is it safe to turn a kettle into a hot plate for boiling solutions?

hello,
i recently realised that my kettle, which consists of just a a kettle shaped container with a hotplate down the bottom,
quickly reaches tempuratures in excess of 100 degrees celcius, and so i have considerd getting a second hand one or a scrap one at the local dump shop, to use in my chlorate cell, to periodically boil the solution once per hour to destroy the hypochlorite and re-absorb the chlorine gas which would normally be lost.

i intend to remove the little hot plate!

i also want to use it, along with some kind of speed controller, or lamp ambience controller or whatever they are called (lamp dimmer), to make a variable tampurature hot plate, using a heat dependant autoresetting circuit breaker to ensure the temp doesnt go above what i want it at.


what i need to know, is  it safe, not for me, but for the kettle, to operate for short periods of time without turning off? or would the resistance coil burn out?
by that i mean 5 -7 minutes, considering its normal run time is at about 1-2 minutes.
or can it safely run on indefinately, with the only damages occuring being melting of wires and the base?

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caarntedd6 years ago
You will just have to try it and see. I personally think that the element will burn out. Elements that are used for boiling water often rely on the water to keep them below their self destruct temperature. Give it a go.
oldmanbeefjerky (author)  caarntedd6 years ago
i just came to realise that some water goes through a small one way valve, into the actual base of the kettle. this water operates a pressure switch, which turns off once all the water has boiled ff, which takes exactly 75 seconds from tap temp water.

do you think that water keeps the "elements" stable?

would that alone keep the kettle stable so long as the water was kept topped up?
Pressure Switch ?
Is it an electric switch that could be used to operate a relay and
turn off the power to the hot plate ?   A
oldmanbeefjerky (author)  iceng6 years ago
nope, its all mechanical, and it wont allow itself to turn back for a minute after it it goes off.

its the thing that pushes back the actual switch you press to start up the kettle. it cant be used.
I still think that you will need to try it to know for sure.

If you are talking about the type of kettle that I think you are (white plastic with metallic element in the bottom), they get real hot real fast if you operate them without water.........I just tried mine and it started to sizzle after about 5 seconds (residual moisture after I emptied it). I assume it has a thermal overload, though I wasn't game to try it, because surely the manufacturers would not rely on people checking the water level to prevent house fires due to incorrect operation of the kettle.

I have seen these units melted, and I have seen at least one house fire started because of this, though I imagine the thermal cutout was faulty in these cases.

In my opinion this type of element won't work as a "stove", but as I said before you won't know for sure till you try it. Do it in a safe place and let us know what happens.
oldmanbeefjerky (author)  caarntedd6 years ago
and if it works ill make it into an instructable!

thanks
iceng6 years ago
Are you worried, what will happen when all of your liquid is boiled away ??

Usually the kettle gets Melted !
After that the insulation in your hot plate is burned off !!
Then a little vibration and your plate shorts out !!!

As long as you have liquid in the kettle a lot of energy is used to make steam.
When all the liquid is goon, that energy has nothing limiting the temperature.

Then it is a race between insulation failure and melting the kettle.
If the kettle is cast iron the insulation looses first. A
oldmanbeefjerky (author)  iceng6 years ago
no, im worried that the kettle will overheat and burn out. i have no intentions of allowing the water to boil off entirely, otherwise electrolysis of my chlorate will cease


i want to attempt to configure the kettle to operate as a hotplate for heating, and i will attach a digital thermometer to it and a heat dependant relay to switch it off when it gets dangerously hot, which will maintain its tempurature as high as practical.

im just worried that it will immediately overheat without a liquid.
how long will it take, on average for it to reach its tempurature of no return? roughly what is that temp anyway?

maybe i would be better off using toaster wire or hair dryer wire, as ive seen it be used to heat a sodium hydroxide sodium metal cell , to 350 celcius and over (it needed to be regulated to stop goiing to high.
The mass ( weight ) of the kettle will determine how fast it will reach temperature.

No doubt you will run timed heating tests to answer this question ?

Calculating this involves too many variables such as hot-plate-power, kettle-mass, solution boiling-temperature, thermal-impedance-plate-to-kettle and ambient air temperatures.

I worry about measuring digitally a temperature of 350 C
Low cost temp devices cannot handle that temp. You may have to use a thermocouple and an Omega controller to phase back your hot-plate. A
Vyger6 years ago
There is actually an interesting principle at play here. As long as there is a solution of some kind in the kettle it will not overheat. The heat that you apply gets converted into a gas, water vapor, and boils off into the atmosphere. It takes a certain amount of energy for that conversion from liquid to gas and as long as that is allowed to happen the solution will remain fairly close to the same temperature. The actual temperature will depend on a number of factors including the air pressure. If the air pressure is increased then the water temperature will rise to compensate until it can once again boil off. This is why a pressure cooker can reach higher temperatures than just boiling water. There are formulas for all this but all you really need to know is that it will be alright as long as it has water in it.
My mom melted a hole in an aluminum kettle once. It was just fine until the water boiled out of it. But once it was dry the aluminum heated up to the same temperature as the burner and melted (It was on high).
The same thing happens with freezing, water will stay at the freezing temperature no matter how cold the air temperature is until it is all frozen, after that the temperature drops.
By the way, the water drawing the heat off of the coil will prevent it from getting as hot as it can with no heat sink, but there is no guarantee that it won't at some point burn out anyway. Everything eventually has its failing point.