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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 02:12pm 01 Nov 2010
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Hi Readers,
I am working on an idea to extract power from the whole of the windmill output waveform into a battery. A bit like the way a direct resistive heating loading would. I still have some more testing to confirm the theory, but here is a preamble:-
Many will realize that a traditional windmill with std rectifiers into batteries, the windings pass current only when the generated voltage is greater than the battery voltage. An effect this causes is hum in the alternator during certain loading. Any windmill controller that allows the voltage to rise and then buck or boost the power to the battery will allow the hum to be generated over a wider power range. Many of the commercial windmills that use a boost converter front end to the controller generate significant hum from the windings.
I am looking at a reverse operation to a traditional GTI. ie instead of the DC-AC converter, I will reverse the process and make an AC-DC converter. This is not a rectifier, but has a rectification aspect. The cct will be a boost function block, and will work in parallel with the normal rectifiers. This will limit the power handling requirement needed.
I hope to incorporate a low power windmill MPPT function as well. The MPPT will use a micro control, that measures windmill rpm and battery voltage for control. The AC-DC converter will need to be analogue and digital, but not a micro. Hopefully these can be made to work together. This is a longer term project, and will hopefully make an alternator very quiet.
Gordon.
PS:- this has the ability to extract power from 1VAC to 20VAC, so is suited to up to a 48V system.
Edited by GWatPE 2010-11-03become more energy aware
VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539
Posted: 02:22pm 01 Nov 2010
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Hi Gordon
Sounds very interesting, I look forward to further developments.
BobFoolin Around
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 12:08pm 04 Nov 2010
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Hi Bob,
I guess what I am on about is hard to grasp for many, but here is a picture, that will help.
There are 3phase waves that most will be familar with.
There is also the 3phase full wave rectified, and the interesting flat red line.
My intention is to provide a loading similar to the flat line. The rectified waveform becomes highly asymetric with loading [especially a battery, or capacitive type].
I have tested a purely resistive loading on my windmill and the resultant alternator sound is silent, while if the waveforms are rectified first with the same resistive loading, the alternator develops hum.
Just have to get the electronics to do their thing now.
Gordon.
Edited by GWatPE 2010-11-05become more energy aware
VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539
Posted: 01:45pm 04 Nov 2010
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Hi Gordon
I can see what you are looking at, as my old mill I have been playing with different things to try to make it more useful at lower wind speeds.
The humming noise you mention was participially bad with it to, but my present configuration has quietened it down considerably and in a way is doing what you are talking about.
The Hum as I understand is caused by the switching transients of the diodes on the coils that have an inductance that is establishing and collapsing every cycle.
What I have done is put a large Cap 350000 uf across the diodes to give them something to charge from virtually 0 volts up, when it reaches 10.5 volts AC the GTI starts to draw current and its MMPT circuit draws more current as the volts increase and when it reaches 21 volts AC the second set of diodes start to conduct and charge the battery.
The GTI has a current limit that comes in at 12 amps so all extra current is diverted through the battery diodes, and in the heavy winds two weeks ago it was maintains 30 amps into the batteries and 12 amps into the GTI, 1200 watts, not bad out of an old 500 watt unit. In gusts it was pegging out the 50 amp meter, I pulled it down after the windy days to see if there was any overheating but none apparent, sorry no nice graphs yet as I am struggling to get some other things finished before I loose more hair getting the logger going.
It runs smoother and quieter than before as it is on the roof of the shed that is noticeable, one other thing is noticeable is that it has reduced the cut in rpm to charge the batteries, I think this is because the coils are conducting earlier they have more inductive reactance and generate a stronger reactance field to react with the magnet. Too long since I did the theory so am not sure on that.
It would be nice to charge the batteries from low speed so I see the potential in what you propose, the only thing that concerns me is the low wattage available as the output to the GTI is only 5 amps before the main rectifiers cut in.
I await your project with interest as I feel it is the way to go.
All the best
Bob
Foolin Around
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 01:18am 06 Nov 2010
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Hi Bob,
souunds like you have just moved the VI curve, to a lower current, and higher voltage operating point.
The configuration I have tested has NO hum, not just reduced hum.
Do you have some objective measurements to confirm a lower rpm battery cutin. Battery state of charge will affect the windmill cutin rpm as well.
I await some logged data of windmill rpm and AC output voltage, comparing different configurations.
Gordon.
become more energy aware
VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539
Posted: 02:06am 06 Nov 2010
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Hi Gordon
No recorded information only observation while its working unfortunately I gave up on the logger for the moment until I can afford a new computer that I can get it to work on, but I think the main problem is me.
I think the different type of alternator is the difference in hum level as mine is an old design per mag rotor not a axfx.
On the rpm it made the cutin come down 355 rpm to 320 rpm measured with the frequency meter on my multimeter, the low voltage cuts in at 250 rpm for 1 amp and gets to 12 amps at 350 rpm.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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