Exavier's Projects


Although  I am studying Applied Economics, I have a genuine interest in mechanics and electricity. In my spare time I try to design and sometimes even build things of which a made technical drawings. Because it is my passion and I can imagine that there are others like me, I made this website to give suggestions and technical information. This information is not always easy to find.

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© exavier   myprojects at telenet.be



My homemade generator "Generax 1500"

(not yet finished)


Once I bought a petrol engine of an old lawnmower on Ibazar (now Ebay) because I wanted to learn how a four-stroke engine worked. I took it apart, cleaned everything, placed new seals and finally mounted everything back together. But she would not start. After having taken my tools again and having put it together a second time, around two weeks later, she gave her old sound again. It was the first time I saw her spinning, and she did great!

Having done all this, I thought, why should I not build something useful with this piece of beautiful equipment? At first, I had the idea of making a powerful water pump with her, but because I could not find suitable parts, I changed my mind and decided to build an homemade electric generator.

For making my electric generator, I started with the engine that I already had. It is a Briggs & Stratton 3.5 HP with a vertical shaft of 7/8 inch (22.22 mm) diameter. Serial number: Model 92908  Type 1282 - 01  Code 82021605 (engine is from 1982!)


Now I had the engine, I made a drawing of the chassis and want to a local company with it. They made it in 4mm thick steel for me, so that it certainly was going to be strong enough for resisting mechanical power of my homemade electric generator. The hole for the engine shaft and oil reservoir they made with a cutting torch. The hole for the alternator shaft I am going to make myself. I mounted the engine a first time.


The next step was the alternator. I got an industrial three-phase (see technical information, later) electric induction motor for free. I was told that they easily could be converted into an electric generator just by turning the axle and by connecting AC (Alternating Current) capacitors in parallel. My intention is to convert the three-phase alternator/generator output into a one-phase one, suitable for home use. I will come back on this when I describe the electric part. At first the induction motor had a damaged grey colour but I painted it dark blue.

The induction motor characteristics (according to motor nameplate):  Manufacturer: Mez motoren;  Phase:  3~; Power: 1.5 KW/2HP; Frequency: 50 Hz;  Y/D 380/220 V; Rpm: 1410; Cos j: 0.82; Current: 3.5/6.2 A; IP44. Click here for manufacturer datasheet.


Because I felt a need for making some welding connections (for attaching homemade generator vertical mounting bracket to chassis) and I did not have a welder, I decided to begin on something else, the terminal. The terminal foresees a main switch, control lamps for primary and secondary voltage (before and after switch) and of course an AC socket. Internally there are two capacitors (C-2C wiring), a fuse (a differential switch would be ideal + connection to ground) and all the wires with their connectors. The terminal plate is made in brushed inox, which I cut out (with a hand saw!) from another piece.



In expectation of the welding to come, I already began with some pulley ratio calculations (click here for .xls file). I supposed after some research that my petrol engine spins at 3600 rounds per minute at full throttle. In Excel I made some calculations and ordered two pulleys of 67 and 140 mm diameter (SPA, cast iron, bushing 1108 & 1610). Nevertheless, I later found a website which told that vertical axle mower engines spin at an rpm of .80 times that of horizontal mower engines. In addition there is a 10% power loss due to the transmission. With all this taken into account I hope that my homemade generator will have an rpm of at least 1550. Otherwise I will have to buy a new motor pulley with a slightly greater diameter or try to speed up the mower engine.

The motor shaft has American dimensions (7/8 inch in diameter) and I thought that 22 mm would do the job. When I tried to attach the pulley it was clear that those .225 mm DO matter.  So, I had to adjust the engine pulley a bit from 22 mm to 22.225 mm (7/8 inch) with a grinding stone on my electric drill (third picture). This is far from ideal and I hope it will work. A lathe would have been a better solution if  of course I had one.



At a container park I spotted an old tricycle. Since I searched desperately for cheap quality wheels this discovery was really a relief. immediately I mounted the wheels under the little wooden cart.


I just ordered the book "Motors as generators for micro-hydro power" of Nigel Smith. Somebody advised me this book because the author explains in detail how the electric wiring of the generator has to be done.

Contents: electric motor selection, efficiency, advantages and disadvantages of induction generators vs. other types of generator, capacitor requirements, voltage and frequency, load considerations, conversion of 3 phase to 1 phase, motor startup


As mentioned my homemade generator is not yet finished. I hope the things I already have made will work together in a successful way.

My basic concern goes to the adjusted motor pulley and the pulley ratio. I also have to find somebody who can weld for me.

We will see...






1. The Generator ...


The only thing I had decided was to make electricity, but how? The more I read about it, the more problems came along.




What I did was the second option, while this was the best and the less expensive one. The best because this setup creates a pure sine wave, and no square wave like an ordinary inverter. The cheapest way because I got an old industrial 3 phase electric induction motor for free from a company that, by coincidence, had a lot of them and wanted to bring them away  for recycling. (I could even choose out of a 100 of them!)

There are two types of induction generators (motors) (also called asynchronous motors or squirrel cage motors). In general, these motors are designed for 1 phase or 3 phase applications. The first type is a motor for home use, while the second is one for industrial use (same load in Kilowatt is divided over three cables, so each cable bears less current and does not get overheated). In my generator I used an industrial type because I got it and I was happy that I found something.  


From what I  heard I can conclude that a 3 phase induction generator is more efficient than a 1 phase generator.  

