Hello again MrAl,
Thanks for the clarification! I think I am ready to start the project now.
Here is everything I am going to use and do, so you can assure me if I am going on the right way.
Okay so the circuit now will consist of:
1- Sealed Lead Acid battery that has 12V and 4.5 Ah. Like this one in Amazon:
https://www.amazon.com/UltraTech-UT...sr=1-18&keywords=Rechargable+Gel+Cell+Battery
2- Three resistances in parallel, each one of them is 15 ohms and able to handle 20 watts.
I will insulate the bottom of the three resistances and attach the top into the metal surface. Is that correct?
If it's correct, then there is another thing I would like to ask you about if you may. I was thinking of recharging my battery by solar energy! So whenever I walk around with my mug in a sunny day, it can charge the battery a bit. To charge it fully I can leave it outside for a long time till it charges for example. I made a diagram combining the circuit I consulted you about (the heating circuit) with another circuit that charges battery by solar energy. My idea is to cover my mug with a flexible solar panel, like these:
https://www.siliconsolar.com/product/flexible-solar-panels.html and attach it to the battery I am using for the heating circuit.
The diagram of the whole thing is attached to my post, please tell me what you think.
The components of the charging circuit are:
First, a high voltage solar panel, higher that the battery I am using but I don't know how much exactly yet, maybe about 20V. Second, a resistance. Third, a voltage regulator chip LM317T, so it regulate the voltage produced by the solar panel and doesn't allow the battery to heat up.
Waiting for your opinion