Induction cooktops, temperature control questions

[Tom Gardner]

On 23/05/19 19:45, John Larkin wrote:

On Thu, 23 May 2019 09:19:35 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-05-23 09:04, John Larkin wrote:
On Thu, 23 May 2019 08:29:49 -0700, Joerg <news@analogconsultants.com
wrote:

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.

Inductive heating must be less efficient than resistive. Resistive is
best if you can make a good thermal connection to your kettle.


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.

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

A resistor in the liquid or pan's metal is 100% efficient. A
poorly thermally coupled resistor is not.

One point about induction hobs is that the "resistor" is
inside the pan's metal. Certainly the pans do heat up fast,
the heat source to the pan can be turned off rapidly (cf
conventional electric hobs), and the hob surface stays warm,
not hot.

 

[John Larkin]

On Thu, 23 May 2019 23:50:30 +0100, Tom Gardner
<spamjunk@blueyonder.co.uk> wrote:

On 23/05/19 19:45, John Larkin wrote:
On Thu, 23 May 2019 09:19:35 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-05-23 09:04, John Larkin wrote:
On Thu, 23 May 2019 08:29:49 -0700, Joerg <news@analogconsultants.com
wrote:

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.

Inductive heating must be less efficient than resistive. Resistive is
best if you can make a good thermal connection to your kettle.


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.

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

A resistor in the liquid or pan's metal is 100% efficient. A
poorly thermally coupled resistor is not.

One point about induction hobs is that the "resistor" is
inside the pan's metal. Certainly the pans do heat up fast,
the heat source to the pan can be turned off rapidly (cf
conventional electric hobs), and the hob surface stays warm,
not hot.

Somewhere there's a frequency converter that's not 100% efficient, and
the induction coils will get hot too.

I didn't suggest poor thermal coupling. Quite the opposite.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Tom Gardner]

On 24/05/19 00:33, John Larkin wrote:

On Thu, 23 May 2019 23:50:30 +0100, Tom Gardner
spamjunk@blueyonder.co.uk> wrote:

On 23/05/19 19:45, John Larkin wrote:
On Thu, 23 May 2019 09:19:35 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-05-23 09:04, John Larkin wrote:
On Thu, 23 May 2019 08:29:49 -0700, Joerg <news@analogconsultants.com
wrote:

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.

Inductive heating must be less efficient than resistive. Resistive is
best if you can make a good thermal connection to your kettle.


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.

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

A resistor in the liquid or pan's metal is 100% efficient. A
poorly thermally coupled resistor is not.

One point about induction hobs is that the "resistor" is
inside the pan's metal. Certainly the pans do heat up fast,
the heat source to the pan can be turned off rapidly (cf
conventional electric hobs), and the hob surface stays warm,
not hot.

Somewhere there's a frequency converter that's not 100% efficient, and
the induction coils will get hot too.

I didn't suggest poor thermal coupling. Quite the opposite.

Having had experience with natural gas, induction,
spiral electric and solid electric hobs, the thermal
contact of the latter two with the bottom of a pan
is /never/ good.

Kettle, yes they can be efficient since the element
is (or can be) in the liquid.

 

[Winfield Hill]

Joerg wrote...

John Larkin wrote:

Inductive heating must be less efficient than resistive. Resistive
is best if you can make a good thermal connection to your kettle.

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.

Yes, resistive heating sends lots of heat to other places.


--
Thanks,
- Win

 

[bitrex]

On 5/23/19 1:43 PM, Joerg wrote:

On 2019-05-23 10:37, bitrex wrote:
On 5/23/19 11:29 AM, Joerg wrote:
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 thought sous vide had to be even tighter than 10F


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.

Sort of like the Ikea engineers who built a wooden "nightstand" that's
exactly 6 rack units high and 19" wide

 

[George Herold]

On Thursday, May 23, 2019 at 2:45:49 PM UTC-4, John Larkin wrote:

On Thu, 23 May 2019 09:19:35 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-05-23 09:04, John Larkin wrote:
On Thu, 23 May 2019 08:29:49 -0700, Joerg <news@analogconsultants.com
wrote:

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.

Inductive heating must be less efficient than resistive. Resistive is
best if you can make a good thermal connection to your kettle.


