What is the best use of your pedaling time on a pedal generator? There are 3 typical avenues you could direct your watts:
- Direct charge: Directly use the watts coming out of your pedal generator, once converted to useful 12 volt current, and charge your devices using car chargers.
- Grid Tie: Use a grid tie inverter to send all your pedaling effort into the nearest wall outlet.
- Battery bank: Charge a bank of lead acid batteries.
There are advantages and disadvantages to each of these.
|Direct charging||Efficient – 90%+ charging efficiency.||You will need to round up enough gadgets to create the appropriate resistance for a good workout.|
|Grid Tie||Directly offsets your utility bill with watts generated.||Grid tie inverters are about 80% efficient in practice. Put in 100Wh from pedaling, only about 80Wh will be put back into the grid.|
|Battery bank||For those living off grid, augmenting their battery bank may be a necessity.||Lead acid battery charge efficiency is only about 85% – so if you put in 100Wh, you only get out 85Wh. Couple this with the efficiency losses of a charge controller and an inverter to get it back out as AC, and you might get 50% of what you put in.|
I advocate for direct charging, and I’ll explain why. Going out on a limb here, but I’ll assume everyone uses a mobile device or two, and maybe a tablet. Assuming you charge these things regularly, let’s look at the scenario of charging these using the methods above.
Pedal generator -> Charge controller (90%+ efficient) -> 12v car charger -> device(s)
Pedal generator -> Grid tie inverter (80% efficient) -> 110VAC wall charger -> device(s)
Pedal generator -> Charge controller (90% efficient) -> Battery bank (85% efficient) -> DC to AC inverter (90% efficient) -> 110VAC wall charger -> Devices(s)
As I discovered in the previous blog post, wall chargers have losses up to 30%+, whereas 2 out of the 3 car chargers tested had losses of just over 1%. Using either grid tie or a battery bank may result in 50% or more of your efforts wasted on conversion losses. I do want to point out that the charge controller used in my pedal charger design is 90%+ efficient, so you will lose up to 10% in that conversion, resulting in a max of about 12% loss if you include the car charger losses – but far better than the other two alternatives!