Induction cooktops, temperature control questions

[Joerg]

On 2019-05-27 12:25, Jan Panteltje wrote:

On a sunny day (Mon, 27 May 2019 11:05:13 -0700 (PDT)) it happened
sroberts6328@gmail.com wrote in
55e4bca7-e269-4ba4-8f70-2e1157dd9968@googlegroups.com>:

Ebay/ Amazon is your friend on this one. Large amounts of OEM Induction Cooker
driver modules for sale. Some have already been hacked, except the hacking
is documented in blog posts, not wen sites, so a little difficult to find.


If
you want to make your heated region an extension pipe off the main tank,
we've had really good luck at the university playing with the 48V 1 KW Royer
Oscillator modules from Ebay. You cant tune them much, so you have to tune
the load design. Easily heats the right diameter pipe, silicon nitride
tube, or screwdriver to glowing red. They are cheap enough to be throwaways
in the lab.


If you are really cleaver, you can design the induction heater as an inverted
/ reentrant finger "Into" the tank. Some form of forced circulation would
be a must.

I've had a 1KW induction hob for 4 years ago, paid 75$ for it, and love it for
heating dishes at parties/meetings at work, and in the local park, where
they provide 110VAC. Not allowed to have propane stoves / charcoal grilles
on the quad at the university unless you are Department Chair or above...
Induction and an extension cord got me a wink from Health and Safety.

Steve

If you ever need some voltage and have no transformer at hand,
then this works fine:
http://panteltje.com/pub/inductive_coupling_real_power_300Vpp_IMG_6092.JPG

Use your induction heater!

The normal kitchen ones need a piece of iron, have a micro switch with magnet
to detect if there is something on it I think.

Jan, since you did frying pan experiments, do you have a feel how much
power transfer is lost at more distance from the coil? IOW would it
matter on an induction cooktop if the steel is 3mm farther away from the
surface? That's about the thickness of the bottom of my aluminum pot and
I'd like to have the steel disc inside. The pot compatibility detection
can be fooled, that's not a problem.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 2019-05-27 08:56, John Larkin wrote:

On Mon, 27 May 2019 08:19:51 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-05-27 07:28, Joerg wrote:
On 2019-05-26 12:40, Joseph Gwinn wrote:
On May 26, 2019, Joerg wrote
(in article <gl06onFeclbU1@mid.individual.net&gt:

On 2019-05-26 09:14, Joseph Gwinn wrote:

[...]

How big is this monster pot? There are pots big enough to cook
missionaries.

It's got 16-1/2" or 42cm diameter. It could not be half an inch shorter
or it woudn't straddle my two cooktops.

How deep? I have some dutch ovens that large, but no stockpots.


Total volume is 13 gallons, it's pretty deep.


Just measured it, it is 15-3/8" or 39cm deep. I am brewing an Irish Red
Ale right now and currently the steeping grains are in. As usual, one of
the cheap Walmart burners is holding it at exactly 156F. It just took 1h
10mins to get there. Since it's cold right now it'll be well over
another hour to get from there to a rolling boil.

It's snowing now a bit uphill from you.

I had to brew inside and we had the wood stove going. At the end of May!
I want my fair share of global warming!

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Jan Panteltje]

On a sunny day (Tue, 28 May 2019 07:57:27 -0700) it happened Joerg
<news@analogconsultants.com> wrote in <gl50ikFfo90U1@mid.individual.net>:

Jan, since you did frying pan experiments, do you have a feel how much
power transfer is lost at more distance from the coil? IOW would it
matter on an induction cooktop if the steel is 3mm farther away from the
surface? That's about the thickness of the bottom of my aluminum pot and
I'd like to have the steel disc inside. The pot compatibility detection
can be fooled, that's not a problem.

Good question, you make me curious.
A few mm distance is OK I think, that is already the thickness of the insulation of the coils I use.
But an alu plate in between?
One moment... grabs some stuff
http://panteltje.com/pub/inductve_coupling_no_alu_shield_IMG_6940.JPG
http://panteltje.com/pub/inductive_coupling_with_alu_shield_IMG_6941.JPG
http://panteltje.com/pub/alu_shield_heats_up_IMG_6944.JPG


It is logical, any metal or conductor will have Foucault currents induced
http://panteltje.com/pub/crucible_with_molten_solder_IMG_5439.JPG
https://en.wikipedia.org/wiki/Eddy_current

Hoe that answers your question.
From the same perspective at least some heating of your alu pot should happen.
May even help to regulate the temperature better, warming up this alu plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure you know.

OK, that was todays experiment then

Bows to the public, curtain...

