Hot Coil Electromagnet

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Author Topic: Hot Coil Electromagnet (Read 80214 times)

Grumpy	Re: Hot Coil Electromagnet « Reply #50 on: 2012-08-10, 00:07:16 »
Group: Tinkerer Hero Member Posts: 3948 tExB=qr	uh yeah and this is 60 Hz...kinda slow change in lieu of encasing the probe in plastic, a thick plate will do - like a small cutting board. if it causes a change in that pulse, it is because the plastic is altering the propagation velocity of the cause of the pulse (in simple terms) humor me and try it

Grumpy	Re: Hot Coil Electromagnet « Reply #51 on: 2012-08-10, 00:10:21 »
Group: Tinkerer Hero Member Posts: 3948 tExB=qr	Quote from: ION on 2012-08-10, 00:03:53 EM said: Actually my resistance is less on the hand wound coil, 3.56 ohms versus 9.56 ohms for the larger unit. I run the smaller coil at it's limit, around 6 amps. what about the inductance of each? get a cutting board - if it alters the pulse, then I know what it is, else it is magnetic and just a curiosity (I discovered this accidentally with a coil set on a coffee cup to raise it off the bench - and wooohooo!!! it lit me up)

EMdevices	Re: Hot Coil Electromagnet « Reply #52 on: 2012-08-10, 01:13:02 »
Hero Member Posts: 805	Quote uh yeah and this is 60 Hz...kinda slow change I know, 60 Hz is very slow, and it's effect can bearly be seen in the spiky waveform, so the voltage spikes are not caused by this 60 Hz directly but indirectly, through the snapping action of the magnetic domains that is the underlying phenomena behind the Barkhausen noise. It's like extending a ruber band untill it snaps, and the snapping is a lot faster than the rate of stretch that is occuring. some good reading. http://www.insightndt.com/papers/technical/t013.pdf

Peterae	Re: Hot Coil Electromagnet « Reply #53 on: 2012-08-10, 09:31:08 »
Group: Administrator Hero Member Posts: 3960	Quote from ION Quote two foot long coiled wire of Nichrome (I guess) If it's really old then there maybe a possibility it's Rhodium, I knew a scrap metal dealer who in the 70's especially looked out for old heating elements because of the use of Rhodium, i don't know to what extent it was used, i seem to remember him especially looking for old storage heaters but maybe it was more widely used in times when it was cheaper. I also knew a scrap metal dealer who made millions by buying up all the surplus spark plugs from the 2ND world war effort, they used platinum for the electrodes

exnihiloest	Re: Hot Coil Electromagnet « Reply #54 on: 2012-08-10, 12:06:22 »
Group: Guest	@ION What mag probe do you use? Do you know for what frequency range it is specified? If its inductance is low, the high frequency components of the signal can be reinforced (especially in the frequency range of its natural resonance) and the low frequencies reduced. So the ratio between the spikes and the sine wave could be false, and the least parasitic peak in the signal be hugely amplified. Several times I have been surprised to see strange signals from the grid. This was due to the filtering of the circuit through which I observed the signal. If the circuit acts as a high pass filter, we can see even radio frequency signals. For example we can see the spikes due to a triac controlling a light elsewhere in the house. Could you put a low resistance (<1 ohm) in series with the heater, and measure the voltage at its terminals, in order to estimate the real current? It is possible with an oscilloscope, with two probes in differential mode.

