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Rheostat to electric heating element?

Posted by sweeby (My Page) on
Wed, Sep 30, 09 at 21:55

In case it isn't perfectly obvious, I'll admit right off that I know nothing about electricity!

Hubby and I are making an electric meat smoker out of an old commercial warming oven we scored at a restaurant supply house similar to the one below. Of course, the 220V electrical bits don't work (which is how we got the gorgeous heavy-duty insulated stainless steel box for only $150), so we were planning to add a heating element.

The best we could find is the 'standard' Brinkman element (the Old Smokey grill element got bad reviews for breaking every three months), but we'd really like to have some way of adjusting the temperature.

My question is - Can we use a rheostat between the outlet and the Brinkman plug to control the heat level?


Follow-Up Postings:

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RE: Rheostat to electric heating element?

Your first statement about elecricity, and than your rheostat question - don't go together.

But - yes - you can use a rheostat to control the heat level.

Pick up a stove/oven rheostat rated for at least the max wattage of your Brinkman element. Possibly one of the rheostats on the warming oven above would work.

Take said rheostat, build a study metal enclosure; have an outlet installed in it; and a heavy duty cord coming off of it... Plug in Brinkman to your control box; plug in control box...

It might be easier to have an appliance place repair your warming oven, sell it; than purchase a smoker designed to be a smoker. Or have the appliance place - wire in the above element...


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RE: Rheostat to electric heating element?

No one uses rheostats for controlling things anymore.

the device is a dimmer, and it uses a triac to chop up the voltage waveform.

It will be fine for a heating element, but you need one with a power rating (watts) at least as large as the heating element.

For reliability you should add some margin in.
Heating elements pull more power when cold then after they are heated up to operating temperature.

You should measure the resistance of the element cold and use that number (watts = volts^2/resistance) to size the dimmer, and always go to the next larger capacity dimmer if you are even close to the rating.


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RE: Rheostat to electric heating element?

The Brinkmann element is 1,500 watts -- and from further research, I hear that's actually quite a heavy load for a rheostat. I also read that a rheostat is an outdated/inappropriate technology, and saw the word 'triac' bandied about. But of course, that word means nothing to me... (Might to Hubby -- he knows a little more than I do.)

Dave - Your thought about one of the temperature controls on the oven still working has also occurred to us. But then, those were designed for 220V -- would they work (even 'sorta' work) on 120V?

There's enough room in the oven to house the workings in a 4-5" space at the top between the insulated box and the removable stainless top. In the unit pictures above, access is through the short & wide side panel, but in ours, the whole top lifts off, leaving a 28" x 22" x 4" area for 'innards'. We can even replace the small metal face plate and add just the few dials and guages we'll need.

Your point about it being easier to buy a smoker is well taken -- but have you really looked at the electric smokers out there? To get this quality 'box', you're looking at spending well over $1,000 -- possibly up to $4,000-5,000, which we won't do. For $300 or less, the boxes you get are pretty flimsy. And despite our lack of electrical knowledge, Hubby is a fabulous craftsman, has tmany of the right tools, and has years of experience working with metal. Me? -- I do the Internet thing and shamelessly look stupid to find the info we need ;-)

Brickeye - Here comes more of the 'looking stupid' part --
Are you saying the part we need is called a triac dimmer? And how big a safety margin should we add in for a 1500 Watt element?


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RE: Rheostat to electric heating element?

Well, let me chime in here...

Truth is that you probably don't want to use a rheostat or a dimmer for this. Virtually all of these types of setups use a thermostat that cycles the element on and off.

I would instead look to repair the existing element/controls. Bet you can fix it right for not much money and have something that's not rigged.


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RE: Rheostat to electric heating element?

You could use a thermostat or a 2000 W dimmer.

Some older electric stoves actually used triacs for temperature control, but were quickly replaced by simple thermostats in the race to the bottom on prices.

