4.5W heating wire

[david74]

Hi, I am not an electrician. Not even good a physics. My question is basic maths. I want to check an answer I got from AI from someone fluent in terms.

So I asked AI, how long a 3mm 8AWG Heating Resistor Nichrome Wire for Heating Elements would have to be to raise temperature of 100ml water from 20°C to 40°C if connected to 2A mobile phone charger. Here is what it writes.

Let's recalculate with the correct logic:

1. Power needed: 4.65W (as calculated earlier)
2. Charger output: 5V, 2A (10W max)

For our heating element, we want to match the resistance to use 4.65W at 5V:

1. Using P = V²/R, we can calculate the required resistance:
   R = V²/P = 5²/4.65 ≈ 5.38Ω
2. For 3mm (approx. 8 AWG) Nichrome wire with 0.15 Ω/m resistance:
   Length = 5.38Ω / (0.15 Ω/m) ≈ 35.87 cm

Does the calculation have merit?

 

[James]

how many watts required will depend on how fast you want to heat the water.
total required assuming zero losses is 2.33Wh

if you are happy to wait an hour then 2.33W will suffice (0.466A at 5v)
if you want it done in 1 second then 8.388Kw is required (1678A at 5v)

 

[davesparks]

As long as the heat input is greater than the heat losses from the container and the resistance is sufficient to limit the current to no more than 2A the wire could be any length.