# Designing a lundell(clawpole ) Type Generator

In summary, the conversation discusses the effect of stator design on bicycle dynamo performance using magnetic circuits and power output. The dynamo is a single phase AC generator with permanent magnets and an armature, and is expected to produce 2.4W at 3V at 30rpm with a 15 ohm load. Attempts were made to use Faraday's Law to calculate the voltage generated, but it was found that perfect magnetic coupling cannot be assumed and the leakage inductance must be taken into account. Further calculations are needed to determine the true load current and ensure proper functioning of the dynamo.

## Homework Statement

I want to know the affect of stator design on bicycle dynamo performance using magnetic circuits, and power output. The bicycle dynamo is a single phase AC generator with permanent magnets on its rotor (mounted on hubshell) and a lundell type armature(mounted on bike axle). At 30rpm, the dynamo is expected give out 2.4W at 3V. Load is 15ohm.

## Homework Equations

I've tried using Faraday' law, Voltage generated=-N(change in flux & area)over time, but I keep getting larger results than expected.

My attempt at applying:

Total B of the magnet is: 4000mT, so for this voltage estimation I am assuming perfect coupling of field through the stators
The coil has a cross area of 483.05mm^2 and 320 turns.
There are 28 poles, so I assume the coil experiences a field change 14 times per second at 30rpm.

So Voltage generated = -(320)(4000mT)(483.05mm^2*14) = 8.65V

How do you factor in the 15 ohm load into the basic equation?

## The Attempt at a Solution

Aside from the attempt in the previous section, I'm stuck. Would appreciate links or recommendations of reference if some reading is in order.

Thank you,
Derek

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I suspect that you cannot assume perfect magnetic coupling. This type of simple alternator lighting generator generally relies on having a significant equivalent series inductance. At low speeds the inductive reactance is negligible, but at higher speeds the increasing frequency makes the reactance increase until it dominates the total circuit impedance.

The net effect is to stabilise the output voltage seen by the lamps against speed variation, so that for instance bulbs are less likely to blow when descending a hill at high speed. Unfortunately, this makes the loading (your 15 ohms) fairly critical: the correct wattage bulbs must always be fitted, and if two bulbs are used in parallel, failure of one tends to provoke rapid failure of the other.

I think you would need to estimate the generator leakage inductance (it's too long since I did magnetics to advise you about that!), work out its reactance at the working frequency, and go on to find the total impedance including the 15 ohm load. Apply your calculated generator voltage across the total impedance to find the true load current.

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I would suggest looking into the design of the stator and how it affects the magnetic flux and power output of the generator. The lundell type armature is known for its efficient and compact design, but there may be other factors at play that could affect the performance of the generator. Some variables to consider could be the size and shape of the stator, the placement of the permanent magnets on the rotor, and the materials used in the construction of the generator.

I would also suggest conducting experiments with different stator designs to see how they affect the power output and efficiency of the generator. This could involve changing the number of turns in the coil, the size and shape of the stator, and the placement of the permanent magnets. By systematically varying these factors, you can determine which design results in the most optimal performance.

In terms of the equation, the 15 ohm load can be factored in by using Ohm's law (V=IR) to calculate the current flowing through the load. This current can then be used to determine the power output of the generator by multiplying it by the voltage generated.

Overall, designing a lundell type generator involves a combination of theoretical calculations and practical experimentation to determine the most efficient and effective design. It is also important to consider the limitations and constraints of the bicycle dynamo system, such as the speed and torque of the bike, and how these may affect the overall performance of the generator.

## 1. What is a Lundell (clawpole) type generator?

A Lundell type generator is a type of electrical generator that uses a claw-shaped rotor and a stator with salient poles. It is commonly used in vehicles and small power plants due to its compact size and high efficiency.

## 2. How does a Lundell type generator work?

The rotor of a Lundell type generator is connected to the engine and rotates at a high speed, creating a magnetic field. The stator, which is stationary, contains copper windings that are positioned in the gaps between the rotor's poles. When the rotor rotates, it induces an alternating current (AC) in the stator windings, which is then converted to direct current (DC) and used to power electrical devices.

## 3. What are the advantages of a Lundell type generator?

One of the main advantages of a Lundell type generator is its high efficiency, which can reach up to 90%. It also has a compact size and low weight, making it suitable for use in vehicles. Additionally, this type of generator has a simple design and is easy to maintain.

## 4. What are the key components of a Lundell type generator?

The key components of a Lundell type generator include the rotor, stator, end plates, bearings, and cooling system. The rotor and stator are the main parts responsible for generating electricity, while the end plates provide support and protection for the internal components. The bearings allow the rotor to rotate smoothly, and the cooling system helps dissipate heat generated during operation.

## 5. How can I design a Lundell type generator?

Designing a Lundell type generator requires knowledge of electrical and mechanical engineering principles. It is essential to consider factors such as the desired power output, speed, and efficiency when designing the generator. Additionally, careful selection of materials and proper sizing of components are crucial for optimal performance. It is recommended to consult with experts and use computer-aided design (CAD) software for accurate and efficient design.

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