Induction cooktops, temperature control questions

Thinking about induction cooktops for beer brewing because the two 1kW burners that my brew kettle straddles result in a whopping 2h+ total just to heat up stuff. On Belgian beers more like 3h. Induction cooktops can be had with 1.8kW but realistically more like 1.5kW on a 15A circuit. That's more and supposedly the induction method is more efficient.

However ... for reasons that I'll never understand the temperature can only be set in 40F increments and very occasionally there are units with

10F steps. Way too coarse for brewing. Even for sous-vide chefs that isn't good enough. I am talking about the usual $50 price range, not $1k restaurant grade. The thermostats on my $12 Walmart cooktops are nicely analog-controlled so I can set them exactly where needed.

I assume the firmware in the internal uC can't be touched so that leaves a hack. If it was an NTC or PTC that reads back the temperature I could hang a potentiometer in series to obtain a vernier control and tape a cheat sheet "real temperature versus indicated" on each cooktop.

Has anyone done that? Did it work well? If not, can these cooktops be controlled "bang-bang" via an external PID loop?

Other question: My brew kettle is aluminum so it would need some sort of steel plate thrown into the bottom. Considerung the thickness of the aluminum bottom this plate would ride 1/8" to 1/4" above the cooktop surface. How much power into the liquid would I lose?

--
Regards, Joerg 

http://www.analogconsultants.com/
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Joerg
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Inductive heating must be less efficient than resistive. Resistive is best if you can make a good thermal connection to your kettle.

How about an aluminum plate, some big resistors bolted to the bottom, a thin gap-pad on top? That would hardly lose any heat, except from the surface of the kettle itself. Wrap it in a cozy.

Or dunk a big resistor into the mash.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

From what I heard and read so far inductiove is more efficient. Power loss in the bridge FETs and coil is so low that a small fan suffices but there is almost no more transfer loss.

That would make kettle cleaning a bear.

Some people use immersion heaters. However, those get in the way because one must occasionally stir. It also would require to crack the lid too much or drill the kettle and mount in permanently. The latter make cleaning tough and stirring nearly impossible. Striing is important when working with malt sirup, dry malt extract or Belgian candi sugar. The latter is indispensable for serious Belgian Tripel or Quad, my favorite beer.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

On a sunny day (Thu, 23 May 2019 08:29:49 -0700) it happened Joerg wrote in :

I have one, bought it some years ago, and everytime I switch that thing on it sort of gives me a headache. So it went into the attic within a day. My theory is that there are magnetic sensitve particles in the brain that get shaken by the stray field. Why my other lower power RF (100 kHz?) ebay one (the bad one is 50 Hz)) does not bother me I do not know. Maybe exitation is then too fast.

So be warned.

Reply to
Jan Panteltje

AFAIK induction cooktops work in the 20-30kHz range. The field is strong but supposedly negligible past 10cm distance. Maybe you are really sensitive to it.

Or did you have too much Beerenburger before the headache set in? :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I thought sous vide had to be even tighter than 10F

Reply to
bitrex

On a sunny day (Thu, 23 May 2019 10:12:01 -0700) it happened Joerg wrote in :

No, will be bit more clear (my fault), with 50 Hz I ment 50 Hz mains, of course ?? I opened mine up to see what caused the problem, and I did not come across a lot of mains filter caps, just a bridge, some switcher, big coils, so the RF (well it is still LF actually) is possibly strongly modulated by the mains frequency 100 Hz from the bridge rectifier.

My ebay induction heater runs on 12V DC, this one:

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The bad one is this one:

was only 55 Euro..

For the ebay one I made a nice cooking coil:

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There is a youtube video of me frying an egg with that:

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You can fry an egg with one small 3 cell 2200mAh 11.1 V RC plane Lipo! Now that is efficient!

Been a while since I had berenburger really... We have European elections today here, now that is also interesting...

Reply to
Jan Panteltje

Yes, that is why I think even the 10F setting isn't good enough for sous-vide. Beats me why they don't improve that. Here is how this can be achieved at a $0.00 BOM cost increase:

The barbecue thermometer I use to monitor the brew kettle via radio link also has only a few temp settings. Rare, medium, done, et cetera. However, the engineers were smart and when you hold the temp set button for a coupe of seconds the controller goes into a custom setting mode. The display starts to blink and now you can set temps to within 1F. Press set once more, blinking stops, done.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

They have to operate that way. Not just because the electrolytic would be expensive and failure-prone but mainly because they would otherwise blow the power factor regulations. Or they would need an extra PFC stage which really adds cost.

