Choosing a wind turbine generator

[alexander424]

I'm doing a school project in which I'm building a wind turbine. The next step for me is to choose a generator but I'm not completely sure what is right for me. I expect to come up to 300 rpm as an average and need the required voltage to for a car battery, which is around 14.4 volt.

My question is one: there is anything else to keep in mind when choosing generator except to meet the voltage requirement.
And second: if something like this for example would work:
https://www.aliexpress.com/item/1PC...-6fdc-44d1-920e-84fb7203cf87&rmStoreLevelAB=0

Best regards.

 

[berkeman]

I'm doing a school project in which I'm building a wind turbine. The next step for me is to choose a generator but I'm not completely sure what is right for me. I expect to come up to 300 rpm as an average and need the required voltage to for a car battery, which is around 14.4 volt.

My question is one: there is anything else to keep in mind when choosing generator except to meet the voltage requirement.
And second: if something like this for example would work:
https://www.aliexpress.com/item/1PC...-6fdc-44d1-920e-84fb7203cf87&rmStoreLevelAB=0

Best regards.

Welcome to the PF.

Be sure to read through the "Similar Discussions" thread list at the bottom of the page. You may be able to get a lot more information to help you by looking over those previous threads first.

Also, what power output level are you targeting? Does it match the input power of the wind and your turbine design?

 

[alexander424]

Welcome to the PF.

Be sure to read through the "Similar Discussions" thread list at the bottom of the page. You may be able to get a lot more information to help you by looking over those previous threads first.

Also, what power output level are you targeting? Does it match the input power of the wind and your turbine design?

I actually haven't taken a look at that, certainly will! Not sure about my power input which indicates I got some reading up to do.
Thanks

 

[sophiecentaur]

My question is one: there is anything else to keep in mind when choosing generator except to meet the voltage requirement.
And second: if something like this for example would work:

Two answers. How much wind do you have available? I used to have a small Rutland (see this link) wind generator and I was very disappointed at the current it would supply at anything but a really good breeze. It was mounted on a short mast on a boat that was moored well out in the open and it rotated to face any wind that there was. But their quoted figure of 1A in a 15 knot wind was very optimistic. Over a week, it just about managed to keep the boat batteries topped up but it was only just adequate. The start battery was always capable of starting a large diesel engine, though. That was a purpose built turbine with an integrated multipole alternator and you will be luck to approach that sort of performance. Thing is, the area of a turbine is really relevant. Big ones (at least several metres across!) are so much better.
The alternator in that advert is a 120V model. Not what you need for 12V battery charging. Many people use permanent magnet model motors and they do work - but only after a fashion. Easy to light small lamps with but not much else, I believe. I find myself always warning people about small Engineering Projects that the actual numbers involved are very important to success or failure. 'Suck it and see' can be a big let down so define what you actually want out of a system and read around as much as you can. There are many articles about projects on the web and you can feed off their efforts. Never just launch out by yourself on a project.

 

[dlgoff]

I find myself always warning people about small Engineering Projects that the actual numbers involved are very important to success or failure.

How much wind do you have available?

Amount of energy is what's important and a good rule of thumb is:

The energy content of the wind varies with the cube (the third power) of the average wind speed.

from http://drømstørre.dk/wp-content/wind/miller/windpower web/en/tour/wres/enrspeed.htm

 

[sophiecentaur]

A few years ago, when you drove around the countryside you would see a number of wind turbines, used as local energy supplies for small remote installations like meteorological stations and for other data logging equipment. I seem to remember some of the old AA Boxes in remote areas of the UK had small turbines, too. Nowadays, PV panels are used on virtually every street for speed warning signs, parking meters etc. etc.. That tells you a lot about the suitability of small scale wind turbine installations, I'm afraid.
This is not to say that you will not get any power out of a self built system but rather that it's all a bit 'knife edge' and you will really need to expect a very modest output. Also, you will need a pretty heavyweight fan for driving any indoor demonstration.

 

[Tom.G]

The alternator in that advert is a 120V model. Not what you need for 12V battery charging.

Actually the specs for that motor show 20RPM per Volt. With the OPs expected speed of 300RPM that is 15Volts; right where he needs it to charge a lead-acid 12V battery. Of course the output won't be exactly where the specs claim and the rotation speed won't be exactly where estimated, so the real-world result will differ slightly. A good learning experience for a first-guesstimate design.

 

[sophiecentaur]

Actually the specs for that motor show 20RPM per Volt. With the OPs expected speed of 300RPM that is 15Volts; right where he needs it to charge a lead-acid 12V battery. Of course the output won't be exactly where the specs claim and the rotation speed won't be exactly where estimated, so the real-world result will differ slightly. A good learning experience for a first-guesstimate design.

Can you assume reversible performance, though? It looks to me that the motor is what is specified as 60W / 2500RPM with 120V supply. It has to be a brush motor and that could greatly affect the volts per RPM at any speed.

 

[Tom.G]

It has to be a brush motor and that could greatly affect the volts per RPM at any speed.

At high speed perhaps, if you get into brush float due to an uneven commutator you could get a lower average voltage. The most noticeable effect of brushes is the excess resistance due to their non-ideal conductivity and non-ideal contact with the commutator. This creates a higher series resistance and leads to worse voltage regulation than an equivalent alternator. And yes, you may see a slightly higher open circuit, or lightly loaded, voltage when used as a generator than when run as a motor at the same speed; at no load there isn't any IR drop in the rotor or brushes.

