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DaveP68
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Posted: 14 May 2017 at 1:29am | IP Logged Quote DaveP68

Interesting story Tony with two year long expeditions to Antarctica. Yes that would allow you to save up a good deposit. There are far to many things to distract or tempt us to fritter away that hard earned money when at home base. Sorry to hear that the hearing is almost gone.

My late Uncle was a scientist with a PhD in biological physics. He did 2 trips to the South pole in Antarctica, not many get to go there. He told me a story of returning to NZ from Antarctica and how you need to clear immigration/customs at Christchurch having been out of the country. The chap in front of him put his occupation on the arrival card as Forestry researcher (was one). The immigration officer observing that he was a Forestry researcher arriving back from Antarctica asked what he was doing down there. He without blinking an eye said "We'll we went down there, had a dam good look around and we're going advise them not to ago ahead"!! Immigration officer goes very quiet, gives back his passport next person please Stupid question...

Been to 51 countries, but not Antarctica. You have too get along with others if you're there over the winter period as there was no way to leave?

Edited by DaveP68 on 14 May 2017 at 1:32am



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Warpspeed
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Posted: 14 May 2017 at 1:58am | IP Logged Quote Warpspeed

Ah yes, the Americans have it pretty easy at McMurdo, fly in, fly out, unlimited water and power (they have a small nuclear reactor) and a trip to "Little America" right at the pole would have really been something.
Their bases are run on military lines, with rank, and the support staff would all have been US navy personnel on assignment. Plenty of civilians there too of course.

With us Aussies it was a whole lot different. Only fifteen of us rat bag Aussie civilians, and we get to unload the ship ourselves, diesel power only, so life for us was a lot more primitive in a great many ways. No flush toilets, and showers and washing clothes was pretty restricted.

I was able to save more than the deposit, in fact I was able to pay fully in cash.
Back in 1972 15K was a hell of a lot of money.
The same block where I still live is now probably worth almost one hundred times that original amount.
I could not imagine a job where two years pay would buy into a similar location these days.



Edited by Warpspeed on 14 May 2017 at 2:07am


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DaveP68
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Posted: 14 May 2017 at 10:34am | IP Logged Quote DaveP68

That's good you ended up paying cash for a house even back then. I call the housing market here in Auckland a Ponzi Scheme, Bernard Madoff set the standard!

I've been mortgage free for about 10 years now so never had a big one to begin with. The only job I can think of that you pay cash for house after 2 years these days in Auckland would not be legal...
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Posted: 14 May 2017 at 9:20pm | IP Logged Quote Warpspeed

Back on topic...

I have been giving some thoughts to this dynamic braking problem as applied to an F&P which is really a synchronous three phase motor/alternator.
Its very different to dynamically braking an induction motor because this has the permanent magnets.

What I expect should work would be a three phase rectifier (which we already have) to generate a dc voltage roughly proportional to rpm, followed by a fairly high constant current load.

The trick is to hold the braking load current high enough to get sufficient braking torque, but not so high it saturate the magnetic circuit. We need to control the load current so that it stays constant, with a rapidly falling dc bus voltage, as the alternator rpm is rapidly pulled down.

That could be a simple hysteric controlled load that switches itself on and off (PWM) around some desired set braking current. If the current falls, the load goes back on. As it rises it is switched off. It self oscillates around some desired mean braking current, holding it almost constant during deceleration.

If you have a circuit diagram for the F&P, it may already show something like that.

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DaveP68
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Posted: 17 May 2017 at 9:56pm | IP Logged Quote DaveP68

Hi Tony

You read my mind. Yes already have the basic circuit which currently works in the voltage trigger mode (40 - 480 VDC). Just need to use a spare LM393 op amp on the boards I have to amplify the small voltage across a current sense resistor. This can then be put into the same variable value comparator input that I currently use for the voltage trigger point. This circuit works by as you say by the same hysteric controlled PWM.

That Blue coloured board in the photo has all the parts on it to perform this function. Just need to make the resistor a lower value and make sure the IGBT device can handle the peak current. The current sense resistor will need to be about 0.01 ohms and rated at 10 W.

What do you think?

Cheers

David

Edited by DaveP68 on 17 May 2017 at 9:58pm
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Posted: 17 May 2017 at 10:17pm | IP Logged Quote Warpspeed

You may need a fairly decent electrolytic across the dc bus to minimize the worst of the wild voltage swings, as the load comes on and off, but that is the general idea.

