

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Re: Alternator Efficiency
« Reply #4 on: September 30, 2005, 08:13:29 AM »
Eh? How can the genny output be greater than the blade output? (the first line). There must be another way to test.
« Last Edit: September 30, 2005, 08:13:29 AM by inode buddha »

DanB

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Re: Alternator Efficiency
« Reply #5 on: September 30, 2005, 08:27:20 AM »
The joker in the deck here is windspeed cubed.  A very small error in that number(windspeed) will pretty much render the output figures totally inaccurate.
« Last Edit: September 30, 2005, 08:27:20 AM by DanB »
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inode buddha

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Re: Alternator Efficiency
« Reply #6 on: September 30, 2005, 08:42:51 AM »
OK, made a note of that and thanks.
« Last Edit: September 30, 2005, 08:42:51 AM by inode buddha »

Flux

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Re: Alternator Efficiency
« Reply #7 on: September 30, 2005, 09:34:30 AM »
Yes, wind speed is the enemy.


Betz limit is about 59% so 42% overall is not beyond the realms of possibility which is more than can be said for many claimed figures.


I believe some of the big machines achieve 45% into the alternator, but anything above 40% is exceptional for small machines.


It would be interesting to measure your alternator efficiency direct from mechanical in to electrical out. This would give a better idea of actual prop efficiency.


I assume from others comments that this is from a vehicle test, I have never done this and would probably be locked up for doing it on roads round here, but all the results I have seen seem optimistic compared with real wind tests that I have done.


Although almost certainly optimistic your results are credible and show a similar trend to what I would expect.


My blades may not be as good as you have used but my overall figures start at 35% and also fall to about 15% at the higher winds.


I find that blade efficiency also falls if I use alternator bench test figures, you may find the same.


Even with electronic tracking of the prop speed with a buck converter I have difficulty holding efficiency to 30% at 25 mph. Not had enough wind to be sure but I suspect it falls to 25% at 30 mph .


Producing accurate power curves is one of the most difficult things and most figures are only meaningful as a comparison if the methods and conditions are similar.


I find my figures to be similar to figures produced by Paul Gipe on similar sized machines. Even if not absolutely accurate they are a valid comparison to me as I use the same equipment for each test.


Flux

« Last Edit: September 30, 2005, 09:34:30 AM by Flux »

Warrior

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Re: Alternator Efficiency
« Reply #8 on: September 30, 2005, 10:22:30 AM »
Actually,


These figures belong to Jerry's modified Hornet (I thought I wrote that in the post). I just used his numbers as an example to compare efficiencies between homemade machines to commercial.


Here are the numbers for OT 17' mill assuming 40% blade eff


Wind Speed  Blade Power  Gen. Power  Gen Eff.  Total Eff


  10 mph          461W       400W         87%        35%

  16 mph         1555W      1500W        96%        39%


Don't know the wind speed for the 3800W output...


Looks like an excellent machine!!!


Warrior

« Last Edit: September 30, 2005, 10:22:30 AM by Warrior »
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DanB

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Re: Alternator Efficiency
« Reply #9 on: September 30, 2005, 10:32:33 AM »
hmmm....

obviously my numbers are rather skewed then, there's no way it's that good ;-)

I came up with numbers in a crude way, watching my anemometer, watching the ammeter.. and plotting little dots on a piece of graph paper.  My anemometer is a cheap one, and its about 20' below the wind turbine on the tower so perhaps that explains a bit...


A machine like mine should always get less and less efficient as windspeed increases I think.


It is an excellent machine though! ;~)  (so far...)

« Last Edit: September 30, 2005, 10:32:33 AM by DanB »
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Flux

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Re: Alternator Efficiency
« Reply #10 on: September 30, 2005, 12:31:44 PM »
Sorry, I thought you had also done some tests.


Your conclusions are right, but the wind speed data is not accurate enough to be certain of the figures. The fact that the results were credible is a tribute to Jerry's thoroughness. When you try it with spot wind speeds at a point away from the prop it goes hopelessly wrong.


Dan would be the first to agree that his wind speed measurements 20 ft below the prop are not nearly good enough for other than rough ball park figures.


Regarding comparison with commercial machines, the best home built are well up with the commercials and are generally optimised for better low speed results. Energy capture will be just as good, but high wind power and efficiency will likely be lower. If you optimise one end you trade it at the other.


