How can I heat water up with an arduino?

Lets say I need to keep 200ml of water at 5-10 degrees celsius so it doesn’t freeze. I can have a sensor read temperature data every 10seconds and trigger a warming device when it’s under 5 degrees until the liquid reacher 10 degrees. The problem I’m having is how do I heat up the liquid? I need to do so as efficiently and cheaply as possible. I can use a bigger heater but do realize I only have 200ml of liquid.

Who’s got the best ideas?

There will not be an efficient way. You are stuck with resistors which due to the Joule effect will produce 1wh of heat for every 1wh of electricity.

I don't know what type of liquid you want to heat. But there are tons of heating elements of different power on the internet. There even exist DC heating elements that work at low voltages (12-24V) that are save in case of discharge.

Some context would be useful. What is the water in? Why is stopping it freezing important? Why heat it to 10 degrees if greater than zero is enough?

I found a way, heating pad :wink: