Anomalous voltage increase

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darkspeed

Anomalous voltage increase « on: 2010-01-31, 06:16:32 »

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Posts: 812

Today I did some experiments to see what the influence magnets have on a coils flyback.

To keep this short I will focus on the only way I found that increased the flyback voltage.

The best result was placing a 2" cube neo on both sides of a coils soft iron core : SN | SN | SN

I connected a 12vdc car battery to an IRF840 switching the positive line.

I drove the IRF840 directly with a 10v square wave from an HP Function Generator at 5000hz

Bear in mind the IRF840 has an internal free wheeling diode..

I placed a Pearson wide band current probe in line with the coil and a x100 probe across the coil.

From my tests it looks like there is a significant voltage increase with the magnets present in the SN | SN | SN setup

SN | NS | SN and SN | SN | NS both decreased the flyback voltage.

coil 1:
20 awg high ohm coil on soft iron core
168v without magnets
212v with magnets
44v increase

coil 2:
20 awg low ohm coil on soft iron core
395v without magnets
540v with magnets
145v increase

At certain frequencies below 5000hz there were some anomalous current spikes that I need to go back and look at, in fact one killed two of the mosfets.

Anyone want to independently verify these results???

NOTE: This requires a really solid mounting for the 2" neo cubes and big neos are very dangerous to work with! Be careful!!

Thanks..
Darkspeed

« Last Edit: 2010-01-31, 07:14:54 by darkspeed »

Peterae	Re: Anomalous voltage increase « Reply #1 on: 2010-01-31, 10:32:59 »
Group: Administrator Hero Member Posts: 4635	Hi ds Sounds interesting, yes i would be up for a rep, but will need to order some magnets to try, but first i need to get my current stuff sorted, i have loads on at the moment. Those are large magnets, can it be scaled down a bit maybe 1 inch square magnets. anyway sounds interesting, keep at it. Peter

stprue	Re: Anomalous voltage increase « Reply #2 on: 2010-01-31, 12:58:19 »
Full Member Posts: 221	Hello darkspeed This sounds very interesting! I have a question, what did the amperage do? Did the draw decrease or increase when using the neos? Also did the current change on the output in any significant way?

darkspeed	Re: Anomalous voltage increase « Reply #3 on: 2010-01-31, 19:00:41 »
Newbie Posts: 812	Peter, I will try it with the next smaller neos I have ( 1 x 0.75 cylinders ) and see if I get anything..

darkspeed	Re: Anomalous voltage increase « Reply #4 on: 2010-01-31, 19:06:00 »
Newbie Posts: 812	stprue, I kept the current probe visible on one of the scope channels and since the coil is firing with the neos and not against them there was no additional current draw in the coil. The only strange current issues were the random current spikes below 5000hz. Im going to do some more work on it today

Peterae	Re: Anomalous voltage increase « Reply #5 on: 2010-01-31, 19:23:26 »
Group: Administrator Hero Member Posts: 4635	ds What are your core dimensions and how many turns was your coil.

darkspeed	Re: Anomalous voltage increase « Reply #6 on: 2010-01-31, 21:34:49 »
Newbie Posts: 812	Core is a 17mm x 17mm x 75mm soft iron core.. I will have to go measure the windings as these were a couple of coils i pulled off the shelf that I had built a while back. The only part of the event that is opposing the polarity of the setup is the flyback and I am not sure why a static opposing magnetic field increases the energy in a flyback event??

darkspeed	Re: Anomalous voltage increase « Reply #7 on: 2010-01-31, 22:12:25 »
Newbie Posts: 812	Replicated the result with 1 x 0.75 n42 neo cylinders 42v increase with two cylinder magnets on each side of core ( compared to the 145v increase with the 2" cubes ) coil : 2.2311mh @ 10khz 2.54ohm @ 100hz / 93.69ohm @ 10khz Anomalous voltage increase CIMG5716.jpg (108.3 kB, 640x480 - viewed 2014 times.) « Last Edit: 2010-02-01, 02:23:37 by darkspeed »

darkspeed

Re: Anomalous voltage increase « Reply #8 on: 2010-01-31, 23:29:19 »

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Posts: 812

I just started from scratch with a different coil / different HP / different scope and was able to reproduce the results

I also just had a friend report that he could get the same results.