 

[Joerg]

On 2019-05-28 09:39, Jan Panteltje wrote:

On a sunny day (Tue, 28 May 2019 07:57:27 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl50ikFfo90U1@mid.individual.net>:

Jan, since you did frying pan experiments, do you have a feel how much
power transfer is lost at more distance from the coil? IOW would it
matter on an induction cooktop if the steel is 3mm farther away from the
surface? That's about the thickness of the bottom of my aluminum pot and
I'd like to have the steel disc inside. The pot compatibility detection
can be fooled, that's not a problem.

Good question, you make me curious.
A few mm distance is OK I think, that is already the thickness of the insulation of the coils I use.
But an alu plate in between?
One moment... grabs some stuff
http://panteltje.com/pub/inductve_coupling_no_alu_shield_IMG_6940.JPG
http://panteltje.com/pub/inductive_coupling_with_alu_shield_IMG_6941.JPG
http://panteltje.com/pub/alu_shield_heats_up_IMG_6944.JPG


It is logical, any metal or conductor will have Foucault currents induced
http://panteltje.com/pub/crucible_with_molten_solder_IMG_5439.JPG
https://en.wikipedia.org/wiki/Eddy_current

Hoe that answers your question.

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

From the same perspective at least some heating of your alu pot should happen.
May even help to regulate the temperature better, warming up this alu plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure you know.

Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

OK, that was todays experiment then

Bows to the public, curtain...

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Jan Panteltje]

On a sunny day (Tue, 28 May 2019 10:58:48 -0700) it happened Joerg
<news@analogconsultants.com> wrote in <gl5b6jFi0f5U1@mid.individual.net>:

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

Nothing much seems to be transfered past the alu plate
Do I understand it right that you want a thick metal plate inside the vessel?

From the same perspective at least some heating of your alu pot should happen.
May even help to regulate the temperature better, warming up this alu plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure you know.


Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

100 kHz here.
http://panteltje.com/pub/inductive_coupling_100kHz_500Vpp_IMG_6101.JPG

The wikipedia entry gives the formula for the eddy current induced power:
https://en.wikipedia.org/wiki/Eddy_current
I see f square for the power
also it is thickness square.

Anyways for a bit over 30$ you can get one from ebay and experiment,
car battery ?
This was on 15 V or so (2 x 7.5 V Meanwell in series, got those for 7euro50 each locally.

Why not use a thick steel plate under the vessel to heat it up?

 

[Lasse Langwadt Christense]

tirsdag den 28. maj 2019 kl. 20.30.19 UTC+2 skrev Jan Panteltje:

On a sunny day (Tue, 28 May 2019 10:58:48 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl5b6jFi0f5U1@mid.individual.net>:

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

Nothing much seems to be transfered past the alu plate
Do I understand it right that you want a thick metal plate inside the vessel?


From the same perspective at least some heating of your alu pot should happen.
May even help to regulate the temperature better, warming up this alu plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure you know.


Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

100 kHz here.
http://panteltje.com/pub/inductive_coupling_100kHz_500Vpp_IMG_6101.JPG

The wikipedia entry gives the formula for the eddy current induced power:
https://en.wikipedia.org/wiki/Eddy_current
I see f square for the power
also it is thickness square.

Anyways for a bit over 30$ you can get one from ebay and experiment,
car battery ?
This was on 15 V or so (2 x 7.5 V Meanwell in series, got those for 7euro50 each locally.

Why not use a thick steel plate under the vessel to heat it up?

then you have the same as a regular resistive heater and losses to the surroundings

 

[Joerg]

On 2019-05-28 11:30, Jan Panteltje wrote:

On a sunny day (Tue, 28 May 2019 10:58:48 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl5b6jFi0f5U1@mid.individual.net>:

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

Nothing much seems to be transfered past the alu plate

That would be bad news for my application.

Do I understand it right that you want a thick metal plate inside the vessel?

Yes, because putting it underneath would be less efficient than the
regular electric burners.

From the same perspective at least some heating of your alu pot should happen.
May even help to regulate the temperature better, warming up this alu plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure you know.


Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

100 kHz here.
http://panteltje.com/pub/inductive_coupling_100kHz_500Vpp_IMG_6101.JPG

The wikipedia entry gives the formula for the eddy current induced power:
https://en.wikipedia.org/wiki/Eddy_current
I see f square for the power
also it is thickness square.

It's a bit more complicated when you have a stack of layers. Minor air
gaps -> 3mm aluminum -> minor fluid gap -> steel disc.