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.

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

Yeah well you gotta transfer heat from R to thing (beer/ mash in this
case.) I could see that my cast iron skillet on induction heater
could be better than skillet on resistive heating element.
My pan becomes the resistor. (I mostly want to run my stove on
low.)

George H.

George H.

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.


That would make kettle cleaning a bear.

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.




Or dunk a big resistor into the mash.


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.

BevMo sells beer.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Mikko OH2HVJ]

Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> writes:

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.

The reason is probably coil whine. We've got a pretty good one (we cook
a lot) and it tunes the coil/frequency depending on the
kettle. Sometimes you can hear the whine, but moving the pan/kettle a
little bit gets rid of that.

Loud whine close to your hearing range or even above that may manifest
itself as headache or strange feeling. I'd bet it's not the EM field.

--
mikko

 

[Mikko OH2HVJ]

Joerg <news@analogconsultants.com> writes:

Thinking about induction cooktops for beer brewing because the two 1kW
...
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.

How is the temperature measured on those ? It might be the difficulty of
doing accurate temperature sensing with the ceramic plate in
between. IIRC some InGaAs photodiodes list this as one application in
their datasheets, but I would not expect to see those in cheaper units!

--
mikko

 

[Phil Hobbs]

On 5/23/19 9:04 PM, bitrex wrote:

On 5/23/19 1:43 PM, Joerg wrote:
On 2019-05-23 10:37, bitrex wrote:
On 5/23/19 11:29 AM, Joerg wrote:
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 thought sous vide had to be even tighter than 10F


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.


Sort of like the Ikea engineers who built a wooden "nightstand" that's
exactly 6 rack units high and 19" wide

Do they still make it?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Martin Brown]

On 23/05/2019 17:47, Jan Panteltje wrote:

On a sunny day (Thu, 23 May 2019 08:29:49 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gknsj3Fkf5cU1@mid.individual.net>:

Thinking about induction cooktops for beer brewing

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.

If that were true you would have one hell of a time in an MRI scanner or
near any of our faster mass spectrometers. The laminated core squeals
when the magnetic field is being swept quickly and you need earplugs!

It is fairly alarming listening to one squeal and ping from outside the
room and loud enough inside to damage unprotected hearing.

I used to wipe my bank cards magnetic stripe fairy regularly when I
worked with high power magnetic fields. Great effort was made to obtain
maximum uniformity in the beam path but at the expense of more than a
little stray field. Modern kit is much better magnetically shielded.

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.

--
Regards,
Martin Brown

 

[Chris Jones]

On 24/05/2019 18:12, Phil Hobbs wrote:

On 5/23/19 9:04 PM, bitrex wrote:
On 5/23/19 1:43 PM, Joerg wrote:
On 2019-05-23 10:37, bitrex wrote:
On 5/23/19 11:29 AM, Joerg wrote:
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 thought sous vide had to be even tighter than 10F


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.


Sort of like the Ikea engineers who built a wooden "nightstand" that's
exactly 6 rack units high and 19" wide

Do they still make it?

I think maybe that the thing you see when you google "lackrack".

 

[Chris Jones]

On 24/05/2019 05:45, Jan Panteltje wrote:

On a sunny day (Thu, 23 May 2019 11:36:49 -0700 (PDT)) it happened whit3rd
whit3rd@gmail.com> wrote in
8bc39ba8-71d4-4b15-aa0f-9189228f8552@googlegroups.com>:

On Thursday, May 23, 2019 at 9:48:01 AM UTC-7, Jan Panteltje wrote:
On a sunny day (Thu, 23 May 2019 08:29:49 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gknsj3Fkf5cU1@mid.individual.net>:

Thinking about induction cooktops for beer brewing

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 ...

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.

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.

Maybe it is ultrasound? I don't like staying close to ultrasonic
cleaners when they are running.

 

[bitrex]

On 5/24/19 4:12 AM, Phil Hobbs wrote:

On 5/23/19 9:04 PM, bitrex wrote:
On 5/23/19 1:43 PM, Joerg wrote:
On 2019-05-23 10:37, bitrex wrote:
On 5/23/19 11:29 AM, Joerg wrote:
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 thought sous vide had to be even tighter than 10F


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.


