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DaveP68
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Posted: 19 June 2017 at 10:09pm | IP Logged Quote DaveP68

Hi oztules

This explains why I was maxing out at 40 Amps and you got 45 Amps.

To date haven't done any high RPM short circuit testing, as didn't see the point for a net Zero output result.

So did a high RPM short circuit tests and the maximum current I got was 44.25 Amps. My shunt was proving to be accurate after all.

So at high RPM my figure of 40 Amps into a practical load still stands as an upper limit, but not quite maximum.

Did try a few different rotor caps to check how close they were at maximum current. Most maxed out around 44 amps with readings of between 43.4 and 44.25 Apms. Also another factor is the variation from stator to stator which is why your stator could be 0.75 Amps higher again than mine. This is of course conditional on your 45 Amp reading being very accurate.


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oztules
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Posted: 20 June 2017 at 7:47am | IP Logged Quote oztules

Accuracy was of no concern to me in those tests, the only thing I was interested in was the theory, and if it was to hold water... which I have not been able to prove in any way shape or form.

I only wanted to see change, and i didn't much care what the empirical figures actually represented... in this case I reckon it was pretty close to what it purported to show.

So the short circuit figure, while interesting, is of no real use, other than to explore the losses in the stator.....Nice to see you got the same magnitude though.

I am intent on making the IC genny version, so will heed your advise, and perhaps band the outside perimeter.

I think that one of these connected to a <200 dollar electric start motor on ebay will be pretty nice to use... simple and idiot proof perhaps.


.........oztules

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DaveP68
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Posted: 20 June 2017 at 10:40pm | IP Logged Quote DaveP68

Hi oztules

Can't help myself on the accuracy part of my readings, probably to do with working in aviation in the past and having to follow strict rules or you could be killed.

Will try replicating the test you did by removing a phase to observe the jump in current from 20 25 amps you noticed. Have an idea why but want to check it out for myself.

If you can get hold of a copper 36 pole stator with a black rotor cap they will output more power for the same RPM or same power at lower RPM by a factor of 40%.

You can of course stick with your 80s 14x 1p star that's already working very well though.
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DaveP68
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Posted: 23 June 2018 at 3:31pm | IP Logged Quote DaveP68

Warpspeed wrote:
This is the general idea:



Hi Tony

Know it's been a year since this topic had it's last post, but have done some more testing and got some interesting results.

Connected an 80's stator up in normal Delta mode and run it up to 646 RPM power output was 560 W 160 VDC at 3.5 Amps. The input power measured by my inline torque meter came to 683 W (Torque reading 10.1 Nm). That is 82% efficiency.

Then took the same stator and wired out each group of 14x coils to their own rectifiers as per your circuit at the top with their DC outputs all in parallel.

Run another test at 673 RPM into the same load and got a power output of 480 W 160 VDC at 3 Amps. The input power was 649 W (Torque reading 9.2 Nm). That is 74% efficiency.

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.

I'm still interested in exploring a form of switch system using a delta configuration and just use different wiring setups to get the desired outcome.

Cheers

David
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Posted: 23 June 2018 at 4:11pm | IP Logged Quote Warpspeed

DaveP68 wrote:

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 on 23 June 2018 at 4:20pm


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DaveP68
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Posted: 23 June 2018 at 4:54pm | IP Logged Quote DaveP68

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 wrote:
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 wrote:
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 wrote:
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 on 23 June 2018 at 6:31pm


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Posted: 24 June 2018 at 7:48am | IP Logged Quote DaveP68

Warpspeed wrote:
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 wrote:
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.

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Posted: 24 June 2018 at 7:06pm | IP Logged Quote DaveP68

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 wrote:
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

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Posted: 28 June 2018 at 1:10pm | IP Logged Quote Gizmo

Settle down guys, please keep it civil.

Glenn

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