Generator circuit question

[axolotl]

Suppose you had several different devices being directly powered by the same manually cranked or pedaled (or wind blown, etc...) DC generator.

For a simple example- not an actual project- say you have 5 10-watt lightbulbs , and the generator can put out anything from 0-50 watts depending on how fast it is spinning.

:idea: :idea: :idea: :idea: :idea:
If you start spinning the wheel faster and faster- I want to make it light only the first lamp until it gets to 10W, and then keep the first lamp's power limited there (so the first lamp doesn't blow out) and start lighting up the second lamp, until it's at 20 watts and both are fully lit, then start lighting the third...

This is either a very simple circuit, or nearly impossible to do- but I'm pretty sure I have seen a demo like my example.

[MikeVDS]

Hmm. I don't know if it can be done with the basic components of a circuit but if you're willing to use a computer and spend a little money, it becomes trivial. Considering you're using wind power and it's less trivial to find low energy consuming chips that will do the job I don't think I'm of much help. Hopefully someone comes along with a simple answer. I will keep thinking about it and ask a friend who'll put some brain power into it since it is a fun little exercise to figure this one out.

[Tiahaar]

hmmm also...what you'd like would be a schematic of a working circuit but my knowledge just extends to knowing something of the theory behind using transistors and feedbacks, I'm way too rusty to design the darn thing. If you are electronically inclined, this is a fun little read: http://en.wikipedia.org/wiki/Current_limiting

Seems a multiple LED power meter could be hacked to make it do what you want? Instead of the appropriate LED it feeds a transistor that gates power over to the 10w lamp for instance.

Be curious to see what your friend turns up Mike VDS.

[spectabillis]

Seems a multiple LED power meter could be hacked to make it do what you want? Instead of the appropriate LED it feeds a transistor that gates power over to the 10w lamp for instance.

would be my lazy approach, except have it wired to a cheap microcontroller board with several relays.

[Zhust]

I want to make it light only the first lamp until it gets to 10W, and then keep the first lamp's power limited there (so the first lamp doesn't blow out) and start lighting up the second lamp, until it's at 20 watts and both are fully lit, then start lighting the third...

Here's the rub: power is voltage times current. So assuming you have some number of lights, you need to measure the voltage output of the generator and the current output and multiply them together. There are analog multipliers, but it would be cheaper to go with a microcontroller and have it do the calculations.

If you want to cheat, you can just have the generator output go to a dummy load -- a heavy-duty resistor. Since the current through a resistor is the voltage across it divided by its resistance (V/R) and the power through a circuit is the current times the voltage, the power in a resistor is V^2/R. Thus, with a 1-ohm resistor, 1 volt across it is 1 watt, 2 volts is 4 watts, 3 volts is 9 watts, etc. Then it's just a matter of lighting an indicator if V>1V for 1 watt, V>sqrt(2) for 2 watts, V>sqrt(3) for 3 watts, etc. This could be done with a voltage regulator, comparators and LED's -- the power consumption of such a circuit would be far less than what you're measuring.

It's possible to do it with large lightbulbs -- 10-watt bulbs, for instance. The thing is, as you add another lightbulb in series, the resistance drops so the voltage increases so your measurement changes -- ack! A microcontroller might just be the best option.

[dragonfly Jafe]

....what about using one of those speaker LED power indicator kits you can buy, such as this one on Ebay;

http://cgi.ebay.com/Velleman-K4307-Audi ... dZViewItem

If that LED isn't big enough, maybe you could hack the leads to power micro relays or something...

[MikeVDS]

For this I'm assuming voltage will remain "constant" and the current will vary with shaft speed. Is that a good assumption for your purposes or is something else going on? Also you give what seems like a simplified version of what you really want and no details (voltage of the outputs, inputs, current range). The solution to this is not going to be a simple circuit with resistors and capacitors. Things can be designed to do what you want but I assume you'll also want to use parts that currently exist. People could come up with 100 solutions but if for example your system is a strange voltage, components that you need which people suggest may not be manufactured.

[Dork]

This was a pretty common thing to have in science centers for kids to play on. The harder you ride, the more lights come on. I remember there being one at the Pacific Science Center in Seattle in the 80's.

[Tiahaar]

For this I'm assuming voltage will remain "constant" and the current will vary with shaft speed. Is that a good assumption for your purposes or is something else going on?

Ah! You could hold the voltage to that of a battery connected to the generator and then the surplus current that the battery doesn't accept would go to the lights. Big homebuilt wind generators use a bank of lights or heaters to dump excess current into much like this. Having the bulbs light in sequence still will take semiconductors/microcontrollers as has been suggested...heh maybe Heathkit used to make a thing for doing this : )

On my small wind gen there's an amp meter and volt meter with a blocking diode to the battery bank with its own volt meter. As the wind gen begins to turn its voltage increases but with no amps showing...until the voltage gets above what the battery voltage shows. With higher wind the gen might be reading >15volts, flowing +4 amps say, and the battery bank voltage starts creeping up from @ 12-13 volts.

[spectabillis]

re: microcontroller

ironic that i mentioned it because i am lazy and its the only thing i can think of, but like the tiahorse suggested i bet there is a diy kit somewhere that does this.