Sort of like the Ikea engineers who built a wooden "nightstand" that's
exactly 6 rack units high and 19" wide

Do they still make it?

Cheers

Phil Hobbs

Looks like they may have discontinued the particular model I've used
before, unfortunately, this one:

<https://www.amazon.com/dp/B01GUHPVK0/ref=dp_cerb_2>

Two Middle Atlantic 6U rack rails and 5 min with a cordless drill and
some self-tapping wood screws and it was BYDU!

 

[Joerg]

On 2019-05-23 17:27, Winfield Hill wrote:

Joerg wrote...

John Larkin wrote:

Inductive heating must be less efficient than resistive. Resistive
is best if you can make a good thermal connection to your kettle.

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.

Yes, resistive heating sends lots of heat to other places.

It does, although when I cup my hands around the bottom of the pot it's
not all that much. The main thing is that one can buy 1800W induction
cooktops but the small coil burners are never much more than 1000W. I
also can't goose those with a step-up transformer because at full bore
there aleady is a noticable red glow.

The other thing is the thermal coupling. It takes some finagling with
folded paper snippets used as shims to get the coil of both burners to
snug the bottom of the pot. I marked them so I know where they go for
the "initial coarse alignment".

--
Regards, Joerg

http://www.analogconsultants.com/

 

[John Larkin]

On Fri, 24 May 2019 07:59:15 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2019-05-23 22:24, Mikko OH2HVJ wrote:
Joerg <news@analogconsultants.com> writes:

Thinking about induction cooktops for beer brewing because the two 1kW
..
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.

How is the temperature measured on those ? It might be the difficulty of
doing accurate temperature sensing with the ceramic plate in
between. IIRC some InGaAs photodiodes list this as one application in
their datasheets, but I would not expect to see those in cheaper units!


From what I saw so far in tear-downs there is a thermistor wadded into
something, right under the ceramic plate in the middle of the coil.
Probably a PTC or NTC resistor.

It may not be too accurate but brewers soon get a good feel for
correction factors. The bi-metal thermostats on my cheap coil burners
should theoretically be much less accurate because they only sense the
temperature at the end of the heating coil, not the surface. Yet I was
able to mark them so I can set them to 156F (for grain steeping) and
later shortly under max but outside the numbered range for "boil-over
avoidance". Holds it to within +/-2F. Inside the house it is always
accurate, outside during summer I have to apply a minor correction
factor if it is under 70F, windy or foggy. After a few dozen brews
outside one knows. So while the grains of the first batch of the day are
steeping I can take a shower and brush my teeth, knowing that the
temperature is going to be fine. It always was.

Bricks, then an aluminum plate with big MIL resistors bolted to the
bottom. Gap-pad stuff stuck to the top, with the pot sitting on that.
Dunk a thermocouple into the brew. Design a controller or buy a cheap
Omega equivalent.

Send me a case in gratitude.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Joerg]

On 2019-05-23 17:22, Tom Gardner wrote:

On 24/05/19 00:33, John Larkin wrote:
On Thu, 23 May 2019 23:50:30 +0100, Tom Gardner
spamjunk@blueyonder.co.uk> wrote:

On 23/05/19 19:45, John Larkin wrote:
On Thu, 23 May 2019 09:19:35 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-05-23 09:04, John Larkin wrote:
On Thu, 23 May 2019 08:29:49 -0700, Joerg
news@analogconsultants.com
wrote:

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.

Inductive heating must be less efficient than resistive. Resistive is
best if you can make a good thermal connection to your kettle.


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.

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

A resistor in the liquid or pan's metal is 100% efficient. A
poorly thermally coupled resistor is not.

One point about induction hobs is that the "resistor" is
inside the pan's metal. Certainly the pans do heat up fast,
the heat source to the pan can be turned off rapidly (cf
conventional electric hobs), and the hob surface stays warm,
not hot.

Somewhere there's a frequency converter that's not 100% efficient, and
the induction coils will get hot too.

I didn't suggest poor thermal coupling. Quite the opposite.

Having had experience with natural gas, induction,
spiral electric and solid electric hobs, the thermal
contact of the latter two with the bottom of a pan
is /never/ good.

