What generator/DC motor do I need for my wind turbine

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I am making a small wind turbine for my A-level RMT and wondering what kind of generator I need to charge a 12volt battery. The turbine is a vertical axis savonius turbine that will probably be about a meter high and half a meter wide. I know I can use permanent magnet dc motors and someone told me I could use a brushed electric motor from an e scooter to generate electricity from the wind. Is this possible and if not what other motor/generator should I try to get.
 

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  • #2
berkeman
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I am making a small wind turbine for my A-level RMT and wondering what kind of generator I need to charge a 12volt battery. The turbine is a vertical axis savonius turbine that will probably be about a meter high and half a meter wide. I know I can use permanent magnet dc motors and someone told me I could use a brushed electric motor from an e scooter to generate electricity from the wind. Is this possible and if not what other motor/generator should I try to get.
Welcome to the PF, Dusty. :smile:

Others will be able to help you figure out the best motor/generator to use in your project, but I'd like to mention that you will likely need a power converter circuit (DC-DC Converter) between the DC generator and the 12V battery that you want to charge.

Consider a simple brushed DC motor connected to your wind turbine. At high wind speeds, you may get 12V out of the generator, but at lower speeds, you will get a lower voltage. The way you handle this is to put a voltage converter circuit between the generator's DC output and the 12V battery. In a simple implementation, it would be a Sepic DC-DC converter that can convert the varying input voltage to the 12V output. In a slight improvement, it should output a higher voltage to actually charge the 12V battery (depending on the battery chemistry), and it should include the usual battery charger characteristics (varying output voltage from full power charging to low power trickle charge).

In further improvements (what is the scope of your project?), you would be able to supply out[put power as well as charging the backup battery, and be able to switch the output power to the battery backup when the wind speed fell too low to generate useful power. And so on.

Does that make sense? Do you have experience with power converters and DC-DC voltage converters? What is your background in electronics? Fun project, BTW. :smile:
 
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  • #3
berkeman
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for my A-level RMT
Just curious, what's an RMT? Which country's university system is that? Just trying to learn more about all the different educational systems. Fun project.
 
  • #4
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Just curious, what's an RMT? Which country's university system is that? Just trying to learn more about all the different educational systems. Fun project.

RMT stands for Resistant Materials and technology. It' basically wood and metal work and it' an A level course in England
 
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  • #5
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Welcome to the PF, Dusty. :smile:

Others will be able to help you figure out the best motor/generator to use in your project, but I'd like to mention that you will likely need a power converter circuit (DC-DC Converter) between the DC generator and the 12V battery that you want to charge.

Consider a simple brushed DC motor connected to your wind turbine. At high wind speeds, you may get 12V out of the generator, but at lower speeds, you will get a lower voltage. The way you handle this is to put a voltage converter circuit between the generator's DC output and the 12V battery. In a simple implementation, it would be a Sepic DC-DC converter that can convert the varying input voltage to the 12V output. In a slight improvement, it should output a higher voltage to actually charge the 12V battery (depending on the battery chemistry), and it should include the usual battery charger characteristics (varying output voltage from full power charging to low power trickle charge).

In further improvements (what is the scope of your project?), you would be able to supply out[put power as well as charging the backup battery, and be able to switch the output power to the battery backup when the wind speed fell too low to generate useful power. And so on.

Does that make sense? Do you have experience with power converters and DC-DC voltage converters? What is your background in electronics? Fun project, BTW. :smile:
I have no experience with DC-DC converters And didn't do electronics I just know the basics from physics A level.
I have thought about using a car cigarette lighter to convey 12v to 5v to charge a phone if it doesn't end up producing enough electricity but I don't know if that's the same thing. Could you maybe help me by telling me what kind of DC-DC converters I need and where i could find them ??
 
  • #6
CWatters
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It's quite difficult to specify a motor for use as a generator on this application. I think the rpm might be too low for most cheap off the shelf motors without using a gearbox. I would look for something like a 24v motor with high motor constant (eg one designed for low rpm).
 
  • #7
CWatters
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Perhaps a truck windscreen wiper motor?
 
  • #8
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It's quite difficult to specify a motor for use as a generator on this application. I think the rpm might be too low for most cheap off the shelf motors without using a gearbox. I would look for something like a 24v motor with high motor constant (eg one designed for low rpm).
when using a gearbox won't it increase the torque which will make it harder to spin
 
  • #9
anorlunda
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You didn't say what kind of 12V battery. Auto lead acid? Lithium? Ni-cad?

