abhijeet080808

In this thread, I am going to discuss the motorcycle charging system found in motorcycles in general, and with specific focus on the lower capacity motorcycles found here in India and how to modify them. This thread will be somewhat technical in nature and basic understanding of electricity and magnetism is assumed. Those here who have zero knowledge in electronics may refer to websites like Wikipedia.com and understand the concepts discussed here. Ok, let’s get started!

The charging system (and indeed all forms of generators, alternators) works on the basis of a principle called Faraday’s Law of Induction. In the simplest form, it states that a conductor when placed in a changing magnetic field will tend to develop an EMF. (Electromotive force or in simpler word a Voltage is developed.) So, for the charging system to work, we need an electrical coil (which acts as the conductor) and a magnetic field that can be varied with respect to time.

Now, let us discuss the coil. Why do we need a coil when a simple wire could also have acted as a conductor? The answer is that, the more the length of wire that the magnetic field can “affect”, more is the EMF or Voltage generated. In case of vehicles, we need around 12V. Hence, the use of a coil made using turns of wire of certain calculated length. Now, the coil is wound around an iron cylinder. Why? When we use an iron core instead of an air core (or core made of any non magnetic material) the number of turns of wire needed decreases to a lower value. Thus, the system can be made compact.

Now, the magnetic field can be generated using a permanent magnet (natural magnet) or an electromagnet. Electromagnets are formed by applying a voltage across a coil. Another law called Ampere’s Law states that a magnetic field will be generated. The voltage applied to the coil determines the strength of the magnetic field. Natural magnets generate a fixed magnetic field. Now, to vary this field, the arrangement used is described below.


Permanent Magnet Charging System

A practical charging system uses many coils arranged in a radial axis. Refer to figure. ("2" is Rotor, "3" is Stator.) These coils are fixed together to the Stator Plate. The magnet is mounted on the crankshaft and rotates to vary the magnetic field around the coils. It is known as the Rotor. This is how the system works.

Now, let us discuss the various methods to vary the output of the coil. The wires used in the coil affect the output. Thicker wires generate more current as the resistance in the coil decreases. But there is a catch. If we go ahead and use the thickest wire available, the system will not work satisfactorily. Why? A thicker wire will allow a lesser number of turns in the same area as we will simply run out of space. Thus the length of the wire used in the stator would be less than before. This will decrease the EMF generated. The coil will not generate the required 12V. The trick is to use the thickest wire possible while still being able to wound the required number of turns around the iron core. Another factor – the speed of the rotor affects the coil output. The faster the magnetic field varied (faster the rotor rotates) greater is the EMF induced. Hence, output of the coil varies with the speed of rotation of the engine. This is why we need a regulator. The third factor is the magnetic field strength of the rotor. The field strength in case of a natural magnet rotor is constant. We can only replace the rotor with a rotor having a stronger magnet to generate higher output from the coils. But a magnetic field generated by an electromagnet can be varied. This means we can vary the magnetic field to control the output generated.

As we have seen, the EMF varies with engine speed, while all electronic devices including the battery, bulbs etc require a constant voltage of around 12V. So how do we regulate the output voltage? In case of a electromagnet rotor system, we can vary the current applied to the rotor electromagnets as speed varied and keep the coil output to a fixed voltage level. This type of system is used in car alternators and BMW bikes among others. All our Indian bikes as well as most of the international big capacity international bikes use the permanent magnet charging system. The output in this case cannot be directly controlled. What is done is that the coil output is short-circuited to reduce the voltage to the desired level. The regulator consists of 2 parts. A monitoring unit determines if the output voltage from the coils exceed the determined voltage limit. If the limit is found to be exceeded, the second part of the regulator short-circuits the coil output and brings down the voltage level. This process occurs continuously. It is seen that a certain portion of coil output is actually wasted. This system has low efficiency but is very simple and rugged and hence is generally used in low power applications like motorcycles.

The rectifier is often a part of the regulator. This is used to convert the AC output from the coil to DC which is needed by the battery.

Now, after studying the underlying principles and working of the charging system, one may ask, what can be done to increase the coil output? A higher output can support higher wattage bulbs, louder horns etc. Firstly we will have to increase the actual output from the stator coil. (The process is commonly called rewinding) Secondly, we will have to change the regulator as the original one cannot take the increased load.

I have done these mods on my P150 myself and will describe what/how I have done in details in my next few posts. These mods require certain electrical knowledge and are not suitable for newbies.