Thermostats provide on-off control (AKA 'bang-bang') resulting in wider deviations in temperature than using electronics to set the heat output to what is desired.

The problem with a simple dimmer is that you will have to play with it and watch it till you find the correct setting, and if the ambient temperature changes the oven temperature will also change.

Industrial equipment can use a proportional control system that adjusts the heater output based on how far off the temperature is.
More heat for large error, less heat as you approach the set point.

This is done by controlling the on-off time, sometimes down to very small times for highest accuracy.

Like on for 10 milliseconds per second.


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RE: Rheostat to electric heating element?

Thanks so much for switching to English for Dummies Brickeye!

So a thermostat is what we want? And what a thermostat does is measure the temperature and cycle the power on and off according to the temperature you set?

Sounds good so far --
Now there are two thermostats already installed in the oven -- it was designed as a Cook & Hold oven, so one is set for higher temperatures and one for lower. (It is POSSIBLE that one or both of these thermostats is still functional, but we bought 'a box' under the assumption that all of the electrical bits are fried.)

So two questions:

- The oven was designed to work with 220V current and we'll only have 120V available where we want to plug it in. If one or both of the thermostats is still OK, could they work under 120V power?

- Is there any way we can tell if one or both thermostats still works? The power cord for the unit has been cut off, so we can't simply plug it in.

On the dimmers, we don't mind fiddling to adjust the temperature, and this box is so well insulated (over 1" thick) that our mild seasonal temperature fluctuations probably won't be a huge deal.


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RE: Rheostat to electric heating element?

"- The oven was designed to work with 220V current and we'll only have 120V available where we want to plug it in. If one or both of the thermostats is still OK, could they work under 120V power?"

The thermostat contacts will handle 120 V fine, and the current should not be an issue either.
It is very unlikely the original heating elements were smaller than he 1500 watt element you want to use.

"- Is there any way we can tell if one or both thermostats still works? The power cord for the unit has been cut off, so we can't simply plug it in."

You can wire them up in a circuit with even a light bulb, then heat the sensor with a hot air gun.

"On the dimmers, we don't mind fiddling to adjust the temperature, and this box is so well insulated (over 1" thick) that our mild seasonal temperature fluctuations probably won't be a huge deal."

If you use a dimmer you essentially have to become the thermostat.
When the unit heats up to the desired temperature you turn the dimmer down, then wait to see if the temperature continues to rise, if it does turn it down some more.
If it starts to fall, turn the dimmer up.

The temperature will change exactly as the amibent changes.
If it gets 20F cooler, the interior temperature will be 20F lower.
The same for hotter.
You are running the system with no feedback to the heating element from the oven temperature.
You are the feedback turning things up and down till it sits were you want long term.

I would really try and use the thermostats.
Electric thermostats with remote sensing bulbs are not that expensive or hard to find if the ones in the unit are bad.


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RE: Rheostat to electric heating element?

I agree that the thermostat is the better choice. The oven control on your range at home is such a thermostat. And the original oven element will work fine at 120 volts, but the wattage of that element at 120 is just 1/4 that of the wattage at 240. It will take longer to heat and the ultimate temperature will be considerably lower than original- but this may be exactly what you want.


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RE: Rheostat to electric heating element?

Thanks for the great explanation Brickeye, and for chiming in Bus_Driver -- You guys have convinced me (and Hubby too) to go with a thermostatic control. So now we get the logic -- the trick is the concrete 'How To'.

The thermostats that came with the oven are pretty complex looking, with 6 different wires going hither and yon. It's easy to see which ones go to the temperature sensors (I think!) because those are simple copper wires that go into the box. But the rest of 'em?! Yikes! Which one(s) to use?

Are these the type of thing we need? And if so, how can we tell which one(s) will work?

