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Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 06:11am 23 Jun 2018

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DaveP68 said
Goes to show that was seems like a great idea on paper can have unintended outcomes. An 8% lower operating efficiency is a big drop.
David

Where do you get this great idea on paper stuff ?
You are not the only person that actually builds and tests things.

This works exactly as I said it does, I even tested it with a 6KVA three phase transformer and a rectifier in both configurations.

Just to show you, I just now took a picture of the original test setup, exactly as it was back then.
Its still connected up in parallel configuration.
Somewhere here I have the diagonal shorting bars to connect it up in series.

Never tried it with a small alternator though, but if there are differences I would expect its because our sine waves may have significant distortion. I don't know what your alternator waveforms are like under load, but the mains waveform here is truly horrible.
That could skew the results significantly for both of us.

Edited by Warpspeed 2018-06-24

Cheers, �Tony.

DaveP68

Senior Member

Joined: 25/11/2014
Location: New Zealand
Posts: 292

Posted: 06:54am 23 Jun 2018

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Tony you were the one who proposed this idea not me.

All I did today was publish some 'actual' results out of an F&P stator which is what you seemed to be after at the time. Didn't mean to cause any upset today.

You were all ok with the test results last year.

DaveP68 said Hi Tony

Have tried wiring up an 80's stator in the configuration you suggested. Removed the star point and wired each set of 14 poles per phase to it's own rectifier as per your drawing below.

Warpspeed said This is the general idea:

Got the exact results as you described.

One advantage to taking this approach is the voltage levels are better than the standard star output.

Standard Star on an 80s is 0.685 VDC per 1 RPM vs Delta at 0.395 VDC per 1 RPM.

With your set up we get a slightly higher volts per RPM in the series mode of 0.787 VDC per 1 RPM. The parallel set up is the same as Delta at about 0.394 VDC per 1 RPM.

I can see merit in the way this works as the cut in RPM can be reduced by about 18 % if required (18 % higher for same RPM).

Good work and keep those new ideas coming through.

Next step is to try out your switching idea with the view to publishing the results. This could take me a week or 2, as got a bit of other stuff on my plate at present.

Cheers

David

Here's your reply.

Warpspeed said Yes, you get slightly more voltage than in star, but also slightly less maximum theoretical current capacity. It does put out a nice clean rectified dc voltage though.

But at very low wind speeds we cannot load the alternator to anything like its full current capacity anyway, without stalling the blades.
The driving torque to do it is just not there, so its not a practical limitation.

Its about the best we can do for max dc voltage at low rpm with just an alternator and some diodes.

The previously suggested mosfet switching scheme should work to give a hazard free changeover, but I have not actually tested this myself. Isolated gate drive power could be provided (initially for testing) from a couple of 9v batteries.

PS edit

Don't see any form of PMA in your photo, let alone a Fisher & Paykel stator which this topic was mostly about.

So Tony I just don't get where your coming from...Edited by DaveP68 2018-06-24

There are realities if you do not accept, will lead to frustration because you will be spending time on wrong assumptions and the results cannot follow! The Dunning Kruger Effect :)

DaveP68

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Joined: 25/11/2014
Location: New Zealand
Posts: 292

Posted: 09:48pm 23 Jun 2018

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Warpspeed said This might surprise you, but with three phases, and a six diode bridge, the RMS current through your slip rings will be 82% of the total final dc current.

On a separate note on things you seem to like pulling me up on the "R" in page that you posted on another topic (also above) stands for "Resistive Load". This is why the figure is you state is 0.82 and not the 0.72 to 0.73 I measured.

DaveP68 said I measured 2.05 Amps AC (True RMS meter) inline between Phase A out of stator into and Phase A input into the rectifier. This will be the current flowing through the slip ring. The DC reading out of the Rectifier was 2.8 Amps.

That's close enough to the 1.4 times I stated before or in other words the AC current was 73 % of the rectifier DC output value for that test. As saturation is approached the reading changed to about 72 % on one test I did.

The load I use for measurement isn't resistive, so my figures are actual and correct. My load uses a PWM system with a low value resistor which changes the conduction angle in the rectifier depending on what current is taken.

A resistive load is different due to the diodes in the rectifier conducting over a much wider range of the waveform.

There are realities if you do not accept, will lead to frustration because you will be spending time on wrong assumptions and the results cannot follow! The Dunning Kruger Effect :)

DaveP68

Senior Member

Joined: 25/11/2014
Location: New Zealand
Posts: 292

Posted: 09:06am 24 Jun 2018

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Oh one more thing Tony you have crossed a line just like Phil (fillm) has many times with me stating this sort of thing...

Warpspeed said Dave,
Barky seems to have the whole plan worked out in very great detail.
Lets just be patient and watch the whole magnificent thing take shape.

Don't think I'll bother with making any more contributions with the way I've been treated on here and that's a shame as I have lots more to offer.

Bye Bye

There are realities if you do not accept, will lead to frustration because you will be spending time on wrong assumptions and the results cannot follow! The Dunning Kruger Effect :)

Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5078

Posted: 03:10am 28 Jun 2018

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Settle down guys, please keep it civil.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

get real
Newbie

Joined: 16/12/2020
Location: United States
Posts: 9

Posted: 11:20pm 23 Dec 2020

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DaveP68 said Oh one more thing Tony you have crossed a line just like Phil (fillm) has many times with me stating this sort of thing...

Warpspeed said Dave,
Barky seems to have the whole plan worked out in very great detail.
Lets just be patient and watch the whole magnificent thing take shape.

Don't think I'll bother with making any more contributions with the way I've been treated on here and that's a shame as I have lots more to offer.

Bye Bye

Is Dave gone for good? Where ole where is Dave. He put out some good info on here.

get real
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Joined: 16/12/2020
Location: United States
Posts: 9

Posted: 02:35am 28 Dec 2020

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Gizmo said Been a bit of interest on adding diodes to the center point of a multi phase star alternator.

About 10 years ago I was talking with a auto electrician mate who said he was starting to see car alternators with the diodes on the star. He said on the test bench they were definitely making more power.

I've been trying to find some more info on google, but its knowing the right question to ask thats the hard bit. On one thread I did read a 10% gain, at a fixed rpm into a battery load. Of course this also means more power is needed to drive the alternator at the testing rpm.

I suspect the power output for a fixed rpm would be somewhere between star and delta.

Gizmo

Is there a pic on here showing how to hook up an F&P Motor to a battery? or can you tell me?

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