Sciencemadness Discussion Board

Heating element, hitting specific temperature success

Fantasma4500 - 28-8-2022 at 05:42

hey, i just wanted to share my struggles and success, so im needing to have a piece of heating element hit a high temperature, about 600*C

dimmer switch blew up and gave up on me

so i went a much more basic route instead, just trying and seeing and then adjusting!

i connected a 12V1A powersupply to a 2.20g piece of coiled heating element, seems about 1mm thickness, 5mm diameter - it climbed to arrive at a temperature of about 210*C
so, i cut a piece at about 0.70g and gave it another go, now it started to glow red, which should be somewhere above 600*C

now, i have one project that requires me to hit 120*C, having the heating element attached to the glasstube was quite a struggle so i cant just be fiddling around with it like ive done it before and i wont be taking it off to weigh it- it could seem like a dimmer switch before a stronger power supply might work

i have tried with DC motor limitors but they seem to just overload whatever test subject i have or not limiting it very much at all, barely noticable when adjusting the knob

by my limited understanding- i should be able to plug in a dimmer switch, then route that to a powersupply lets say.. 12V10A? and then adjust it using the dimmer switch? or should i adjust the output coming from the powersupply with dimmer switch?

i have also looked into making my own .. rheostat, essentially wrapping steelwire around a heatproof something, you can get this as some kinda gardening wire, PVC coated at hardware stores, and then with a sliding mechanism that taps into the coiled wire, you can limit the power like so, this is supposedly whats used for industrial power limitors

for accurate temperature control of heating elements i see "variable transformers" are used... and they cost about 600 euros and weigh a silly 17kg?

Metallophile - 28-8-2022 at 08:41

It seems like a lamp dimmer should work, although they often have lower Amp ratings than regular light switches. You may have exceeded that, causing the failure. A variable transformer (variac) will definitely work, and they can be found for much cheaper than 600 euro. I found a 500VA variac on Amazon for about $60. They are heavy though, as you noticed. I use a variac plugged into a Kill-A-Watt meter, so I can monitor the power directly as I make adjustments.

Rainwater - 28-8-2022 at 13:51

nichrome wire properties are well documented.
This pdf is old but dead on accurate. The information within will enable you to calculate and reach any temp you want up to 1400c.
Hope it helps and good luck. Post a pic of you get bit and feel gods power coercing through your body.

Remember that heat = power(Watts)/surface area(m²)

Attachment: NiCrTechTips.pdf (5MB)
This file has been downloaded 400 times

Rainwater - 28-8-2022 at 14:21

Quote: Originally posted by Antiswat  

by my limited understanding- i should be able to plug in a dimmer switch, then route that to a powersupply lets say.. 12V10A? and then adjust it using the dimmer switch? or should i adjust the output coming from the powersupply with dimmer switch?

If the power supply is an old transformer with a rectifier then yes, you can use a dimmer to control the mains power, do not use a triac dimmer, but a resistive based. Will be hard to find nowadays.

If it is an smps, then no.
For the same price you can get a 36v 10amp bench power supply from amazon.
Dc is safer than ac with voltages under 45
Quote:

i have also looked into making my own .. rheostat, essentially wrapping steelwire around a heatproof something, you can get this as some kinda gardening wire, PVC coated at hardware stores, and then with a sliding mechanism that taps into the coiled wire, you can limit the power like so, this is supposedly whats used for industrial power limitors

Emanuel coated wire also known as magnetic wire, used for coiling transformers is the standard. Keep the coil diameter large and the spacing small. Where your slider contacts the wire, the enamel coating can be removed with acetone.
Quote:

for accurate temperature control of heating elements i see "variable transformers" are used

Standard test equipment. Shop around for the best price.

A crude setup can be made by using incosdicent (old school) light bulbs connected in series with your heater. They will keep the power below their rated wattage and can be connected in series and parallel to obtain your required current at the cost of efficiency

Mateo_swe - 29-8-2022 at 01:39

You could use a temp controller lika a MyPin TA-4, a SSR, a temp sensor and a heating wire coil.
Or you could just use a dimmer and a heating wire coil but then there is no temp regulation.

Fantasma4500 - 31-8-2022 at 10:57

MyPin TA-4 seems to be 20 euros price with 2-3 months delivery from china, so this is basically some kind of transformer you can adjust..?

