I want to heat the contents (water) of a two liter thermos flask using a low power (50-100 watt) 12 volt DC heater.
Rather than buying a tiny little immersion heater, I've got some nichrome wire knocking about my workshop, would it be electrically safe to use a length of bare nichrome wire directly in the water to heat it?
My natural reaction is not mix electricity with water, but when I think about it I can't really envisage any real problems.
My intention is to use two length of wire, one about 100watts to heat the water in the first place, and a 2nd, about 3 watts to keep it warm once it's boiled.
Update for the curious… The flask is a traditional glass thermos, my intention is to to use this in a caravan with solar cells charging a 12v battery. The hope is that I can provide myself with a low power solution that will give me a permanent supply of hot water for occasional tea/coffee. Experimentation has indicated that I can keep a 2 liter thermos at about 95 degrees with only a couple of watts, and it only takes a few minutes of 100watts to heat the water again after drawing off a cup.
I think the electrical safety questions have been answered, but I'll try to do a bit more research about how healthy nichrome wire in drinking water may be.
Thanks
Best Answer
No, it doesn't seem to be safe. You have full potential gradient accross the wire immersed into water. Therefore, you have to consider electrolysis reaction where some interesting compounds may emerge depending on impurity of water. Even if you make it AC, I don't think that all of the reactions will be reversible with each alternation because of possible convection currents of liquid. So, isolation is required.