Selecting the right resistor

[Jesse]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

So far so good.

The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.
Resistors are available in a huge array of OHM values and
watts and what is utterly bewildering to someone like me is
probably mindlessly simple to many of the experts who frequent
this group.

Any suggestions?

Jesse

 

[Rich Webb]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

So far so good.

The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.
Resistors are available in a huge array of OHM values and
watts and what is utterly bewildering to someone like me is
probably mindlessly simple to many of the experts who frequent
this group.

Where is the sense point for the digital controller? Perhaps moving it
to somewhere closer to the header might reduce the overshoot. AIUI, some
home thermostats have a small local heat source (e.g., a hot resistor)
near to their temperature sensor so that the sensor gets hot faster than
the room air, so it turns off the heat just a little sooner and lets the
residual heat "coast" to the final room temperature value.

Ultimately, you'll probably need a more sophisticated control setup,
with, say, a triac controlling the heater so that you're not running a
bang-bang control (full on - full off) but one that can taper off as it
gets closer to the set-point, or turn on just a little if just a little
heat is needed.

 

[Ecnerwal]

I have a DIY cooking project with which I'd appreciate some
help. ....
The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

Zeroth question - other than you fussing about it, is this really all
that big of a deal? Few cooking or culturing processes care all that
much about a lousy degree, F or C.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.

Get another heater just like the first one. Run the two in series.
That's exactly the size and power handling you'll need for a resistor,
and it's already packaged/built. Each heater will only deliver 75 watts
at half voltage, but the two together will deliver 150. If you find that
150 is still too much (and it probably is if you're at 10% duty cycle
with 300W), move one heater into a separate tank of water. Or just get a
smaller heater to begin with - seems like 50W would be about right (you
have 10% - one minute out of 10 - with 300W - so 30W would do, and 50 W
gives you a bit of reserve for variations, along with a heater that will
be on more than half the time, rather than 10% of the time.)

If you really think you need super precision, a microcontroller and PWM
control are the way to go. But it could be that you really don't need so
much precision. I don't know what you're trying to culture at that
temperature, but things like yogurt cultures really couldn't care less
about a few degrees variation (and happily work down at 105-110F.)

 

[BluntChisel]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

So far so good.

The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.
Resistors are available in a huge array of OHM values and
watts and what is utterly bewildering to someone like me is
probably mindlessly simple to many of the experts who frequent
this group.

Any suggestions?

Jesse

I'm not an electronics expert, but I'm interested in what other more
knowledgable people in the group think of the following suggestion:

- If you want to reduce the power by half, would a series diode be a more
efficient way of doing it? A series resistor would have to dissipate
150watts, which is more than most can handle.

 

[Jamie]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

So far so good.

The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.
Resistors are available in a huge array of OHM values and
watts and what is utterly bewildering to someone like me is
probably mindlessly simple to many of the experts who frequent
this group.

Any suggestions?

Jesse

You move the sensor closer to the heater elements or get a digital
heat controller that has a PID controller in it.

With a PID ("Proportion-Integral-Derivative"), you can use the "D"
parameter to slow down the heating cycle when it starts to approach
the SP (Set point).

Dropping the heating wattage may not be such a good idea, it's better
to have some reserve.

Of course, if you were using a RTD or simple PTC/NPC, one could whip
up a basic voltage comparatar with some Lead (Derivative) in it to
throadle it back when it gets close to the set point.

Jamie

 

[Sjouke Burry]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

So far so good.

The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.
Resistors are available in a huge array of OHM values and
watts and what is utterly bewildering to someone like me is
probably mindlessly simple to many of the experts who frequent
this group.

Any suggestions?

Jesse

Making the physical bulk of the heater as small as possible,
for a given power , will reduce overshoot.
A long,thin, well insulated heater wire looses the remaining heat
very quickly, and causes less overshoot.
Increased turbulence will distribute heat faster to all parts, and
will let your sensing circuit react faster.
Last, by using a dimmer to reduce power in reverse proportion
to the present temperature error, a balance may be achieved, and the
power never goes completely off, eliminating overshoot.

