Induction Hobs

[rusty69]

18 minutes ago, magnetman said:

Much as I realise that Tesla and Sterling products are the porn of the devil I quite like the recessed design of the Sterling hob with a remote control.

 

That is actually rather a Good Idea. 

It also means that if you plug it into a smart plug, you can turn it on from the helm whilst out working the boat. 

 

Culinary bliss 

[magnetman]

The Sterling piqued my interest.

 

I like this one..

 

https://www.nisbets.co.uk/buffalo-compact-induction-heater-1000w/fd059

 

has got the remote control but a nicer item. 

 

I don't think these can be recessed into a worktop because the intake for the cooling fan seems to be on the side of the round part. I believe the idea is one would mount it into a ring of some sort with the hole in the worktop being larger. 

 

[rusty69]

If I'm not allowed to roast squirrel, I'm sure buffalo is out of the question too.

[magnetman]

This one is only a heater. 

 

You can use the 'I am only heating the Buffalo' exclusion clause and cook to your hearts content. 

 

I think this is why it is deliberately not advertised as a cooker. 

 

Clever. 

[rusty69]

Sterling do a similar thing. Not sure I would want to cut a hole in my work surface though

 

https://sterling-power.com/pages/induction-hobs

 

 

Edited November 30, 2023 by rusty69

[magnetman]

Similar issue with my fire. It is a heater so I can cook pasta on it without the Pasta Protection League targeting me for online abuse and death threats.

 

 

Just now, rusty69 said:

Sterling do a similar thing. Not sure I would want to cut a hole in my work surface though

 

https://sterling-power.com/pages/induction-hobs

I wouldn't buy a Sterling product they are too expensive and no good. 

 

 

No need to have the digital display. Its a gimmick. The Buffalo controller is a far better design. 

[robtheplod]

We have induction at home at its great. These are mainly single hobs - wouldn't people want to have 4, but then the consumption is definately an issue.... are people using one hob purely from a power point of view and if so they can't be that viable on the average boat?

[IanD]

Just now, robtheplod said:

We have induction at home at its great. These are mainly single hobs - wouldn't people want to have 4, but then the consumption is definately an issue.... are people using one hob purely from a power point of view and if so they can't be that viable on the average boat?

 

Induction hobs are high power when they're on (at least, on full power) but this is usually only for short periods, the energy used in kWh per meal is typically much smaller than you might think -- but of course still has to come from somewhere. The peak power can also be a problem on a boat with relatively small (especially LA) batteries and a relatively small inverter, but then it would be silly to use an induction hob on a boat like this... 😉

 

If you want to go full-size induction hob/gas-free then that's a different kettle of fish which needs much heavier-duty and expensive electrics and a means of providing the power when away from shoreline -- could be solar in summer if the boat has a lot fitted, but means a generator in winter. Which may already exist for other reasons, but if not would need to be added -- more expense. Doing all this just for electric cooking doesn't make sense...

[magnetman]

The little ones can be set as low as 2 or 3 hundred watts. They do work but it depends what you call cooking! 

 

 

The 1kw Buffalo induction hob has ten power settings for warm or cook.

 

I think provided it was installed properly and you have a durable electrical system this could be a very nice addition to the Boat.

 

I would not be without bottled gas as it is so useful but one of these hobs for when there is too much solar is actually not a bad plan. 

[nicknorman]

17 hours ago, Theo said:

I have been cogitating on the idea of an induction hob on the boat.  We have recently bought a new cooker for our house kitchen with an induction hob for the house and have fund it completely excellent.

 

I have looked up the literature on how they work and all the articles say that they work by the induction of eddy currents in the base of the pan.  If this is the case they should work perfectly well with any metal pan.  This is not the case.  They don't work with thick or thin ground based or otherwise aluminium pans.  AFAICT they only work with ferro-magnetic based pans.  We have one or two cast le Creuset pans and they work perfectly.  The new ones that we bought are, presumeably, a ferro-magnetic stainless steel.

This indicates to me that eddy currents pay little part in the heating.  It also indicates that a more likely heating effect is by the repeated magnetic cycling giving rise to hysteresis "losses". When we use our new pans on our induction hob they make sometimes make a low buzzing noise as the coils in the cooker are energised.