Is this a known effect that I somehow just missed before??

Anyone know of this??

Iv been working with earplugs all day because the 5-6khz tone will rive you insane..

« Last Edit: 2010-02-01, 00:00:18 by darkspeed »

MileHigh

Re: Anomalous voltage increase « Reply #9 on: 2010-02-01, 00:35:38 »

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Posts: 1888

Darkspeed:

You may be a bit surprised to learn that the magnitude of the spikes has nothing directly to do with the magnets. Somehow the magnets are causing secondary effects that are influencing the main parameters that affect the maximum spike voltage.

The first parameter is the amount of current flowing through your coil. There is no need to switch the square wave to the MOSFET gate at 5 or 10 KHz. Try 50 Hz instead. This will likely ensure that you have the maximum possible current running through your coil when you switch the MOSFET off and you will not go insane from the high frequencies that you are suffering though now.

The second parameter is the speed the MOSFET switches off. The cleaner and sharper you can make your square wave to the gate the higher the spike voltages you will get.

The third parameter is the inductance of your coil, the higher the inductance the higher the voltage spike.

Your external magnets are somehow affecting the above three parameters to give you increased voltage on your spikes.

The formula for the spike voltage is v = L di/dt. You should try searching on that.

Careful if you start tuning and getting higher and higher spikes I assume that you will likely blow your MOSFET.

MileHigh

darkspeed

Re: Anomalous voltage increase « Reply #10 on: 2010-02-01, 01:39:48 »

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Posts: 812

Thanks MileHigh!

That reminded me to do something I forgot to do... remeasure the inductance with the magnets in place..

That may be effecting it.. I will check it out..

The best result so far has been feeding the HP through a Wavetek so I could adjust the duty cycle.

Setting it to 5khz on the HP and 10us on the Wavetek, then inverting the output, so 5000 times per second the mosfet turns off for 10us

darkspeed	Re: Anomalous voltage increase « Reply #11 on: 2010-02-01, 03:00:12 »
Newbie Posts: 812	Ok.. Now I feel like an idiot.. I was not expecting it to change the resistance of the coil.. Resistance without magnets 2.54ohm @ 100hz / 93.69ohm @ 10khz Resistance with magnets 1.93ohm @ 100hz / 43.14ohm @ 10khz Inductance without magnets 9.268mh @ 100hz / 2.5528mh @ 10khz Inductance with magnets 3.844mh @ 100hz / 1.2589mh @ 10khz The resistance and the inductance drops with the magnets

Grumpy

Re: Anomalous voltage increase « Reply #12 on: 2010-02-01, 13:59:01 »

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Cyril Smith (PhD. Physics? - he's associated with MPI) posted something about this a few years ago.

Might be in one his articles here:
http://74.125.113.132/search?q=cache:SAeqsKBrsqUJ:jnaudin.free.fr/html/meg.htm+cyril+smith+magnet+coil&cd=1&hl=en&ct=clnk&gl=us

Is the inducatance and resistance different with the polarity of the magnets reversed?

(I see that the differences with and without the magnet are nonlinear.)

ion

Re: Anomalous voltage increase « Reply #13 on: 2010-02-01, 14:25:09 »

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It's turtles all the way down

Quote

The resistance and the inductance drops with the magnets

Generally we speak of resistance at a particular frequency as "impedance", otherwise some might get confused and infer an actual change in DC resistance with the magnets. This is not the case.

Nice to see that your inductance bridge allows excitation frequency selection, makes impedance plots easier.

