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can i build a hot plate by just pumping electricity through wire?

Legolessed

i want to make my own hot plate and i was brainstorming ideas when i thought that i could just plug into my 120v outlet on the wall and then pump that electricity through a small wire that zigzags along the surface to make heat from resistance. would this work? 

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It should. Though you could kill yourself, start a fire, or end up with melted wire all over the floor if it wasn't strong enough to take the heat. But those are pretty minor. You'll be fine. /s

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Just now, Zando Bob said:

It should. Though you could kill yourself, stat a fire, or end up with melted wire all over the floor if it wasn't strong enough to take the heat. But those are pretty minor. You'll be fine. /s

so thats the way to go? one of my ideas works? xD 

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Just now, Lazaro said:

SUPER FUCKING DANGEROUS don't even attempt.

how should i do it then?

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1. Working with 120V AC is extremely dangerous. I suggest making a prototype using lower voltage DC

2. You need extremely long wire to do that. Look up resistivity.

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4 minutes ago, Legolessed said:

i want to make my own hot plate and i was brainstorming ideas when i thought that i could just plug into my 120v outlet on the wall and then pump that electricity through a small wire that zigzags along the surface to make heat from resistance. would this work? 

There are immersion heaters such as this, note there are dangerous versions that will physically pass electricity through the water to heat it, do not use those for obvious reason and if you do never touch it when powered.

https://www.amazon.com/Lewis-N-Clark-Portable-Immersion/dp/B001U0PA7M/ref=sr_1_2?ie=UTF8&qid=1498276519&sr=8-2

 

 

 

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Just now, Legolessed said:

so thats the way to go? one of my ideas works? xD 

Yup. Hey, at least it isn't as explosive as the rocket idea. Though I'm sure you'd be fine if you made and RGB rocker with a homemade hotplate attached just for the cool factor. Ask @Damascus, he'll tell you all about how RGB enhances safety, performance, longevity, fps, cooling, etc once attached to a component. 

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2 minutes ago, Legolessed said:

how should i do it then?

Dig an old one out of the dump to salvage the heating coil and a proper plug. Then attach it to your chosen plate and a heatproof stand. Just don't plug it in 'till you're sure it's safe. Or you'll turn into a giant LED!

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Just now, Zando Bob said:

Dig an old one out of the dump to salvage the heating coil and a proper plug. Then attach it to your chosen plate and a heatproof stand. 

dont all hotplates basically pump electricity through them? 

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3 minutes ago, Legolessed said:

dont all hotplates basically pump electricity through them? 

Yeah, but the metal in the heating coil is the right alloy at the right gauge to handle the electricity flowing through it. Normal wire would just sparkle and then snap. It'd be roasted by the electricity. You could try pulling the resistance wire from and old toaster and using a car battery. Much less chance of dying. 

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6 minutes ago, Zando Bob said:

Yeah, but the metal in the heating coil is the right alloy at the right gauge to handle the electricity flowing through it. Normal wire would just sparkle and then snap. It'd be roasted by the electricity. You could try pulling the resistance wire from and old toaster and using a car battery. Much less chance of dying. 

ah. how do you not get electrocuted by a hotplate though, or do you? ive never touched one when its on

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4 minutes ago, Legolessed said:

ah. how do you not get electrocuted by a hotplate though, or do you? ive never touched one when its on

Because hotplates use an insulator. Some special one use a totally different technique called induction (where you generate heat by a moving electro magnetic field)

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1 minute ago, FTL said:

Because hotplates use an insulator. Some special one use a totally different technique called induction (where you generate heat by a moving electro magnetic field)

is there any insulator thats common that i can use? i dont really fancy sending 120v through me accidentally again. trust me, the tounge is the worst

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6 minutes ago, Legolessed said:

is there any insulator thats common that i can use? i dont really fancy sending 120v through me accidentally again. trust me, the tounge is the worst

Haha, the Voltage is not what hurts you. Some household items you touch everyday can generate hundrets of Volts (Carpet...). Just make sure the Amp is low or use insulators like Glass, which doesn't conduct electricity. Everything over 30mA could be dangerous.