Each battery type needs specific voltage versus time profile. A DC-DC converter is often called a battery charger.

If you overcharge a battery, it could be damaged or explode.

So you must specify the battery before the generator.
 
  • #10
CWatters
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when using a gearbox won't it increase the torque which will make it harder to spin
Nothing in life is free.

Most cheap 12V motors are likely to be designed for >1000 rpm. In other words they will only generate 12V if spun quite fast. How fast is tour turbine likely to spin? I think you should establish that early on.

You can use a DC-DC converter to step up the voltage to charge the battery but that will increase the current and torque required in much the same way as a step up gearbox will (although a DC-DC converter might be more efficient than a gearbox).

Ideally you want a motor that doesn't need either (or gets you most or the way there). For example a generator/motor that is wound to produce the required charging voltage at the rpm your turbine produces. Such a motor will have a high or very high motor constant compared to the majority of standard motors.

Using a 24V or even higher voltage motor may help. If the motor/generator produces 24V at say 1000rpm it will generate 12V at a lower speed, say 500rpm and 500rpm might be nearer to the rpm your turbine can produce.
 
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  • #11
Hairry
I'd like to humbly suggest you poke around on the internet a bit- there are many how-to's for this sort of thing, and finding one that suits your budget and skill level is pretty easy. I suggest this not to stop you from figuring out all the basics- RPM, volts, converters, batteries etc. but because some nicely explain what to do in your circumstance with your stuff... e.g., the relation between motor RPM, rated voltage, and volts is succinctly covered in (the presenter notes he will have difficulty achieving the required RPM with his motor, and goes through several motors to get the right voltage/RPM)
Other videos show use of ... treadmill motors, Fisher Paykel washer motors, ceiling fan motors...etc, and vertical as well as horizontal axis style windmill. So you can do anything from design your own to follow a proven "recipe".

Good Luck- this is an awesome project!!

Some day I will follow this path myself- I hate paying for power I could generate myself using cheap/free scrap parts.
Must be cuz I'm 1/4 scottish ;)
 
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  • #12
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I'd like to humbly suggest you poke around on the internet a bit- there are many how-to's for this sort of thing, and finding one that suits your budget and skill level is pretty easy. I suggest this not to stop you from figuring out all the basics- RPM, volts, converters, batteries etc. but because some nicely explain what to do in your circumstance with your stuff... e.g., the relation between motor RPM, rated voltage, and volts is succinctly covered in (the presenter notes he will have difficulty achieving the required RPM with his motor, and goes through several motors to get the right voltage/RPM)
Other videos show use of ... treadmill motors, Fisher Paykel washer motors, ceiling fan motors...etc, and vertical as well as horizontal axis style windmill. So you can do anything from design your own to follow a proven "recipe".

Good Luck- this is an awesome project!!

Some day I will follow this path myself- I hate paying for power I could generate myself using cheap/free scrap parts.
Must be cuz I'm 1/4 scottish ;)
Thx, i have looked a lot on the internet, i found a couple videos that say you can use a washing machine motor and so i dismantled a washing machine and then found out later through some more research that these are AC motors so I wouldn't be able to use them
 
  • #13
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You didn't say what kind of 12V battery. Auto lead acid? Lithium? Ni-cad?

Each battery type needs specific voltage versus time profile. A DC-DC converter is often called a battery charger.

If you overcharge a battery, it could be damaged or explode.

So you must specify the battery before the generator.
lithium acid battery im guessing but im more interested about knowing about what kind of motor to use
 
  • #14
anorlunda
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lithium acid battery im guessing but im more interested about knowing about what kind of motor to use
You probably mean lithium ion, not lithium acid, but you also need to specify how big a battery or how many batteries in parallel. Do you need one big enough to charge one cell phone, or one big enough to power a city? Or will you vary the batteries to fit the capacity of your wind turbine (how powerful is that?)

Here's an article with what you need to know about charging lithium ion batteries.
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

I know you're most interested in the motor (generator) but you really need to start at the battery end first.
 
  • #15
jim hardy
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so i dismantled a washing machine and then found out later through some more research that these are AC motors so I wouldn't be able to use them
Many newer washing machines have a permanent magnet motor driven by a computer controlled variable frequency drive. Those are popular with the DIY windmill crowd.

Add words "Fisher Paykel" to your search and you'll find youtubes of people rewiring such motors to make AC which is easily rectified into DC.

Another possibility is an automobile heater fan motor.
 

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