Author Topic: Comparison of Two Turbines  (Read 2243 times)

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Offline ChrisOlson

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Comparison of Two Turbines
« on: April 14, 2012, 01:13:03 pm »
Since I've built both ferrite and neo generator MPPT 3.2 meter turbines, I've been trying to figure out which one is better.  This is a video I snapped yesterday of the ferrite one, using my wife's camera that has zoom on it.  The wind was gusty and turbulent and the the machines were yawing wildly back and forth all day:


As far as performance, there is no difference in the two machines.  The two machines are identical except for the generators - they both have the same gear ratio - they both furl at 36-40 mph, they both reach 1 kW @ 19 mph, 1.7 kW @ 25 mph and 2.5 kW @ 28 mph.

The ferrite is 16 pole and its output is much smoother than that of the neo.  The current frequency is higher with the 16 pole.  It reaches 60 Hz @ 180 rotor rpm @ 10-11 mph wind speed and 150 watts output.  The neo gen reaches 60 Hz @ 15 mph wind speed and 450 watts output.  The higher current freq makes the ferrite generator run VERY nice - it's totally quiet except for a very slight hum in the tower.  The lower current freq of the 12 pole neo gen causes more vibration and it's noisier running and more "buzzy" at certain frequencies and speeds.  The Classic seems to like the higher frequency of the 16 pole ferrite generator.  It appears to "pulse" the output from the neo machine, which causes the analog ammeter needle on that turbine to wiggle at lower outputs.  The output from the Classic with the ferrite gen is just silk smooth.

The rotating assembly in the ferrite generator also weighs 46 lbs.  The big 46 lb flywheel running at up to 1,200 rpm stores a LOT of energy in it, and it smooths the output in gusty winds.  The neo machine is like it's on and off the gas all the time in gusty and variable wind.

The ferrite machine runs up against the voltage clipper at 88 volts @ 2.5 kW, which is 84 amps into the battery.  The Classic controller is 92% efficient at that output, so the turbine is actually developing 2.7 kW @ 88 volts, or 30.8 amps from the generator.

The neo machine runs up against the clipper at 125 volts @ 2.5 kW.  The generator amps is 21.7 @ 2.7 kW at the generator with that one.  The internal resistance of the neo stator is .47 ohm vs .55 ohm for the ferrite.  So in theory, the neo should be more efficient.  But I've never seen this increase in efficiency in the amount of energy production logged from the machines, nor in real-time output.  They're always within a tenth of a kWh from one another on any given day.

The primary method of over-speed control on both turbines is the voltage clipper.  Furling is no longer used on these machines for power control.  It is only there for extreme winds in storms and whatnot to let the machine turn to the side of the tower to take some of the load off the tower.  Using the voltage clipper is a positive and very accurate means of controlling turbine speed - I can tune it to within +/-10 rpm.  Furling is just about useless as a method of power or over-speed control.  Ultimately I went with the same setup that Bergey has used for years with the Excel - furl the machine at very high wind speeds just for storm protection and use the control electronics to do the heavy lifting for power control otherwise.  I've long believed that furling is one of the most unreliable methods of primary control there is, and flying these very high performance turbines has only reinforced that fact.

I think I'm trying to talk myself into liking the lower voltage ferrite machine better.  That's just because of its super smooth operation and output, I think.  That could be achieved with a neo as well - but at considerably higher expense.
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Offline ghurd

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Re: Comparison of Two Turbines
« Reply #1 on: April 14, 2012, 01:51:51 pm »
Quieter from the ferrite doesn't make any sense to me, unless its from the extra weight, or a different physical charicteristic of the assembly.

Smoother doesn't make any sense to me either.  Higher frequency should be a far smoother output, and not worse enough to make an analog meter pulse if the lower frequency machine is smooth.

Any ideas about that stuff?

The only thing I can come up with (grasping at straws) is maybe a bad connection or something.
Not likely, and it wouldn't account for all of it combined (I don't think).

2 things I really like about this post.
1)  Same power output, with the same dia, from very different machines.
2)  The power difference between 25MPH /1.7KW and 28MPH /2.5KW (12% increase in wind for a 47% increase in output).

