Need a simple circuit

[jyl]

In need of a simple electrical circuit.

My bicycle has a generator hub, with two contacts, hot and ground. When riding at 10+ mph, it produces 6 volts AC and will drive two LED headlights wired in parallel. Voltage and frequency are speed dependent. At 7 mph it produces 5 volts, at 5 mph 3 volts. When the bicycle is stationary, such as at a stoplight, the hub produces 0 volts, obviously.

Goal 1: to incorporate a rechargeable battery or super capacitor in the circuit, so that one (or if possible both) of the lights will stay illuminated for a few minutes when the bicycle is stationary.

Goal 2: to switch power from both lights to only one light, when the hub voltage drops below 5 volts, then to switch power back to both lights, when hub voltage rises above 5 volts.

Goal 3: to do this with common electrical components, all analog stuff, that even I can solder together.

Goal 4: to fit this all in a very small, weatherproof box (ideally about Altoid tin size) that can be mounted to the underside of my front rack.

Any ideas?

[rick-l]

Cannibalize a solar light add a rectifier and use the battery/battery protection included?

[jyl]

But what about goal 2 then?

[rick-l]

When the battery voltage drops the protection circuit will shut it all down.

[quint22cp]

Hi John,

This will do what you want but you have left out some information that I have had to make a guess at.

For C1 you can use a large electrolytic cap'. The bigger the cap' the longer the light stays on. As I don't know what light you are using I can't say how long. A super cap is better, but more expensive and they are relatively low voltage devices (usually 3.3V or 5V) If you apply more voltage then they will fail.

It works like this. The variable a.c. voltage from you generator (alternator) gets rectified into a variable voltage d.c. and this lights LED D2. When the voltage is higher, the +ve input of the comparator (LM311) is > -ve and the output is HI turning on the MOSFET Q1 and so the second LED light.

regards
Pete

[Hugh R]

You sure the generator produces AC, not DC? If AC I'd think the hertz would be dependent on hub speed.

[rick-l]

Originally Posted by Hugh R

You sure the generator produces AC, not DC? If AC I'd think the hertz would be dependent on hub speed.

The frequency is dependent on speed. It gets rectified to DC before the LEDs


Now you need to measure the voltage across the LEDs and the current through them (or a part number). Is there a current limiting resistor?

[jyl]

I don't have the LEDs in hand yet. They are supposedly designed for 6 volts and are advertised to have over voltage protection built in. Ordering them from the UK . . .

[rick-l]

I was thinking more along the line of a battery that you charge as you ride to cover slow moments.

If you use this all you would have to add is a way to limit charge to Capacity/5 (if you knew the alternator output) and a current limit resistor to the LEDs (if you knew what they were). It will shut off when fully charged and discharged. Look at the schematic on page 9 of the data sheet. This is to keep it from catching fire

MIKROE-1120 MikroElektronika | Mouser

[intakexhaust]

Take the guts out of a portable / emergency weather radio with LED flashlight, USB charger, etc. Powered by choice of generator, battery + ac/dc transformer.

Find them $15.

[Hugh R]

Originally Posted by rick-l

The frequency is dependent on speed. It gets rectified to DC before the LEDs


Now you need to measure the voltage across the LEDs and the current through them (or a part number). Is there a current limiting resistor?

Bikes have come along way, when I was a kid 50 years ago, they were DC generators that were powered by a little wheel that rubbed against the tire. I guess with today's electronics, an alternator makes a lot of sense.

[rick-l]

Originally Posted by Hugh R

Bikes have come along way, when I was a kid 50 years ago, they were DC generators that were powered by a little wheel that rubbed against the tire. I guess with today's electronics, an alternator makes a lot of sense.

That little silver thing you clicked against the rear tire may have been just a magnet spinning in a coil of wire i.e. an alternator. An incandescent bulb would not care.

[herr_oberst]

Originally Posted by rick-l

An incandescent bulb would not care.

Nor would it try very hard, ha ha! I remember those things being weak as kittens, no matter how hard I pedaled!

[rick-l]

Originally Posted by intakexhaust

Take the guts out of a portable / emergency weather radio with LED flashlight, USB charger, etc. Powered by choice of generator, battery + ac/dc transformer.

Find them $15.

The DW01, the FS8205 and the battery (click the battery data sheet from the Mouser website) are the main parts your after.

DW01 protection circuit https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwi6wOGMnvvMAhWG6CYKHRF-B6oQFggcMAA&url=https%3A%2F%2Fcdn.sparkfun.com%2Fassets%2Flear n_tutorials%2F2%2F5%2F1%2FDW01-P_DataSheet_V10.pdf&usg=AFQjCNESLW0teltQjoOZY1_fWnENDIKgug&sig2=VIkgEFUTMehVDmcZRGEtkA&cad=rja



Dual MOSFET https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwjqyfSZn_vMAhXLpYMKHffUDXYQFggcMAA&url=http%3A%2F%2Fwww.ic-fortune.com%2Fupload%2FDownload%2FFS8205A-DS-12_EN.pdf&usg=AFQjCNGVY7D-BO_HpylsuyYqepFWqa_95g&sig2=kt1apzIxXGLLise6XZB8wg&bvm=bv.122676328,d.eWE&cad=rja

Of course an estimate of how much power you need and how much is available would help also.