Since Lidl have got 2kW induction hobs on offer for £30, What are the chances that one could be used or modified do something useful? Possibly a new coil could be reverse engineered and any interlocks defeated.
I'm feeling the need to go shopping...
Mark Rand RTFM
Shout Kippers 3 times and the induction master will appear :)
Kippers Kippers Kippers
Im interested to know too
Dave
Shout Kippers 3 times and the induction master will appear :)
Kippers Kippers Kippers
Im interested to know too
Dave
... that's my cue ! Enter stage left.
There has been much talk over the past couple of years about using them on the Yahoo group Electro_cast
AWEM
I'll raise you two kippers and a metre of black pudding,..........yummeee
A metre?? Wash your mouth out with a pint of Stella. Everybody knows that black pudding hasn't gone metric yet. Only available in 340ths of a furlong at our local butcher...
Regards, Tony
Unless you live in the Northwest those are not real black puddings. The holy objects only come from Chadwicks in Bury market! See
In article , John S writes
A metre?
That'll be from an Irish pig, then.
You don't want to eat that mate, funny things will happen.
Hi, I have no experience on this particular application, but I am an ex Induction Heating engineer.
The idea of getting as much energy into the peice you are working with is to get it coupled up right. Maximum power transfer occurs when you have it coupled up properly, such maximum current, and the volts are at their highest.
Generally on equipment I have worked are parelle tuned systems, but this will be series tuned system, which means there is little/no reactive current flowing, but there large reactive voltages appearing across the inductance (otherwise known as the work coil), and the tank capacitor. This means that you don't have to cool the inductor and the capacitor. In parallell tunder circuits the reactive current is roughly input current times to Q factor. Q is known as Xl/R. Similarly in a series syste, reactive volts are roughly Vin times the Q factor. You normally aim for a Q value of about 10 for various reasons.
So the point of what I am saying is that the coupling factor is crucial to getting power into your work peice. As a guide, this works far better with steel, and iron workpeices for obvious reasons, ie a magnet will stick to it. Trying to get heat into an aluminium peice is much more difficult. It's not impossible but you have to go for a higher Q value in your work coil.
Another point is what is the frequency of operation? If you can hear it then it's below about 10kHz. If it's higher, then it may be difficult to get heat into large peices. If you are heating something large then you will require a lower operating freuquency because of skin effect.
Has this helped? Ask me some questions!
Rob.
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No, the principle used there is the curie point of the metal - when it ceases to be ferro magnetic the sensor coil no longer couples to the drive coil by transformer action.
AWEM
Yes that it true, when you get to Curie point, it is more difficult to get any more energy into the piece. I have known systems whereby at curie point you have a contactor that changes over so that the Q of the coil is doubled, so you can put more ergs into the peice, but this is difficult and technically can be unreliable because you are switching reactive currents.
I'm not sure your statement is correct about trnaformer action though. When it's below curie, the heating is more to do with eddy currents and molecular agitation in the peice and. When you're past curie, you *are* using transformer action, as you are inducing ebergy into the peice and basically driving a short circuit secondary.
Rob.
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Rob,
All is in the context! The Wild Barfield heat treatment furnace uses resistive heating elements (not induction) controlled by a system detecting the critical temperature by the curie point of the metal being treated.
AWEM
Andrew, My understanding maybe incorrect but in your last posting you appear to be describing an actual furnace with heating elements embedded into brickwork. The machine I am trying to describe had a single ring coil that was actually cold unless a piece of metal was put in close proximity. I also remember a sign not allowing people with pacemakers within a set distance because of frequency generation playing hell with the pacemaker.
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No doubt W B made (make?) a range of kit - I'm describing their classic heat treatment furnace
AWEM
Hi Guys, If it's a Water Cooled work coil, then that says that it was a parallel resonant coil, with the Tank Capacitor in parallel with it. Because of the reactive current circulating in the tuned circuit, the I^2.R losses would be enourmous, hence the water cooling. Live water cooled Bus Bars were common place, and still are.
Reistance furnaces would not have water cooled elements for blatantly obvious reasons.
I actually did some work on a point nose heater, which was used for hardening a point crossing casting.
Billet heaters were two a penny. I did do some interesting stuff with Gas Turbine disks in that we used a single turn induction heating coil to expand the shat cup, such that you would separate the disk from the shaft. They used to use gas torches, and it took them hours to separate disks from shafts. You would have to do this if the turbine disk had shown up an anamoloy in the ultrasound test, but the shaft was still good. Using induction heating the shaft would drop off the disk about a couple of seconds of applying energy to it from the coil. We won a technical innovation award for that one they were so pleased with it.
Rob.
Below Curie point, alternating magnetic flux heats steel workpieces by the combined effects of eddy currents and hysteresis loss.
Eddy current loss is the I squared R loss produced by circulating currents induced into the workpiece resistivity.
Hysteresis loss is the result of the failure of the flux density in the workpiece to pass through zero as the exciting flux passes through zero.
Permanent magnet materials have extremely high hysteresis loss (they retain most of their magnetism when the magnetising field is removed). Soft iron has a much lower but still significant hysteresis loss. Hardened steel is intermediate.
When the Curie point is reached the iron is no longer ferromagnetic which means that the permeabilty (the factor by which it increases work coil inductance) drops to one and zero flux is now coincident with zero exciting flux.
This means that the hysteresis loss disappears and there is a reduction in work coil inductance. The disappearance of the hysteresis loss increases the work coil Q and the reduction of work coil inductance requires an increase in tank capacitance to return it to its previous resonant condition.
Jim
Very well explained.
Rob.
You're making it far too complicated...
Above the Curie point the relative permeability is (to all intents and purposes) 1. Below it, it is from 500 to 2000 for steels. The leakage reactance of the work coil stays the same, the mutual reactance between work coil and work goes to hell and the field through the work drops.
Therefore the induced currents become less because they are a function of the rate of change of flux and less heat is produced.
Inductance isn't a function of hysteresis loss, it's a function of permeability. Mumetal will heat better than Alnico!
regards Mark Rand
Whoooooooosh------>>>>>>>>
Straight over my head those last two...
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