Making a 120 volt heating element/general heating element info?

If anybody has some general tips/calculation about wire thickness, length, material. Im not even sure which way to adjust. If I make an element that doesn't get hot then I either need to make the element wire thinner or shorter, right? I'm trying to make a 20-50 watt element. Variable would be nice. I have a multimeter. seem to be having trouble getting a steady reading on lengths of wire for some reason. 

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Well I think the easy way to do this is to just buy a cheap 30 watt soldering iron, and then power it through a lamp dimmer. Turning the knob on the lamp dimmer will enable you to easily vary the power from roughly 0 to 30 watts. If you need it to be 0 to 60 watts, then use two cheap 30 watt soldering irons.

If you want the heat to be diffuse rather than all in one spot, I think a soldering iron in a buried in bucket of sand would work for this.

If you really want to to make your own heating element, the trick to this is the knowledge that a heating element is essentially a resistor, and the power dissipated by a resistor is given by Ohm's law.

Recall: V=I*R, and P=I*V = I^2*R = V^2/R

If you know V, the rms voltage across the resistor, and P, the rms power dissipated by the resistor, then use the formula P = V^2/R. Solve for R and get:

R = V^2/P

For example, if V=120 V and P=20 W, then:

R = V^2/P = 120*120/20 = 720 ohm

If you want 50 watts, then the same formula gives:

R = V^2/P = 120*120/50 = 288 ohm

Now supposing you actually have some wire. The way wire works is the resistance of a piece of wire is proportional to its length.

R = K*L

where K is resistance per unit length, i.e. it has units of ohms/meter, or ohms/inch, or whatever. This is the number you look for when you shopping for resistance wire, and you choose a resistance per length number so that you can get a length L that is not inconveniently long.

Nichrome is probably the best choice for the kind of wire, for a do-it-yourself heating element. There are tables to inform you of which gauge (thickness) has what resistance per unit length. E.g.

Also it is possible to buy actual resistors rated for this much power.
E.g. buy six 50 ohm resistors, each rated at 10 watts, then put them all
in series to give you a 300 ohm resistor rated at 60 watts. Note: 120*120/300 = 48 W

avocadostains (author)  Jack A Lopez2 years ago

Had to read your answer a few times and wait a couple days for it to sink in. Very thorough, thank you.

I see the two of us like Multi-Paragraph replies eh?

I'd Second the Soldering iron, (also known as a pencil heater) As a Bounus, many come with a temperature controller right on board!

Why re-invent the wheel, when you just need to mount it differently?

Try not to Zap you're self; Good luck !

Lucky for you, I have one laying around that I took apart so you can see...

And yes that is Perfection, I just didn't want to edit it out :P

avocadostains (author)  Wired_Mist3 years ago

That is exactly what I need or to reverse engineer/copy. Im baffled by the nichrome element. It's a coil yet it looks like its all shorted together by that piece of nichrome running lengthwise. I guess if its too resistive then just keep shorting the coil together in spots till its less resistive. Im curios about the temp regulator. Is it a potentiometer and if so how many ohms is it? Thanks for the pictures!

I bought this for $20 (the most it will run you should be $30) and all of five minutes to dissasemble it

So what is your personal time worth to you?

I'd love to tell you the rating on the pot, but it really won't mater. the pot feeds into a temp controller then into an AC Triac, so unless you use the same chips it won't help you :(

Between the temp Ajst and the built in safety features, If you can adapt the heating element to heat what you need The soldering iron is your best bet !