Anyways for a bit over 30$ you can get one from ebay and experiment,
car battery ?
This was on 15 V or so (2 x 7.5 V Meanwell in series, got those for 7euro50 each locally.

Why not use a thick steel plate under the vessel to heat it up?

Then I might as well stay with the electric burners I have now, they
will be slightly more efficient. Only one area with minor gaps (burner
surface to pot) and no electronics that introduce losses.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Jasen Betts]

On 2019-05-28, Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

tirsdag den 28. maj 2019 kl. 20.30.19 UTC+2 skrev Jan Panteltje:
On a sunny day (Tue, 28 May 2019 10:58:48 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl5b6jFi0f5U1@mid.individual.net>:

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

Nothing much seems to be transfered past the alu plate
Do I understand it right that you want a thick metal plate inside the vessel?


From the same perspective at least some heating of your alu pot should happen.
May even help to regulate the temperature better, warming up this alu plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure you know.


Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

100 kHz here.
http://panteltje.com/pub/inductive_coupling_100kHz_500Vpp_IMG_6101.JPG

The wikipedia entry gives the formula for the eddy current induced power:
https://en.wikipedia.org/wiki/Eddy_current
I see f square for the power
also it is thickness square.

Anyways for a bit over 30$ you can get one from ebay and experiment,
car battery ?
This was on 15 V or so (2 x 7.5 V Meanwell in series, got those for 7euro50 each locally.

Why not use a thick steel plate under the vessel to heat it up?

then you have the same as a regular resistive heater and losses to the surroundings

you could solder the steel plate to the base of the vessel

--
When I tried casting out nines I made a hash of it.

 

[Joseph Gwinn]

On May 29, 2019, Jasen Betts wrote
(in article <qcllvt$m0m$2@gonzo.revmaps.no-ip.org&gt:

On 2019-05-28, Lasse Langwadt Christensen<langwadt@fonz.dk> wrote:
tirsdag den 28. maj 2019 kl. 20.30.19 UTC+2 skrev Jan Panteltje:
On a sunny day (Tue, 28 May 2019 10:58:48 -0700) it happened Joerg
news@analogconsultants.com> wrote in<gl5b6jFi0f5U1@mid.individual.net>:

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

Nothing much seems to be transfered past the alu plate
Do I understand it right that you want a thick metal plate inside the
vessel?


From the same perspective at least some heating of your alu pot should
happen.
May even help to regulate the temperature better, warming up this alu
plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure
you know.

Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

100 kHz here.
http://panteltje.com/pub/inductive_coupling_100kHz_500Vpp_IMG_6101.JPG

The wikipedia entry gives the formula for the eddy current induced power:
https://en.wikipedia.org/wiki/Eddy_current
I see f square for the power
also it is thickness square.

Anyways for a bit over 30$ you can get one from ebay and experiment,
car battery ?
This was on 15 V or so (2 x 7.5 V Meanwell in series, got those for
7euro50 each locally.

Why not use a thick steel plate under the vessel to heat it up?

then you have the same as a regular resistive heater and losses to the
surroundings

you could solder the steel plate to the base of the vessel

The temperature coefficients of Aluminum (21-24 ppm/F) and steel (11 to 12.5
ppm/F) are very different. Such a bi-metal assembly will likely warp and tear
itself apart.

Joe Gwinn

 

[Joseph Gwinn]

On May 28, 2019, Joerg wrote
(in article <gl51d5FftnrU1@mid.individual.net&gt:

On 2019-05-27 10:47, Joseph Gwinn wrote:
On May 27, 2019, Joerg wrote
(in article <gl2aggFsd7tU1@mid.individual.net&gt:

On 2019-05-26 12:40, Joseph Gwinn wrote:
On May 26, 2019, Joerg wrote
(in article <gl06onFeclbU1@mid.individual.net&gt:

On 2019-05-26 09:14, Joseph Gwinn wrote:

[...]

What I did in the old days, when electric-coil hobs had four settings
(including off), was to use such a hob set to full power, but driven fro

a
variac. Now days, one would use a solid-state variable power control
intended
for a hot tub.

A big dimmer would suffice. With electric burners it's not needed
because even the cheap ones have nice analog controls. That's still not
as good as a thermostat though because these cheap cooktops really
regulate the coil temperature and thus (indirectly) the temperature at
the bottom of the pot. On cold and windy days outside I have to set it
slightly higher and it still works.

It sounds like what you need is acommon industrial temperature controller
plus a 12-volt DC relay to turn the hob AC power on and off, replacing the
internal coil-temp thermostat. Attach thermocouple to bottom of pot away
from
the heating coils, in a bit of aluminum pressed up against the bottom of the
pot. Or have it dip into the mash fluid.

