Exercise Bike Calorie Calculator.

Okay, so I took a stationary bicycle and modified it with a large DC motor from an electric scooter. The motor is rated for 24 volts at 100 watts. When pedaling it is easy to generate 50-150 watts. I put a current sensor and a voltage sensor to monitor the power being used by electric devises attached to the bike. This includes fans, lights, speakers, and measurement tools such as a heart beat sensor. What I am trying to do though is calculate how many calories the user is burning based on the wattage being used. I did some math in the program and I can accurately calculate the power being used and convert that to calories but I can tell its much to low for a stationary bike. I did some googling and consensus says a stationary bike will burn 200+ calories in 30 minutes. I am getting about 20-50 with the pure electricity. I assume that there is inefficiencies in the bike and gearing as well as when a human makes the movement. Is there anyway I can calculate this to make it more accurate? If so how? I know I can measure how much power the motor uses to spin the bike parts.

Thank you guys!

If you know the what the electric motor takes to turn the parts, the human has deliver the same effort. A human is about 25% efficient, so multiply by four.

Cool! This doesn't have to be exact so this is perfect. So if it takes 50 watts to run the parts at 24 volts and I am using say 100 watts of electricity that's 150 watts being used and then times 4 so 600 watts and then convert the 600 watts to calories? Does that sound right?

1 watt = 1 Joule/second
4.184 Joules = 1 calorie
1 food calorie = 1000 calories

You need to factor in the inefficiencies of the human to generator coupling and the motor generator, which are significantly less than 1. As stated above, humans are about 25% efficient at converting calories to mechanical work.