Kettle, yes they can be efficient since the element
is (or can be) in the liquid.

My favorite heating method is what I do for cooking, a big old fire from
a small pile of manzanita or almond wood. I only cook two out of seven
days per week but always outside. Rain, shine, hail, sleet, wind,
howling storms, doesn't matter. There have been times where I had to tie
the barbecue to a pillar near the main entrance and secure the lid with
strong wire, so things don't get blown down the driveway.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[John Larkin]

On Fri, 24 May 2019 10:10:17 +0100, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

On 23/05/2019 17:47, Jan Panteltje wrote:
On a sunny day (Thu, 23 May 2019 08:29:49 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gknsj3Fkf5cU1@mid.individual.net>:

Thinking about induction cooktops for beer brewing

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.

If that were true you would have one hell of a time in an MRI scanner or
near any of our faster mass spectrometers.

Do you do FTMS? I have stories. And a nice controller design that
probably will never be sold.

https://www.dropbox.com/s/1pvax542n1erhfz/IMG_0304.JPG?dl=0

https://www.dropbox.com/s/0e71x4r2a72y86m/FTMS_Cell_top.jpg?dl=0


The laminated core squeals

when the magnetic field is being swept quickly and you need earplugs!

It is fairly alarming listening to one squeal and ping from outside the
room and loud enough inside to damage unprotected hearing.

I used to wipe my bank cards magnetic stripe fairy regularly when I
worked with high power magnetic fields. Great effort was made to obtain
maximum uniformity in the beam path but at the expense of more than a
little stray field. Modern kit is much better magnetically shielded.

There was a conference room at Varian that had a daisy chain of paper
clips touching one wall and extending in mid-air out into the room.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Joerg]

On 2019-05-23 22:24, Mikko OH2HVJ wrote:

Joerg <news@analogconsultants.com> writes:

Thinking about induction cooktops for beer brewing because the two 1kW
..
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.

How is the temperature measured on those ? It might be the difficulty of
doing accurate temperature sensing with the ceramic plate in
between. IIRC some InGaAs photodiodes list this as one application in
their datasheets, but I would not expect to see those in cheaper units!

From what I saw so far in tear-downs there is a thermistor wadded into
something, right under the ceramic plate in the middle of the coil.
Probably a PTC or NTC resistor.

It may not be too accurate but brewers soon get a good feel for
correction factors. The bi-metal thermostats on my cheap coil burners
should theoretically be much less accurate because they only sense the
temperature at the end of the heating coil, not the surface. Yet I was
able to mark them so I can set them to 156F (for grain steeping) and
later shortly under max but outside the numbered range for "boil-over
avoidance". Holds it to within +/-2F. Inside the house it is always
accurate, outside during summer I have to apply a minor correction
factor if it is under 70F, windy or foggy. After a few dozen brews
outside one knows. So while the grains of the first batch of the day are
steeping I can take a shower and brush my teeth, knowing that the
temperature is going to be fine. It always was.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Lasse Langwadt Christense]

fredag den 24. maj 2019 kl. 16.43.51 UTC+2 skrev Joerg:

On 2019-05-23 17:27, Winfield Hill wrote:
Joerg wrote...

John Larkin wrote:

Inductive heating must be less efficient than resistive. Resistive
is best if you can make a good thermal connection to your kettle.

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.

Yes, resistive heating sends lots of heat to other places.


It does, although when I cup my hands around the bottom of the pot it's
not all that much. The main thing is that one can buy 1800W induction
cooktops but the small coil burners are never much more than 1000W. I
also can't goose those with a step-up transformer because at full bore
there aleady is a noticable red glow.

The other thing is the thermal coupling. It takes some finagling with
folded paper snippets used as shims to get the coil of both burners to
snug the bottom of the pot. I marked them so I know where they go for
the "initial coarse alignment".

add some help, https://www.ebay.com/itm/162315122285

 

[Tom Gardner]

On 24/05/19 15:54, John Larkin wrote:

There was a conference room at Varian that had a daisy chain of paper
clips touching one wall and extending in mid-air out into the room.

Was there an adjacent collection of skeletons with
stainless steel inserts?