 

[Rich Grise]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

So far so good.

The problem is that even though the heater powers on for less
than a minute (out of even ten), when it turns off, the
residual heat overshoots the mark, causing twice the range in
temperature (.6C) necessary with the thermostat.

So I'd like to prevent the heater from getting so hot,
reducing the wattage by approximately half.

I'm pretty sure that wiring in a resistor into the hot lead to
the element would do it, but I don't know the specifics.
Resistors are available in a huge array of OHM values and
watts and what is utterly bewildering to someone like me is
probably mindlessly simple to many of the experts who frequent
this group.

Any suggestions?

Lamp dimmer?

Good Luck!
Rich

 

[Phil Allison]

"BluntChisel"

I'm not an electronics expert, but I'm interested in what other more
knowledgable people in the group think of the following suggestion:

- If you want to reduce the power by half, would a series diode be a more
efficient way of doing it?

** Absolutely.

Long as the immersion heater has no wires exposed to the water - all is
fine.

Yes, there is a DC component created in the AC supply, but too small to
matter.

My 1500 watt " Black and Decker " hot air gun uses a single diode for the
" Lo" setting.


..... Phil

 

[amdx]

I have a DIY cooking project with which I'd appreciate some
help.

I'm trying to hold several gallons of water at 130F with
minimal variation. A digital thermostat regulates the
temperature (to within .3C), an aquarium air pump provides
circulation, and a small immersion heater (Norpro 559) heats
the water. The latter draws 300W on a standard 110VAC line.

Not sure I like the idea of pumping 72* F air bubbles through a system I'm
trying to keep at constant 130*F.
There is a better way to mix your water.
Mikek

 

[Rich Grise]

Are you using the air pump as a bubbler or as a recirculating pump?

I wonder what he cooks at 130°F ± 0.3°F! =:-O

Cheers!
Rich

 

[amdx]

I wonder what he cooks at 130°F ± 0.3°F! =:-O

Cheers!
Rich

I don't care to have any drug research done on my computer.
What's he cooking Rich?
Mikek (-:
PS. Guess I could look up acetone and alcohol boiling points.
Hmm.... Acetone 133*F
Ok, what dissolves in acetone?

 

[Jesse]

I have a DIY cooking project with which I'd appreciate some
help.

<snip>

Many thanks to all who troubled to share their thoughts. I
thought I would be lucky to get even a single reply, but in
only a few days there have been fifteen from almost as many
individuals.

Rather than reply to each individual message, I'll try to
clarify matters with a single response. I hope everyone who
replied will see this contribution to the thread.

First, to respond to Ecnerwal

Zeroth question - other than you fussing about
it, is this really all that big of a deal? Few
cooking or culturing processes care all that
much about a lousy degree, F or C.

And Rich Grise

I wonder what he cooks at 130°F ± 0.3°F! =:-O

Over the past several years, within the general realm of
"molecular gastronomy" exists that of "sous vide" (French for
"under pressure") cookery.

Misleading nomenclature to the contrary, what this is really
all about is instead of cooking, for example, a beef roast at
350 degrees and removing it when it reaches the desired
internal temperature, it's wrapped and placed in a water bath
of the desired temperature (130 for example) to begin with.
It's then cooked not just for hours, but sometimes for days.

Okay, what's the point?

There are several advantages (google to acquaint yourself with
them) but among the most important is that, as in pit BBQ,
this "low and slow" cooking has a tenderizing effect, offering
the chance to turn the lead of cheap chuck into the gold of
rib eye and having it STILL come out medium rare.

Being a somewhat new approach to cooking, however, it simply
isn't known what effect temperature fluctuation has on the
process. The general consensus is that less is better. I knew
when I bought the thermostat that it only allowed a .3C
variance and was content with that.

Many have used a PID controller, as whit3rd noted, but I
thought that even though it allowed much greater temperature
stability, its complexity was beyond my capacity to properly
configure.