@Rainwater
the bulb idea sounds like i would have to construct a panel to plug in the bulbs and it would take up a lot of space... and basically exhaust my power by running it through bulbs? plus i dont quite see how that would work as i consider a light bulb, a dead-end, its a piece of resistance wire that leads back excess power through the input cable?

i looked around at dimmers and they can be extremely expensive, like 100 euros for one small device, at that point i'd rather just hook up goddamn batteries to get what i want, or an actual chemistry powersupply

i just had a 12V1A powersupply fry itself from running a piece of wire at about 600*C for maybe an hour, and this was even one of those powersupplies that come in a polished stainless steel box made out of holeplate, could seem like theres no easy way for this, maybe its just my usual bad luck with electronics.

Pumukli - 31-8-2022 at 11:06

Maybe that 1A was the bottleneck.
What if you tried a 12V 2A power supply next time?
(I bet you did not measured the current that your piece of glowing wire was drawing from the supply, did you?)

Rainwater - 31-8-2022 at 12:17

Sorry about the disconnected and rambling thoughts. Kinda of a complex topic im passionate about. Might be easier to experiment but some basic information never hurt anyone

If you can provide more details, i can give more specifics for your situation.
What is the cold resistance of your heating element?
What is the average or rms voltage being applied to the element?
Do you have an electrical meter to take measurements with?


You stated that your dimmer failed. Most likely do to either connecing the circuit while the dimmer was on, or an overload condition.
Quote:

i dont quite see how that would work as i consider a light bulb, a dead-end, its a piece of resistance wire that leads back excess power through the input cable?


This is just a cheap adjustable mains power supply and can easily get someone killed. I can not express in words how dangerous electrical systems can be.

By connecting bulbs in series with your heater makes a cheap resistive current limiter.

Simple circuit is as follows.

Screenshot_20220831_150550.jpg - 106kB

$3 keyless fixture
$4 plug
$7 wire

So about 15 bucks to get you started.

A 60 watt incandescent bulbs are the equivalent to a 60watt rated resistor. To find the ohms value of that resistor you need to know your mains voltage. Most of the world operates residential voltages of 230 while the US uses 120.
A cold bulb will have a lower resistance than a hot one, which will also need to be taken into your calculations.


Up to you, but a bench power supply would be your safest way.

The best method is to size your heating element to the correct length, surface area, and resistance for your application. You listed weight. Sorry but thats not helpful without the wire gauge.

Start with ohms law and work your way backward to determine the correct values required for your heating element. From that use a materials property chart to determine the required gauge and length of wire t9 get the correct ohms required. From there calculate your wire's surface area and wattage to calculate your temperature delta.

Once delta t has been found, check if it's too high. If it is increase the wire gauge and recalculate everything, repeat until delta t is acceptable, or increase your heat dissipation area by other means

Using the proper materials it is possible to create a self-regulating heating element that will maintain a specific temperature at a given BTU.

To answer your question fully, you're going to have to study ohms law in detail. As well as thermal exchange.

By calculating the temperature change of your apparatus at a given wattage, then recording the amount of time required for the apparatus to cool, the R value can be easily calculated, which can be used to determine the necessary wattage.

Notes. Some data sheets do not list delta t. They will instead list P/M² power/meters². For general applications, you want that value to be less than 15.
For consumer applications with a UL listing, it has to be below 10 in the us but varies country to country.

Edit: this excell sheet should help with the math.

[Edited on 31-8-2022 by Rainwater]

Attachment: Heater Coil Calculations.xlsx (11kB)
This file has been downloaded 256 times

Mateo_swe - 4-10-2022 at 11:06

If you want to keep it simple and cheap buy a high power dimmer and some heating wire.
For example a dimmer like this:
https://www.ebay.com/itm/401089441241?hash=item5d62cb2dd9:g:...

Its US $7.88, plus 2$ shipping worldwide.
But there will be no temperature regulation so you have to turn it up a bit and see what temperature you get and adjust knob some more until you find your target temp.
These dimmers can used on heating mantle sleeves witch is just a heating wire coil in a fiberglass sleeve.
And use a ground fault breaker and be careful when using 230VAC, one gets very angry when zapped with live voltage, if you live to be angry that is.

Otherwise a 230V, 10A variac is little bit expensive but so useful to have for all kinds of stuff and experiments.
Highly recommended.