I've started riding my bike to work some, and I'm enjoying it immensely. One part that I hate is having to pull the battery pack for my light every night and recharge it, and the cost of built-in dynamo hubs is a little frightening. I've found a 12 volt AC, 6 watt dynamo that is driven by the back tire for $20 on Amazon, but my light needs 5v DC. I also need to make the power to the light constant. The dynamo gives nothing while stopped, and the light will shut off, forcing me to turn it on every time I ride away from a traffic light. Since I fabbed a neat little mount that put the light over the front tire, that's not an option. I'm hoping I can wire in the existing battery pack so the dynamo charges it continuously, and the battery pack drives the light without dead spots. So, all you low voltage experts, take a look and let me know what you think:
I'm not an electrical engineer but I did stay at a Holiday Inn last night and I think maybe it might work.
The danger of your circuit is that you overcharge the NiMH battery with all your manly coasting downhill :) . You need a smart charging circuit in there and that is a lot of soldering. The easy way is to buy a small 12v smart charger for $14 off amazon and patch it in between the rectifier and the battery.
I'm also assuming you left out the discreet comps (caps, resistors, etc) to feed the Vreg and so on... to simplify the drawing.
In reply to Giant Purple Snorklewacker:
yeah, overcharging is my main concern. 12v smart charger you say....
As for the other stuff...assume nothing. I'm a chemist that occasionally wires stuff. What am I missing?
Okay, so doing some more web-mining I came up with this:
In my case the transformer is replaced by the dynamo. It looks like all I was missing was a smoothing capacitor.
the 12v charger may be an issue since the voltage regulator will drop it to 5 V. Using the LM78 type voltage regulator also means the most I can get out of 12v AC is about 10v regulated DC. What I need is a cheap chinese USB-powered charger for AA batteries....off to Amazon...
Don't know how much the tire driven generators have improved in recent years, but they were fantastic brakes back when I was a kid. The drag they produced was tremendous. You might want to check on that for the unit your looking at.
RossD
PowerDork
4/22/14 3:27 p.m.
What about a small solar panel and some rechargeable AA?
You want a cap at about .33uF across the rectified output (between LM780x) input and GND and something around .1uF between the Vreg output and GND ala
I'd be inclined to hook up your dynamo and the battery pack both up to the light through a pair of auctioneering diodes. Set up the dynamo through an adjustable regulator to be just a bit higher voltage than the battery pack.
That way the dynamo isn't trying to charge the battery, just run the lights, but if dynamo voltage drops the light will be automatically supplied by the battery pack. Considerably less circuitry and less chance of frying the battery pack.
