A strong rider can put out 60v or more from the motor, and you're going to have to drop that down before you can charge a buffer battery. This means a voltage regulator - and since the A. the potential voltage is so high, B. The potential voltage is so low, and C. lithium batteries require precise input voltage, it's going to require an extra special voltage regulator.
We have just such an amazing regulator that unfortunately we don't sell separately from our bike A similar regulator is sold here here. It is the absolute best solution but it's going to cost you.
This regulator also does the job, but in testing it doesn't work quite as well. It doesn't seem to make the generator "grab" as strongly, so you have to get unrealistically high RPMs to generate the energy you need. There may be a way to fix that, but we just went with the better regulators. If anyone can explain why these regulators work differently, I would love to hear it.
Here you can see the motor mounted on the left side of the rear wheel. That means we're running the motor in reverse and need to reverse the polarity. If you look closely black is wired to red and red to black on the voltage regulator to compensate.
The regulator is then going to feed into the batteries via to 12v female cigarette ports. The batteries will then run the equipment.
Two 12V ports here coming out of the regulator. They will actually be putting out 14.1V, just above the minimum charge voltage of the Sherpas (14V).
The reason for having a battery is to provide a buffer so when someone stops pedaling the electricity doesn't suddenly cut out. We do events for cities and whatnot so it's mission critical that the "show must go on" - therefore we bring enough battery power for the entire event, and hope to leave again with full batteries.
Others may prefer to have the event stop if the audience isn't generating the electricity, to further drive home the concept.
We use two Goal Zero Sherpa 100 lithium batteries. Why lithium? Because it's lightweight and energy dense. Other bicycle generator designs online use lead acid, which is simpler to charge but weighs a ton and wears out fast. That might be an option for you, but for us it's important that the system be as light as possible so we can actually ride with it.
Additionally, the Sherpa 100's offer 2 USB ports, as well as 19v and 12v outputs built right in. You can charge everybody's phone (10 watts each!), run a mini-fridge (okay, you might need two bikes), or whatever you can think of. Our projector requires 19v so... bingo.
The Sherpa 100 batteries will take an input charge of 45 watts each, while our projector pulls over 60 watts. This leaves us at a deficit and it is impossible to charge faster than the battery is being depleted To solve this we use two batteries chained together in order to input 90 watts total into the system. This allows us the rider to stay ahead of the projector. At good events with adult riders, we have arrived with the batteries at 50% and left with them fully charged!
Here is everything put together and on the bike. The generator sits on a hinge so you can pull it off while riding around (unless you want to keep generating electricity, in which case - leave it down by all means!). You can see I upgraded here to a mountable dual 12V port and also added a watt-meter inline.
Here is an early design that we mounted on the rear-rack of a regular bicycle. I showed it here so you can get an idea of different options. It worked quite well and if we had the R&D budget I would build a version of this combined with the rotating rack-stand and make it a stand-alone package that can work on nearly any bike. But, priorities!