Any suggestions/clarifications are welcome.

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ken cool

Initiative Approved

Great initiative Abhijeet! Really appreciate this gesture.

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abhijeet080808

Thank you, Ken!

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Old Fox

Great stuff there Abhijeet. Very lucid expression and you could not have made it simpler.

Its been more than a day and a half since this topic has been approved and apart from Ken and Abhijeet himself, there has been no response to this exceedingly simple, vital and well presented write-up. Even though it relates to an aspect of motorcycles vis a vis its lights, improving which has been virtually discussed to death on a few threads here, people have viewed it but none had anything to say.

A lot of time and effort is expended in posting replies to discussions upon which bike looks good, in what colour and with what tyres. There is endless interaction on which bike has a higher top speed(even though there is a mere 20-30cc difference in the engine capacities making the 'faster' and more 'powerful' claims amusing if nothing else), what after-market parts can make yours go faster (by how much??5kph...10kph....??) and which is the widest/fattest tyre I can use on my little 150cc commuter.

All this reduces the motorcycle to a mere fashion accessory. A fadist status that suffers from an appalling lack of even an iota of the spirit and soul of motorcycling in it.

Strong words these but then this displaced focus verily dilutes the actual purpose of a forum such as this. Which is to help us evolve into better motorcyclsts and also human beings through the process of sharing. Relevant sharing actually. Will a blue bike instead of a black one make the rider more skilled? Will a round headlamp instead of a square one reflect badly upon your education and status. Come on guys, life is not that superfluous. Its somewhat more than skin deep if not deeper. And when it involves an activity like motorcycling which can be a matter virtually of life and death, at least be a trifle partial towards knowledge and knowing that will equip you better for survival. Red or blue, fat tyre or thin, round headlamp or square, they all look the same as a mangled heap. And they all become the same 'junk' when they fail to work and a lack of 'knowing' makes the rider a failure too.

I know I have gone way off on a tangent with this post. OT is what this can rightly be classed as. Yes, I could have done an independent write-up on this issue on Hard Torque. But then I would have lost the reference to this post above by a knowledgeable member who is keen on sharing a vital but rather 'unglamorous' aspect of motorcycling here. Sharing can only be amongst numbers. Abhijeet knows all that he has posted. He doesn't need to know it. It is for the rest that he has done the effort. So do many others with quality posts. Please don't let their efforts go waste.

OF

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balajidiwakar

Abhijeet bhai nice initiative...ur threads are always filled with seeds of information

I guess I need to develop better knowledge in english to understand words like these. Man u r gr8

abhijeet080808

Looks like xBhpians are electronically challenged! Well, then I see no use in posting the mods I did and how I did them. I rewound the stator and designed a custom regulator. Total cost was around 200 bucks for both the jobs. I am using 60/55W at the moment and will try out 100/90W in some days and let you guys know.

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velociraptor13

Abhijeet-Thats a good piece of information that you have posted.Its true that a majority of us don't go for such mods because such modifications as per my experience require good expertise,which though is hard to find in cities like mumbai.I feel the guys in cities like bangalore are damn lucky cause u find good people at every nook and corner.Here in mumbai people are interested in sticker jobs.
Please post in the info about the mods u have carried out.It would be very helpful for me.

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Andante

Not all are electronically challenged. Most just don't bother modifying things like the stator windings or other things related to the electrical system, other than their LED strings and other glowing stuff. OF had a good point there, most people talk about looks more than about the actual nitty gritty of motorcycles.

I would be curious about your mods, it's not like I'm going to be modifying my brand new bike any time real soon, but I love a good technical discussion and learning some new stuff. I'd be especially curious about your custom regulator. Is it a common shunt type regulator or is it something a little more ingenious?

Puneet1

great stuff abhijeet please post some info regarding rewinding to increase power output.

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rahul9985

very well described.. i have been trying to learn and understand the concepts magnetism for a few years now... the way abhijeet has described, has made the it so simple.. although i wont be doing such mods till i get financially independent, i would love to go through such technical forums where i can learn new things and when i can do it, i would be more than happy to do the job on my own..
i totally agree with OF sir.. people are bothered more about the looks of their bikes.. they dont even have the basic idea of how things work when they are driving..

i have a doubt- when the winding has been changed, more current is being produced.. wont that damage the existing electricals that are working on 12V and a particular rating of current?

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