When I'm busy in work, I forget about my coffee continue with my work. After sometime It becomes cold and I use to go with it.
So I made a Coffee cup warmer which maintains the Coffee temperature and the temperature is also controllable using Android App. In some circumstances I need to make coffee while travelling so I added Battery to it to make Coffee on the go. I can also make Tea, Hot water, Hot milk with it.
While Washing the Coffee heater cup I found small holes in the battery charge connector plug which may allows water to pass through and damage the circuit. So added IDT wireless charger to make it waterproof.
Total power = V*I = 5*0.961 = 4.8 watts (u will get 45 C)
After connecting 5.2 ohm to 5 volt supply u can feel warm around the resistor. USE 2 watts Resistor... I used 1/2 watts and burnt it.
If you want to produce more heat then use 2 amp power bank and change the resistor to 2.7 Ohms (power = 10watts).
For uniform heating of coffee cup, I used two resistor on each sides.
So connect two 10 ohm Resistors in parallel to make 5 ohm like shown in the image.
Attach the Resistor to the Coffee Cup and apply Thermal Paste.
Open the Power bank carefully you will find battery and DC-DC converter. You can also use the powerbank directly without opening it, but I did this to reduce the size.
Now test the Coffee cup by connecting two ends of the Resistor wires to Powerbank output through USB cable. You can feel the increase in temperature and connect IDT wireless Receiver to the Powerbank input. Now the battery can be charged using Wireless receiver. Now add a transistor switch (TIP 29) in between the powerbank output and resistors I.e cut the usb cable +vcc wire and attach collector of transistor to one end and emitter to other end of the cable so that the heater can be controlled by transistor base voltage.
Prepare the case for coffee cup, I used a Flask and attach the wireless receiver to the bottom of the case.
Stick the wireless Receiver to the bottom of the case and Connect powerbank to it.