Here is a suitable unit. I buy stuff from Automation Direct, and it all has
worked.

.<https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-
_measurement/temperature_-z-
_process_controllers/solo_basic_temperature_controllers

The unit in question is a "SOLO Basic Temperature Controller", and costs
$40 (not including power relay and thermocouple).

I already have this controller:

https://www.amazon.com/dp/B00V4TJR00

Currently used whenever I brew too much and need to use our old
downstairs fridge as a fermentation chamber. You can even set the
hysteresis on these controllers. For some reason mine came with a UK
outlet so I use my homemade UK travel adapter.

For brewing a simple bi-metal thermostat suffices, you can get those to
hold to within +/-2F.

If it´s always 156 F, one can buy fixed-temperature thermostats plus an AC
power relay. Attach thermostat to center bottom of the pot and a concentric
ring heater coil also to the pot. Use thermostat to control ring heater.
Attach thermostat plate to pot using silicon rubber adhesive.

.
[snip]
How big is this monster pot? There are pots big enough to cook
missionaries.

It's got 16-1/2" or 42cm diameter. It could not be half an inch shorte

or it woudn't straddle my two cooktops.

How deep? I have some dutch ovens that large, but no stockpots.

Total volume is 13 gallons, it's pretty deep.

And 15-3/8" or 39cm deep, from the other email.

This is 108 pounds if full to the top.

I bought it for two reasons. Mainly to straddle two cooktops and then to
reduce the chance of a boil-over. Those are very messy in brewing.

It's filled with a little over 5-1/2 gallons of filtered water at the
beginning, then malt extract, dry malt extract and other stuff is added
but at least 1/2 gallon of water boils off as steam.

However, yes, the two cooktops underneath must be able to support a
combined weight of up to 50lbs. I was considering brewing a double-batch
a few times and then it would be almost 100lbs but so far haven't done
it. Mostly because the cooktops lack heating power.

Need a jib crane for loading and unloading as well.

..

.
[snip]
I never knew that pots and pans also were rated for mains voltag
ra
ges
in Europe.

Sometimes they have that built in. We've got some but now all Amer
can

after moving here from Europe.

The difference is between cooktops (with hobs) and cookware (pots an

pans,
only some of which can be heated by an induction hob).

Ok, here I meant the cooktops, of course. The pot presents another
problem as mine isn't induction-suited.

Yep. Most of my pots aren´t either, but some do very well.

That's my issue, the brew kettle is not induction-suited so if I can't
make that compatible with a steel plate in there induction isn't going
to work. Mainly because it is tough and probably very expensive to find
an induction-suited stainless pot with such a large diameter so it can
straddle two cooktops.

As has been discussed, one can sit the pot atop a piece of mild steel that
is
heated by the induction heater. But that´s way more complex than an
electric coil, a thermocouple, and an industrial temperature controller.

It also nixes all the advantages of induction, and then some. You'd
incur roughly the same amount of contact losses plus the power losses in
the electronics of the induction driver. If a steel plate must be put
under the pot instead of inside I will stay with traditional electric
cooktops.

Yep. KISS. Fixed thermostat and coil heater, discussed earlier. Maybe 220
Vac, for sufficient power for a double batch. No electronics.

Joe Gwinn

 

[Joerg]

On 2019-05-29 06:11, Joseph Gwinn wrote:

On May 28, 2019, Joerg wrote
(in article <gl51d5FftnrU1@mid.individual.net&gt:

On 2019-05-27 10:47, Joseph Gwinn wrote:
On May 27, 2019, Joerg wrote
(in article <gl2aggFsd7tU1@mid.individual.net&gt:

On 2019-05-26 12:40, Joseph Gwinn wrote:
On May 26, 2019, Joerg wrote
(in article <gl06onFeclbU1@mid.individual.net&gt:

On 2019-05-26 09:14, Joseph Gwinn wrote:

[...]

What I did in the old days, when electric-coil hobs had four settings
(including off), was to use such a hob set to full power, but driven fro

a
variac. Now days, one would use a solid-state variable power control
intended
for a hot tub.

A big dimmer would suffice. With electric burners it's not needed
because even the cheap ones have nice analog controls. That's still not
as good as a thermostat though because these cheap cooktops really
regulate the coil temperature and thus (indirectly) the temperature at
the bottom of the pot. On cold and windy days outside I have to set it
slightly higher and it still works.

It sounds like what you need is acommon industrial temperature controller
plus a 12-volt DC relay to turn the hob AC power on and off, replacing the
internal coil-temp thermostat. Attach thermocouple to bottom of pot away
from
the heating coils, in a bit of aluminum pressed up against the bottom of the
pot. Or have it dip into the mash fluid.

