Micro wind turbine from a fan - Page 1
Forum section: electronics / general

author: Swake
author_rank: Frequent Contributor
timestamp: September 10, 2017, 12:28:39 pm
content: 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!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.

author: dr.diesel
author_rank: Super Contributor
timestamp: September 10, 2017, 12:41:57 pm
content: You can't generate from a synchronous AC motor, you need either a permanent magnet DC motor or an alternator of some type.

author: rs20
author_rank: Super Contributor
timestamp: September 10, 2017, 12:49:24 pm
content: Quote from: dr.diesel on September 10, 2017, 12:41:57 pmThat 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 generatoris 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?

author: Ian.M
author_rank: Super Contributor
timestamp: September 10, 2017, 01:04:23 pm
content: It probably uses apermanent-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.

author: Swake
author_rank: Frequent Contributor
timestamp: September 10, 2017, 03:38:14 pm
content: 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

author: SeanB
author_rank: Super Contributor
timestamp: September 10, 2017, 06:24:25 pm
content: If you have the indoor unit look there, many use a BLDC motor, especially Daiken, and those run at 36VDC with a built in inverter. You then can use the windings and the magnet to build a small 36VAC 3 phase supply, and use a buck converter to drop it to charge the battery.

author: krystian
author_rank: Contributor
timestamp: September 12, 2017, 12:44:22 pm
content: You can use 3 phase asynchronous motor as a generator without modifications. It's called self-excited asynchronous generator, i dont remember principle of its operation but I've seen it once. Self excitation was created using capacitors, something like LC resonant circuit. But it's not very practical.You can modify electric motor by placing permament magnets on the rotor. People are doing it in the internet. But it's not an easy solution.You could use for example alternator from a car, connect it to your fan blades through some gears. I dont think that the wind will be strong enough to spin it quickly enough for alternator to start working without gears.

author: Codebird
author_rank: Regular Contributor
timestamp: September 16, 2017, 08:40:05 am
content: Most types of alternator, including those which can be made from a repurposed or minimally-modified motor, operate properly only at high rotational speed. Wind turbines are high-torque, low-speed devices. This is a problem. There are few motors which can be used as generators at wind turbine speeds, so you only have three options:1. Replace the motor with a low-speed-optimised alternator.2. If your mechanical engineering it up to it, use gears to speed the rotation up.3. Modify the existing motor.You probably want to reuse the existing motor, because it already has all the mechanical fittings and bearings and fits in the mounting nicely. In which case, you need to modify it. I'm sure the community here can help you, but we need to know a bit more about it first - exactly what sort of motor are we looking at here? Can you give a model number or photos? Brushed or brushless?This is going to involve a bit of mechanical skill, as well as electronics.I have practical experience with automotive alternators, and can confirm that they cannot work at wind-turbine-friendly speeds. They like to spin fast. You can rebuild the electronics and maybe halve the required speed, but that's still too fast.

author: Simon
author_rank: Unknown
timestamp: September 16, 2017, 07:45:41 pm
content: I don't think a fan will work very well as a wind turbine, I'm sure the impeller design is different. Your best bet it to find a suitable generator and a suitable impeller and combine them.

author: Audioguru
author_rank: Super Contributor
timestamp: September 17, 2017, 12:57:01 pm
content: Please do not try to charge a lithium ion battery without a proper battery charger circuit and knowledge of how it prevents an explosion and fire.

author: Nauris
author_rank: Regular Contributor
timestamp: October 08, 2017, 07:40:45 pm
content: Quote from: Swake on September 10, 2017, 12:28:39 pmOne of those things I would make if I had more free time. Would make nice garden light.Using that type of motor as wind generator is a quite bit more complicated than just a rectifier but certainly doable.You get the idea if you think running AC motor with variable frequency drive in braking mode and taking power out from the DC-bus.So basically you need three-phase bridge that you run a bit slower than the fan rotates to generate proper magnetization. That's the basic idea, then you just need some nice alghoritm to decide what is the optimum speed for the fan to rotate at in varying wind speeds.

author: brmaustria
author_rank: Newbie
timestamp: October 09, 2017, 04:20:48 pm
content: I am glad to be a part of such forum and important discussion.. Thanks People

author: Simon
author_rank: Unknown
timestamp: October 09, 2017, 04:28:02 pm
content: Quote from: brmaustria on October 09, 2017, 04:20:48 pmAnd you thought you would just drop by to a random topic to announce that as your very first post? consider yourself watched!