When I discovered that my STC-1000 thermostat exhibited a
small but significant overshoot, I thought it was probably
acceptable but I wondered if there was an easy way to reduce
it.

One obvious approach was to keep the heating element from
getting so hot. I now realize that a simple resistor simply
won't work, it would have to be massive to reduce the current
by the required amount.

I'd like to use a less massive heating element, as Sjouke
Burry pointed out, but finding something ready made that can
be immersed in water, isn't so easy. A home aquarium heater
can be hacked to remove its thermostat, but this isn't a
project I'm comfortable doing.

Rich Grise saw a good solution

Lamp dimmer?

It looks like $5 spent at Home Depot should do the trick.

Mikek had another insight...

Not sure I like the idea of pumping 72* F air bubbles
through a system I'm trying to keep at constant 130*F.

And John Fields...

Are you using the air pump as a bubbler or as a
recirculating pump?

To mix the water.

Originally, I tried placing the stockpot on a hot plate
(connected to the thermostat) without the bubbler, hoping that
natural convection would do the trick, but the overshoot was
pretty bad. Adding the bubbler helped, but using the immersion
heater and bubbler was the best solution so far.

Cooling the water by bubbling room temperature air through it,
I knew, wasn't such a good idea, but the only economical
alternative I could think of was something like a submersible
tabletop fountain pump, like a Sunterra. The question was
whether it would tolerate such hot water. I emailed the
company and inquired, but received no response.

Rather than delay any longer and worried about mixing
electrical current and water, I thought the air pump, despite
its disadvantages, was probably the better option.

Perhaps some who have followed this thread may have a thought
on this topic. Would one of these tiny submersible pumps
function at 130F temperature? For very long? Would it simply
fail and need to be replaced or result in some disaster?

Anyway, for less than $50 - compared to $1400 for a Fisher
laboratory circulator or even $400 for a retail Sous Vide
Supreme - I'm cooking sous vide.

And very happily too. Like pit BBQ, of which I am also a fan,
my few attempts so far have revealed that it can create
genuine culinary magic.

Thanks again to all for so generously sharing their knowledge.

Jesse

 

[Jesse]

oups.com:

Very interesting Jesse,
Do you worry about some kind of bacteria growing at 130F?
And how long do you have to let the meat cook? I was the
lunch cook at a fairly nice restuarant for about a year.
The first thing I did when I came in the morning (~5:30 AM)
was to start the prime rib for the evening. Started at
~220F for a few hours and then dialed down to 170F IIRC.

I think you are obsessing excessively about a few degrees,
of temperature fluctuation.

Bon appetit,
George H.

Thanks for the reply.

Bacterial growth is of great concern, but has been studied
extensively - google Doug Baldwin, for example, for more info.
From all available info, both theoretical and practical, the
130 mark is accepted as safe.

As for the concern over temperature fluctuation, you may well
be right. I wouldn't call my concern "obsessing" and I'm
content with what I already have, but if was easy to keep the
range a little smaller, and it seems that it is with a dimmer,
I'm willing to polish the setup to make it a little better.

Lastly, please realize that heat transfer in liquids is MUCH
greater than that in air, some 23 times as much, as I
understand.

Putting your hand in a 350 oven for ten seconds is no big
deal. Doing so in the same temperature oil is rather
different.

Jesse

 

[Jesse]

oups.com:

Sure that just gets you up to the right temperature faster,
once your piece of meat is at whatever cooking temperature
you desire it will take the same time to 'cook'. (Hard for
me to call 130 F cooking... can you hold your finger in the
130 F water?)

Getting to the right temperature faster goes, at least in
part, to the health question you raised initially.

The idea is that you want to go from refrigerator temperature
to "cooking" temperature (I agree, 130 is cooking?) as quickly
as practical.

Why?

To minimize time at the temperatures at which problem
organisms flourish.

Which is why most limit the size of cuts to about 3" thick to
make sure that internal temperature is reached soon enough to
be safe.

I think that you're right though, once it's at 130, a standard
oven might work too. Although, since we've already troubled to
build the water bath, it's probably just as easy to just use
it and keep things both simple and within a narrower
temperature range common with standard ovens.