ion	Re: Hot Coil Electromagnet « Reply #55 on: 2012-08-10, 13:56:07 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Quote from: exnihiloest on 2012-08-10, 12:06:22 @ION What mag probe do you use? Do you know for what frequency range it is specified? If its inductance is low, the high frequency components of the signal can be reinforced (especially in the frequency range of its natural resonance) and the low frequencies reduced. So the ratio between the spikes and the sine wave could be false, and the least parasitic peak in the signal be hugely amplified. Several times I have been surprised to see strange signals from the grid. This was due to the filtering of the circuit through which I observed the signal. If the circuit acts as a high pass filter, we can see even radio frequency signals. For example we can see the spikes due to a triac controlling a light elsewhere in the house. Could you put a low resistance (<1 ohm) in series with the heater, and measure the voltage at its terminals, in order to estimate the real current? It is possible with an oscilloscope, with two probes in differential mode. ex: My main mag probe is a Magnetek 100mV / Gauss @ 60 Hz. (Magnetek Corp. Boulder Colorado) I also use other pickup coils to verify that it is not an artefact of the probe, such as long telephone coil relay electromagnet around 3" long with many turns of fine #36 wire on an iron slug, and other coils with and without magnetic cores. All nearly the same spiky waveform. If you have not read the whole thread, you will note that I have used a 0.01 ohm resistor shunt to measure the current. This is a four wire "Kelvin" type resistor, 2 leads for current, 2 sense leads to the scope. No artefacts in the current waveform I tried another similar heater, coiled Nichrome element in a quartz tube. same effect a little less intense. I am guessing they are Nichrome. based on the hot to cold resistance ratio. determined initial reading and current drawn when hot, which can be worked back to find hot resistance. I have shown this to another seasoned engineer like myself and he is also puzzled. Together we have over 80 years of experience designing and troubleshooting all types of power circuitry. Barkhousen noise is not a good fit for what is happening here. At this point I'm wasting too much time answering questions that were priorly answered and am going back to the bench to investigate further. Read the whole thread!!! Cheers to all.....ION --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

ion	Re: Hot Coil Electromagnet « Reply #56 on: 2012-08-10, 15:38:57 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Ok further tests on the bench this morning revealed some of the truth. EM was right, this is a saturation effect of the type of Nichrome that has a high iron content. I tore apart another jnfra-red quartz heater and laid the element on the bench so that I could slip sense coils over it. This heater had weak but more noticeable attraction to a magnet. The effect can now be seen sharply and in phase with the zero crossing. It is noticeable at much lower current levels as I ran it off a variac. More pronounced at higher currents, but always sharply at the zero crossing, and a very large spike. I cannot explain the many spikes seen in the earlier analog scope shots and will research it further. I wonder if pure iron wire will have the same effect? Worthy of research. Back to the bench! --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

poynt99	Re: Hot Coil Electromagnet « Reply #57 on: 2012-08-10, 15:53:03 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	--------------------------- "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

exnihiloest	Re: Hot Coil Electromagnet « Reply #58 on: 2012-08-10, 15:56:04 »
Group: Guest	Quote from: ION on 2012-08-10, 13:56:07 ... If you have not read the whole thread, you will note that I have used a 0.01 ohm resistor shunt to measure the current. This is a four wire "Kelvin" type resistor, 2 leads for current, 2 sense leads to the scope. No artefacts in the current waveform I tried another similar heater, coiled Nichrome element in a quartz tube. same effect a little less intense. I am guessing they are Nichrome. based on the hot to cold resistance ratio. determined initial reading and current drawn when hot, which can be worked back to find hot resistance. I have shown this to another seasoned engineer like myself and he is also puzzled. Together we have over 80 years of experience designing and troubleshooting all types of power circuitry. Thank you for having clarified and synthetized your results , and also your experience and level of expertise, this will avoid me now to propose the simplest explanations that qualified people like you have already discarded but that can constitute traps for the laymen. Quote At this point I'm wasting too much time answering questions that were priorly answered and am going back to the bench to investigate further. Read the whole thread!!! Cheers to all.....ION I understand. I confess that I had not carefully enough read the whole thread. I don't well master English and so, it's tedious for me to find the good information when it is scattered throughout the thread, and I miss some points. That's my poor excuse .

