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Author Topic: Claimed OU circuit of Rosemary Ainslie  (Read 641787 times)

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #15 on: June 18, 2009, 12:40:26 AM »
If there is anything useful to you all here, feel free to
repost:
http://www.energeticforum.com/renewable-energy/4314-cop-17-heater-rosemary-ainslie.html

Hmm. Interesting thread, full of ideas.
I do note one thing, though--those who are reporting lots of heat in the load seem to be using longer duty cycles. I like Stiffler's calorimeter setup, but I think I can do even better. And I guess I'll have to try Lindeman's circuit too.
Now, I have a question: In the original circuit in the pdf, Ainslie uses a 555 timer circuit, not specified, to drive the MOSFET gate. What voltage is being applied? I'm using as much as 10 volts, which is more than spec, but not enough yet to cause shoot-through. Could her drive voltage be even higher? I am having trouble getting my load to heat up, because of the short duty cycle.
Or is it possible that the 3.7 percent figure is a misprint?
It's hard for me to imagine that the MOSFET type itself would make that much difference. The one I'm using is an exact replacement for about 90 percent of all applications of the IRFPG50, has the internal diode and everything. But I'm ordering the IRFPG50 anyway, now that I don't think I'll smoke it (ten bucks!) right off the bat. No telling when it will arrive.

Anyway, I replaced my original 2.5 ohm shunt with a 0.25 ohm shunt as specified, and it made a lot of difference in the behaviour of the circuit. I'm uploading a video now, and I'll post a link when it's up.

Groundloop

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #16 on: June 18, 2009, 01:21:43 AM »
@TinselKoala,

She used 12 volt to drive the 555 circuit.

Groundloop.

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #17 on: June 18, 2009, 01:39:56 AM »
OK, thanks, I'll build it and compare.
But can you explain the notations on the resistors like
 "[R]/50   k ohm/50%"
I don't understand what that means.

But from that, it certainly looks like my gate voltage isn't the problem. However the output of that circuit is likely to be less "clean" than my FG, which might be a good thing as it could help drive the MOSFET into the "O-zone", where the horizontal becomes vertical and the vertical goes ballistic...

So far:
http://www.youtube.com/watch?v=trip8gjoxMQ

Groundloop

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #18 on: June 18, 2009, 01:58:08 AM »
@TinselKoala,

Here is a cleaned up drawing of the circuit.

[EDIT] Added the Eagle CAD files. (For those of you that uses Cadsoft Eagle.)

GL.
« Last Edit: June 18, 2009, 02:24:25 AM by Groundloop »

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #19 on: June 18, 2009, 02:14:26 AM »
It's so pretty! Thanks, much easier to work with. I get the resistor values now.
 :)

Groundloop

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #20 on: June 18, 2009, 02:31:46 AM »
@TinselKoala,

I have read the papers of RA. She noted that the frequency of the HEXFET was different (higher) than the oscillator frequency. Have you noticed such behavior in your circuit?

GL.

poynt99

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #21 on: June 18, 2009, 02:48:35 AM »
The input Gate drive parameters are not critical. It's there only to elicit and maintain parasitic oscillation in the MOSFET.

.99

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #22 on: June 18, 2009, 03:22:07 AM »
@TinselKoala,

I have read the papers of RA. She noted that the frequency of the HEXFET was different (higher) than the oscillator frequency. Have you noticed such behavior in your circuit?

GL.

Well, there's that ringdown frequency, which is quite a bit higher than the 2.4 kHz drive. But without seeing a scope trace I don't know if that's what she's talking about. So far, except for the spikes, my mosfet tracks the input frequency exactly, up to 2 MHz, which is where my FG tops out.
I don't quite understand what's happening in her circuit to produce the "random oscillations" that she talks about in the paper. She says she has to turn the gate drive down?? to get that? I guess I'll have to build the 555 portion to see what it introduces into the mix. That will be tomorrow, though.
Maybe the particular MOSFET does make a difference. I hate waiting for stuff. I wish I could find one locally.

poynt99

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #23 on: June 18, 2009, 03:49:58 AM »
I don't quite understand what's happening in her circuit to produce the "random oscillations" that she talks about in the paper. She says she has to turn the gate drive down??

The Gate drive parameters may not critical in terms of frequency and duty cycle. In fact each device type and even between batches there will be variances. Again, the input is only a stimulus to excite parasitic oscillation natural to the MOSFET. This is of course the opposite effect one normally wants to achieve.