avocadostains (author)  Wired_Mist3 years ago

Agreed. I was looking on ebay. seems like I can find one similar to yours for around 13 dollars. However, this prpoject strives to become a small business. I have built an incubator controlled by microcontroller like in the sous vide instructables. (built with some help. Tried to wire I second one myself and blew it up when a wire fell out and shorted to the clothes dryer chassis. Anyways the goal is to have it cheap, not for my own sake but to be able to sell units so people can rise yeast, make yogurt, etc. Ideally for 19.99 or less. (You know, affordable,) Therers the cost of the insulated box to consider as well. I dont know as people would go for one made out of wheatpasted together cardboard or something. Considering a regular yogurt maker runs 20-50 and you can only use the rinky dink irreplacable pastic cups they give you, I think the sale of units could be profitable. the simpler the better. Skip the microcontroller on this one. although I recently saw microcontroller for humidity on ebay for 20 dollars and would like to explore that as well. The more you reverse engineer stuff the closer you get to the raw material cost. (Though Ebay China here may prove to have the soldering iron cheaper than I could make an element.) Heating Elements are an intersest of mine, from keeping pipes from freezing with smalle amounts of electricity, to heated clothing. I am thinking that household heating could be way more efficient. My parent have a gas heater installed below a giant glass window. I dont know if this is an accurate anology but I'm starting to think of electricity as a change in temperature along a length of wire, and as a heater directly under a window as a short circuit robbing most of the heat. Also the crazy temperatue difference in a house from floor to ceiling. I sleep on the floor. Though the room is warm while standing, at floor level it is cold. Im thinking It must be way hot up around the ceiling. I know Ive read that a cieling fan can lower heating cost. The best solution i think rather than blowing the air around, cooling it off like a spoonful of hot campbell's soup, is radiant heating, now only done with hot water, initial cost of installation done professionally being in the thousands. I would think it could be done with electric. Electric Carpet? Not sure I'd want to heat the stink of carpet up though. How bought an electric area rug?

Anyways, for the incubator I have sourced a 5v fan and power supply on ebay each for a dollar from China. There is air circulation so the unit is hopefuly evenish temp from top to bottom. That length of nichrome would cetrainly be cheaper than a soldering iron. If I could make it variable that would be great, otherwise just try to barely overshoot the heat and add in small holes that could be plugged to manually vary the heat losses. Of course I'd also like to sell the super spiffy, accurate 50-100 dollar version. Also, google 'Brew belt. That is another solution at least in term of incubating a glass container of yogurt.

By the way, found mini 10 watt glue guns at a dollar store today for 1 dollar.

hop on ebay and search for something like heating pad.

The large aira will help heat disapation. If you buy them in bulk direct from china they will be dirt cheep !

avocadostains (author)  Wired_Mist3 years ago

There is something so close something so close: It's only 7 watts though, It runs off 5v.

Theres also this option with a light bulb base.

There's this too which is interesting:

Foil heating elements? Like aluminum foil I wonder? Or some other foil? the thinnest aluminum foil you can get is at dollar tree. For kitchen use it's terrible but for this use it could be the 'finest' foil available. May have to make a trip to the DT tomorrow.

(DT-dollar tree)

avocadostains (author)  Wired_Mist3 years ago

Something else I was thinking about. People pay to run refrigerators all winter when it's freezing cold outside. To use electricity to cool the air that you are simultaneously using electricity to heat...If there was some way to put a duct, like a dryer duct, actuall an actually dryer duct with some insulation around it, running from outside your house into your fridge, and then control an inline blower motor to draw air in from the outside as need for cooling, and hopefully the strength of the fain will be enough to open and close a flap.

What gave me that idea is my brother dryer doesnt have tht flap close off the otside cold air from falling through the duct into the dryer when it's nor running, and when you open the dryer door in the winter, it's really cold in there! Like a fridge. You can feel the cold air pouring in.

Hey, that's a pretty picture! I think it's the first soldering iron I have seen with a power-control, or temperature-control, built right into the handle. Thanks for upping that.

lol thanks !

Not the same one, but close enough

Yeah. I seem to have trouble answering questions in less than one paragraph. I dunno. Just trying to be clear.


avocadostains (author)  Jack A Lopez3 years ago

I'm trying to figure out how a simple potentiometer dimmer works. I'm confused If I need one rated for 30 watts. Because they get pricey at that rating. Im wondering could I get by with a much lower wattage rated potentiometer if it was well heat sinked.

A potentiometer and lamp dimmer are NOT the same thing.

A potentiometer is a resistor with a "wiper", a sliding metal contact. Moving the wiper changes the resistance between the wiper and the other two terminals.

A lamp dimmer is more complicated. Bascially it is a circuit which limits the power to an AC load, by chopping up the AC waveform into one with lower RMS voltage. That is to say the output from a lamp dimmer is only turned on for part of the wave (e.g. 10% of the time), and the rest of the time it is turned off.

Internally, a lamp dimmer is complicated, but from the perspective of wiring one up and using it, they're simple, and they work well with resistive loads, like a soldering iron. Also they're cheap. A lamp dimmer capable of dimming a 300 watt (or smaller) load should cost less than 20 USD, at the time of this writing.