Here is a suitable unit. I buy stuff from Automation Direct, and it all has
worked.

.<https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-
_measurement/temperature_-z-
_process_controllers/solo_basic_temperature_controllers

The unit in question is a "SOLO Basic Temperature Controller", and costs
$40 (not including power relay and thermocouple).

I already have this controller:

https://www.amazon.com/dp/B00V4TJR00

Currently used whenever I brew too much and need to use our old
downstairs fridge as a fermentation chamber. You can even set the
hysteresis on these controllers. For some reason mine came with a UK
outlet so I use my homemade UK travel adapter.

For brewing a simple bi-metal thermostat suffices, you can get those to
hold to within +/-2F.

If it´s always 156 F, one can buy fixed-temperature thermostats plus an AC
power relay. Attach thermostat to center bottom of the pot and a concentric
ring heater coil also to the pot. Use thermostat to control ring heater.

That's exactly what I have now and the cheap electric burners even have
an adjustable thermostat. Which is needed because later I must avoid
boil-over and that requires a setting in the 210F region, adjustable
depending on wind and outside temperature.

Attach thermostat plate to pot using silicon rubber adhesive.

If I had a material that would improve the coupling between electric
coil and the never 100% even pot bottom that would help a lot. Not for
the thermostats in the cooktops because they are already sufficiently
accurate but for heat transfer.

.
[snip]
How big is this monster pot? There are pots big enough to cook
missionaries.

It's got 16-1/2" or 42cm diameter. It could not be half an inch shorte

or it woudn't straddle my two cooktops.

How deep? I have some dutch ovens that large, but no stockpots.

Total volume is 13 gallons, it's pretty deep.

And 15-3/8" or 39cm deep, from the other email.

This is 108 pounds if full to the top.

I bought it for two reasons. Mainly to straddle two cooktops and then to
reduce the chance of a boil-over. Those are very messy in brewing.

It's filled with a little over 5-1/2 gallons of filtered water at the
beginning, then malt extract, dry malt extract and other stuff is added
but at least 1/2 gallon of water boils off as steam.

However, yes, the two cooktops underneath must be able to support a
combined weight of up to 50lbs. I was considering brewing a double-batch
a few times and then it would be almost 100lbs but so far haven't done
it. Mostly because the cooktops lack heating power.

Need a jib crane for loading and unloading as well.

Nah, due to lower back issues I always siphon it into the fermenter. It
sits on a foldable dolly for the trip to the temperature-controlled chamber.

.
.
[snip]
I never knew that pots and pans also were rated for mains voltag
ra
ges
in Europe.

Sometimes they have that built in. We've got some but now all Amer
can

after moving here from Europe.

The difference is between cooktops (with hobs) and cookware (pots an

pans,
only some of which can be heated by an induction hob).

Ok, here I meant the cooktops, of course. The pot presents another
problem as mine isn't induction-suited.

Yep. Most of my pots aren´t either, but some do very well.

That's my issue, the brew kettle is not induction-suited so if I can't
make that compatible with a steel plate in there induction isn't going
to work. Mainly because it is tough and probably very expensive to find
an induction-suited stainless pot with such a large diameter so it can
straddle two cooktops.

As has been discussed, one can sit the pot atop a piece of mild steel that
is
heated by the induction heater. But that´s way more complex than an
electric coil, a thermocouple, and an industrial temperature controller.

It also nixes all the advantages of induction, and then some. You'd
incur roughly the same amount of contact losses plus the power losses in
the electronics of the induction driver. If a steel plate must be put
under the pot instead of inside I will stay with traditional electric
cooktops.

Yep. KISS. Fixed thermostat and coil heater, discussed earlier. Maybe 220
Vac, for sufficient power for a double batch. No electronics.

Oh, if I could get a large diameter 240W heater at high power and
reasonable cost I'd be happy. It would need to be 3500W or more to yield
an advantage versus my current setup.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 2019-05-29 09:07, Jan Panteltje wrote:

On a sunny day (Wed, 29 May 2019 08:30:33 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl7msiF3204U1@mid.individual.net>:

That's exactly what I have now and the cheap electric burners even have
an adjustable thermostat. Which is needed because later I must avoid
boil-over and that requires a setting in the 210F region, adjustable
depending on wind and outside temperature.

I was wondering, I have a big steel induction cooking pan (thick bottom),
just fill it with water and put the vessel in it?
Can never overheat (100C it boils), automatic temperature control!