ion	Re: Hot Coil Electromagnet « Reply #59 on: 2012-08-10, 20:20:07 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	EX: No problem, I consider you one of the brighter guys out there, you ask the right questions and are obviously well experienced in the art of electronics. I also ran the heater from a high power amplifier, sweeping frequency to about 10K. The saturation spike gets higher and sharper with increasing frequency up to a point, then rounds of a bit. I need to go back at some point and check that first "Martel" heater, the one that produced the myriad of pulses on the analog scope. I bypassed the bi-metal thermostat and the tilt shutoff switch, but the noisy pulses were still visible. Tested also a coil of pure thermocouple grade iron wire that I had wound a few years ago. It does not exhibit anything like the Nichrome effect. Worthy of research would be a test of many different types of pure wire and wire alloys to determine the magnetic effects. Wish I had the time and materials on hand. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

exnihiloest	Re: Hot Coil Electromagnet « Reply #60 on: 2012-08-11, 10:25:50 »
Group: Guest	Quote from: ION on 2012-08-10, 20:20:07 ... Worthy of research would be a test of many different types of pure wire and wire alloys to determine the magnetic effects. Wish I had the time and materials on hand. This is a good way for the investigation. The effect could be due to the temperature of the wire that oscillates at each half-period before reaching its nominal value, either around the Curie point (presuming NiCr weakly magnetic) or simply changing the permeability or less likely, inducing a phase change in the metal. Therefore it would be depending on metals or alloys. In the past I had modulated a filament bulb with AC audio around a CC current and was able to demodulate the light signal that I received with a LDR. There was a low-pass filter effect but the voice was perfectly understandable. This demonstrates that the filament temperature can change at a rapid rate up to Khz, contrarily to our intuition. According to your oscilloscope screen shots and the width of the spikes (around 1/20 of the 60Hz period), their frequency domain is about 1200 Hz.

Peterae	Re: Hot Coil Electromagnet « Reply #61 on: 2012-08-11, 13:44:14 »
Group: Administrator Hero Member Posts: 3960	I will try to get some nichrome wire, i should be able to drive this from my Class A. I am running out of time for this month my Daughter is about to get married in a couple of weeks.

ion	Re: Hot Coil Electromagnet « Reply #62 on: 2012-08-11, 13:59:11 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Here is some additional information that adds a bit of mystery to this finding. I wound two long thin coils like the ones in the Martel heater for testing. One was made of thermocouple grade iron 14 guage. This is a pure soft iron. It should be easy to saturate. It did NOT put out a saturation pulse anything like the Nichrome. In fact there was no sign of any saturation effect. The mag probe and other pickup loops showed a well rounded sine wave at several test currents. The second coil was made of a thermocouple wire material called Constantan, 45% Nickel, 55% Copper. This coil also showed no pulse effect like the Nichrome. I have some Chromel on hand which is 90% Nickel, 10% Chromium. I will try to test this next. Looking at my inventory, I have a large stock of Nichrome V made by Driver Harris Corp. I will have to research this further, but it is unlike the Nichrome in the heaters, very weakly magnetic. Another set of tests would be to wind these wires into a given toroidal shape and use as an inductor core to determine saturation effects when current is not passed through the wire. Too much research to do, too few hands.....anyone want to join the fun? --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

ion	Re: Hot Coil Electromagnet « Reply #63 on: 2012-08-11, 14:02:46 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Quote from: Peterae on 2012-08-11, 13:44:14 I will try to get some nichrome wire, i should be able to drive this from my Class A. I am running out of time for this month my Daughter is about to get married in a couple of weeks. Peterae: Hope you have a good time at the wedding Before you buy any Nichrome, we need to identify the exact type used in these heaters. If you could use a heater around the house there are several vintage types on ebay, as well as replacement elements. Looking at my inventory sheet reveals that the Nichrome I have on hand is 80% Nickel, 20% Chromium with temper "A" made by Driver Harris Corp. It is NOT what is used in the heaters. The heater stuff has a very noticeable (not weak) attraction to a magnet, It must be the 24% iron type. Wiretronic has a free downloadable wire calculator here: http://www.wiretron.com/free.html This site seems to indicate that Nichrome 60 Alloy 675 is predominately used in infra red heaters. http://www.infraredheaters.com/nicrcoil.html It has the following: Nickel 57 to 58% Chromium 16% Silicon 1.5% Remainder Iron (about 24%) « Last Edit: 2012-08-11, 14:40:12 by ION » --------------------------- "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 #64 on: 2012-08-11, 14:45:38 »
Group: Administrator Hero Member Posts: 3960	Thanks ION very handy wire calculator I just looked high and low and located some very old replacement Halogen quartz heater spares, i knew they were around somewhere, i am not sure if they are any good, but worth a try, if i shake them i can hear the coiled element ratling, as they are sealed and halogen i guess i could break one to have a better look at the wire infact looks like 1 is broken anyway. They are 400 Watt 240V 1.7 Amps, now i wish i had bought a bigger variac which is only rated for 0.75A Grrr, still it might warm it up enough to have a sniff at the field. Exactly the same as these here http://www.amazon.co.uk/Halogen-Heater-Replacement-Bulbs-400Watts/dp/B000R2CSDS/ref=pd_sim_sbs_kh_2 the heater element is only about 5-6mm OD spiral wound.