Parasitic oscillations come about when the MOSFETs are allowed to operate in their analog (or linear) region for a long enough time for a parasitic oscillation to get going. This region exists between the MOSFET gate threshold voltage and saturation voltage. MOSFETs have extremely high voltage gain, combined with very high capacitances, which makes the devices very prone to parasitics unless steps are taken to prevent them.

There is an optimum value of series gate resistance with all setups. Variance from optimum will result either in spiky edges as seen in your scope shots, or oscillation.

"Turning down the Gate Drive" means introducing more and more series gate resistance, Rg, until the things breaks into continuous parasitic oscillation.

Quote
Maybe the particular MOSFET does make a difference.

Almost all will oscillate, especially the higher voltage and current devices. Even obtaining the same part number she specified may not guarantee you'll get the same results. You may have to tweak the duty cycle, frequency, and Rg.

.99

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #24 on: June 18, 2009, 05:10:27 AM »
The Gate drive parameters may not critical in terms of frequency and duty cycle. In fact each device type and even between batches there will be variances. Again, the input is only a stimulus to excite parasitic oscillation natural to the MOSFET. This is of course the opposite effect one normally wants to achieve.

Parasitic oscillations come about when the MOSFETs are allowed to operate in their analog (or linear) region for a long enough time for a parasitic oscillation to get going. This region exists between the MOSFET gate threshold voltage and saturation voltage. MOSFETs have extremely high voltage gain, combined with very high capacitances, which makes the devices very prone to parasitics unless steps are taken to prevent them.

There is an optimum value of series gate resistance with all setups. Variance from optimum will result either in spiky edges as seen in your scope shots, or oscillation.

"Turning down the Gate Drive" means introducing more and more series gate resistance, Rg, until the things breaks into continuous parasitic oscillation.

Almost all will oscillate, especially the higher voltage and current devices. Even obtaining the same part number she specified may not guarantee you'll get the same results. You may have to tweak the duty cycle, frequency, and Rg.

.99
Yes, thanks for the review.
You will note that Ainslie uses a 100 ohm pot to vary the gate drive. I didn't know that when I put my circuit together, so I used 200 kilo ohms. So I can "turn down" my gate drive through her available range and much further. Plus I can vary the output attenuation of the FG.
The parasitic oscillations that she generates in her circuit are absent in mine. When I turn the gate drive down with short duty cycles, the MOSFET simply turns off and stays off. Did you watch my video? You can see me doing this several times. No wild parasitic oscillations evident. With longer duty cycles even the full 200K isn't enough (with 10V p-p on the FG output) to shut off the mosfet, and it happily amplifies, relatively cleanly, the 2.4 kHz input pulse. Still no parasitic oscillations. So I'll put more resistance in there, and I'll continue to wonder about the numbers in Ainslie's paper. 3.7 percent duty cycle? 100 ohms gate resistance? 2.4 kiloHertz? With these numbers I get no heating of the load. If I increase the duty cycle to 30 percent or more I get plenty heat of load and mosfet. But at 3.7 percent I get no parasitic oscillation, and no heat on the load.
So perhaps I have a "good" mosfet, or perhaps my circuit layout is "better", that is, less prone to oscillations, or perhaps her 555 driver is forcing the oscillations to happen.
I just can't get my circuit to misbehave properly, and yes, I've explored the parameter space, up to 2 MHz, as I said, and from 3 to 97 percent duty cycles, and 0 to 200K Rg (Vgs=10V)

derricka

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #25 on: June 18, 2009, 10:29:13 AM »
Another thing to consider here, is stray capacitance.  I'm not sure if Rosemary used a breadboard to wire her circuit or not, but you can easily get 12pF (I've seen 20 on some) of capacitance between contact strips.  By comparison, your clean, point to point wired circuit, may be too stable for the task at hand. You could try soldering a few centimeters of wire onto the MOSFET gate to act as an antenna. Sometimes it just takes a bit of outside noise to tickle a circuit into oscillation.


ramset

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #26 on: June 18, 2009, 10:09:18 PM »
TK
If I may ,I have a question[while you wait for parts][like you have nothing better to do]
As you know a few weeks ago I met with that fellow who filed a patent app
for a mag motor
I mentioned he had a levitation disc ,a 12 inch circle cut in a piece of 1/4 inch plywood, in the circle was a 11inch [approx] plastic disc hovering in the field
he claimed people could stand on this Disc and not free it from the field