It would work but probably not efficiently because the water in the pan
underneath would constantly boil off. I'd have to keep filling with
pre-heated water.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Jan Panteltje]

On a sunny day (Wed, 29 May 2019 08:30:33 -0700) it happened Joerg
<news@analogconsultants.com> wrote in <gl7msiF3204U1@mid.individual.net>:

That's exactly what I have now and the cheap electric burners even have
an adjustable thermostat. Which is needed because later I must avoid
boil-over and that requires a setting in the 210F region, adjustable
depending on wind and outside temperature.

I was wondering, I have a big steel induction cooking pan (thick bottom),
just fill it with water and put the vessel in it?
Can never overheat (100C it boils), automatic temperature control!

 

[Jan Panteltje]

On a sunny day (Wed, 29 May 2019 09:27:03 -0700) it happened Joerg
<news@analogconsultants.com> wrote in <gl7q6hF3nt4U1@mid.individual.net>:

On 2019-05-29 09:07, Jan Panteltje wrote:
On a sunny day (Wed, 29 May 2019 08:30:33 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl7msiF3204U1@mid.individual.net>:

That's exactly what I have now and the cheap electric burners even have
an adjustable thermostat. Which is needed because later I must avoid
boil-over and that requires a setting in the 210F region, adjustable
depending on wind and outside temperature.

I was wondering, I have a big steel induction cooking pan (thick bottom),
just fill it with water and put the vessel in it?
Can never overheat (100C it boils), automatic temperature control!


It would work but probably not efficiently because the water in the pan
underneath would constantly boil off. I'd have to keep filling with
pre-heated water.

Condensor (old car radiator), fan, water back to pan.

 

[Clifford Heath]

On 30/5/19 1:30 am, Joerg wrote:

On 2019-05-29 06:11, Joseph Gwinn wrote:
Yep. KISS. Fixed thermostat and coil heater, discussed earlier. Maybe 220
Vac, for sufficient power for a double batch. No electronics.
Oh, if I could get a large diameter 240W heater at high power and
reasonable cost I'd be happy. It would need to be 3500W or more to yield
an advantage versus my current setup.

What about a replacement heating coil for a 240V electric range?
There'd have to be some available at 3500W, I think?

Clifford Heath.

 

[Joseph Gwinn]

On May 29, 2019, Joerg wrote
(in article <gl7msiF3204U1@mid.individual.net&gt:

On 2019-05-29 06:11, Joseph Gwinn wrote:
On May 28, 2019, Joerg wrote
(in article <gl51d5FftnrU1@mid.individual.net&gt:

On 2019-05-27 10:47, Joseph Gwinn wrote:
On May 27, 2019, Joerg wrote
(in article <gl2aggFsd7tU1@mid.individual.net&gt:

On 2019-05-26 12:40, Joseph Gwinn wrote:
On May 26, 2019, Joerg wrote
(in article <gl06onFeclbU1@mid.individual.net&gt:

On 2019-05-26 09:14, Joseph Gwinn wrote:

[...]

What I did in the old days, when electric-coil hobs had four setting

(including off), was to use such a hob set to full power, but driven
fro

a
variac. Now days, one would use a solid-state variable power control
intended
for a hot tub.

A big dimmer would suffice. With electric burners it's not needed
because even the cheap ones have nice analog controls. That's still no

as good as a thermostat though because these cheap cooktops really
regulate the coil temperature and thus (indirectly) the temperature at
the bottom of the pot. On cold and windy days outside I have to set it
slightly higher and it still works.

It sounds like what you need is acommon industrial temperature controlle

plus a 12-volt DC relay to turn the hob AC power on and off, replacing t
e
internal coil-temp thermostat. Attach thermocouple to bottom of pot away
from
the heating coils, in a bit of aluminum pressed up against the bottom of
the
pot. Or have it dip into the mash fluid.

Here is a suitable unit. I buy stuff from Automation Direct, and it all
has
worked.

.<https://www.automationdirect.com/adc/shopping/catalog/process_control_
a
-
_measurement/temperature_-z-
_process_controllers/solo_basic_temperature_controllers

The unit in question is a "SOLO Basic Temperature Controller", and costs
$40 (not including power relay and thermocouple).

I already have this controller:

https://www.amazon.com/dp/B00V4TJR00

Currently used whenever I brew too much and need to use our old
downstairs fridge as a fermentation chamber. You can even set the
hysteresis on these controllers. For some reason mine came with a UK
outlet so I use my homemade UK travel adapter.

For brewing a simple bi-metal thermostat suffices, you can get those to
hold to within +/-2F.

