How to Make a Bicycle Generator That Only Powers a DVD Player and Projector While Pedaling

I am a mechanical engineer by trade, a wannabe artist by hobby, and a complete electrical novice. That said, I was hoping the community might have some thoughts about whether an art project I have in mind would be feasible to put together for a novice with time and energy on his hands:

I would like to put together an art project which would use bicycle-generated power to run a pico projector and portable DVD player. The bare bones of that seems simple: several manufacturers supply pre-packaged bike DC generator systems equipped with power pack inverter/battery combos, which the projector and DVD player could be powered from.

The part I'm unsure of is: The concept would be that the video (the "art" side of the project) would only play when the bike is being pedaled, or for a preset time period after the pedaling ceases. This would serve two purposes: prevent the battery from being consistently drained and damaged by a constant load from the electronics, and fit with the alternative energy theme/message of the project. I think this would require some sort of control loop involving all the components of the system, but I have no idea where to start.

I would greatly appreciate any thoughts, advice, examples of similar projects, suggestions of websites/literature to read up on, products to look into, or companies to contact. Thanks very much for your time!

I'm not familiar with the "pre-packaged bike DC generator systems" you cite, but it seems to me they would include battery management, and thus would prevent deep discharge. Also, if the system is designed properly, the battery will be such that it can survive whatever power cycling (no pun intended it would be subjected to in typical use. But, then, the manufacturer's definition of "typical use" may not apply to your application, so something to consider.

Another possible concern might be power glitches to the DVD player. But, I did a little reading on the Pico Projector, and (at least the one I looked at--the Pico Pocket Projector), it can store videos in it's own memory or on an SD card, so you probably don't even need the DVD player.

Another problem might be getting it to display the video on start up (without the need to queue it up or hit a "Play" button). If it can be put into some sort of "Kiosk" mode, that might do it.

If the Kiosk mode can be achieved, then I would remove the battery and use the Power Adaptor input, but instead of using the power adaptor, fashion a cable that supplies power via a capacitor. The size of the capacitor will be determined by the amount of power the Pico Projector uses (might need a super cap). That way, there is no worries about deep cycling a battery, and you can control how long the video plays after they stop pedaling. Perhaps you could jury-rig the existing power adaptor by adding the capacitor in parallel. You could also take advantage of the low voltage input and avoid the inverter (on the bicycle generation system) altogether.

Steve - I appreciate the reply, that's a lot of good info. It may take me a while to digest and consider this, but I hope you don't mind if I get back to you in a couple days with some further questions. Thanks for your help,

--Dan

Better if you ask the forum -- I don't, necessarily, have all the answers ;)

And, if your question is specific enough to warrant a new thread, by all means...

Rule of thumb: the more exposure your question gets, the more likely you are to get an answer. And, consider that the only eyes on new questions in this thread, are those of the ones who have responded so far--and, of course, you. As of this writing, that would be you and me ;)

Also, specific questions are more likely to get a response. Broad questions, like "how do I make a beanie propeller spin?" are less likely to be covered than a question like: "Would it be better to drive a beanie prop motor with a MOSFET or with a bipolar transistor?"

The simplest solution I have in mind consists of a small relay and a diode.

The generator powers the relay coil. The relay connects/disconnects the projector from the battery. The diode isolates the generator/relay coil node from the battery. The relay is a NO (normally open) type.

Operation:
When the generator is not turning the relay coil is not energized and the relay does not connect the battery to the projector. When the generator is turning the relay coil is energized and the relay connects the battery to the projector.

Comments:
The relay will pull-in before the generator voltage is high enough to charge the battery. If someone does not spin the generator fast enough the battery will not charge yet it will discharge into the projector.

how do these things work ? do they use a bright led for backlite projection through an lcd screen ?
if so wouldnt just using the cycle to power the back light be a better option ? then no re-booting or pressing playback would be required.
just a thought

There are "off the shelf" items that can function to do all the things you require. I would suggest a small automotive alternator. Most car alternators (one wire) have bulit in voltage regulators and it has the mount and pulley where belt drive can used to drive it from a pulley placed at the rear axle. That way you retain the gearing of the sprockets and it will allow you to choose a comfortable speed. The alternator requires the use of a battery. From the battery you can go straight to a small pure sine wave inverter. Make sure the alternator, battery and inverter all have the same voltage rating and the inverter has a large enough watt rating to run the devices you intend to run. To be sure to add the load items up and add at least 25% to be sure your inverter can handle the load. DO NOT overload the inverter. Most small inverters will be permanently damaged if overloaded. More expensive models have larger outputs and overload protection. I think your hardest part will be to adapt the rear axle to drive a pulley. A machinist with a lathe could turn one out in a short time or you may be able to use a smaller diameter wheel and belt around the outer rim. You should also fuse the power coming off the battery as close to the battery as possible. A switch to turn the ac power off/on If you already have the bike the rest of it could be done for under $500 with new parts. The best part of this is the voltage regulator will prevent backflow from the battery to alternator and prevent overcharging the battery. Depending on the inverter you could also have computer output for an instant indication of power output. Since you are already using automotive components you could use auto gauges on the dc side, all depends how fancy you want to get