Jesse

 

[Jesse]

Blech, boiled beef. You have to caramelize it to make it
taste good. Roasted at 425F in a convection oven or over
charcoal is the One True Way.

Cheers

Phil "obligate carnivore" Hobbs

I really don't want to debate the merits of this method, but
was only seeking information on how to economically implement
it.

Since Phil already replied, I'll make a single exception and
point out that food is not boiled, it's first packaged in a
water tight pouch (eg FoodSaver) and then gently poached.
Rather than searing before hand (to achieve the Maillard
reaction) it is usually seared afterward.

If you're interested in learning whether this cooking
technique is for you, this newsgroup probably isn't the best
forum for doing so. There's lots of information on the 'net
about it, by those who have studied it at length.

I'm not here to advocate anything one way or another. In fact,
I too was skeptical at first, dismissing sous vide as yet
another, soon to pass, fad. I decided to build this
experimental DIY rig to settle the issue one way or the other
and, to my surprise, am glad that I did.

Jesse

 

[amdx]

Very interesting Jesse,
Do you worry about some kind of bacteria growing at 130F? And how
long do you have to let the meat cook? I was the lunch cook at a
fairly nice restuarant for about a year. The first thing I did when I
came in the morning (~5:30 AM) was to start the prime rib for the
evening. Started at ~220F for a few hours and then dialed down to
170F IIRC.

I think you are obsessing excessively about a few degrees, of
temperature fluctuation.

Bon appetit,
George H.

I'd like to add a new wrinkle, "meat glue" butchers have started gluing
small pieces of meat together to make full size pieces and it is
difficult to tell.
Besides possible problems with the chemical, any bacteria that was
on the outside is now on the inside. If you cook it rare you won't kill
the bacteria.
Jesse's method may kill the bacteria, but usually the recommended temp is
160*,
his long cooking time at 130* may kill bacteria.
Meat Glue video.

My short search finds no ban in the US.
Mikek

 

[Jesse]

Jesse's method may kill the bacteria, but usually the
recommended temp is 160*...
Mikek

Thanks for the response, but please understand that I am no
expert on this subject and it is hardly "my" method. What I
know about it, I've learned from the 'net, which you can do at
least as well as I have.

Perhaps chief among my doubts about this approach was that of
safety. In that, as both you and George have pointed out (as
well as many before us) I was hardly alone.

Still, the 130 threshold seems to be the magic number, one of
the reasons why hitting it and holding it is so important. If
it rises too high, you loose the medium-rare target you're
trying to hit. Too low and you offer pathogens an increasingly
hospitable habitat.

Interestingly, this setpoint applies exclusively to beef. In
cooking pork or poultry, little concern over the result being
medium-rare is present, so these can and often are cooked at a
higher temperature.

What is actually of concern here, I think, is really just
pasteurization. If you've ever done any camping, or maybe just
watched Survivor, you probably know that rendering water
potable is not just a function of temperature, but of time as
well.

Thus eggs can be made safe by heating them until the yolks are
set (~160°F). But it's thought that they can also be cooked in
the shell at 135°F in a sous vide water bath for at least 1
hour and 15 minutes to achieve parallel safety.

For a general introduction to sous vide cookery, please see...
www.douglasbaldwin.com/sous-vide.html
Of particular interest is the section on Safety (Part 1
Section 1).

For some background on the approach, please see Amanda
Hesser's piece, Under Pressure,
www.nytimes.com/2005/08/14/magazine/14CRYOVAC.html?_r=1
&pagewanted=1&ei=5090&en=3d5db17005368139&ex=1281672000
&partner=rssuserland&emc=rss

For lots more information on sous vide, please search
egullet.com.

I'm afraid this is the best I can do in explaining the method.
It was precisely because I wanted to avoid becoming the go to
guy to learn all about this lunatic cooking approach was the
reason why I left out the specific nature of my "DIY cooking
project". It was only because some were growing uncomfortable
with just what is was that I was, uh, "cooking" that I
reluctantly mentioned it all.

