Electrical help with lighting system



Greetings all...

I am trying very hard to come up with a powered lighting system for my bike. I just started working the graveyard shift and realized that the crappy bike lights I have are inadequate for my nighttime 15 mile commute. I am planning on using a 12v 7ah battery with (2) 20w headlamps and a .8w led taillight. I have all the lights and battery worked out but I am trying to find some manner of generator or dynamo to charge the battery. I have looked at some of the dynamo hubs and I think that is a good option but I don't think any of those will generate enough power to completely release me from having to charge the battery at night. Could I use (2) 6v dynamos? Maybe both a hub dynamo and bottom bracket dynamo run through some kind of charge controller circuit? If I were to use the above mentioned dynamos what would I have to do to protect the battery? Could I use a solar battery charge regulator? Is that overkill? Could I just use some diodes like has been mentioned here? I like the idea of renewable power. Some of yas seem to be rather knowledgeable on this area and I wanted to get some input since I don't know too much about electrical stuff and circuitry. I appreciate any assistance that anyone might offer. Thanks in advance. :)



Active Member
Local time
6:22 AM
Jan 11, 2008
Mount Vernon, Ohio, USA
about 45 minutes, with 41 watts is 31.5 watt-hour. If you need lights for both directions, 63 W-H

There are essentially 4 approaches you could take.
  1. Dynamo Hub(s)
  2. Extra mag coil/stator
  3. external generator]
  4. Wind or Solar recharge

1: A dynamo hub is 3W at 10mph, apx. 6 W at 20 MPH. That's only 4.5 W-H for your commute each way (9 total.) We'll assume that the ride will be mostly at speed, but even so, a dynamo would come nowhere close to your needs, if you stay with those big honkin' headlights

On the other hand, 2 20W headlamps may be overkill, too. The new 3 watt single-LED bulbs, with good optics, put out a lot of light. MagLite is going that route now, and a mag-lite is awfully bright, and is focusable. I believe that a good hub dynamo has the potential to work, now that LED technology is catching up to conventional bulbs. The key is proper power management. An onboard battery & charger/regulator to store every watt beyond the lighting requirements. I've got my Sturmey-Archer hubbed wheel on the way back from the wheelmaster right now, and I'll be working on this approach shortly. Once I get it working, (or, even if not) I'll report back.

2: You haven't told us what kind of motor you're running, but another approach could be, if there's room, adding another mag pickup coil inside the engine. That way, you could take the white wire & use it as a generator only. No worry about killing the engine if you pull extra juice. But, I don't know if the wiring is heavy enough to support a 40 watt draw. Again, good LEDs could come to the rescue.

If you have a pull start engine, then I'm also looking into the mitsubishi clone engine electric starters that are on some pocket bikes. These starters bolt between the engine and the existing pull start. And, when they're not starting, can be used as 12V generators. I don't know if they can be installed on any of the small pull start engines though. Given the heavy coil size of a starter, there would be no problem with it pumping out enough amperage, for 40 watts of lighting. (Plus, having an electric start would be way cool;)).

3: Another alternative is the use of a small DC motor as a generator. A 1/10th HP DC motor would easily provide the power you need. However, given that we're using such small engines to begin with, and providing 40+ watts of electricity would suck nearly 1/10 HP from your engine, you may be further ahead going with 1 or 2 of the 3W LED lamps, and then a 20th HP motor would generate more than enough power. (or front and rear hub dynamos.)

4: Finally, you have the green recharge option. I won't go into the wind option - there are plans and packages for small wind turbines that could do the trick, but the expense would be more than you would probably want to spend. If you set up a solar charge, you would need to restore 70 W-H or so, over the course of a day. Assuming 8 hours of charge time, you would need a little less than 10 watts. If you are located in the desert, you can be pretty much assured of sunny skies, so you could get by with a 10 watt solar panel. However, if you're located in the pacific northwest, you can be assured of clouds & rain a good deal of the time. So, you would need to go with at least double that, or maybe even triple. For most of the country, I would suggest a 20 watt panel, to account for inclement weather.

In order to avoid overcharging the battery, which tends to boil away the electrolyte, you will need a solar panel charger - the one you've linked would work.

Keep in mind that if you limit the wattage requirements with the hi-power LED lighting, you can reduce these requirements substantially.


Ok... I have a Grubee SKyhawk 2 with a Hua Sheng (chinese honda gxh 50 clone) 49cc motor. You can see it here. I would love an electric starter if anyone knows of one that will fit on my engine. I saw some were using an electric motor as a generator to generate power for lighting but I am without a welder to be able to install something like that at present. I would have no problem using an LED bulb instead of the halogen to reduce the power I need but I need to know where to get something comparable. I just want something bright so I can see where I am going and big, heavy cars can see me before they run over my poor mangled corpse. I like the looks and mountability of those specific lights and I can probably use an LED replacement for the bulb. I will work on finding a lower power LED solution but I still need to know about the regeneration of the power. If I can get the power down to say 10 watts, is it feasible to use the 2 dynamos running through a solar charge regulator to power everything while I'm riding? Please let me know your thoughts folks. Thanks!


Ok I believe I have found a suitable LED replacement bulb for my headlight. My only problem is that as this is a JC Whitney light, there is little to no specs or information listed with it that would allow me to make sure I am getting something that will fit or work. I suppose I could just use the outer shell of the light with an mr16 light socket to fit the bulb but I'm not even sure if the darn thing will fit. I guess old Mr. Whitney doesn't want folks buying replacement bulbs from anyone else. In any case I found a 3w 240 lumen led bulb that claims to be comparable to a 40-50w Halogen. My only problem is that these are designed for use in track lighting or display cases and I'm not sure how well that translates into bike lighting. They come in a 15 degree viewing angle which is similar to most bike lights I have seen but I am still unsure if this will work. It's a shame I'll have to spend $30 to find out. Blah... :-/


Ok I believe I have found a solution to my problem. I think I am going to give up on the JC Whitney light (even though they look really nice) in favor of a homebrew solution. Check it out here. This is a cheaper setup and has the potential to look really nice if I do the job correctly. Also, I bought one of these led lights to try out with this setup. If anyone is interested in some cheap lights for their bike this is a good solution. I'll post once I receive my parts and get everything together. Also, with this lighting setup I have reduced power enough to charge the battery and power everything indefinitely with 2 dynamos and a charge controller circuit. I am starting off with one light and if this one works out well I will make another and move forward with my charging setup.