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4 minutes ago, Legolessed said:

is there any insulator thats common that i can use? i dont really fancy sending 120v through me accidentally again. trust me, the tounge is the worst

Tricky. It'd need to be heat proof. I'd say (again) to get an old one from a dump and dissect it to see how it's made. 

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1 minute ago, FTL said:

Haha, the Voltage is not what hurts you. Some household items you touch everyday can generate hundrets of Volts (Carpet...). Just make sure the Amp is low or use insulators like Glass, which doesn't conduct electricity.

Best example is a police taser. They can get up to 1 million volts, but they do t roast you. It's because there isn't any power (Amps, AFAIK) behind it. 

 

So would a car battery be safe? IDK how many Amps there are, by it should be safer than a 120v house plug. Till your dad tries to start his car, that is. 

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4 minutes ago, FTL said:

Haha, the Voltage is not what hurts you. Some household items you touch everyday can generate hundrets of Volts (Carpet...). Just make sure the Amp is low or use insulators like Glass, which doesn't conduct electricity. Everything over 30mA could be dangerous.

lol i was just saying a fancy thing for wall socket. i know like when you shock someone your sending millions of volts thorugh them but at a very low amapge and for a very short period of time. i took middle school science class xD 

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I'm not sure if anyone mentioned this yet, but nichrome wire. Definitely control the voltage and current carefully or it will get so hot that it will melt itself. This is the wire in toasters. 

ASU

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22 hours ago, Hackentosher said:

I'm not sure if anyone mentioned this yet, but nichrome wire. Definitely control the voltage and current carefully or it will get so hot that it will melt itself. This is the wire in toasters. 

This^^. Just some nichrome wire, a thermocouple and a cheap pid controller will be enough to make a decent hot plate. You just want to ensure that the powered heater is insulated well enough to avoid danger.

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4 hours ago, bob345 said:

This^^. Just some nichrome wire, a thermocouple and a cheap pid controller will be enough to make a decent hot plate. You just want to ensure that the powered heater is insulated well enough to avoid danger.

You might be able to salvage the heated bed part of the Marlin 3D Printer firmware to do just this with an arduino.

ASU

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Playing with mains electricity is very dangerous. Usually heating elements are some wire with high resistance inside a tube made out of some insulator which will also let heat pass through it, like ceramics or other materials. Cheap heaters used wire inside bricks

 

If you want to make a heating plate for some low temperatures like 50-100c , you could make something that's powered from something safe like 12v (a computer power supply).

 

Voltage = Current x Resistance

Power = Current 2 x Resistance  = Current x Voltage

 

Knowing the formulas above you can connect resistors in parallel to reach a desired total power.

 

For example, there are 7w / 10w / 15w / 20w rated resistors wrapped in cement or ceramic material , which can handle at least up to 155 degrees Celsius, and some better ones can do up to 250-350c

 

For safe continuous use, it's best to not go over about 80-85% of their rated power, so for example for a 10w rated resistor, you'd want to not exceed let's say 8 watts.

 

So if the voltage is 12v we can just pick a resistance value which will give us a dissipated power less than the 10w rating. 

 

For example, let's go with 18 ohm..  so V = I x R ... then 12v = I x 18 ohm, which means I = 12/18 = 0.666A  ...and now we can do the math and we have P = 0.6662 x 18 = 8 watts. Perfect.

 

Now if you want a 40w heater, you can simply connect 5 of these in parallel at 12v on your power supply, put some thermal paste on top of them and some thin metal sheet to spread the heat more uniformly.

If you want 400 watts, then you need 50 such resistors spread as uniformly as possible over the surface.

If you want some exact temperature it would simple to just use a temperature sensor glued to the metal plate and a tiny controller which would turn on and off strands of resistors to adjust temperature or keep it at some level.

 

Here's such resistor, good for up to 155C, $0.45 for 10 or $0.23 for 100  : https://www.digikey.com/product-detail/en/yageo/SQP10AJB-18R/18W-10-ND/18741

And a bit more expensive version but which can go up to 350c

 

You could also make series of resistors and then connect these series in parallel ... for example, let's say you connect 4 x 1 ohm 10w resistors in series, which gives you a 4 ohm 40w resistor.  At 12v input, you have 12v / 4ohm = 3A  and the power dissipation will be 3x3x4 = 36 watts ... which is reasonably close to maximum 40w rating.

Then you can connect such series of 4 resistors in parallel to reach your desired wattage.

 

There's also other resistors, like the ones which you can screw onto something.. for example TO-220 resistors like this: https://www.digikey.com/product-detail/en/riedon/PF2203-5R6F1/696-1688-5-ND/2448079

 

The above 5.6 ohm resistor is rated for up to 35w if you screw it to a heatsink (which can be a basic metal sheet)  .. so with 12v DC voltage the resistor will dissipate up to around 26 watts of heat into the metal... so basically like 3-4 of those resistors above. It's more expensive but would concentrate heat in a smaller spot.

 

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Ok mains power you need a license to build an appliance. If not you must live in developing country.

 

most hot plated use mineral insulated elements.

so inner core is a high temp alloy, I believe it has nickel or tungsten but I'm not 100% sure of its make up.

this is coated in a ceramic

this is then coated in another metal I am not sure exactly what the metal is.

this allows heat transfer with electrical isolation. It is also why they take longer to heat than an induction/glass top stove. This is also why they break easily. The manufacturing process is not great so under Aus/nz regulations they get more leniency for resistance to earth.

 

if you want to build a heater that is not illegal then look up peiltier coolers. You should be able to run it off a battery. In my country It's only illegal to build stuff when it's connected to the mains

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@SCHISCHKA What you do in your own house is legal, you can burn down your house if you want to (and are willing to accept the consequences like fines from firemen etc)

 

For commercial products, indeed you have a lot of rules to follow and certifications to obtain and prove that your product would be safe.  You can reduce the number of certifications and approvals you need by using a third party power supply that's already certified and which has an output voltage below some threshold, for example 24v - anything below 24v in general requires less approvals and certifications.

 

That's one of the reasons you see on laptops power supplies topping at 19-20v and you don't see anything reaching 24v, and another reason why usb-c is capable of up to 20v at 5A (100w) but nowhere close to 24v.

 

This is one of the reasons some of the first 3d printers made with Kickstarter and other funding methods used computer power supplies (12v) for the heating plates and the extrusion heads .. no need to get certifications and approvals to sell the product. 

 

I suggested using a computer power supply because of this reason, because it would be safer and would make it easy to turn on and off resistors and therefore adjust amount of heat.

 

Peltier elements are too expensive and inefficient for a heating plate.

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16 minutes ago, mariushm said:

@SCHISCHKA What you do in your own house is legal, you can burn down your house if you want to (and are willing to accept the consequences like fines from firemen etc)

 

For commercial products, indeed you have a lot of rules to follow and certifications to obtain and prove that your product would be safe.  You can reduce the number of certifications and approvals you need by using a third party power supply that's already certified and which has an output voltage below some threshold, for example 24v - anything below 24v in general requires less approvals and certifications.

 

That's one of the reasons you see on laptops power supplies topping at 19-20v and you don't see anything reaching 24v, and another reason why usb-c is capable of up to 20v at 5A (100w) but nowhere close to 24v.

 

This is one of the reasons some of the first 3d printers made with Kickstarter and other funding methods used computer power supplies (12v) for the heating plates and the extrusion heads .. no need to get certifications and approvals to sell the product. 

 

I suggested using a computer power supply because of this reason, because it would be safer and would make it easy to turn on and off resistors and therefore adjust amount of heat.

 

Peltier elements are too expensive and inefficient for a heating plate.

I am actually licensed in nz so do not tell me what is legal when it is not. Like I said you must be in a developing country to be allowed to build an appliance without license. In a country with standards, anything that connects to mains must comply and go through a safety check by a licensed worker.

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