# Conception details for an electric generator (wire diwm. length, magnets size/force)

I'm working my way around electric generator, with a LOT of videos on YouTube, but not very much data, detailed information, so I hoping you will guide me.

I know what I need as output. (220v 9000w for the workshop, then transformed to 110v for the house)
I know what I have as input (mechanical force. Wind, water and legs/bicycle).
How do I compute the number of turns (the more the better?), the diameter of the Cu wire, (or Al wire? or Or wire?) how many turns?
How about the magnets? Quantity, size, force, ... perm. magnets or electromagnets?

I just can't find a chart, that would allow me to "compute" my device. I've seen many videos that goes way beyond this, like 50000v and such, I want to make sure I know what I'm doing before starting drawing the circuit plan. (with three different source, a gearbox, etc ...)

Found this:

Generators, transformers, motors, all have the same relationship for the maximum power of a winding.

The amount of power you can safely put through a winding depends on the amount of copper you use, measured either as mass or volume. It doesn't matter whether it's a few turns of thick wire, or many turns of thin wire, the current carrying capacity varies in inverse proportion to its working voltage, to yield constant power.

While the voltage rating is quite easy to measure or compute, the current carrying capacity is more of a 'ratings' exercise. You have to do two things, (a) keep the windings cool enough and (b) keep voltage drops due to V=IR

As a rule of thumb, small to medium power transformers and motors tend to run about 3 A/mm² current density, but that can change substantially with different cooling arrangements. Fortunately it's quite easy to measure winding temperature when assessing how much current you can use over how much time. The resistance of copper increases by about 10% for every 25°C rise in temperature. Measure the winding resistance at room temperature, and then again after a period of running. I tend not to like exceeding 50°C rise.

9 coils, 3 phases, but magnets are too strong and provide a break effect when not enough mechanical force.
=> I'm thinking this could be overcome by using electro-magnets with strength increasing as mechanical power increases ...

In a generator, the output voltage is proportional to the speed at which it is turning, and the current is proportional to the torque. So,

E∝ω
I∝τ

If you want to reduce torque, you must reduce current.

It seems that Cu wire diameter (gauge) and length doesn't have any effect on the current produced?

Using weaker magnets would decrease the strength of the stator field, and perhaps allow cheaper magnets. Using fewer turns in the rotor windings accomplishes the same thing, and allows thicker wire to be used, which reduces resistive losses in the wire.

• You need to focus on specific questions that can actually be answered instead of expecting a dissertation on generator design and construction. Commented Jul 1, 2021 at 15:59
• Focus on 240V split phase 120+ 120 Commented Jul 1, 2021 at 16:32
• Or get 10 car alternators ganged wired in series with shunt current voltage regulator. Commented Jul 1, 2021 at 16:38

I just can't find a chart, that would allow me to "compute" my device.

Designing an electric machine is a bit more complicated than that. You need to study the theory of electric machines before attempting to design one. Even with a good theoretical background, you would have a lot of difficulty obtaining or producing the parts.

Here are a two questions that may provide a better idea of what is involved.

Shape of magnets used in an AC generator and its relation with the obtained waveform

Calculate properties of electric generator?

Your idea of three alternative input sources, wind, water, human power is also problematic. Wind and water turbines tend to have very different optimum operating speeds. Human power may be barely sufficient to overcome the mechanical losses for a 9 kW machine and drive train.

My profile lists several electric machinery references.