How to Build a Bicycle Generator With 24V 250W DC Motor to Compare LED vs Incandescent Bulbs

Hello,
I'm building a bicycle generator that will be used to power and test the energy usage difference in incandescent light bulbs vs LED light bulbs for my son's 5th grade science experiment. I've found some plans online that involve a 24v 250w dc scooter motor, a 12v 18aH battery, 20 amp 300w charger, zener diode and 12v (input) 110v (output) 400 watt inverter.

What I want is an end product where a person can pedal the bike and see the energy difference in the light bulbs as they pedal (ie the incandescents will flicker and require heavy pedaling, the LED's will be constant and require light pedaling). Here is a link to YouTube video with essentially the same thing:
https://www.youtube.com/watch?v=o1Z7GERQniI

So basically as you pedal the bike, the rear wheel is connected via belt to the motor, which is then connected to the battery and charger and finally the inverter. I believe this is so because the intended use for the bike generator is to supply electricity during an outage, but that is not what I want to use it for. In order to get the desired affect I want, can i connect the 24v motor directly to the 12v (input) inverter (ie bypass the battery and charger)? I will likely have 3-4 60w bulbs plugged in to the inverter (ie 4 incandescents, then I'll unplug those and plug in 4 LED's). My concern is that the motor can generate up to 24 volts but the inverter can only input up to 15.

Thanks for the help!!!
Brian

Hi Brian.

First off, on the DC motor. Since you'll be using it as a generator, then its output voltage will range from 0 to 24V at maximum pedalling/rotating speed.

Caveman solution (faster but risky):
If you have a voltmeter, you can test the maximum voltage yield of the motor-turned-generator when your son is pedalling at max speed just to be safe.

The "I-have-to-buy-something" solution (safer but slower):
You can use a voltage divider circuit to be truly safe (2 resistors in series, 1 end of the resistor at motor output, the middle node connected to the inverter input). Any value will do as long as the rated power isn't exceeded. With 1 Watt resistors, two 500 ohm resistors will do.



Note (if you can't do any of the solutions above):

The battery and charger doesn't have any rectifying/clipping effect but I do not recommend removing them because sinked current (due to the battery) is taken care of by the charger block (notice the really high ampere and wattage rating of the charger). I do not know how the battery and charger will be connected so this is the best insight I can give.

Hope this helps in some way.

Regards,
Justin

Thanks for the reply. Here is a link to the build and equipment:

http://www.instructables.com/id/How-to-Build-a-Bicycle-Generator-1/

Based off this. If I test max pedal speed as suggested above and don't get more than 15v, can i go straight from the motor to the inverter?

Thank you!