DIY Permanent Magnet Alternator/Generator (PMA-PMG) Construction Plans

  

 

Introduction

This article will guide you to build a very productive Permanent Magnet Alternator/Generator or "PMA"/"PMG", for use in wind power or hydroelectric systems and offcourse is suitable for all similar power generation projects that you got in mind.

wind power and hydroelectric systems

Permanent Magnet Alternator use moving permanent magnets instead of Electromagnets to induce current in coils of wire. PMAs do not need definite environmental conditions to work properly which allows them to be used in a wide range of energy projects. One of their advantages, is that the voltage regulator receives always a constant power regardless of the power demand on the alternator, so the voltage regulator is not affected by the load and can deliver the proper voltage to the stator.

There are two types of PMA/PMG alternators:

types of alternators

1) The radial flux alternator which require more cylindrical parts, special casing, curved magnets, etc. and

2) The axial flux alternator, also known as a pancake generator. Its rotor is made from a flat thick disk, with the magnets arranged evenly close to the perimeter and rotates on a shaft above the stator coils level.

The axial type has also the ability to vary the air gap between the coils and the magnets, according to your needs. It is much simpler, easier and cheaper to construct a axial than the radial type!

PMA basic efficiency characteristics:

There are some basics to remember.

1) Voltage is a function of rotor speed, and current is a function of rotor torque.

2) The higher the torque, the higher the current that is produced from the PMA.

3) In order to control the turbine connected to the alternator, the resistive load can be changed.

4) The lower the resistance, the higher the current and torque that will be produced.

5) Resistive loses from the coils, mechanical friction and weight of rotor always affects its efficiency.

To the experienced out there it will be easy to replicate. For the new commers before you start building it, I suggest to get some coil/magnet knowledge first. There are many online tutorials to help you get the idea of producing electricity using magnets and coils.

This PMA has sixteen magnets and twelve coils. The problem with DIY alternators is that you will never fully know the final wattage until its finished. You count to the powerfull neodymium magnets and the well made coils, as well as the distance of those two to be minimum. This alternator will give you more than 1KW power at 120rpm speed. But construction from construction differs and there are no standards in DIY setups.

The good PMA need attention to the details. Choose good materials and start building..


PMA/PMG Construction

Step 1:

Choose your magnets and make the rotor.

Get to the e-shops and find the strongest magnets that fits to your design. They are expensive so be carefull with their sizes. My magnets was available from a past project so I was lucky to have them ready. But If you want to use the same type as mine, their size is 35mm diameter 20mm height.

For practical reasons and because my system is indoor somehow, I decided to use sea-plywood of 20mm thickness. You can use teflon if your budget allows it, or any other material that suits you. Or you can 3d print the rotor to be exact in any way. (Sea plywood can be sealed more, covered with epoxy resin or any other special sealant, and be surprisingly suitable for many applications so think about it).

Strong Neodymium magnets

Remember: You need to make the best possible coils, and place them as near as possible to the magnets.

The 16 magnets that I use are round disk neodymium magnets. They are very strong and need special handle. Their thickness 20mm fits perfectly to my plywood.

First take a square plywood 33cm x 33cm and draw the two diagonals. At their center place your caliper and draw a 31cm diameter circle (15.5cm radius).

Next, Mark the equal distances of the center of the magnets. Use your caliper and ruler to mark them. for opening the magnet holes later.

This is where you will cut it with your saw. The final rotor will be 30cm diameter but we left 5mm perimeter error for correcting it later. Next, you make the center shaft hole and the holes for the flange. The type of flange is up to you. You can find flanges in web or make your own.

After you finish with the flange holes on the wooden disk, you place and screw well the flange as it was ready to run. Then the flange has to be connected to a lathe or a type of lathe so to make the rotor perfectly circular and straight using cutting tools and sandpaper.

Next, use your vertical drill with the 35mm cup to open the holes for the magnets.

plywood disk rotor with the holes done

Photo of the plywood disk rotor with the holes done.


My flanges was taken from an old AC motor top and end cups. The shaft is also taken from the same motor. The two bearings was used as a alignment of the shaft to be perfectly vertical with the flange. So the bearings are not used as bearings rather as spacers and later they will be glued.

plywood disk rotor

Photo of the plywood disk rotor, top/bottom flanges, bearings and shaft rod.


Dont forget that the magnets are placed north, south, north, south, etc. Apply epoxy glue to the perimeter of magnets and the wood hole as well. Stick all magnets with extreme care because is very dangerous to move so strong magnets so near to each other. Put on thick gloves and take all percussions. Maybe this is the most difficult part as it needs strength and accuracy as well. But once you finish them you are ready to proceed to the stator part.

Pushing magnet to its hole using a deadlocked vice

Pushing magnet to its hole using a deadlocked vice.


magnets placed in their positions

All magnets placed in their positions.


Rotor and shaft in place

Rotor and shaft in place (the bearings acts as spacers, they will be locked later on)


Step 2:

Make the Coils. Remember! The higher the number of turns in the coils, the higher the voltage that will be induced.

Use 1mm enameled copper wire (magnet wire). You can buy it from transformer factories or from Ebay, etc. 3Kgr wire will be enough. Use your imagination to make the winding reel for the coils. If you have 3d printer, it will be very easy to make it. If not use anything available.

coils ready

The coils ready at the left and the base wooden plate of the mold at the right.


