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PMG construction manual
Hugh Piggott - Scoraig Wind Electric - February 2001 comments welcome at hugh.piggott@enterprise.net

Contents 1. Introduction 2. List of materials and tools 3. Jigs and Moulds 4. Stator construction 5. Rotor construction 6. Assembly 7. Testing and connecting 8. Additional information
This manual was commissioned by
Dr Smail Khennas Senior Energy SpecialistIntermediate Technology The Schumacher Centre for Technology and Development Bourton Hall Bourton on Dunsmore Warwickshire Tel +44-1788-661 100 Fax: +44 -1788 44-(0)1788-661 101 Email: smailk@itdg.org.uk Url: http://www.oneworld.org/itdg Url:http://www.itdg.org.pe Company Reg No 871954, England Charity No 247257 with funding from the UK government DFID

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On site assembly inPeru

PMG manual

Page 1

February 2001

1. Introduction
This manual describes how to build a 'permanent magnet generator' (PMG). We can also call it an 'alternator', because it generates alternating current (AC). It will not generate 'mains voltage' or 'utility power' AC. It generates low voltage, 'three phase' AC, and then changes it into 'direct current' (DC) for charging a 12 voltbattery. What this PMG is made of SPINE

1. EXPLODED PMG

REAR ROTOR

SHAFT

STATOR

FRONT ROTOR RECTIFIER 12V BATTERY

The PMG (see diagram 1) consists of:• A steel spine and shaft. • A stator containing coils of wire • Two magnet rotors • A rectifier The stator contains six coils of copper wire, cast in fibreglass resin. This stator casting is mounted onto the spine; it does not move.Wires from the coils take electricity to the rectifier, which changes the AC to DC for charging the battery. The rectifier is mounted on an aluminium 'heatsink' to keep it cool. The magnet rotors are mounted on bearings, which turn on the shaft. The rear rotor is behind the stator, and enclosed within it. The front one is on the outside, fixed to the rear one by long studs which pass through a holein the stator. The wind turbine rotor blades will be mounted on the same studs. They will turn the magnet rotors, and move the magnets past the coils. Magnetic flux passes from one rotor to the other through the stator. This moving magnetic flux is what produces the electric power.

PMG manual

Page 2

February 2001

Building the PMG This manual describes how to build the PMG. Read rightthrough it before starting. Section 2. is a list of materials and tools for the job. Section 3 explains how to build the special tools (called jigs) and the moulds which are needed. You can build more than one PMG with them. There are many possible ways to make these jigs and moulds, but there is only room in this manual to describe one way to do it. Section 4 is about the stator. It describes howto wind the coils of enamelled copper wire, and cast them in resin, using the jigs and moulds. Section 5 shows how to build the magnet rotors, using magnet blocks and steel disks, set in another resin casting. Section 6 shows how to assemble the parts into a whole PMG. It explains how to build the mechanical parts, how to balance the rotors, and what is required to connect the wiring from thestator. Section 7 is about testing the PMG. It contains procedures for checking that it is correctly balanced and ready to use. It describes the options for connecting up the electrical output. It also explains how to connect the PMG to the battery. Section 8 contains additional information about the use of polyester resins, and about using the PMG for hydro power. What this PMG can do This PMG ismade for small wind generators (see diagram 2). To build a complete wind generator, you also need • a tower : perhaps a steel pipe, supported with guy ropes, • a 'yaw head' swivelling on the tower top, • a tail, to keep it facing towards the wind, • a set of blades, to turn it. The spine of the PMG bolts on to the yaw head. The blade assembly fits on to the front of the PMG. The yaw head and tail...