Equivalently, induced voltage in a conductor in a magnetic field is proportional to rate-of-change of the magnetic field. That handles the generator aspect. The motor aspect is that the speed is such that the induced rotor voltage is equal to that required counteract the the effective rotor voltage. Effective rotor voltage is the applied voltage minus the IR loses in the winding and brush resistance.

 

[sophiecentaur]

@Tom.G that kind of makes sense. Though it implies that an even better generator would have even more turns - but few enough and thicker to handle the current that's actually required.
It does make me wonder why, by your arguments. people use alternators for that purpose. I thought that cars switched to alternators just a soon as the right diodes were available. Perhaps the power available is so different from a small wind turbine, compared with from a car engine.
Speed variation is just as much a problem with a wind turbine as with a car engine.

 

[Tom.G]

Though it implies that an even better generator would have even more turns - but few enough and thicker to handle the current that's actually required.

Yup. More turns, higher speed, stronger magnetic field; any of them will increase voltage. Thicker wire obviously will handle more current, but you will also need more mechanical input powe to get more output power.

A bit [off-topic] for this thread, but here goes.

It does make me wonder why, by your arguments. people use alternators for that purpose. I thought that cars switched to alternators just a soon as the right diodes were available.

I don't know for sure why the switch, but here is my take on it. The Commutator on the Rotor is replaced with Slip Rings, thus eliminating most of the sparking when the brush contacts bridge commutator segments. With the sparking eliminated the Brush and Commutator wear are greatly reduced. The Diodes are effectively replacing the Commutator. IIRC, the Rotor of an alternator is the Field winding and carries nowhere near as much current as the Stator is designed for. The 'extra' energy required to generate the output power is is supplied as the mechanical energy to turn the Rotor. Output Voltage Regulation is accomplished by varying the Field Current.

EDIT: also you can get a LOT more copper on the stator than you can easily get on the rotor, no centrifugal force to contend with. That and the availability of decent diodes as you mentioned, are probably the driving factors.

[end off-topic]

 

[jim hardy]

In addition to the mechanical considerations @Tom.G . mentioned, car alternators will deliver current at idle which the old DC generators did not. Does anyone remember the reverse current cutout coil on 1950's electromechanical voltage regulators?
Alternator's claw rotor with perhaps 14 poles gives seven flux reversals per revolution . Compare that to the one or two reversals you get with a 2 or 4 pole generator. E = n X dΦ/dt ...

My question is one: there is anything else to keep in mind when choosing generator except to meet the voltage requirement.

Current requirement.
The little motor OP linked in first post is rated 60 watts output , and as @sophiecentaur points out 120 volts . That'll be on the order of a half amp which at 15 volts is 7.5 watts.
It'lll probably deliver more current at risk of overheating the windings.

 

[sophiecentaur]

@Tom.G : You have pointed out the advantages of an automotive alternator but there are so many low power alternators used commercially, from bicycles to wind turbines, and I have not heard of a brush / commutator dynamo being used in any circumstance but an elementary 'project' / demonstration. The traditional 'Bicycle Dynamo' was always a permanent magnet alternator, often with a multipole magnet.
Btw, I seem to remember that DC 'Dynamos' in cars would not support any of the recent additional loads in modern vehicles like heated windscreens etc..
@jim hardy : You mentioned slow speed performance. This has got to be the most relevant factor for a wind generator. Most of the time, and in most locations, the wind is between a zephyr and a breeze. I know all about watching a wind turbine spinning merrily and, even with its purpose built alternator, producing about 50mA.

My question is one: there is anything else to keep in mind when choosing generator except to meet the voltage requirement.

The required starting torque is very relevant. When the wind is low speed, a turbine can stay annoyingly stationary. when hooked up to a generator. Perhaps we should also be discussing the actual turbine in your project. How big and what torque does it (will it) produce? Also, what is your projected operating height?

 

[jim hardy]

@jim hardy : You mentioned slow speed performance. This has got to be the most relevant factor for a wind generator.

Yes, same logic as hydro plant generators lots of poles to get decent dΦdt.

Hobbyists are rewiring those newfangled many-pole permanent magnet washing machine motors for wind generation.

 

[alexander424]

Thank you for all the replies, will try and take everything into account! :)

 

[alexander424]

@Tom.G : You have pointed out the advantages of an automotive alternator but there are so many low power alternators used commercially, from bicycles to wind turbines, and I have not heard of a brush / commutator dynamo being used in any circumstance but an elementary 'project' / demonstration. The traditional 'Bicycle Dynamo' was always a permanent magnet alternator, often with a multipole magnet.
Btw, I seem to remember that DC 'Dynamos' in cars would not support any of the recent additional loads in modern vehicles like heated windscreens etc..
@jim hardy : You mentioned slow speed performance. This has got to be the most relevant factor for a wind generator. Most of the time, and in most locations, the wind is between a zephyr and a breeze. I know all about watching a wind turbine spinning merrily and, even with its purpose built alternator, producing about 50mA.The required starting torque is very relevant. When the wind is low speed, a turbine can stay annoyingly stationary. when hooked up to a generator. Perhaps we should also be discussing the actual turbine in your project. How big and what torque does it (will it) produce? Also, what is your projected operating height?

Will be operating somewhere at 4 meters heigh and the rotorblades is planned to have a diameter of 2 meters. Not sure about the torque, perhaps an indication I should look into it.