That part I said in a post and yes I held it in my hand [not heavy}
This part I did not say
 It was partially disassembled [missing mags that had come out of the glue over time]but still hovering ,only to one side

It just occurred to me what I had in my hand
The disc was STUCK to one side [attraction] because the mags on the other side[that used to pull it back and center it] were missing
I know you have MUCH magnet experience
 Have you ever done this?
It was claimed to be the BIG piece of a motor concept
 Before I replicate this [Quite simple concept]
Will it be easier to turn/spin ,floating in attraction 
Is it possible that when he says magnets can shield themselves.
He meant, in a field like this??
I value your opinion tremendously and won't waste time replicating a paper weight
Did I describe this well enough for you to know what the hell I'm talking about?
Chet
PS
 in the motor, he said this same disc would be hovering about 4 inches[what ever that means]

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #27 on: June 19, 2009, 01:25:24 AM »
Another thing to consider here, is stray capacitance.  I'm not sure if Rosemary used a breadboard to wire her circuit or not, but you can easily get 12pF (I've seen 20 on some) of capacitance between contact strips.  By comparison, your clean, point to point wired circuit, may be too stable for the task at hand. You could try soldering a few centimeters of wire onto the MOSFET gate to act as an antenna. Sometimes it just takes a bit of outside noise to tickle a circuit into oscillation.

Probably the first time I've ever been "accused" of being too neat.  :P
First I'll try the 555 gate drive circuit and the IRF mosfet. Then we'll see what else needs to be done.
I was finally able to get some chaotic oscillations out of my rig...by cranking the duty cycle past 40 percent and the pulse voltage past 10 volts...and disconnecting the 24 volt battery completely!

TinselKoala

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #28 on: June 19, 2009, 01:34:43 AM »
TK
If I may ,I have a question[while you wait for parts][like you have nothing better to do]
As you know a few weeks ago I met with that fellow who filed a patent app
for a mag motor
I mentioned he had a levitation disc ,a 12 inch circle cut in a piece of 1/4 inch plywood, in the circle was a 11inch [approx] plastic disc hovering in the field
he claimed people could stand on this Disc and not free it from the field

That part I said in a post and yes I held it in my hand [not heavy}
This part I did not say
 It was partially disassembled [missing mags that had come out of the glue over time]but still hovering ,only to one side

It just occurred to me what I had in my hand
The disc was STUCK to one side [attraction] because the mags on the other side[that used to pull it back and center it] were missing
I know you have MUCH magnet experience
 Have you ever done this?
It was claimed to be the BIG piece of a motor concept
 Before I replicate this [Quite simple concept]
Will it be easier to turn/spin ,floating in attraction 
Is it possible that when he says magnets can shield themselves.
He meant, in a field like this??
I value your opinion tremendously and won't waste time replicating a paper weight
Did I describe this well enough for you to know what the hell I'm talking about?
Chet
PS
 in the motor, he said this same disc would be hovering about 4 inches[what ever that means]

So the hovering plastic disk had some magnets on it, but some were missing, and the plywood was the outer frame and it had magnets on it too?
I think you are describing a sort of magnetic bearing, of the type that I call the "2-df magnetic trailer hitch".
It's tricky to get the stable position, and I've never seen one support that much weight, but I think the concept is good, and I know it's used in some commercial sophisticated high-speed magnetic bearings, like are used on some kinds of turbo-molecular high vacuum pump systems. They don't simply levitate but hold in attraction as well due to the configuration of the magnets. Of course these systems are generally hybrids of electromagnets and permanent magnets.
If you can find a strong donut magnet, a clear plastic tube that fits in the hole, and a rod or cylinder magnet that fits inside the tube, you can discover some interesting things including, I believe, the levitation/attraction configuration. But with just these few magnets you need the plastic tube to keep things stable.
The fact that you saw it offside, and stuck on one side, seems very normal to me. Getting it to center and remain stable is the trick, using only permanent magnets.

ramset

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Re: Claimed OU circuit of Rosemary Ainslie
« Reply #29 on: June 19, 2009, 02:02:25 AM »
TK
Thanks for the response,Yes held in "attraction' Does seem amazingly difficult.
That would explain all the layout lines he had crossing the disc every 1/4 inch
Thanks
Chet
 PS
and Bill seems to have learned something from this [his  comment that magnets can shield themselves??]
I will take your suggestion to do this and see what I can learn