I'm Googling "How to install Oven Thermostat" and the all basically say to install the capillary tube (no sweat - everything's accessible), to mount the thermostat on the control panel (also no sweat - simple mechanics), then wire in the new one the way the old one was wired. BZZZ! That's where we have no guidance. The old thermostats had SO MANY wires going all sorts of places, and most of which we assume to be broken. (They don't sell $5,000 ovens for $150 if they're easily fixed... Besides, Hubby disconnected them already.)

So how many wires will the simplest thermostats have/need? I'm guessing the wires won't come with the thermostat? What about wiring instructions? I'd guess at a minimum, there needs to be a wire going out to the temperature sensor -- got that, easy to spot in the pictures above. And one (set?) to the device being controlled -- makes sense. And another (set?) to the electrical supply? Any more? And how to tell all of these wires apart and which to hook up where... The 'nose' thing is for the knob to turn?


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RE: Rheostat to electric heating element?

Retraction! Hubby took out the whole 'panel' -- so the wiring is intact.

If he sets the controls back in place and I post a photo -- will that help?


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RE: Rheostat to electric heating element?

The thermostat does not turn the power to the heating elements on and off directly.
If there is not a schematic with the unit you are going to have a lot of trouble trying to rewire anything.

The thermostat feeds a relay, and the relay controls power to the heating element.

There are also safety elements in various of the wires to try and prevent overheating and fire if failures occur in the control circuits (like the thermostat sticks on, the relay sticks on, etc.).

If you do not have a decent amount of appliance and electrical experience it may be pretty hard to learn everything on the fly and rewire this unit.


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RE: Rheostat to electric heating element?

Thanks Brickeye -- And I absolutely agree with you on this part:

"If you do not have a decent amount of appliance and electrical experience it may be pretty hard to learn everything on the fly and rewire this unit."

... which is why I was attracted to the 'plug 'n' play' dimmer idea. The oven's original wiring setup was pretty complex -- definitely over our heads. Plus, the heating elements in this oven (originally a commercial 'cook and hold' oven) are designed to provide gentle, even, allover heat -- which is not what we want in a smoker, which is better with a small area of more intense heat.

Really, we just want to be able to hook up a heating coil placed on the bottom of the box interior and control the heat without opening the box to let out all the smoke.

So the oven thermostats shown above -- is that the type of part we need? And if so, any guidance for installing it?


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RE: Rheostat to electric heating element?

How about if you go to the manufactures site of one of
the 'cheaper' smokers and see if you can buy the working
parts, (the 'guts' as they say). I have one of those
cheaper smokers and it has a wonderful digital control
that works perfectly for keeping temperatures at anywhere
from 175 to 350 degrees. But I agree that the box itself
is rather chintzy. By the way, how are you going to
introduce your wood chips into your smoker?


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RE: Rheostat to electric heating element?

Thanks for jumping in Lbpod -- And we have looked at the 'guts' of the cheaper smokers and actually want to run that way - but with better quality parts. (We'd like the parts to be easily-replaceable when they inevitably break.)

Instead of the Brinkmann heating element, we decided to use an old commercial-grade hotplate we bought when our kitchen was under-renovation. The hotplate has two standard electric coil burners -- 1250 watt and 1800 watt, and two 'adjust the heat' dials that I'm guessing work like dimmers. Hubby took the hotplate apart and figured how move the heating coil section to the bottom interior of the oven and rewire in the dial controls to a new control panel on the unit's top front. That should give us good-looking adjustable temperatures for now -- but I really would like to integrate a thermostat -- a box this good simply deserves one!

For the wood chips, we got a perforated stainless steel chip box at Lowes for $10 -- looks very nice.


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RE: Rheostat to electric heating element?

If you're looking to control the temperature with the accuracy you want for controlled smoking, then you probably want a thermistor or thermocouple, a PID, and a SSR. The first senses the temperature, the second is a controller designed for this, and the last converts the low-level output of the PID to being able to control the 10A or so load of the heating element. Probably something around $100 in parts to do that. Take a look on the coffee boards for parts lists -- places like Home Barista -- search on "PID" and "Silvia" and you'll find all sorts of options (they like to control the boiler temperature).