Again, there's tons of stuff on the 'net on all this. If
anyone in this group wants to know more, google is your best
guide.

Jesse

+

All truth passes through three stages... &c &c &c.
~ Arthur Schopenhauer

 

[amdx]

"Jesse" wrote in message

Jesse's method may kill the bacteria, but usually the
recommended temp is 160*...
Mikek

Thanks for the response, but please understand that I am no
expert on this subject and it is hardly "my" method. What I
know about it, I've learned from the 'net, which you can do at
least as well as I have.

Perhaps chief among my doubts about this approach was that of
safety. In that, as both you and George have pointed out (as
well as many before us) I was hardly alone.

Still, the 130 threshold seems to be the magic number, one of
the reasons why hitting it and holding it is so important. If
it rises too high, you loose the medium-rare target you're
trying to hit. Too low and you offer pathogens an increasingly
hospitable habitat.

Interestingly, this setpoint applies exclusively to beef. In
cooking pork or poultry, little concern over the result being
medium-rare is present, so these can and often are cooked at a
higher temperature.

What is actually of concern here, I think, is really just
pasteurization. If you've ever done any camping, or maybe just
watched Survivor, you probably know that rendering water
potable is not just a function of temperature, but of time as
well.

Thus eggs can be made safe by heating them until the yolks are
set (~160°F). But it's thought that they can also be cooked in
the shell at 135°F in a sous vide water bath for at least 1
hour and 15 minutes to achieve parallel safety.

For a general introduction to sous vide cookery, please see...
www.douglasbaldwin.com/sous-vide.html
Of particular interest is the section on Safety (Part 1
Section 1).

For some background on the approach, please see Amanda
Hesser's piece, Under Pressure,
www.nytimes.com/2005/08/14/magazine/14CRYOVAC.html?_r=1
&pagewanted=1&ei=5090&en=3d5db17005368139&ex=1281672000
&partner=rssuserland&emc=rss

For lots more information on sous vide, please search
egullet.com.

I'm afraid this is the best I can do in explaining the method.
It was precisely because I wanted to avoid becoming the go to
guy to learn all about this lunatic cooking approach was the
reason why I left out the specific nature of my "DIY cooking
project". It was only because some were growing uncomfortable
with just what is was that I was, uh, "cooking" that I
reluctantly mentioned it all.

Again, there's tons of stuff on the 'net on all this. If
anyone in this group wants to know more, google is your best
guide.

Jesse,
But we all found it interesting, we wanted to hear about it.
I just added the "meat glue" info because it was new to me.
Mikek

 

[Rich Grise]

Sure that just gets you up to the right temperature faster, once your
piece of meat is at whatever cooking temperature you desire it will
take the same time to 'cook'. (Hard for me to call 130 F cooking...
can you hold your finger in the 130 F water?)

Sorry for the obsessing comment.

How hot is the air that comes out of the car heater by your foot? I
once heard a UL about some guy who was driving and felt drowsy, so
he pulled over, but left the engine running, with the windows
open a bit so he wouldn't gas himself, and the heater going so he
wouldn't freeze.

Anyway, the UL was that the guy slept for several hours and when
he woke up, he found that his foot had been cooked. It sounds a
little implausible; I wonder if that UL debunker has anything on
that.

What's the URL of the UL debunker site?

Thanks,
Rich

 

[Rich Grise]

On May 9, 11:54 am, Phil Hobbs

Oh come on now Phil, Certainly you like a nice pot roast. Slow
cooked all day with lots of taters, carrots and onions. Our 'secert'
family recipe calls for half a jar of horse radish spread on top to
the roast after it's browned. mmmm, all this food talk is making me
hungry.

All the cooking shows that slow-cook beef say to first brown it all
over in a searing-hot skillet first, _then_ slow-cook it, and also
use the liquid from the sear in the stew or pot-roast recipe.

BTW, it's nice to see such a long on-topic thread. ;-D

Cheers!
Rich