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There are several ways:
* The easiest way is just to use a transformer to step down main voltage.
* you could use your PC sound card and an audio amplifier...
* you could use a programmable alternator and a transformer
* you could use an synchronous AC generator with excitation winding.
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the input power is a blower.
frequency 50 hz or more , no problem it will be rectified.
No problem, I think that the synchronous ac generator with excitation winding is a good idea, but where can i find an ac Generator or alternator of 10 w to 20 w 18v per example .
Ah, now i see, you want a generator as power supply....
I misunderstood, sorry.
You rectify... is DC also possible? With a brushed DC motor?
yes, 10..20W AC with excitation will be hard to find. Generators for bicycles will have permanent magnet. Wind generators have much more power rating...
Stepper motors have permanent magnets...
Building yourself ... but is it worth the effort for 10...20W?
Other power source? Solar panel? Water?
The only place which generates AC at this power level is the mag generator found in some small motor bikes, or used to be found! My Honda C50 step through had DC indicators and brake lights but AC headlights. The problem is the generator is built inside the flywheel which is within the engine housing. So get a scrapped engine and remove everything that is not used for the generator.
Frank
You should tell us... Till now you never spoke about size.
There will be many different DC motors with about 10W available.
But i don´t know if they all can be used as generator.