Only way you could do much better than that at lower rpm, would be to energise the original F&P motor drive fets to slow astern. I have no real idea how an F&P actually does all this, even though I have one in the laundry. Its never missed a beat so I have never had the covers off.



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DaveP68
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Posted: 15 June 2017 at 7:43am | IP Logged Quote DaveP68

Warpspeed wrote:
Only way you could do much better than that at lower rpm, would be to energise the original F&P motor drive fets to slow astern. I have no real idea how an F&P actually does all this, even though I have one in the laundry. Its never missed a beat so I have never had the covers off.



Have been thinking of doing some more work on this Electronic Dynamic braking and I think you're idea to energise the stator is great to get the RPM down to a minimum amount. This can be done by firing an opposing waveform back into the stator. This can be a closed loop controlled system by making use of the RPS unit (Rotor Position Sensor) that sits on the side of the stator.



Refer to the white device that is sitting at the 2 o'clock position on the stator in the above photo. In this setup it's only going to be used to measure the exact operating RPM of this stator.
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DaveP68
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Posted: 21 June 2017 at 10:50am | IP Logged Quote DaveP68

For those that are interested in following this topic on F&P Electronic Dynamic braking, have now got the circuitry working that can perform this function.

Doesn't require any complex electronics like a microprocessor, just a bunch of op amps!

Will publish the circuit diagram once I've done some fine tuning to how it will operate in the real world. This will soon be tested out on a real wind turbine.

This circuit can be adapted for use on basically any PMA including an axial-flux unit(s).

Have a furling system as a backup is a wise choice, so not trying to say that that function has been superseded.

Just like the concept of a fully automatic system that requires no manual input from the end users perspective.

Edited by DaveP68 on 21 June 2017 at 10:51am
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DaveP68
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Posted: 30 June 2017 at 11:37am | IP Logged Quote DaveP68

Attached are some photos of 2 modified F&P motor control modules set up for constant current control and constant voltage control with adjustable settings. The original circuit was designed for fixed constant voltage control of 400 VDC.

They all use an IRGBC20S IGBT as the switch device with a 20 ohm 1 kW peak rated resistor which sits in the top of the heat sink as the dump load.

Here is the first modified board for current control, top and bottom.


Note the LM358 op amp bottom center left. This has been added to the board in place of an optocoupler that was removed as not used in the brake function. The current sense resistor is 0.22 ohms 5 W located in the middle of the board above the heat sink, below the left hand black 250 VDC capacitor. The red & blue wires are for 12 VDC supply. The feed DC into the board to be controlled is via diode kathode bottom left and the yellow wire.



Next is a board modified for constant voltage control over a 40 - 460 VDC range.




These last 2 photos are of an original non modified F&P board.

Note the optocoupler is still in place in this non modified board.


In their present configuration they're not much use in a real world application. Have put them into use recently to prove that the concept of dynamic braking can be done with simple circuitry without the need of complex microprocessor control.

When I get time will scan a copy of the actual circuit diagram if it's of anyone who would like to try to build their own.

Edited by DaveP68 on 30 June 2017 at 12:28pm
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Posted: 30 June 2017 at 7:45pm | IP Logged Quote Warpspeed

Thats really interesting Dave.

A three phase induction motor also behaves as a brake if you flow a steady dc current through two of the three star windings connected in series.

A schematic of what you have there would be very helpful.

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DaveP68
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Posted: 02 July 2017 at 5:02am | IP Logged Quote DaveP68

Hi Tony

Once again thanks for taking interest in a topic not discussed that much, but could yield some good results in time if set up properly.

Here is a scanned copy of the basic circuit as requested.



The current control has about about a 20 % drift in this set up. Setting the current to 2 amps at 60 VDC it goes up to 2.4 amps when at 200 VDC. It's good enough to prove that the concept works in principle.

Will make some improvements when time permits> Having a business to run on week days, children to keep occupied on weekends burns up most of that.

The resistors and IGBT switching devices can be paralleled to provide more current capability with lower voltage operating range.
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kitestrings
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Posted: 03 July 2017 at 3:34pm | IP Logged Quote kitestrings

Quote:
Will make some improvements when time permits> Having a business to run on week days, children to keep occupied on weekends burns up most of that.


Start 'em young Dave


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