I would be really interested to hear other people's views on this.

 

Nick

 

It's a good question. One can induce eddy currents in aluminium just as one can in iron. And aluminium has higher resistance!

According to brief research on Wikipedia, it is to do with the skin effect. The induced currents in aluminium go quite deep and therefore there is a relatively large cross sectional area of conductor, hence not much heat. With ferro-magnetic materials the skin effect is very powerful and so the current only flows in a very shallow layer, hence small x-section, hence high resistance, hence lots of heat. Apparently the coils used to generate the field are made from a special wire that is in fact lots of tiny wires, to reduce this skin effect in the wire and stop it overheating.

I'm not sure I totally buy this yet, since I thought skin effect was mostly a high frequency thing and induction hobs are not high frequency. More research needed!

[bronskimac]

Getting back to the original question. The magnetic eddies part of the description is true, but they miss out the next step. Those eddies induce a current that heats the iron pan due to resistance in the metal. Technically, aluminium and copper can be heated by an induction method, if the frequency of the induction current is high enough, and Panasonic have a "Met-All" hob that does that. Presumably cost is a factor in making such a device, as they only sell one for commercial kitchens. https://www.prnewswire.com/news-releases/panasonic-introduces-groundbreaking-new-induction-cooktop-providing-extraordinary-commercial-cooking-performance-with-all-kinds-of-metal-cookware-300404902.html

P.S. I have an induction hob in my bricks and mortar home and love it 🙂

Edited November 30, 2023 by bronskimac

[IanD]

1 minute ago, nicknorman said:

 

It's a good question. One can induce eddy currents in aluminium just as one can in iron. And aluminium has higher resistance!

According to brief research on Wikipedia, it is to do with the skin effect. The induced currents in aluminium go quite deep and therefore there is a relatively large cross sectional area of conductor, hence not much heat. With ferro-magnetic materials the skin effect is very powerful and so the current only flows in a very shallow layer, hence small x-section, hence high resistance, hence lots of heat. Apparently the coils used to generate the field are made from a special wire that is in fact lots of tiny wires, to reduce this skin effect in the wire and stop it overheating.

I'm not sure I totally buy this yet, since I thought skin effect was mostly a high frequency thing and induction hobs are not high frequency. More research needed!

 

Skin depth at 25kHz (typical induction hob switching frequency) is about 0.5mm compared to 0.07mm in iron (7x bigger). On top of this the resistivity of iron is 3.7x higher than aluminium. So for a given induced current, the heating power in iron is 26x higher than in aluminium.

 

The coils in induction hobs use Litz wire to minimise losses.

 

https://en.wikipedia.org/wiki/Litz_wire

 

"Litz wire is frequently found in power applications in frequencies ranging between lower tens to higher hundreds kilohertz, namely induction cookers and transmitters of inductive chargers (e.g. the Qi standard). "

[nicknorman]

The "magnetic cycling" theory seems to have some validity. See here, but you can skip all the equations!

https%3A%2F%2Folewitthansen.dk%2FPhysics%2FThe_physics_of_induction_stoves.pdf

[IanD]

10 minutes ago, nicknorman said:

The "magnetic cycling" theory seems to have some validity. See here, but you can skip all the equations!

https%3A%2F%2Folewitthansen.dk%2FPhysics%2FThe_physics_of_induction_stoves.pdf

And that article is simplistic and completely ignores skin effect, which makes a massive difference to the generated power and hob efficiency... 😉

 

(and the author "assumes 1kHz", which is far too low)

 

It's a bit like the theoretical analysis trying to answer the question "What is the terminal velocity of a cow dropped from an aeroplane?" which goes through a lot of analysis, but turns out only to be valid for a smooth spherical cow... 🙂

Edited November 30, 2023 by IanD

[bronskimac]

7 minutes ago, IanD said:

And that article is simplistic and completely ignores skin effect, which makes a massive difference to the generated power and hob efficiency... 😉

 

(and the author "assumes 1kHz", which is far too low)

 

It's a bit like the theoretical analysis trying to answer the question "What is the terminal velocity of a cow dropped from an aeroplane?" which goes through a lot of analysis, but turns out only to be valid for a smooth spherical cow... 🙂

😂

[blackrose]

4 hours ago, rusty69 said:

I suppose that depends on the size of the induction hob and whether it is built in. 

