Hot Coil Electromagnet

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Author Topic: Hot Coil Electromagnet (Read 80235 times)

Peterae	Re: Hot Coil Electromagnet « Reply #150 on: 2012-08-30, 19:00:33 »
Group: Administrator Hero Member Posts: 3960	Here's another test, here i use the yellow trace to monitor the voltage across the kanthanal element. Also there's something very strange happening, the pulse shape depends on either the position of where along the heating elements length i place my sniffer coil or the pulse shape changes between switch on and off. If you look at this video i switch on and off then reposition the snifffer coil because the waveform did not look right, i then having moved the sniffer coil further along the element then switched on again, and then i have a totally different shaped waveform, i have now seen this a few times. It may also just be how close and the orientation of the sniffer coil is relative to the kanthanal element [youtube]http://www.youtube.com/watch?v=Ud2jqcqnfNU&feature=youtu.be[/youtube]

ion	Re: Hot Coil Electromagnet « Reply #151 on: 2012-08-30, 19:55:51 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Good work Peterae, looks like Kanthal is the stuff. I should be getting a sample in the mail soon. I get the largest spikey pulse when at the very end of the coil, either perpendicular or parallel. For the record, when I test my mag probe against an external coil of copper wire excited at 60 Hz, I get a nice clean sine wave. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

Peterae	Re: Hot Coil Electromagnet « Reply #152 on: 2012-08-30, 20:21:03 »
Group: Administrator Hero Member Posts: 3960	Right yes ION i need to work on the pick up coil, what i will say is i am only using a short piece of element so i am relatively low voltage and high current, and the difference also with this wire is i can hear audible noise from the element which i could not with nichrome. I did try my hall, although the sine picked up was buried in noise and although it was sine shaped there was no sign of spikes that matched but there really was a lot of noise so i would say it was inconclusive. I also believe i could maintain a set temperature by turning my variac down and being able to maintain the pulse indefinitely, but i do need to confirm this, i have the wedding tomorrow so am out of experimentation time for a couple of days. During my tests the amount of wire i used was 5.1Ohm and my yellow scope Chan was 20V/Div so i am about 70V/pk-pk giving me a peak current of 13.7 Amps I am feeding power via the green and yellow crock ------------------------ Hot Coil Electromagnet SAM_1792.JPG (579.39 kB, 1024x768 - viewed 782 times.)

Peterae	Re: Hot Coil Electromagnet « Reply #153 on: 2012-09-02, 18:56:24 »
Group: Administrator Hero Member Posts: 3960	God my bench needs cleaning up Anyway here's another test, i straightened a length of Kanthanal as best as i could and powered it up enough so i had the pulse but not enough for it to get too hot that the pulse disappeared, i then used my sniffer coil to run down it's length to trace out the wave patterns that were picked up, the spiked pulse appear to be nodal if that makes any sense, how do you work out the nodal spacing in a piece of wire for 50Hz? Is anyone able to explain why the pulse changes down the length of wire. [youtube]http://www.youtube.com/watch?v=U8RR29uChmM&feature=youtu.be[/youtube]

poynt99	Re: Hot Coil Electromagnet « Reply #154 on: 2012-09-02, 21:03:44 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	Peter. I would like to suggest you do the same test again, but this time firmly mount the wire on a piece of wood or something. This way it will be stretched out, not curved, and not moving. Taken a step further, I would then attach your sniffer coil to a rail mounted above the wire so that the transition along the coil can be smooth and consistently the same distance away. I think then you would be in a better position to determine if there are nodes or maybe even regular nodes along the wire. You'll also get a better idea how the wave form changes as you go along, and perhaps if the wave form repeats itself. Start there, then we have something to analyse. --------------------------- "Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa

Peterae	Re: Hot Coil Electromagnet « Reply #155 on: 2012-09-02, 21:14:25 »
Group: Administrator Hero Member Posts: 3960	Thanks for the advice Darren, yes i have just been trying to also improve this test, i think i may need to track down some uncoiled wire though, because this heating element is virtually impossible to straighten, but that's a great idea to try stretching it from 2 pillars. I can then use a tube of something that does not melt and thread the wire through it and glue my coil into that, i could also wind axially a coil over the wire as well and run that down the length to see what gets picked up.

