# Power Consumption

### DSLR camera (Canon 450D) A Canon 450D DSLR requires a battery rated at 7.4 V 1.080 Ah and a power supply rated at 8.1 V 1.080 A (Note: if no current rating is provided, we could safely assume that it should match the current rating specified in the battery.)

My DSLR camera requires an input voltage of 8.1 V 1.08 A. To compute for the energy consumption, we refer to the formula P = VA, which translates to 8.1 V × 1.08 A = 8.748 watts consumed for every hour (assuming that the device operates at maximum power). Its battery has an output of 7.4 V 1.08 Ah and thus is capable of supplying 7.4 V × 1.08 Ah = 7.99 Wh. This means that if the camera operates at maximum power, it will only have 7.99 Wh ÷  8.748 W = 0.91 hours of battery life. In my case, my camera typically lasts for 4 hours on a typical imaging session. We estimate power rating through indirect proportion: 8.748 W is to 0.91 hours = P : 4 hours. The power rating would be 8.748 W × 0.91 hours ÷ 4 hours = 1.99 W. It means that during a typical imaging session, the DSLR camera only consumes 1.99 watts for every hour.

### Mount

My mount operates at 6 V 1 A. To compute for the energy consumption, we refer to the formula P = VA, which translates to 6 V × 1 A = 6 watts consumed for every hour (my mount always operates at maximum power).

### Dew Heaters

My dew heaters have coils with resistance of 60 ohms for the main scope, 96 ohms for the guidescope, and another 96 ohms for the finderscope. Power dissipated by each coil is computed using the following formula: P = V²/R (where P = power, R = resistance, V = volts ). All these are powered at 12 V (assuming that my heaters operate at maximum power).

Heaters for the main scope: P = 12² volts ÷  60 ohms, P = 2.4 W
Heaters for the guidescope: P = 12² volts  ÷  96 ohms, P = 1.5 W
Heaters for the finderscope: P = 12² volts ÷  96 ohms, P = 1.5 W

To ward off dew, my heaters usually operate at these power levels.

1. Tony says: