Freestanding electric cooker, induction hob problems.

[simpson93]

Evening all, I’ve had a fault recently with a hotpoint free standing electric cooker and wondering if anyone has had a similar problem.

The problem itself is with the induction hob part of the cooker, the hob had blown when a pot was placed on top and the mcb tripped Within a few minutes. The mcb was reset and the hob part of the cooker would no longer work but the cooker section was still was functional.

After having a like for like cooker installed a month or so later the same thing has happened with the same pot which had not been used since the last fault.

 

[littlespark]

Is it an especially heavy pot? Its maybe pressed down too hard on the induction plate and made 2 parts touch that aren't supposed to.

Shot in the dark, mate.


I did have a look at a Zanussi induction hob. It came up with an error code. Apparently if the pan is too wide or too narrow a diameter, the induction plate senses it and doesn't come on.

 

[buzzlightyear]

Maybe you havenot the right pan
For the induction hob .
The magnet field may not recognise the bottom of it

 

[simpson93]

Supposedly the second time the pot was almost empty.

The mind boggles tho, two cookers same fault 6/7months in between only correlation between the two is the pot used.


Client is looking into a zanussi cooker as a replacement as it goes.

 

[simpson93]

Maybe you havenot the right pan
For the induction hob .
The magnet field may not recognise the bottom of it

But surely it wouldn't cause the motherboard to blow?

It just wouldn't turn on.

 

[chris gray]

I’m guessing other pans have been tried to prove it doesn’t work?

 

[ruston]

And did that pan ever work ?

 

[simpson93]

I’m guessing other pans have been tried to prove it doesn’t work?

The motherboard for the induction hob has blown taking out all of the hob once the pot had been used.

Other pans working beforehand

 

[simpson93]

And did that pan ever work ?

Not too sure, by the sounds of it not been used often seeing as it was months between being used for a second time.

 

[Midwest]

Have you contacted your retailor and or manufacturer?

 

[marconi]

Did you/the client note down any error codes? What was this pot made of - copper and aluminium are unsuitable for basic induction hobs. What is the rating of the mcb and the maximum power requirement of the hob from the rating plate?

 

[SparkyChick]

Did you/the client note down any error codes? What was this pot made of - copper and aluminium are unsuitable for basic induction hobs. What is the rating of the mcb and the maximum power requirement of the hob from the rating plate?

What would be the effect of using the wrong pot? I had a quick read when this thread was posted and noted that copper and aluminium can be used but they need different frequencies? to work.

Would they result in too much power being consumed by the coils, and hence causing damage to the controls?

 

[marconi]

The basic high frequency (20kHz - ish) induction hob is designed to work with magnetic metals like cast iron and some steels. The principle of induction heating is create eddy currents in the surface boundary layer of the bottom of the pan/pot. These eddy currents, are the free electrons of a metal flowing through the surface resistance (ie the resistance of the boundary layer not the bulk of the base of the metal bottom) create Ohmic heating according to Isquared R. The problem in using copper or aluminium is that they are better conductors than iron or steel which means that their surface resistance is lower - thus the Ohmic heating is less from Isquared R. Also, cast iron and some steels, being paramagnetic - which means they do not readily maintain their magentic polarisation but the bound (as opposed to free) electrons do tend to align their spin axes with the applied HF magnetic field. As the applied HF magnetic field is alternating they suffer hysteresis - which creates heat too. To be able to use copper or aluminium one has to use higher frequencies which will produce thinner boundary layers and this effectively a higher skin/surface resistance.

So, what I think has happened is the HF oscillator has been mismatched to its load - it expects to drive a higher impedance load than the pot/pan in question provides - and thus as you say more of the power generated by the oscillator is dissipated in the hob coil and power electronics because the HF current on the primary side of this transformer system is higher than it is designed for. Effectively - think Thevenin equivalent circuit of the primary side of the induction transformer - the lower Zload causes a high current I through the source impedance Zsourse - which does not do it (the HF source ) any good - the Ohmic heating of the resistive part of Zsource is higher. My great surprise in all this is that this problem is highly likely so I would expect some clever electronics to detect it and shut down the HF before irreparable damage occurs - hence the question about fault codes.

 

[SparkyChick]

As usual a great explanation. Thanks @marconi

 

[marconi]

http://docs.hotpoint.eu/_doc/19513659000_GB.pdf

The reference is to a hotpoint induction hob.

See EN6 about suitability of pans and pots and EN 11 refers to fault codes.