If it´s always 156 F, one can buy fixed-temperature thermostats plus an AC
power relay. Attach thermostat to center bottom of the pot and a concentric
ring heater coil also to the pot. Use thermostat to control ring heater.

That's exactly what I have now and the cheap electric burners even have
an adjustable thermostat. Which is needed because later I must avoid
boil-over and that requires a setting in the 210F region, adjustable
depending on wind and outside temperature.

Attach thermostat plate to pot using silicon rubber adhesive.

If I had a material that would improve the coupling between electric
coil and the never 100% even pot bottom that would help a lot. Not for
the thermostats in the cooktops because they are already sufficiently
accurate but for heat transfer.

A sheet of silicon rubber is traditional. Such things are sold in kitchen
stores for various purposes.

Attaching the thermostat with silicon rubber adhesive serves to thermally
connect it to the pot.

This will prevent wind disturbances.

.
[snip]
How big is this monster pot? There are pots big enough to cook
missionaries.

It's got 16-1/2" or 42cm diameter. It could not be half an inch sh
rter
or it woudn't straddle my two cooktops.

How deep? I have some dutch ovens that large, but no stockpots.

Total volume is 13 gallons, it's pretty deep.

And 15-3/8" or 39cm deep, from the other email.

This is 108 pounds if full to the top.

I bought it for two reasons. Mainly to straddle two cooktops and then to
reduce the chance of a boil-over. Those are very messy in brewing.

It's filled with a little over 5-1/2 gallons of filtered water at the
beginning, then malt extract, dry malt extract and other stuff is added
but at least 1/2 gallon of water boils off as steam.

However, yes, the two cooktops underneath must be able to support a
combined weight of up to 50lbs. I was considering brewing a double-batch
a few times and then it would be almost 100lbs but so far haven't done
it. Mostly because the cooktops lack heating power.

Need a jib crane for loading and unloading as well.

Nah, due to lower back issues I always siphon it into the fermenter. It
sits on a foldable dolly for the trip to the temperature-controlled chamber.

..<https://www.northerntool.com/shop/tools/product_200651805_200651805>

May exceed the budget, but the back is safe.

Ok, here I meant the cooktops, of course. The pot presents another
problem as mine isn't induction-suited.

Yep. Most of my pots aren´t either, but some do very well.

That's my issue, the brew kettle is not induction-suited so if I can't
make that compatible with a steel plate in there induction isn't going
to work. Mainly because it is tough and probably very expensive to fin

an induction-suited stainless pot with such a large diameter so it can
straddle two cooktops.

As has been discussed, one can sit the pot atop a piece of mild steel th
t
is heated by the induction heater. But that´s way more complex than an
electric coil, a thermocouple, and an industrial temperature controller.

It also nixes all the advantages of induction, and then some. You'd
incur roughly the same amount of contact losses plus the power losses in
the electronics of the induction driver. If a steel plate must be put
under the pot instead of inside I will stay with traditional electric
cooktops.

Yep. KISS. Fixed thermostat and coil heater, discussed earlier. Maybe 220
Vac, for sufficient power for a double batch. No electronics.

Oh, if I could get a large diameter 240 Vac heater at high power and
reasonable cost I'd be happy. It would need to be 3500W or more to yield
an advantage versus my current setup.

I bet you do not require anything like 3500 watts with good thermal contact
between pot and heater.

By heater coil, I meant a coil intended for an electric stove; these are
readily available as spares in Home Depot et al for a few tens of dollars.
But use multiple coils connected in series, so they don´t get red hot and
burn the silicon rubber.
The other thing that´s needed is a safety thermostat, that will trip and
cut the power if things get too hot. Or, design it to be self limiting,
stabilizing at a safe temperature even if the thermostat is stuck in the
heat-on position.

Do not depend on your personal vigilance for such things. Unless you use a
one-legged
stool:<http://lateralscience.blogspot.com/2014/10/scottish-nitroglycerin-one-
legged-stools.html>

Joe Gwinn

 

[Jan Panteltje]

On a sunny day (Wed, 29 May 2019 21:53:33 -0400) it happened Joseph Gwinn
<joegwinn@comcast.net> wrote in
<0001HW.229F6F1D01B238E17000006822EF@news.giganews.com>:

Do not depend on your personal vigilance for such things. Unless you use a one-legged stool:
http://lateralscience.blogspot.com/2014/10/scottish-nitroglycerin-one-legged-stools.html

Genius!!
Every Tesla needs one to prevent the driver falling asleep when auto-pilot activated !!!

