hi, can anyone suggest a circuit for charging four 1.5 V cells using, say a bicycle dynamo. planning to make a contraption to drive a miniature turbine using power of small waterfalls along trekking routes in mtns. then to use these btys to power LEDs for tentage lighting. thanx.
In your 'walking' shoes I would get "el cheapo" garden lanterns, those with solar panels. When trekking you will have many hours of charging, much easier than carrying an hydroelectic plant on your back. And Ni-Cd's like lllloooonnnnggg slow charging better than massive current short duration.
Just my 2c.
Happy trekking.
Stanislaw Slack user from Ulladulla.
Unless you are going out for a week or more, just loading LED flashlights with alkalines will give you lots of hours of light.
If you want to go solar for cheap, buy a set of those solar yard lights for under $5 each. Remove the stakes and plastic difractor and just keep the top piece with the solar cells, nicads, and led.
Luhan
The mechanical design will probably be more critical than the electronics. So much depends on the velocity and volume of the water, and how much this will be affected by the generator. There will be a peak power point where the most energy can be extracted. As a starting point, design the turbine so that it can spin a small dynamo (DC PM motor) at close to its maximum RPM with no load, and then add loading while checking the power generated. The charger circuit could be designed to do this automatically. I would think this peak power point may be something like half the no load maximum RPM.
The motor (generator) should be sized at about the maximum expected power, so four 1.2 V 1000 A-H NiCads at 0.1C would be about 1/2 watt. This would provide 5 watt-hours of power for tent lighting after ten hours of running. Everything needs to be scaled up to get a faster charge or more power.
A quick approximation of the amount of power obtainable with water power is by using the formula HP = T * RPM / 5252. A waterwheel with pint-sized cups at a radius of 12", spinning at 60 RPM, should generate about 0.01 HP, or
7.5 watts.Paul
A bicycle wheel turns about 200RPM with the dynamo creating a current of maybe 750mA at 1000Hz. Just make a bridge rectifier from 4 1N4002, get some old mechanical timer from a microwave or better kitchen stove and put the 4 batteries in series. Measure the average current with a multimeter and set the timer to 140% of the capacity of the batteries. good to empty them each time to avoid overcharging.
-- ciao Ban Apricale, Italy
Cheers! Rich
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