#### Mad-Scientist_In-Training

##### Newbie level 4

Hi;

I am going to build a coffee cup warmer plate using resistors - as an experiment.

Instead of using a USB port from my computer I am going to use a 5V, 700mA cell phone charger.

Using Ohms Law I have calculated that I there will be 7.14\[\Omega\] of resistance so I have ordered 3 x 2.4\[\Omega\] 5W resistors (Yageo - through-hole) and also 3 x .12\[\Omega\] resistors (Yageo - through-hole) in case they are all at the bottom end of the 5% tolerance for each resistor ((3x2.4) + (3x.12) x.95) = 7.182\[\Omega\] ... just slightly larger than the 7.14\[\Omega\] required for the circuit.

I would like to try to determine ahead of time what will be the heat dissipated from the resistors so I can 1) learn how to estimate heating of circuit components, and 2) know if I will need to use a larger or smaller supply (and resistor values).

I have not done any calculus before and I am wondering if someone can assist me with a quick tutorial on how to use the ∫ (integral) symbol to calculate the heat that would be dissipated from resistors.

I have this forumla W= ∫ V(t) I(t) dt ... with a t2 at the top of the ∫ symbol and a t1 at the bottom of the ∫ symbol.

Here's an image of the formula:

The values that I am using are:

5V,

.7A,

7.14\[\Omega\]

100% duty cycle - always on.

Thanks for any assistance.

EDIT: For clarification, I would like to try to determine the temperature that the resistors will achieve.

I am going to build a coffee cup warmer plate using resistors - as an experiment.

Instead of using a USB port from my computer I am going to use a 5V, 700mA cell phone charger.

Using Ohms Law I have calculated that I there will be 7.14\[\Omega\] of resistance so I have ordered 3 x 2.4\[\Omega\] 5W resistors (Yageo - through-hole) and also 3 x .12\[\Omega\] resistors (Yageo - through-hole) in case they are all at the bottom end of the 5% tolerance for each resistor ((3x2.4) + (3x.12) x.95) = 7.182\[\Omega\] ... just slightly larger than the 7.14\[\Omega\] required for the circuit.

I would like to try to determine ahead of time what will be the heat dissipated from the resistors so I can 1) learn how to estimate heating of circuit components, and 2) know if I will need to use a larger or smaller supply (and resistor values).

I have not done any calculus before and I am wondering if someone can assist me with a quick tutorial on how to use the ∫ (integral) symbol to calculate the heat that would be dissipated from resistors.

I have this forumla W= ∫ V(t) I(t) dt ... with a t2 at the top of the ∫ symbol and a t1 at the bottom of the ∫ symbol.

Here's an image of the formula:

The values that I am using are:

5V,

.7A,

7.14\[\Omega\]

100% duty cycle - always on.

Thanks for any assistance.

EDIT: For clarification, I would like to try to determine the temperature that the resistors will achieve.

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