ion	Re: Hot Coil Electromagnet « Reply #65 on: 2012-08-11, 14:51:03 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	I don't think those quartz heaters will do it, they are usually tungsten wire, but I will test a similar item. Here is the stuff: http://www.ebay.com/itm/Nichrome-resistance-wire-18-AWG-gage-30-feet-foam-cutting-sealing-heating-/221087194159?pt=LH_DefaultDomain_0&hash=item3379d2dc2f This has the 24% iron. You may be able to get a free sample from a wire house. Too bad I have in stock over 6000 feet of the wrong stuff, the 80/20. The pulse you will see with the right stuff is pronounced, very interesting, and defies all theories so far. I thought (and agreed with EM) that it was simply saturation effect, but now am doubting this theory based on tests with the pure iron wire. Something about that alloy Type 60 that is different. I wonder what would happen if we designed the alloy for the optimum pulse? --------------------------- "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 #66 on: 2012-08-11, 14:58:32 »
Group: Administrator Hero Member Posts: 3960	yep i have some on order I have a lot of things i want to test out, IE pulse 1 with 1000V pulses using my Marx avalanche pulser, resonate a tuned coil made of the stuff etc and yes as always i am getting ahead of myself first i need to see the effect I am just limited by time for a few weeks so it will appear not much is happening $:-\$ I will try one and see if i can get any results while waiting for the nichrome to arrive.

poynt99	Re: Hot Coil Electromagnet « Reply #67 on: 2012-08-11, 15:58:09 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	Quote from: ION on 2012-08-09, 15:37:12 Here are two camera shots of the scope traces. Forgive the fuzziness. Smooth sine curve is the heater current. Spike waveform is superimposed. First shot (001) is spikes as picked up with mag probe full amplitude at initial time up to 5 seconds vs. current. Second shot (002) shows spikes decaying after 5 seconds versus current. Judging from the scope shots, it appears the spikes are produced both when the current quickly changes from increasing to decreasing, and when the current changes direction at the zero-crossings (more pronounced). Notice the polarity of the spike is the same for when the current goes from increasing to decreasing, and from positive to negative at the zero-crossing? The spike is the opposite polarity when changing from negative to positive current at the zero-crossing. This sounds very much like inductive kickback. A very small change in current seems to be causing this IK. Could this be? Could the heating/diminishing effect be caused by the added resistance largely damping out the spike's amplitude? --------------------------- "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 #68 on: 2012-08-11, 16:16:31 »
Group: Administrator Hero Member Posts: 3960	Quote The most common way for a toaster to create the infrared radiation is to use nichrome wire wrapped back and forth across a mica sheet, like this: It looks like toasters use nichrome as well, infra red radiation

ion	Re: Hot Coil Electromagnet « Reply #69 on: 2012-08-11, 16:27:22 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Quote from: poynt99 on 2012-08-11, 15:58:09 Judging from the scope shots, it appears the spikes are produced both when the current quickly changes from increasing to decreasing, and when the current changes direction at the zero-crossings (more pronounced). Notice the polarity of the spike is the same for when the current goes from increasing to decreasing, and from positive to negative at the zero-crossing? The spike is the opposite polarity when changing from negative to positive current at the zero-crossing. This sounds very much like inductive kickback. A very small change in current seems to be causing this IK. Could this be? Could the heating/diminishing effect be caused by the added resistance largely damping out the spike's amplitude? Hi Poynt Interesting observation, yes it does seem to possibly be inductive kickback, but why is it nonexistent in pure iron wire? And why so sharply sensitive to change in current and direction? The resistance only changes about 5 to 6% from cold to glowing orange, even less over the sharp point at which the decay occurs. (11.07 amps). I think we have identified the Curie point and fading ferromagnetic property of iron as the cause of the sudden decay (at around 11.07 amps on my heater). The time to decay is quicker if the element has not cooled all the way to room temp. --------------------------- "Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy

poynt99	Re: Hot Coil Electromagnet « Reply #70 on: 2012-08-11, 17:32:20 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	Quote from: ION on 2012-08-11, 16:27:22 Hi Poynt Interesting observation, yes it does seem to possibly be inductive kickback, but why is it nonexistent in pure iron wire? And why so sharply sensitive to change in current and direction? I'm speculating that is has something to do with the alloy mix. Pure iron as a magnetic core has a relatively poor high frequency response. It would be interesting to try your experiment with Permalloy tape, or something with a similar alloy mix. --------------------------- "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 #71 on: 2012-08-11, 18:16:44 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Quote from: poynt99 on 2012-08-11, 17:32:20 I'm speculating that is has something to do with the alloy mix. Pure iron as a magnetic core has a relatively poor high frequency response. It would be interesting to try your experiment with Permalloy tape, or something with a similar alloy mix. Yes the alloy is the key, but then the question is "what is the optimum alloy"? I'm not sure if I have Permalloy tape on hand, I have a few unidentifiable tapes. --------------------------- "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 #72 on: 2012-08-11, 18:47:40 »
Group: Administrator Hero Member Posts: 3960	1st attempt with limited equipment and a foot high buried bench My variac just wont handle the power of this tube, i am still running with a 100 Watt bulb in series with my variac to save my day. I have wound a coil over the quartz this has a 1K resistor in parallel just to help look for a bit of power in the spikes. I am scoping across the 400watt heater with Chan 2 and Chan1 is the sniffer coil. All i am getting is dc pulses when i switch on and off. I am not sure what my next move is, i could connect straight to the mains but it will burn hot real fast. Maybe i could take the element out and measure the length/resistance and try to work out which wire it is and then maybe use a small amount of wire to hook up to my 15 Watt class A [youtube]http://www.youtube.com/watch?v=V5pjtTvJbns&feature=youtu.be[/youtube]

ion	Re: Hot Coil Electromagnet « Reply #73 on: 2012-08-11, 21:34:20 »
Group: Elite Hero Member Posts: 3537 It's turtles all the way down	Peterae: I've already tested a quartz heater (sealed glass tube type) as used in fuser assembly of laser printer. There was nothing unusual to find. Tungsten filaments as used in this type of heater have a large positive temperature coefficient (PTC). I would be very careful trying to drive this from your class A. The low cold resistance will cook your transistors fast. Better to use your Variac and a step down transformer. BTW, I built the JLH class A many years ago. It is a fine little amp. I was an avid reader of WW. JLH will be missed. If you measure the ohms cold, then work backwards from the amps draw hot, knowing the applied voltage you can determine the hot resistance easily. --------------------------- "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 #74 on: 2012-08-11, 21:52:40 »
Group: Administrator Hero Member Posts: 3960	Hey that's great, it's a fantastic amp, i did the low ohms mod and drive a 1.2 ohm secondary of a mains transformer and use the other 1.2 ohm secondary to drive my heater, it has no trouble with low impedance drive. I just cut a meter of wire from that halogen tube and it reads 5.4 Ohm doh which is useless without me knowing the diameter, looks like i am stuck until i get some nichrome through the post. I just tried a neo magnet near it and i cannot detect any attraction, if it does attract its a very small amount. EDIT warning welcomed , would hate to blow my amp, at some point i want to pipe some audio through it So yes indeed looks like i got Tungsten Now who do i know who has a heater i can borrow and strip I wonder if the Mrs hair dryer might do it although i could be dicing with death if she See's that apart

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