Electronics > Power/Renewable Energy/EV's

Micro wind turbine from a fan

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Got a fan from a dismantled external AC unit and I want to make a wind turbine!
Call me crazy and you'll be completely correct!  :-DD I understand this thing will never produce large amounts of energy and that is fine. My goal is more to experiment, not to make any form of money or reduce the electric bill.

Let's say I want to charge a small lead-acid battery or Li-Ion cells, Where to start? A rectifier and a buck converter?

The motor on the fan is a single phase 230V/50Hz/60W unit. I know this thing wil never generate that much, but even 1 or 2 Watt is good enough to play with.

You can't generate from a synchronous AC motor, you need either a permanent magnet DC motor or an alternator of some type.


--- Quote from: dr.diesel on September 10, 2017, 12:41:57 pm ---You can't generate from a synchronous AC motor, you need either a permanent magnet DC motor or an alternator of some type.

--- End quote ---

That statement isn't strictly true in general*, but it's certainly true that if you read those instruction with "wind power" as your proposed source of power; it's very clear that wind turbine + inductor motor as generator is a completely hopeless combination; the lack of regulation of rotational speed and lack of connection to the grid are difficult challenges to solve. As you say, much easier to get a permanent magnet DC motor or alternator.

* And yes I know I'm conflating synchronous AC motors with induction motors here; but I'm pretty sure the OP's motor will be an induction motor and a synchronous motor is more suitable for conversion to a generator in any case anyway?

It probably uses a permanent-split capacitor induction motor.  There is no practical way of converting it for DC output as you cant get the rotor to reliably generate its own magnetic field.   

An induction motor *CAN* be run as a generator, but to do so you generally have to run it above synchronous speed while connected to an existing mains frequency AC source.  There are some tricks for standalone generation involving resonating the windings with a capacitor and *hoping* residual magnetism in the rotor provides enough of a kick to start it off, but such arrangements must be run up to speed before any load is applied, and tend not to produce any usable output below a threshold speed that's a significant fraction of the nameplate speed. Its existing fan blades wont spin it fast enough in anything less than a hurricane.

If you do get it to generate, it will typically output AC of between 50% and 110% of the nominal motor voltage depending on speed, and the best option for your application would be a universal input, low power, current limited SMPSU, either set to 13.8V for Lead acid or feeding a LiPO charger.  You may need to mod the SMPSU to increase its input DC bus reservoir capacitance and add a holdoff circuit to its startup circuit to prevent the high startup surge collapsing the generator output.

Thanks for this information. I understand it has to rotate at its nominal speed + some prior to being capable of generating anything useful. Unfortunately that will not happen often on a standard day without Irma.
Chances are that fan will end up as... well... a fan


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