---------------------------

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Peterae	Re: Anomalous voltage increase « Reply #14 on: 2010-02-01, 16:10:47 »
Group: Administrator Hero Member Posts: 4635	Nice work ds, you didn't understand the effect and now you do, as do we, thanks This gives me another test to add to my pulse experiments. Peter

darkspeed

Re: Anomalous voltage increase « Reply #15 on: 2010-02-01, 17:31:13 »

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Quote from: Grumpy on 2010-02-01, 13:59:01

Is the inducatance and resistance different with the polarity of the magnets reversed?

(I see that the differences with and without the magnet are nonlinear.)

Good question.. I tried that and both the resistance and inductance stays the same when i switch polarity... but with opposing magnets on each side both rise..

got me really thinking about the orbo and how this works in a toroid

darkspeed	Re: Anomalous voltage increase « Reply #16 on: 2010-02-01, 17:33:50 »
Newbie Posts: 812	Haha yes ION "impedance" im bad about that, just like i call neons spark gaps and bulbs resistors lol...

darkspeed	Re: Anomalous voltage increase « Reply #17 on: 2010-02-01, 17:34:57 »
Newbie Posts: 812	Quote from: Peterae on 2010-02-01, 16:10:47 Nice work ds, you didn't understand the effect and now you do, as do we, thanks This gives me another test to add to my pulse experiments. Peter Thanks Peter, im the master at learning stuff the hard way..

Grumpy

Re: Anomalous voltage increase « Reply #18 on: 2010-02-01, 18:17:30 »

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Quote from: darkspeed on 2010-02-01, 17:31:13

Quote from: Grumpy on 2010-02-01, 13:59:01

Is the inducatance and resistance different with the polarity of the magnets reversed?

(I see that the differences with and without the magnet are nonlinear.)

Good question.. I tried that and both the resistance and inductance stays the same when i switch polarity... but with opposing magnets on each side both rise..

got me really thinking about the orbo and how this works in a toroid

write this down and make a diagram

can you change the impedance of a toroidal transformer with a magnet? - sure you can

EDIT:

What "is" the imaginary part of impedance?

darkspeed	Re: Anomalous voltage increase « Reply #19 on: 2010-02-01, 18:22:35 »
Newbie Posts: 812	write this down and make a diagram ?? are you talking self inductance?

darkspeed	Re: Anomalous voltage increase « Reply #20 on: 2010-02-01, 18:25:52 »
Newbie Posts: 812	When I think orbo I think ed leedskin magnet

Grumpy

Re: Anomalous voltage increase « Reply #21 on: 2010-02-01, 18:54:55 »

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Quote from: darkspeed on 2010-02-01, 18:22:35

write this down and make a diagram ??

are you talking self inductance?

I'm talking about how the magneici effects the impedance and inductance

I wonder if it will effect the permittivity of a dielectric? Hmm - got a doorknob or other plate cap around?

In answer to the question about imaginary part of impedance: http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/impcom.html

darkspeed	Re: Anomalous voltage increase « Reply #22 on: 2010-02-01, 19:02:39 »
Newbie Posts: 812	I have a case of 40kv 2000pf doorknobs - outline what you have in mind

Grumpy

Re: Anomalous voltage increase « Reply #23 on: 2010-02-01, 21:46:53 »

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Quote from: darkspeed on 2010-02-01, 19:02:39

I have a case of 40kv 2000pf doorknobs - outline what you have in mind

actually forget the doorknobs

Do you have vacuum caps?

See if a magnetic field alters the permitivity of free-space within the vacuum cap.

http://74.125.95.132/search?q=cache:nJYwn_GMsLIJ:hyperphysics.phy-astr.gsu.edu/HBASE/electric/elefie.html+permittivity+%22magnetic+field%22&cd=1&hl=en&ct=clnk&gl=us

darkspeed	Re: Anomalous voltage increase « Reply #24 on: 2010-02-01, 21:56:16 »
Newbie Posts: 812	I actually dont have any vacuum caps.. If I ordered one any advice on pf to get.. http://cp.literature.agilent.com/litweb/pdf/5980-2862EN.pdf