Flux

« Last Edit: September 30, 2005, 12:31:44 PM by Flux »

steak2k1

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Re: Alternator Efficiency
« Reply #11 on: September 30, 2005, 03:05:35 PM »
Well the bottom line is that an anemometer is the first pce of equip one should put up...If I have learned anything...that little ditty is a "for sure".


As you mentioned Flux, optimize on the low end and the high end suffers.  One just cannot have his/her cake and actually expect to eat it as well.  (-%


...and to think I didn't like/do well in high school...I've learned more about electricity/wind and a whole bunch of other things in my short time here than the 4 years of canned BS in high school.!


College was different...I was there/did well because I wanted to learn..same applies here.


Thanx..


stk

« Last Edit: September 30, 2005, 03:05:35 PM by steak2k1 »

benjamindees

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Re: Alternator Efficiency
« Reply #12 on: September 30, 2005, 04:20:13 PM »
This is just a nitpick, but your figure for "air density" seems to include a correction factor.  Here's a more clear version, with the correction factor explicitly stated:


Power [watt]=  0.0083 [corr factor] x (1/2) x 1.204 [air dens, kg/m^3] x area [ft^2] x windspeed³ [(miles/hr)^3] x eff %


The correction factor is there to make up for the odd mixture of units.  You can substitute different values for air density into this formula.

« Last Edit: September 30, 2005, 04:20:13 PM by benjamindees »

windstuffnow

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Re: Alternator Efficiency
« Reply #13 on: September 30, 2005, 06:07:01 PM »
  Warrior,

    This is actualy a very interesting subject.  I've been racking my brain trying to come up with a group of formulas to aid in testing different units as well as predict the outcome of another similar unit.  


    Unfortunately, there are so many variables that contribute to the end result, it's difficult to do with a high percentage of accuracy.  


    I usually start out with some numbers from my test unit.   For instance, the one I'm working on right now is 12 sq ft, produces 1 amp in an 8 mph wind.  The alternator has a resistance of 1.2 ohm.  Then I simply run down through a bunch of formula's to find what I'm looking for, in this example I'm looking for the rotor efficiency.


    First I start out with the total possible watts in the wind.  8 mph has 31.2 watts going through a 12 sq ft area.  My unit is making 1 amp at 12.6 volts or 12.6 watts so the overall efficiency is 40% ( 12.6 / 31.2 ).  The alternator is making 1 amp and its resistance is 1.2 ohms so were loosing 1.2 watts in heat.  The way I see it is the rotor needs to produce 12.6 + 1.2= 13.8 watts in order to produce this output.  So the blade efficiency is 13.8/31.2 = 44% efficient in that wind.  


    Another example, the same unit makes 101 watts in a 19 mph wind.  The total power available in that wind is 418 watts, the unit is making 101 watts which makes the overall efficiency about 24% ( 101 / 418 ).  The alternator is loosing 58 watts in heat so the blade is collecting 159 watts to produce that output.  The blade efficiency at this point is at 38% ( 159 / 418 ).  


    I usually take my numbers and average them to get an overall outcome of what the unit is doing and remove 10% as an error factor.  In this case it would be (44+38)/2 = 41 x .1 = 4.1 and 41 - 4.1 = 36.9% blade efficiency.  


    Although its not a 100% given, it gives me a base to work with for designing another one using the same design.


I like the "corrected" formula better, it gives me a better efficiency result.... but I'll stick to my old formula.


If there is a better way to do this, please post it.  My way is time consuming!


.

« Last Edit: September 30, 2005, 06:07:01 PM by windstuffnow »

Jerry

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Re: Alternator Efficiency
« Reply #14 on: September 30, 2005, 07:52:10 PM »
Hi Warrior.


Not sure how this fits in here but SW Windpower says the 403 dose 400 watts at 28.8 MPH and it has a 46" blade?


                            JK TAS Jerry

« Last Edit: September 30, 2005, 07:52:10 PM by Jerry »

ghurd

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Re: Alternator Efficiency
« Reply #15 on: September 30, 2005, 11:08:00 PM »
The Mod Hornet is 62" blades, not 49".


If I have cross referenced correctly.

G-

« Last Edit: September 30, 2005, 11:08:00 PM by ghurd »
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Flux

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Re: Alternator Efficiency
« Reply #16 on: October 01, 2005, 12:08:10 AM »
Jerry


Paul Gipe makes it nearer 350W at that speed, even so it is an impressive figure for your sales literature.


