How do we determine the ideal size for our wind turbine's generator?

• Onjii
In summary, you are designing a wind turbine from the bottom up. You and a colleague are designing a double stator axial flux generator. Your requirements are that you deliver about 10 W at nominal rotation speed. It is a direct axis driven generator propelled by a VAWT. You found some rather advanced articles on the back-torque of the machine but are still a bit lost. So to put your concerns into a question. What is a common design parameter that makes a generator too heavy/too light to drive?

Onjii

Hi!

I'm working on a project where we are building a windturbine from the bottom up. Myself and a colleague are designing a double stator axial flux generator for our turbine. Our requirements are that we deliver about 10 W at nominal rotation speed. It's a direct axis driven generator propelled by a VAWT. The issue that has been bothering us is how we determine the size of the generator. We found some rather advanced articles on the back-torque of the machine but are still a bit lost. So to put our concerns into a question. What is a common design parameter that makes a generator too heavy/too light to drive?

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• Axial generator drawing 1.pdf
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Designing a generator for a specific purpose usually requires considerable technical knowledge .

I see though that you are building a very small system intended to deliver just 10 W . At that power level there are many ready made dynamos and motors that could be made use of at very little cost .

I'm aware that we are essensially building a bike dynamo. But the project is to build all the components ground up (including coils etc). We already have a simulink model giving us the emf from the rotation speed which tells us how many poles and so forth we will need. We just feel that we are lacking some knowledge on how to model the back-torque to make sure our turbine can drive it once we assemble the whole machine
.

Must you calculate the torque from first principles, or just estimate it?

If efficiency is 100%, then torque*speed = voltage*current (after suitable units conversion.) Most generators are pretty efficient, so a guess of 75% efficiency for your home made generator seems to be pretty conservative. So just divide the required 10 watts by 0.75 to get estimated torque*speed.

To improve efficiency, my guess is that the bearings are more important than the weight.

Is your apparatus required to be self starting? You may need significantly more torque to spin it up starting from zero RPM than to keep it running at rated RPM, and the acceleration does depend on weight. If self start is not required, then a push by the hand to start it spinning would be allowed. Alternatively, he electric load could be removed for startup and switched in after achieving rated speed. Both alternatives mean manual intervention.

Onjii
You have the rotation speed . Make a conservative guess at the dynamo efficiency .

Shaft torque * (revs/sec) * 2 * Pi = dynamo output power / dynamo efficiency

Torque in N-m and power in W .

Example : shaft speed = 50 revs/sec . (3000 rpm)
output power = 10 W
efficiency = 0.4

Shaft torque * 50 * 2 * 3.142 = 10 / 0.4

Shaft torque = 0.08 N-m

Onjii
Appreciate the help guys!
I think we will settle with approximating the torque like you just described.
Thanks!

1. How do I determine the appropriate size for a generator?

The size of a generator is typically determined by the power requirements of the equipment it will be powering. This can be calculated by adding up the power ratings of all the equipment and appliances that will be connected to the generator. Additionally, it is important to consider any potential future power needs and choose a generator with a slightly higher capacity to accommodate those needs.

2. What factors should be considered when selecting a generator?

When selecting a generator, it is important to consider the power needs of the equipment, the type of fuel it runs on, the availability of that fuel, the portability of the generator, and its noise level. It is also important to consider the reliability and warranty of the generator, as well as the cost.

3. How do I determine the required voltage for a generator?

The required voltage for a generator is determined by the voltage rating of the equipment it will be powering. Most household appliances and equipment operate on 120V, while larger equipment may require 240V. It is important to make sure the generator's voltage output matches the voltage requirements of the equipment.

4. Can I connect a generator directly to my home's electrical system?

No, it is not recommended to connect a generator directly to a home's electrical system. This can be dangerous and can potentially cause damage to both the generator and the home's electrical system. It is important to use a transfer switch to safely connect the generator to the home's electrical system.

5. How often should a generator be maintained?

A generator should be maintained regularly, at least once a year. This includes checking the oil level, changing the oil and air filters, and inspecting the spark plugs and other components for any signs of wear or damage. It is also important to run the generator for a few minutes every month to keep it in good working condition.