I like the kind with a big knob, rather than the variety with a slider. In fact I've got a few pictures of the lamp dimmer box I use with my soldering iron, here:

BTW, a lamp dimmer is superior to a potentiometer for limiting power to a load, and the reason why is because a potentiometer (called a "rheostat" in this context) must dissipate large amounts of power, because it's a resistor. In contrast the lamp dimmer limits power just by, essentially, turning on an off really fast.

The section of Wikipedia's "Dimmer" article, linked above, has a blurb on "rheostat", i.e. a large power rated potentiometer, and why they're power-wasteful.

avocadostains (author)  Jack A Lopez3 years ago

Found this baby at Lowes the other day:

Lutron Credenza 1.5-Amp White/Gloss Slide Dimmer

Also they sell a router speed control at harbor freaight and menards for 20 dollars. Does not have an outlet on it though. Good job with your soldering dimmer. I see you dont have any sweet spots for temperature marked on it with a sharpie or something. I imagine it would take several minutes to dial in the temp, no? What with waiting for the element to heat the tip. Like trying to get the water temp right in the shower. I got this from ebay:

2 or 3 dollars and I believe it does the same thing, though I dont really understand how it works. Definitely controls the motor speed on my universal motor grinder. Also the brightness of an incandescent bulb. I tried it with a hot glue gun to make a low temp one but I couldn't tell if it was working right or not with waiting for the element to heat up. I didn't know if I was turning it down and that why the glue was cooling down or if I was turning it all the way off. The thing is called 'silicon controlled rectifier'. rectifier to me means DC output and in this case probably half wave rectification. However when I tested the voltage at the terminal outputs of the thing I got no reading for dc and on AC I just got the same as regular (120-125v ac constant.) I asked my sister about it who is an electrical engineer. Though so is wicked smart in what she does, there is still I believe a great deal of 'on the job training' and there many more 'basic' seeming electrical scenarios which are not her area of expertice. She is by no means a technician of any sort. She loves the math and the coding, the acadaemia.

avocadostains (author)  Jack A Lopez3 years ago

What you say is true. I was reading about dimmers though and it seems the eary dimmers were simple potentiometers. I think the cost of high wattage rated potentiometers has gone up because of being phased out because of the cost of electricity wasted as heat.

However, in this particular case, what I am trying to make is a variable heating element. Resistive heat losses due to voltage drops are exactly what I'm after. as long as the potentiometers adds to the heat produced, a fancy triac dimmer may actually be more efficient in this case, even if it has only a fraction of the conductance inefficiency. By the way at this point I am realizing I dont think I mentioned in my post that I'm building incubators. Probably would have been hopeful to know from the getgo. Sorry. Anyway, I understand the slider wiper potentiometer. At least I think I do, check me here. It's like a regular wire wouind resistors except you are able to complete the circuit at different points along the coil. I am imaging that such a thing would not be too terribly difficult to make, but as I'm currently living in my parents house and am not familiar with what is what on their breaker box, I dont have quite the freedom of experimenting willy nilly plugging coils into 120 volts. The golden nugget of info I havent quite found is the approximate length of what type of wire will give me what wattage at 120 volts. Ideally instead of a tightly wound resistor it would be more like an electric blanket grid or at least like the shape of a electric stove burner to spread the heat out from the bottom up like radiant heating in a home.

avocadostains (author)  Jack A Lopez3 years ago

Soldering idea-brilliant. Numbers stuff-vaguely makes sense. Looks legit. A bit over my head past the V=IR Thanks!

Example of what a 50 ohm, 10 watt, resistor looks like:

Six of these wired in a series makes a 300 ohm resistor, 60 watt, resistor.

avocadostains (author) 2 years ago

With a combination of Rick Harris and Jack Lopez's answers I came up with this:

heating elemt.PNG
rickharris3 years ago

You need to use Nichrome wire.

The thickness (gauge) will define the resistance

the resistance will control the current through the wire.

is a calculator to sort out your needs

Best answer?

avocadostains (author)  rickharris2 years ago

You could have been best answer too now that I understand the calculator. Thats what I actually used once I understood the theory behind it. Good find on that one. Thanks!

avocadostains (author)  rickharris3 years ago

I used that calculator for a long time. Seems very helpful to get an understanding. Still not sure exactly what gauge/length would be appropriate. Im guessing something similar to whats in a soldering iron

avocadostains (author) 3 years ago

Wow lots of helpful simple stuff. Thanks everybody!