I made the winding reel in my 3d printer, but you can use any materials to make the winding machine you need.

The center rod of the winding reel is 6mm (diameter of center air hole in coil). The coils are circular 18mm height (coil thickness) and the diameter of ~48mm. The height must not exceed the 18mm so the coils will be covered completely later in epoxy resin.

The diameter of coils is not so critical in terms of 5-8 turns more or less. Meaning that some turns more, some less will be ok. Just use as much copper as possible at the coils to minimize the empty spaces between them.

Make 12 coils.

coils electrically connected

The coils electrically connected, placed on the base plate .


Place them on the base plate and make the electrical connections between them.

You can choose from two viral types of connection. The star or the Delta connection type.

Star and Delta type of connections for three phase systems

Star and Delta type of connections for three phase systems.


Star Connected System.

The "star" connection is used where we require Neutral terminal to obtain Phase voltage. The Phase voltage is root 3 times less than line voltage and require less insulation level. This type of connection is commonly used where low starting current is required.

Delta Connected System.

In "delta" connected system line voltage is equal to phase voltage and phase current is v3 times less than Line current. Insulation level is high because the line voltage is equal to the Phase Voltage and is commonly used where where high starting Torque is required.

So the star type is more suitable in our case.

12 coils - 3 phase star connection circuit diagram

12 coils - 3 phase star connection circuit diagram.


Step 3:

Make the Stator. You can make more than one stator and rotor on the same shaft. It is up to your needs to decide.

This particular project has 1 rotor and 1 stator. The stator has to be made with epoxy resin. The reasons for using epoxy are many and discussed several times. It offers structural durability, good protection from the environment, good heat dissipation, absence of metal, and the list is endless.

Use the 2 parts epoxy resin. two litters will do the job. But first you have to make the mold from wood again. Use cheep straight cheep wooden boards 40cm x 40cm. You will need 3 of them.

the 2 plates forming the mold

the 2 plates forming the mold.


making tight connections of wires

Placing the coils to check the spaces and making tight connections of wires.



The first 40x40mm board goes as the base, the second will be cutted to make the wanted mold, and the third will be the cup to seal it and wait for it to be ready.

Mark the perimeter of the stator on the second wood and cut it. Then place it on top of the (base) wood, align it, glue it and screw it with the (base) wood.

Cut a circular wooden circle to place as center at the mold. This will be the center gap where the shaft will pass. Screw it on the base board.

make sure everything is in place abd tight before you put the epoxy resin.

Cover all area of the mold (where the epoxy will go) with wax or grass or thick oil so the epoxy will not stick to the wood.

plexiglass cloth

Ready to cut the plexiglass cloth to exact size of the mold.


Get 1 meter by half meter plexiglass cloth/mesh for both endings. Cut them to exact size both. Place the one fiberglass cloth under the coils, then the coils on the top, as they will be in final position, see if the distances from the center are correct. Make sure that the centers of the coils pass from the centers of the magnets. Align them and make sure they fit perfectly. Because you will make the mold to be ready for epoxy. You have to make also 3 terminals for the three phases. secure coils using with instant glue and connect the terminals to the coils.

two plexiglass cloths cutted to exact size

The two plexiglass cloths cutted to exact size.


Connections are tight and coils are glued together

Connections are tight and coils are glued together.


When you finish position them to the exact symmetrical position and secure them with some glue. Its time to connect the terminals.

center circular wood is screwed on base

center circular wood is screwed on base and coils are connected to terminals.(bottom plexiglass is missing at photo)


Before filling it with epoxy, take a carefull final look at the coils. Make sure everything is aligned and symmetrical.

Typical 2 part epoxy resin

Typical 2 part epoxy resin. Get 2 liters and mix them gently to avoid bubbles.

Poor the epoxy carefully, make sure it will cover completely the coils and make sure no bubbles (air) are traped. Place a second plexiglass mess on top and poor some epoxy more after that, to be just little more than enough.

Now its time to close it with the third wooden board and seal it with screws very well. Keep it 3-4 days at this horizontal position. dont turn it. don't move it. Just wait.

When 4 days pass take all the wood off, carefully and using saw where is difficult.

Stator ready after 4 days

Stator ready after 4 days.


Clean the edges and sand them to be nice and smooth.

Open the 4 holes at the stator and make the bearings base either in 3d printer or use your imagination to make it and place then one at the stator and one on another plywood of the same size or any other stable material that is available. From now on the changes are going according the needs.

Stator with holes and screws secured on another plywood plate which cury the bottom bearing

Stator with holes and screws secured on another plywood plate which cury the bottom bearing.


Close look of the terminals

Close look of the terminals


Alternator almost ready. Only top cover missing

Alternator almost ready. Only top cover missing


spacer/bearing is blocked and secured with shaft

spacer/bearing is blocked and secured with shaft

The top plywood plate is in place. The closer the magnets are to the coils, the higher the voltage that will be induced. Magnetic flux density drops off with the square of the distance, so it is important to reduce the air gap between stator and rotor for better efficiency. So distance of magnet from coils is adjusted to minimum possible and the alternator is ready for the first test.