Author Topic: Trying to fabricate electromagnet, requesting help please  (Read 21241 times)

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #45 on: August 03, 2014, 03:36:06 PM »
<a href="https://www.youtube.com/watch?v=yjOdNuXGrJM" target="_blank">http://www.youtube.com/watch?v=yjOdNuXGrJM</a>


Hi, first test of magnet piston. Promising results, proceeding with the rest of fabrication.

Offline dieselpilot

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #46 on: August 03, 2014, 08:58:21 PM »
I found that by keeping the duty cycle below 50% it works really well with a PMA and removes the braking effect created from the back EMF.

It doesn't remove back EMF. It can't. The best you can hope for is it converts the generated voltage to a more suitable load voltage with loss of efficiency. This makes it appear as though it's easier to turn the generator. This is strictly due to mismatch of the generator and load. You'll find the most efficient generator system has no voltage regulators or transformers. Boost converters for solar exists for the same reason. The panel voltage doesn't match the battery voltage, so it's worth a few percent loss in conversion to get the panel operating at maximum efficiency. This is great when the sun provides power for free. If you're turning a generator by hand, you don't want additional losses through conversion.

Greg

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #47 on: August 03, 2014, 09:17:41 PM »
Hi, thanks the for info. Without the circuit I could not even turn the generator using the same load.



This not my project but it shows the benefits of the same type circuit.
<a href="https://www.youtube.com/watch?v=0TE38SOdf64" target="_blank">http://www.youtube.com/watch?v=0TE38SOdf64</a>
« Last Edit: August 03, 2014, 09:23:08 PM by burnit0017 »

Offline dieselpilot

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #48 on: August 03, 2014, 10:31:31 PM »
Like I said, load mismatch. The simple, efficient, and cheap solution? A 6USD, 120V LED bulb. I replaced my 50W GU10 bulbs with 9W LED's and couldn't be happier. With wide input range on the power supply these bulbs operate from 80-250VAC.

There is a reason for everything, but it takes a lot of education and research. Now, if your intent is grid tie generation, MPPT complexity, loss, and cost is worth it, maybe.

Greg

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #49 on: August 03, 2014, 10:55:59 PM »
Hi, no, I  just plan to use it just for charging batteries, off grid. I am using a F&P that will generate approximately 1 volt per RPM, so matching the load is not possible. The circuit works well for my application. Cheers.   
« Last Edit: August 03, 2014, 11:19:20 PM by burnit0017 »

Offline PStechPaul

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #50 on: August 03, 2014, 11:33:58 PM »
The reason the alternator is hard to crank with direct connection to the load is caused by the non-linear resistance of an incandescent lamp. The 48W 12V bulb has a resistance of about 4 ohms at 12V, but below incandescence, it can be about ten to fifteen times lower. So with the cold filament, you will be pushing not the 4 amps you might expect, but (at least momentarily) as much as 40 amps, and since current is proportional to torque, you will have to strain ten times harder until the lamp starts to glow. This is the well-known "incandescent tungsten" load. I have seen this error in another video where someone measured the cold resistance of a lamp and then used that to determine that he was generating a lot more power than he was putting in.

http://en.wikipedia.org/wiki/Incandescent_light_bulb

Your buck converter or MPPT circuit probably has built-in current limiting so it will never try to output the current needed to power the load at low RPM, but it does charge its energy storage capacitor. Once that voltage becomes high enough it will dump its energy into the load and it will start to glow, so the current will drop. Eventually you will have it at full incandescence where it will dissipate about 48 watts and if your circuit has typical efficiency of 90%, you will be exerting about 55 watts of power on the crank, and the energy storage of the circuit components will smooth out the variations in torque (torque ripple) that is typical of single phase alternators (but less so for three phase, which is what most automotive alternators are). Automotive alternators are typically rather cheaply built and have poor efficiency, perhaps 50-75% at best, so they are a poor choice for wind power.