poynt99	Re: Hot Coil Electromagnet « Reply #156 on: 2012-09-03, 02:01:55 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	Peter, I was thinking more along the lines of stapling the wire to a length of wood, perhaps every 4 inches or so, but whatever works for you is ok with me. --------------------------- "Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa

ion	Re: Hot Coil Electromagnet « Reply #157 on: 2012-09-03, 16:42:16 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Quote Is anyone able to explain why the pulse changes down the length of wire. I think POYNT implies it is because the wire is not completely straightened and has undulations. I tend to agree, pending more tests. Good work Peterae. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

Peterae	Re: Hot Coil Electromagnet « Reply #158 on: 2012-09-03, 17:13:26 »
Group: Administrator Hero Member Posts: 3960	Indeed it does not make sense to me if there is a variation down it's length either, but will try to rule it out just to make sure. I don't have staples but i think i have some horseshoe tacks somewhere but like staples they will be iron and surely they would affect the field as well.

ion	Re: Hot Coil Electromagnet « Reply #159 on: 2012-09-03, 17:29:13 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	If you enjoy exotic test fixtures, a 2 foot length of threaded rod driven from a toy gearmotor will smoothly and uniformly move your pickup coil along the length of a 2 foot wire that is tightly stretched between two posts. A small block of insulating material with a hole drilled into it is glued to the pole of the pickup coil. The wire is threaded through the hole. This maintains precise distance from the wire as the threaded rod moves the pickup coil. There are many simple variations on this. Enjoy the wedding! Fixtures can wait. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

Peterae	Re: Hot Coil Electromagnet « Reply #160 on: 2012-09-03, 18:43:39 »
Group: Administrator Hero Member Posts: 3960	I could go that way ION but i do not have a warehouse of bit's like yourself LOL so would need to buy bits. So let's remove one variable MOVEMENT So the plan is to make stationary tests that as i progress down the wire, with the wire stretched tight and the sensor fixed distance from wire by a hole and piece of wooden block and see how that goes.

Peterae	Re: Hot Coil Electromagnet « Reply #161 on: 2012-09-06, 18:34:57 »
Group: Administrator Hero Member Posts: 3960	Looks like i am out of this until i can find a higher amperage variac, i spent a good half hour last night trying to sniff the nodes and the patterns but what i did not realize was my variac inside my box was starting to cook along with the isolation transformer, when i realized i let it all cool down but today it looks like i fried both. What i will say though is there are some strange goings on, i had one cycle sine peak with a spike that had a sharp left shoulder then i would move about 4cm down the wire and find the same sine peak and spike with a sharp right shoulder and then when i moved another4cm i had the same sine with no spike, i then moved another 4cm and the pattern appeared to cycle over again, it took me a while to trace out the pattern, if i moved my sniffer coil up passed the heater wire i would have my sine one way, if i moved it down so i was the other side, my sine flipped which is what i would have expected, in between this flip was a null spot where just the spike could be observed, and it was this process i gradually worked down the wire length. Any magnets nearby would greatly enhance the spike or pulse and they would not need to be really close to affect the waveform. Sorry no pictures and no data, this was going to follow today, i can give you a picture of where i marked the wood that the spikes appeared See the up & down arrows i drew on the wood, up arrows had sharp left transition and down arrows had sharp right shoulders to the spike transition, you can also see the gap in between where there was a sine cycle but it had no spike. Maybe if i place 2 x 100Watt bulbs in series with the heater i can drop enough mains to run the tests without a variac or isolation transformer. Also i had the wire bolted at each end and stretched it as much as i could, it made a nice note like a guitar string but i could not get it totally straight for the tests as can be seen. EDIT also you will notice the gap in the middle is not equal to 2 pulse widths it's less and i cannot explain that either. ------------------------ Hot Coil Electromagnet SAM_1799.JPG (514.19 kB, 1024x768 - viewed 644 times.)