G-

Offline ChrisOlson

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Re: Comparison of Two Turbines
« Reply #2 on: April 14, 2012, 05:04:19 pm »
Quieter from the ferrite doesn't make any sense to me, unless its from the extra weight, or a different physical charicteristic of the assembly.

I'm convinced it's because the ferrite is a 16 pole where the neo is a 12.  The generator in the neo unit makes groaning noises at various speeds and at one certain speed makes a howling noise that reminds me of some experimental stators I wound once.  If you put blindfolds on and somebody led you to the base of the tower with the 16 pole ferrite on it, you'd swear there's a 31-20 Jake on that tower.  That's exactly how it sounds.  It's got a nice hum to it that gets slightly louder with more power output.  But none of the groaning and howling that the neo generator makes at certain speeds.

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Smoother doesn't make any sense to me either.  Higher frequency should be a far smoother output, and not worse enough to make an analog meter pulse if the lower frequency machine is smooth.

I believe that's something in the Classic controller that does that.  The DC output pulses at low outputs from 5-10 amps.  At least with the neo one it does.  With the ferrite machine it does not do that.  I attributed that to the fact that the ferrite machine has such smooth DC input to the controller, where the neo is probably a little "bumpier".  I don't know for sure.

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2 things I really like about this post.
1)  Same power output, with the same dia, from very different machines.

They're actually the same machine with different generators.  VERY different generators.  I designed the neo one to run at higher voltage, as my thoughts were to use the clipper for heating water with the higher voltage turbine.  That didn't really pan out because it requires the machine to operate at maximum rpm all the time.  I found out that it's better to use the solar Classic controller with what they call "Waste Not Hi" mode in the controller to heat the water.  And I also found out that the multiple Classic controllers play VERY nicely with one another.

I did design the different generators to have very similar power curves, although on paper the neo one should've been a little more powerful.  And it may be - but I think the reason they are both so close is that I'm running my blades right up against the edge of their performance envelope with either generator.  To get the extra capacity from that neo generator that I know it has in it, I'd have to put bigger blades on the turbines.  At 21-22 amps and 125 volts, the stator windings barely get warmed up in it.  It's wound with 13 AWG and it could easily handle 30 amps.  But 30 amps @ 125 volts is 3.7 kW.  And it could easily handle running at 150-180 volts.  But 30 amps @ 180 volts is 5.4 kW.  It takes 35-40 mph wind to get that from my 3.2 meter blades.

The neo generator is incredibly powerful.  Watch this video, which is a demonstration of throwing the shorting switch and engaging the clipper load at Full Dawg.  To bring a 45 lb 10 foot rotor to a dead stop like that, that fast, takes some VERY powerful braking:


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2)  The power difference between 25MPH /1.7KW and 28MPH /2.5KW (12% increase in wind for a 47% increase in output).

You bet.  As the wind picks up, that's where your power is.  I've had the ferrite machine pushing over 4 kW @ 100 volts when I first built it and was experimenting with it to see what it would do.  But it takes 35 mph wind to get it.

The thing is, the Classic controller is good for 94 amps on a 24 volt system, which is 2.8 kW @ 30 VDC.  BUT - the Classic will de-rate itself as it gets hot from continuous high output.  So if the controller gets hot it might de-rate itself down to only 84 amps.  So I have amp output limit set in the controller at 84.  When the DC amps to the battery gets to 84 and the wind picks up more, the controller starts to unload the turbine and let the input voltage climb.  When it climbs to where I have the clipper set to kick in, the clipper takes over and brakes the turbine by applying ever increasing load if it tries to speed up more.

So my end arrangement on these turbines, that I settled on, was to limit the power to the battery to 2.5 kW and use the clipper for a brake to keep the turbine out of over-speed.  And forget about using the clipper to heat water.  It takes too complicated of a system, too much wire, and too many elements to heat water with three phase power.  The system I have set up now where the factory stock thermostats in the water heaters switch elements as the water heats up works good.  And I'm only running one 2 kW heating element at a time during the process.
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Chris