Another thing to consider is that a MPPT circuit does not necessarily result in maximum efficiency. The maximum power point for an alternator and similar devices occurs at a point where the power lost in the device is equal to that transferred to the load. Think of it as a 12V battery and a 1 ohm resistor. If you have a 12 ohm load the total resistance will be 13 ohms and the current will be 12/13 or 0.92A, and the load power will be 10.4W while the generator dissipates 0.85W and efficiency will be about 93%. If you have a 0.5 ohm load the total resistance is 1.5 ohms and the current will be 12/1.5 = 8A. The load power will be 0.5*8^2=32W, and the generator will have losses of 64W, for efficiency of 33%. For maximum power, the load should be 1 ohm, where current will be 12/2=6A, output power is 36W, and efficiency is 50%.

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #51 on: August 04, 2014, 09:56:24 AM »
Hi, thanks for the input. I always viewed it as with the circuit I am sending current to the load. Without the circuit I am generating heat at the PMA and cooking the generator. I only know of two US companies that offer a MPPT circuit that will work with a permanent magnet alternator. On my circuit ; which is  basic; the output current is only controlled by varying the duty cycle. Nice observation about charging the input cap. Thanks again.
« Last Edit: August 04, 2014, 10:13:13 AM by burnit0017 »

Offline Ian S C

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #52 on: August 04, 2014, 02:41:16 PM »
Don't know if this has any relevance, this is a free piston Stirling Engine, the magnets are ex micro wave oven,  and the coils are old chokes from power supplies.   Ian S C  Ooops got a wrong one there, that's a Neuport 24 replica powered by an Australian built Rotec radial of 150 hp.
« Last Edit: August 04, 2014, 02:53:06 PM by Ian S C »

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #53 on: August 04, 2014, 04:44:54 PM »
Hi, great looking plane, I am interested in the Stirling Engine. Is there a thread started, will it work with a wood fire. I always wanted to try to fabricate a Alpha, but at that time I did not have my modest collection of machine tools.

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #54 on: August 17, 2014, 12:22:35 AM »










Hi, just some quick photos showing progress. I hope to be testing in few days.

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #55 on: August 18, 2014, 02:11:57 PM »
Hi, I have completed my experiment.
Results:
I was not able to generate enough stored power at the capacitor for self operation.
It was great learning experience in that I was able to gain a good physical sense of how the configuration operates when both sides are balanced and now I have building block for a larger steam engine. Thanks for all the comments and help.   

Offline Ian S C

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #56 on: August 18, 2014, 03:03:13 PM »
     The Neuport is powered by the 9 cylinder(I think) Australian built radial, I think there was something about the original cylinders being ex VW, but I think they make their own now.  The aircraft is a Microlight, the owner had a heart attack a year or so ago and lost his PPL but wanted to keep flying. The plane started life in the USA.
      The hot air engine is a GAMMA type, fuel with LPG.  The power piston is a bit of cast iron about 3" long X 1 1/4" diameter(heavy piston is required).  Under the magnet on the piston is another with the like pole facing up to repel the piston there by acting as a spring,  When first built I did use springs.  The displacer has a fat rod, and works as a Ringbom type motor.  This motor could be run on solar power, although I have not tried as yet.       Ian S C
 

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #57 on: August 18, 2014, 03:27:30 PM »
Hi, what is the RPM? What are you using for lubrication?

Offline burnit0017

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #58 on: December 26, 2014, 02:50:47 AM »
<a href="https://www.youtube.com/watch?v=y3FKYs-Yljw" target="_blank">http://www.youtube.com/watch?v=y3FKYs-Yljw</a>

Hi, I fabricate a pulse motor using the electromagnet. Needs improvement but it is working. :insane: It will also function as a test fixture.

Happy hoilday...

Offline PStechPaul

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Re: Trying to fabricate electromagnet, requesting help please
« Reply #59 on: December 26, 2014, 04:44:24 AM »
I'm not sure exactly what you are trying to accomplish, but this looks like a switched reluctance motor (SRM). I have done some research on them and they have a great deal of promise. I made one with four lobes on the rotor and six electromagnets which are switched on and off and with switched polarity at a rate determined by timing from a PIC. It is not self-starting, but once it gets "in synch" it has a reasonable amount of torque. I may have presented this before, but have a look at my video. This is part 1, and I have plans to make a more powerful and possibly practical motor in the future using similar techniques:

<a href="https://www.youtube.com/watch?v=W6LwlhsnT-k" target="_blank">http://www.youtube.com/watch?v=W6LwlhsnT-k</a>

 

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