The price you pay for optimising in a gale is that it produces nothing at 10 mph.


I imagine the main market is for marine use, not land use and with the higher wind speed at sea it performs quite well. It is no use in a low wind speed area on land.


Flux

« Last Edit: October 01, 2005, 12:08:10 AM by Flux »

Jerry

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Re: Alternator Efficiency
« Reply #17 on: October 01, 2005, 07:28:41 AM »
I removed the 62" Hornet blades and replaced them with my 49" blades.


Some time back I posted a chart 13 diferant motor conversions, Hornet, tape drive, tredmill, Garbogen, dual disc with Lowes ceramics and the 403.


At 15 mph the 403 was doing 144 watts nothing below this mph. At 30 mph I was seeing 325 watts. This is less than Paul Gipe got in his test.


I was thinking my test may be showing higher #s do to being truck tested. However my #s are lower than his on the 403.


Hopefully this means my other test #s were not over stated either.


Heres a list of gennys the did over 95 watts at 15 mph and there blades size.


Garbogen  49" 250 watts.


SW403     46" 144 watts.


1.5 hp conversion 3 phase

          49" 123 watts.


6 pole furnace conversion

          49" 120 watts.


GE ECM at 48 volts

          49" 120 watts.


moded Hornet 49" 95 watts.


Big TDM   55" 144 watts using blade extensions.


All these units have my plastic blades accept the 403.


The mast on the test truck is in the bed. The wind coming up over the hood and cab could be excelerated? But if so my 403 #s should be higher than Paul Gipes 403 #s?


The mast is 7 ft.


I still plan on building the wind tunnel.


I gather the data from a very nice analog amp meter, Fluke true rms multi meter and the trucks speedo. I checked the speedo with the State Police road side speed indecator, the thing that tells you your going this fast and its off by maybe 1/2 mph at 55?


I usually average wind speed in 2 directions to accont for prevaling wind.


               JK TAS Jerry

« Last Edit: October 01, 2005, 07:28:41 AM by Jerry »

DanB

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Re: Alternator Efficiency
« Reply #18 on: October 01, 2005, 08:43:27 AM »
Yes, another issue with truck testing which would probably tend to yield 'unoptimistic' tests is turbulance.  Im sure Paul Gipe is testing on a very good high tower with very little turbulance.


Truck testing is fun, and it's definitley a nice /fairly easy way to draw comparisons if nothing else.  I find it handy for adjusting the power curves between blades/alternators.  I used to be able to run a test, then change the configuration of the windings, or cut down the blade etc...  and kind of fine tune the machines that way.


I kind of quit doing it I think mostly because most of the machines I build are identical to past machines... or...  they're just too big.  10' diameter is quite a lot for the nose of my truck ;~)

« Last Edit: October 01, 2005, 08:43:27 AM by DanB »
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Jerry

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Re: Alternator Efficiency
« Reply #19 on: October 01, 2005, 06:33:28 PM »
Maybe my wind tunnel will work better? At least I won't have to drive and write at the same time. I won't have to worry about conners, cats dogs cows school buses kids car piling up behind me and all that hastle.


The data will be much easyer to record and wind speed and direction easyer to conrol.


I plan on 4 each 24" blades driven by 10 hp. 12 ft long, 8X8ft.


                       JK TAS Jerry

« Last Edit: October 01, 2005, 06:33:28 PM by Jerry »

Warrior

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Re: Alternator Efficiency
« Reply #20 on: October 03, 2005, 05:56:10 AM »
Hey Jerry,


Hope you didn't think that I was trying to state your numbers are overrated. I was just trying to see if the formulas I was using are valid for calculating output and efficiency.


I made an Excel spreadsheet that does all the numbers. You simply input blade dia. and wind speed. While reading one of you post from last week I just borrowed those numbers. Since the results were a little weird I decided to ask on the board if I was doing the math right.


Actually, I'm really considering build some blades similar yours cause they work so good. My induction conversion cuts in at 230 rpm, but using it direct drive with a 6.6 ft two blade, TSR 7. It seems to max out at around 500 rpm with a moderate breeze, and the generator is just make 5-6 amps at this speed. I wouldn't want to have it turn much more faster than this (scary). A smaller blade will probably be better.


Thanks,


Warrior

« Last Edit: October 03, 2005, 05:56:10 AM by Warrior »
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