Nice!

Took a long time though but maybe because you held the pan at 1cm or more distance. Be careful taxing the batteries so much, it takes away some of their useful life. It may be better to use an automotive battery.

Maybe you need that Berenburger when the results come in 8-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

torsdag den 23. maj 2019 kl. 17.29.44 UTC+2 skrev Joerg:

get an all in one wonder

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Reply to
Lasse Langwadt Christensen

Aside from the cost that would not help much because it's 2500W, only

25% more than what I have now.
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Or, maybe just an allergy to something that outgasses (in which case, the year in the attic will cure it), or (scary thought) ozone from a high voltage section.

Reply to
whit3rd

A resistor is 100% efficient. The only better thing would be a heat pump.

The cute knitted cozy slips right off. The gap-pad stuff stays stuck to the heater plate; the kettle just sits on it for good heat transfer.

BevMo sells beer.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

the 2 back burners to the front, so there are 7 KW on the 2 front plates together. It is better not to go far away when using that; a pot may behave like a volcano after a short time ;-)

While normal steel pans don't work on induction, I was delighted that Grandma's old cast iron pans (like for a goose) work nicely.

Maybe the aluminium pot even shields the lossy iron from the induction coils, so it may be better to put the iron plate below the alu pot.

Making beer seems to be a fundamental problem of man. Hammurabi's stone stele talks about it (punishment for those who don't do it right) and the nordic gods once went to war against the giants over a huge brewing kettle. Seems more acceptable and understandable than over non-existing weapons of mass destruction.

9pm, good time for a beer.

cheers, Gerhard

Reply to
Gerhard Hoffmann

Am 23.05.19 um 21:08 schrieb Gerhard Hoffmann:

Maybe a large "Tauchsieder" would do, or two of them.

Ah. WordReference calls it immersion heater.

Reply to
Gerhard Hoffmann

On a sunny day (Thu, 23 May 2019 11:36:49 -0700 (PDT)) it happened whit3rd wrote in :

It is not like that, it is immediate, some buzzing in your head, and gone when you switch it off. Almost like standing next to a leaking microwave oven .. Maybe their circuit creates harmonics into the infinite, I sure do not like their circuit, and the ceramic top plate does not shield against anything.

Reply to
Jan Panteltje

So is the electric coil cooktop but getting the heat into the wort is the trick.

The gap pad would probably help but I don't see how that's going to perform much differently than ye olde Walmart cooktop.

Yes, they sell some good stuff. It still can't hold a candle to homebrew. Once you got used to that you don't want any other. The only beer that remains acceptable to me is fresh from tap but only if brewed right there and very fresh. Plus commercial beer that is bottle-fermented but except for some Hefeweizen brands and very few Belgians commercial breweries stopped doing that for cost reasons. Bottle fermentation is one of the key upside of homebrew.

When some of us were close to receiving our engineering degrees and found out that our ivy league place didn't even have as much as a tassel hat ceremony we rented a whole bar for a night. Brew was not included so we brewed like crazy and then bought a stack of Grolsch crates because the place would be packed. So our beer wouldn't suffice. Grolsch is nice beer but everyone wanted our beer and when it was all gone they were moping.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

That's like American power levels. I believe the large front burners of our range are 3.5kW each. There are seven burners but the ones in back have less maximum power:

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That's what most people do but it nixes the induction advantages. You essentially turn it into a regular electric hotplate, minus the losses in the electronics and stuff. Makes no sense.

Don't nobody touch my brew kettle!

That's when I'll have a Belgian Quadrupel. Homebrew, of course. And maybe a Barley Wine before that.

That is what some brewers use. I can get such heaters up to 5500W but it's messy.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I forged a letter to get out of attending my college graduation. Imagine standing in a black robe for a few hours in the sunshine in New Orleans in June, listening to fatheads drone.

The Brat's graduations, at Cornell and UC Berkeley, were pretty neat, with tolerable temperatures.

Grolsch has a nice bottle but it's otherwise bland. Lately we like Guinness Blonde, Purple Haze, Widmer, and Harp. Mo likes Fat Tire but I think it tastes funny.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

That is very different at my school (RWTH Aachen University, Germany). Now that they started having the tassel hat parties they've got food stands and beer! See 0:34min here:

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This isn't the old Grolsch anymore. The company was bought up twice and IMHO that hasn't been good for the taste.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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