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My Turbines

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John-Som:
If I were you John I would definitely wear wellies and stand on a rubber mat next time you take it to max revs. On the other hand you could consider selling the surplus back to the national grid ?

JohnS

bogstandard:
John,

Selling back to the national grid mmmmmmmmm, don't know about that, 240 volts running a 2HP compressor = ££££'s against mini turbine giving out about 24v DC = naff all, sums don't quite add up. Maybe I could patent it as a super ungreen machine.

Reminds me of another type of machine - The Irishman.






A simple machine for turning Guinness into urine.



Bogtrotter

Look it up to find the meaning

Chris_b:
Re your leds...

If you're happy to have a separate battery involved (eg a PP3), then there's a magic chip the LM3914 that will measure a voltage and switch on up to 10 leds as the voltage rises (could also do the buzzer). Maplin say they keep them in their shops and you could solder it on to a scrap of veroboard and have the whole thing done in an hour. I could scribble you a circuit if you give me a bit more detail on the number of leds and the range of voltages that your turbo-generators produce

If you want the only source of power to be the generator then it's a bit harder. As Darren correctly observes, you need resistors to limit the current. Also some other trickery to make the leds come on as the voltage rises. Easiest would be to put a resistor and a zener diode (which is a special diode that require a set voltage across it before it starts to pass current) in series with each led. You can get zeners with a range of turn-on voltages, though they aren't in nice steps and Maplin don't sell them.

So the LM3914 route is probably best, not least because you can easily change the range it works over. What do you think?

Chris

bogstandard:
Chris,

For my way of thinking, a battery would not be acceptable. I am trying to physically show what is being generated not a measurement of it.

I think I might go for small incandescents in series, they can start off dim and grow brighter as it comes up to speed. As you know LED's also have a slight voltage range, a much smaller range than incandescent, and that is how I did it last time. They all started dim, and grew brighter. Just that I didn't have enough in series to cope with the extra voltage produced, and they went over their limit and committed suicide.

But please, do show us a sketch of the battery method, as I am sure Ralph is biting at the bit to see how it is done, and you never know, I might be able to be swayed in that direction.

Many thanks.

Bogs

Chris_b:
I quite agree, too much electronics can certainly spoil the simplicity. Incandescent lamps should be ok; they are a lot more forgiving. Changing led brightness is best done by varying the current through the leds not the voltage across them. That sounds strange but the relationship between voltage you apply across a led and the resulting current that flows is exponential which is why it's easy to blow them up if you're applying a voltage. Controlling the current is particularly hard in the situation you have!

I'll put a circuit together for the LM3914 and post it

Chris

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