Another type of AC motor is the synchronous motor/generator. This motor is more rare and I assume that you have to use your power electronics knowledge to make these motors generate. This is the car alternator type. There are windings in rotor and stator and stator gives variable power to rotor to determine correct stator voltage (in generator operation). All commercial generators use this type. A man who can make this motors generate can be found here.

A third type of electric motor called universal motor is less useful. These are motors in small home appliances like drilling machines, vacuum cleaners fans but also alternators. They work on both DC and AC.  So do not use this or this but this. I assume that this motors can be used as electric generators but then you need to have electronics knowledge. These motors typically have windings in their stator AND rotor, and thus NO squirrel cage (see last picture above).

This website gives information about all kinds of electric motors.


As you could already see, I used an induction motor to generate my power. I will now go further on this.

I said that I used an industrial "three phase" induction motor as generator. What I also told is that power is divided over three leads to prevent overheating. You could wrongly assume that these leads are connected in parallel. No, reality is more complicated. In fact these three AC leads have a "phase shift" of 120° (360°/3) so connecting these leads would result in a short circuit. If you want to know more about this, click here.

In an industrial (3 phase) induction generator /motor you can make two possible wiring connections, a Delta (∆) and a Wye (Y).

If we start from the generator perspective, the two connection possibilities create different resistances. This resistances bring different voltages with them.

Please remark that a 3 phase induction motor has three leads (possibly with a fourth one, the "neutral"), compared to a home use induction motor that has only two (one phase + neutral). I will come back later on this.



          The same concept for Wye: voltage is higher and current lower.


All this information can be seen on the nameplate of the electric motor.

Besides how many Watt, power will also be given in Horsepower (HP)


Click here for the copy with explanation that the guy gave me.


note:  For some industrial electric engines, each of the three “legs” will consist out of more than one coil. The terminals are then numbered from 1 to 9 or 12  in stead of 1, 2, 3.



2. The Transmission  ...


If you want to generate electricity, you need to attach the induction generator to the petrol or diesel motor (or to something more environment-friendly like a wind or water turbine).

You can also connect an other electric motor (from 12v, 24v to 230v) to the induction generator, e.g. if there is only a 12V DC battery available and you need 120/230V AC.


There are multiple options of connections between this two main parts.  

         The rpm of the driving motor will be the same as that of the induction generator (or other kind of generator).




I made my homemade generator using the second option, a V-belt coupling.


While gathering information of course I found websites where you can buy transmission parts.

The Epicenter ; Mfgsupply ; Robocombat ; Phoenix-mfg. Also in local mower/electric motor stores you can find parts.


note:  It is very important to install a proper belt/chain guard. Moving parts are very dangerous for your hands and children!



3. The Engine ...


The only key component that is still missing now is the power source. As I said this can be everything that

has an axle. For electric generators it is common to use a 4-stroke petrol or diesel engine, like I did.

The best known brands are Briggs & Stratton, Honda and Tecumseh. The last one has I think the best and the most long lasting engines.


It is important to choose an engine that is powerful enough to drive the homemade generator. A fact is that, if a load is applied to the generator, the engine has to work harder to drive the generator. A trick to make the engine stronger is to create a good transmission ratio, whereby the engine turns faster than the alternator (generator). Typical petrol engine rpm's are 1800 rpm in idle and 3400-3600 rpm in full throttle.

My ratio is 2.09:1


To be sure it is best to multiply the engine's Horsepower by 746 and then by .50 .


Let me explain. In theory a Horsepower is equal to approximately 740 Watt. So you could argue that it is all right to connect an electric generator of 2590 Watt to a Briggs & Stratton 3.5HP engine. In practice this doesn't work at all. If you try this setup you will see that the engine “stalls”, the rpm's will go in freefall. This comes because neither the petrol engine, neither the induction generator has a 100% efficiency. An overall efficiency of 50% sounds thus far reasonable to me.


note:  When setting every part of the electric generator in place you have to be careful not to place the fuel tank too close to the exhaust pipe. You will understand that this could create a dangerous situation.



4. The Electric System ...


Earlier I mentioned the use of one and three phase electric induction motors as electric generators. These two approaches demand different wiring. However, each approach demands the use of capacitors. As ns8o says: “The capacitance helps to induce currents into the rotor conductors and causes it to produce AC current”. You can do it without capacitors but then the generator has to be connected to the electric grid.

Frequency will be determined by the power source's speed and voltage will be determined by the capacitor capacitances.

3 phase motors as generator

With this kind of industrial electric motor you have three leads (+ a neutral). This is a problem as you will be connecting 1 phase home loads (like lamps, electric drill, refrigerator, etc.) to your homemade generator.

There are two ways of using the industrial motor as electric generator in home appliances:


               A reference is to multiply the generator's REACTIVE power in KW (Kilo Watt) by 7.35 for C. Power is taken parallel over the C connection.  

            When choosing the capacitor values it is important to choose those with sufficient voltage rating. They could blow when this rating is underestimated. For                 safety choose 350V capacitors at least (1.5 times nominal rating).

1 phase motors as generator

This kind of induction motors are maybe easier to find, as they are used to drive water pumps, electric lawnmowers and washing machines. However this kind of induction generators (designed as a motor) also need capacitance ( in parallel over the motor leads) and the principle is the same. However, they will be needing more capacitance than 3 phase systems will need. See spreadsheet tab 'single phase motor > single phase generator)'.


Additional information, important!




          Manual control will be needed.  

          Although manual control is just fine, there exists also an electronic voltage/frequency control.       

            Just search “induction generator controller  (IGC)” in Google or Yahoo.




If you should have any questions or suggestions, mail me at myprojects@telenet.be


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