You'd want some knowledge of electricity and electrical safety before hooking up anything like that (or the other options described here).

On a side note, if you're remembering something with a big knob and lots of copper windings, it's probably a Variac, not a rheostat. Rheostats have the unfortunate property of literally "burning off" the excess power, and can get as hot as the heating element in some cases.


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RE: Rheostat to electric heating element?

The 1800 watt coil alone is too much for a 15 amp circuit,
(figuring 80% loading). Both coils running together is
too much for even a 20 amp circuit, at 120 volts.
For a smoker you don't need that much heat. Another
thought....how about the 'guts' out of a toaster oven?
(buy a new one for your kitchen and use the old one
for parts). But as sfjeff said: "remember to wire everything safely", and make sure you've got good grounds
and there is a GFCI where you plan on plugging in.
Good luck and let us know how you make out.


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RE: Rheostat to electric heating element?

So here's our baby so far:

Smoker Exterior

Smoker Interior

We've got the heating elements working, and yes, they're clearly much more powerful than we need! We'll see if working one burner on low power is low enough to get us what we want.

But isn't she pretty?


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RE: Rheostat to electric heating element?

I like it!! What is the gauge at the top of the unit?
Also, is there insulation on the floor of the component
compartment, (to keep that area from getting too hot).
Maybe a small fan in that area to help keep components
from overheating. When you get it running, check the
draw with an ampmeter to ensure you don't go much above
12 amps if the outlet you are using is on a 15 amp
circuit.


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RE: Rheostat to electric heating element?

We moved her to a 20 amp circuit, and found that one burner on a setting of 4 (out of 10) was able to hold the temp at a steady 225 (40 degrees above our ambiant). We did a simple test run last night, and ended up replacing the solid tray under the wood chips and water with a wire rack -- may need to get a few more of those.

The gauge at the top is a long-stemmed meat thermometer. It's just sitting on top in the pictures, but we were wondering if we might be able to connect it to a copper thermostat wire that runs from the top mechanical area into the very top of the box. Didn't seem to work, but we haven't given up on the entire idea yet. We'd love to be able to install an accurate oven thermometer on the instrument panel, as it turns out the cheapie hanging one really isn't very visible when the chamber gets smokey -- even when moved right in front of the door.


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RE: Rheostat to electric heating element?

I installed a mechanical thermometer in the cover of my
gas grill that I found in the outdoor grill section at
Lowes. It fit in a 1/2 inch hole and a nut screwed on
the back of it. The walls of your cooker are probably
too thick for this though. I also use one of those
remote read thermometers with the probe that goes in
the meat and a small braided cable goes out to the
transmitter. The thermometer can go anywhere,even
clips to your belt. I use this remote read on both
the smoker, the grill, and even the kitchen oven.


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RE: Rheostat to electric heating element?

I just ordered a dual-probe thermometer today. Would have loved another dial on the faceplate, but accuracy's more imporatnt.

Do you know if one of the probes will work in 'air' or does it need to be immersed in some liquid or meat to work? In a perfect world, I'd want one probe for oven temp, and the other for the meat.


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RE: Rheostat to electric heating element?

Do you know if one of the probes will work in 'air' or does it need to be immersed in some liquid or meat to work?

A probe thermometer for you kitchen, like the ones Polder makes? Sure, they sense air temperature although response to temperature changes might be a little slower than if the probe was in liquid or meat.


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RE: Rheostat to electric heating element?

Thanks Mike - That's exactly the thermometer we got and just what we needed to know.


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RE: Rheostat to electric heating element?

Well, the directions on the Polder say not to leave it in the oven, so I guess it'll be for meat only.

Hubby got a BBQ Pit thermometer and threaded it into the side, so this weekend, we'll see how well it works.


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