 

[Jasen Betts]

On 2019-05-29, Joseph Gwinn <joegwinn@comcast.net> wrote:

On May 29, 2019, Jasen Betts wrote
(in article <qcllvt$m0m$2@gonzo.revmaps.no-ip.org&gt:

On 2019-05-28, Lasse Langwadt Christensen<langwadt@fonz.dk> wrote:
tirsdag den 28. maj 2019 kl. 20.30.19 UTC+2 skrev Jan Panteltje:
On a sunny day (Tue, 28 May 2019 10:58:48 -0700) it happened Joerg
news@analogconsultants.com> wrote in<gl5b6jFi0f5U1@mid.individual.net>:

Thanks, but not really. It is good to know that the aluminum heats up as
well. What I am more concerned about is whether, for example, instead of
1500W only 800W gets transferred because the coupling between coil and
lossy material becomes too loose. IOW the other 700W not being lost but
just not transferred and thus not taken out of the power outlet. All
minus the usual circuit losses, of course.

Nothing much seems to be transfered past the alu plate
Do I understand it right that you want a thick metal plate inside the
vessel?


From the same perspective at least some heating of your alu pot should
happen.
May even help to regulate the temperature better, warming up this alu
plate to 52 C took almost a minute!

But the same principle is used to screen IF coils in radios as I am sure
you know.

Aluminum works quite well as a shield with real RF. Induction cookers
work in the 20-30kHz range AFAIK.

100 kHz here.
http://panteltje.com/pub/inductive_coupling_100kHz_500Vpp_IMG_6101.JPG

The wikipedia entry gives the formula for the eddy current induced power:
https://en.wikipedia.org/wiki/Eddy_current
I see f square for the power
also it is thickness square.

Anyways for a bit over 30$ you can get one from ebay and experiment,
car battery ?
This was on 15 V or so (2 x 7.5 V Meanwell in series, got those for
7euro50 each locally.

Why not use a thick steel plate under the vessel to heat it up?

then you have the same as a regular resistive heater and losses to the
surroundings

you could solder the steel plate to the base of the vessel

The temperature coefficients of Aluminum (21-24 ppm/F) and steel (11 to 12.5
ppm/F) are very different. Such a bi-metal assembly will likely warp and tear
itself apart.

I've got some stainless steel pots with aluminium heat spreaders, the
only failure mode I've seen is all the aluminium melting if it gets too hot.

For induction cooking you can't use a copper heat spreader because it
would reflect half of the energy. so these stainless steel pots have an
aluminium spreader and have a stainless skin on the bottom of that.

skin depth in 410 stainless is less than 0.1mm at 20KHz
skin depth in iron is even less.

--
When I tried casting out nines I made a hash of it.

 

[Joerg]

On 2019-05-29 10:29, Jan Panteltje wrote:

On a sunny day (Wed, 29 May 2019 09:27:03 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl7q6hF3nt4U1@mid.individual.net>:

On 2019-05-29 09:07, Jan Panteltje wrote:
On a sunny day (Wed, 29 May 2019 08:30:33 -0700) it happened Joerg
news@analogconsultants.com> wrote in <gl7msiF3204U1@mid.individual.net>:

That's exactly what I have now and the cheap electric burners even have
an adjustable thermostat. Which is needed because later I must avoid
boil-over and that requires a setting in the 210F region, adjustable
depending on wind and outside temperature.

I was wondering, I have a big steel induction cooking pan (thick bottom),
just fill it with water and put the vessel in it?
Can never overheat (100C it boils), automatic temperature control!


It would work but probably not efficiently because the water in the pan
underneath would constantly boil off. I'd have to keep filling with
pre-heated water.

Condensor (old car radiator), fan, water back to pan.

Pretty soon my brew place looks like the shop of Gary Gearloose

I wouldn't mind but I have to schlepp everything back and forth when
brewing.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 2019-05-29 18:09, Clifford Heath wrote:

On 30/5/19 1:30 am, Joerg wrote:
On 2019-05-29 06:11, Joseph Gwinn wrote:
Yep. KISS. Fixed thermostat and coil heater, discussed earlier. Maybe
220
Vac, for sufficient power for a double batch. No electronics.
Oh, if I could get a large diameter 240W heater at high power and
reasonable cost I'd be happy. It would need to be 3500W or more to
yield an advantage versus my current setup.

What about a replacement heating coil for a 240V electric range?
There'd have to be some available at 3500W, I think?

I thought about it but that turns the whole thing into a science
project. They have no holders, no low-temp contacting, no reflector, no
drip pan, nothing. The only way would be to find a discarded range or
oven with built-in range and hacksaw a part of the range out of it, then
make an enclosure.

--
Regards, Joerg

http://www.analogconsultants.com/