exnihiloest	Re: Hot Coil Electromagnet « Reply #162 on: 2012-09-06, 19:58:12 »
Group: Guest	Quote from: Peterae on 2012-09-06, 18:34:57 ... What i will say though is there are some strange goings on, i had one cycle sine peak with a spike that had a sharp left shoulder then i would move about 4cm down the wire and find the same sine peak and spike with a sharp right shoulder and then when i moved another4cm i had the same sine with no spike, i then moved another 4cm and the pattern appeared to cycle over again ... A possible explanation is that each sections of wire is source of magnetic fields that constructively add or cancel at the probe position, depending on its location. Quote Any magnets nearby would greatly enhance the spike or pulse and they would not need to be really close to affect the waveform. In my experiment (see Reply #121), a magnet made the spikes to disappear, and I also observed that it had not to be very near the wire. I suppose that the effect depends on the magnetic properties of the wire. In any case, interesting that you have confirmed the effect of a weak static field, Peterae.

Peterae	Re: Hot Coil Electromagnet « Reply #163 on: 2012-09-06, 20:40:29 »
Group: Administrator Hero Member Posts: 3960	one thing worth mentioning though is my pickup sniffer coil has an iron core so that could also be affected by a magnet being in close proximity, just as a quick test i sniffed my crocodile clip lead which feeds power and i do get the same sine waveform but without the spikes.

ion	Re: Hot Coil Electromagnet « Reply #164 on: 2012-09-07, 03:19:09 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Peterae: What is the resistance per foot of your wire? Seems to me it should be pretty low, in which case you can get away with a much higher turns ratio on your stepdown transformer e.g. if it is now 24 volts you can use a 6 or 12 volt secondary to unburden your Variac and transformer. Variacs can be repaired if not too far gone. They need to be taken apart and varnished on the inner part of the core. I have brought quite a few back to life. By the way, when unrolling a coil best to put a dowel through it and unwrap the winds perpendicular to the dowel, this way the wire is free of curls. I put one end of the wire in a vise and pull the dowel away from the vise. Neat results with the sniffer coil, I'll have to check that out when my heater wire comes in. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

Peterae	Re: Hot Coil Electromagnet « Reply #165 on: 2012-09-07, 08:19:43 »
Group: Administrator Hero Member Posts: 3960	The variac's wire is embedded in a thick glass epoxy, apart from where the wiper touches at the bottom. The total cold resistance of my test wire right now is about 5 Ohms Good thinking ION i have a microwave transformer i rewound to use as a valve HT 320-0V but i also put on a very thick 6V secondary and i could add turns if need be, looks like i could be back in business shortly. « Last Edit: 2012-09-07, 08:45:33 by Peterae »

ion	Re: Hot Coil Electromagnet « Reply #166 on: 2012-09-07, 14:41:16 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Quote from: Peterae on 2012-09-07, 08:19:43 The variac's wire is embedded in a thick glass epoxy, apart from where the wiper touches at the bottom. The total cold resistance of my test wire right now is about 5 Ohms Good thinking ION i have a microwave transformer i rewound to use as a valve HT 320-0V but i also put on a very thick 6V secondary and i could add turns if need be, looks like i could be back in business shortly. When I need high current low voltage, I use an old variac core and wind whatever turns through the center are necessary to get a good match to my load. The MOT will do just fine if you have the room on the core. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

EMdevices	Re: Hot Coil Electromagnet « Reply #167 on: 2012-09-07, 18:39:26 »
Hero Member Posts: 805	Very interesting Peter. The repeating paterns is indicative of standing waves. Magnetostriction plays a part, which is the coupling mechanism between acoustic strain energy propagating in the wire and the magnetic field. Here's something to try: Clamp a metal wrench or pliers to the wire at various distances and see how that affects the standing wave patern. You might find there are nulls around the place you clamped. EM

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