 

Thw one we have is one of those one pan portable jobs. It's an 800W thing, but I think the lowest setting is 200W.Easily stored in a cupboard when not in use. Great should the gas run out unexpectedly. 

 

Ok I'd assumed a built in hob. Yes anything which doesn't take up too much space is worth having. 

2 hours ago, rusty69 said:

If I'm not allowed to roast squirrel, I'm sure buffalo is out of the question too.

 

I actually had some buffalo the other day in a bowl of noodle soup. Much like beef as one would imagine.

2 hours ago, magnetman said:

I wouldn't buy a Sterling product they are too expensive and no good. 

 

Not in my experience. I've got lots of their stuff. It works well and if something does go wrong their customer service is amazing. 

[magnetman]

Experience is no substitute for assumption.

Ideally one would never need to know anything about customer service. 

 

I imagine if they get plenty of practice they will be good at it. 

[TheBiscuits]

2 hours ago, IanD said:

"What is the terminal velocity of a cow dropped from an aeroplane?"

 

0 m/s

 

It's not terminal until it suddenly stops ... 

 

[IanD]

1 minute ago, TheBiscuits said:

 

0 m/s

 

It's not terminal until it suddenly stops ... 

 

What if it's a whale? Or a bowl of petunias?

[nb Innisfree]

 

Dont bother, just place an upturned flowerpot over a candle and you have an excellent stove + it will heat the whole boat esp with an Ecofan fan on it, make sure to open all outside doors to prevent tropical heat. 

[rusty69]

For those of you that don't want a full size hob, they do usb coffee cup induction warmers.

 

Kind to your battery too

Edited November 30, 2023 by rusty69

[Theo]

5 hours ago, system 4-50 said:

from Wiki:

For nearly all models of induction cooktops, a cooking vessel must be made of, or contain, a ferrous metal such as cast iron or some stainless steels. The iron in the pot concentrates the current to produce heat in the metal. If the metal is too thin, or does not provide enough resistance to current flow, heating will not be effective. Induction tops typically will not heat copper or aluminum vessels because the magnetic field cannot produce a concentrated current, but cast iron, carbon steel and stainless steel pans usually work. Any vessel can be used if placed on a suitable metal disk which functions as a conventional hotplate.

 

That, to me as an ex physics teacher, looks all wrong.  Iron does not concentrate current.  It has a higher resistivity than copper or aluminium but the current will be distributed through iron in the same way as through other metals.

8 minutes ago, Theo said:

That, to me as an ex physics teacher, looks all wrong.  Iron does not concentrate current.  It has a higher resistivity than copper or aluminium but the current will be distributed through iron in the same way as through other metals.

Hm...

 

I had ignored the skin effect.  Thanks all.  As said, more research required.

 

N

[nicknorman]

45 minutes ago, Theo said:

That, to me as an ex physics teacher, looks all wrong.  Iron does not concentrate current.  It has a higher resistivity than copper or aluminium but the current will be distributed through iron in the same way as through other metals.

Hm...

 

I had ignored the skin effect.  Thanks all.  As said, more research required.

 

N

 

As a physics teacher you can perhaps understand that magnetic permeability is also in the mix somewhere. One makes transformer or solenoid cores out of iron, not out of aluminium even though the latter would be much lighter. This being because the magnetic permeability of iron is about 5000 times greater than aluminium.

[IanD]

4 hours ago, nicknorman said:

 

As a physics teacher you can perhaps understand that magnetic permeability is also in the mix somewhere. One makes transformer or solenoid cores out of iron, not out of aluminium even though the latter would be much lighter. This being because the magnetic permeability of iron is about 5000 times greater than aluminium.

That's true, but magnetic permeability has a strong effect only in relatively closed magnetic circuits like solenoids. Induction hobs aren't like that, most of the magnetic circuit is air so the iron/steel makes very little difference to the magnetic fields.

 

The heating method in induction hobs is field-induced eddy currents in the pan, and iron/steel ones work much better than aluminium because of higher resistivity and thinner skin depth, not magnetic properties as such.