Re-winding the Coils to Convert the 6V Electrical System to 12V (PART1)

01-8.jpg How to

Nowadays, all motorcycles, from mopeds to large vehicles, have a 12V electrical system, but until the mid-1980s, some moped class models had a 6V system. However, until the mid 1980's, there were some moped class models with a 6 volt electrical system. Converting to a 12 volt electrical system is an effective way to upgrade a 6 volt motorcycle with a dark headlight, unstable blinkers, or other lighting issues. In this article, we will explain how to understand the role of the charging coil and how to change the power generation voltage by rewinding.

6V motorcycles have a lower voltage but require a larger current

02-13.jpg The coil base of this motorcycle (Yamaha POKKE) has a source coil for ignition on top and two charge coils on the bottom. The charge coil that charges the battery and the lighting coil that lights the headlight and tail light are integrated. The ignition has evolved from contact points to CDI, but the electrical system remains at 6V. The charge coil is disconnected from here.

03-11.jpg The two yellow wires are the lighting coil and the thin wire coming out of the right side is the charge coil. One end of the charge coil is soldered to the core and grounded to the motorcycle body.

Up until the 1980s, it was commonplace for mopeds to be kick-started only, regardless of whether they were sport models, family models, or scooters. The electrical system used in these motorcycles was a 6V electrical system. A 12V battery is required to mount a cell motor, but without a cell, a 6V battery is more compact and has a simpler power generation and charging system.

If you ride a motorcycle with 6V specification with modern sense, you will feel the unreliability of electrical system. Aside from riding, when you are stopped at a traffic light, the headlight is dark and the indicator is weak, so you want to raise the idling speed or agitate the throttle. The popularity of out-of-print mopeds is on the rise not only in the large vehicle class but also in the moped class, so there are many riders who switch from recent models to out-of-print mopeds, or even increase their number of mopeds.

Why is the light system of 6V motorcycle weaker than 12V? It can be understood by the relationship of voltage (V) x current (A) = power (W). For example, to turn on a headlight bulb with a power consumption of 36W, a current of 3A flows in a 12V battery, and 6A in a 6V battery.A 6V battery requires twice as much current as a 12V battery for the same amount of powerThis means that you will be

If we replace these with a bucket and water, the pressure of the water flowing out of the bucket = the magnitude of the voltage changes depending on the height of the bucket. On the other hand, even if the height of the bucket is the same, if you change the amount of tilting the bucket, the amount of water flowing out = the electric current changes. If this is applied to the headlight, the 6V electric motorcycle cannot do the same work as 12V without flowing twice as much water although the height of the bucket is half.

Both 12V of the current motorcycle and 6V of the old motorcycle charge the battery by rectifying the alternating current generated by the AC generator by the rotation of the engine into direct current, but the generating current of the generator of the 6V motorcycle  must be twice as much as that of the 12V motorcycle to break even. If you think about it the other way around. If you double the generating voltage of a 6V motorcycle to 12V, it can do the same job as a 12V motorcycle even though the current is half. It becomes a thing. All of this is obvious, but this is the benefit of the 12V conversion.

POINT
  • Point 1: Mopeds up to the 1980s, which were kick-start-only, generally used 6V electrical power.
  • Point 2: 6V electrical equipment, which requires half the voltage but twice the current compared to 12V, tends to be vulnerable when performing the same work.

Generation voltage of charge coil is proportional to the number of turns

04-9.jpg While being careful not to cut the copper wire, break the varnish for insulation and unwind the coil. At this time, it is important to count the number of turns so as not to forget the number of coils. If there is a part where the lighting coil is overlapped in the middle of the charge coil, unwind that as well. We will not rewind the lighting coil this time, but if you are going to use AC for the lights, measure the voltage generated as well as the charge coil before disassembling the coil.

05-11.jpg If you unwind the charge coil and the lighting coil, you can see that each coil is wound with independent copper wire, and the charge coil, which was wound 187 times, has only this many turns because it is 6V, but the copper wire for the source coil is much thinner and has much more turns.

While mid-size and larger motorcycles perform all their electrical components on power supplied by the battery, there are some differences in the electrical systems of the moped class. Specifically, electricity to spark the spark plug is generated by the ignition coil, electricity to charge the battery is generated by the AC generator's charge coil, and the headlight and tail lamp are lit by electricity generated by the lighting coil. Some models have a different mechanism, but we will explain here using the method that is generally adopted.

The key to converting a 6V motorcycle to 12V is the charge coil and the lighting coil. Although it varies from model to model, these two types of coils often share a single core and are wound with thin copper wire. The alternating current generated by the charge coil is converted to direct current by the rectifier, the rectifier, and then charges the battery, from which power is supplied to the blinkers and horn. The power generated by the lighting coil remains AC, and only the voltage is controlled to flow to the headlights and tail lights.

Since this structure is similar for both 6V and 12V.Change the battery and light bulbs to 12 specifications, and only install a regulated rectifier for 12V to convert to 12V.There is also a way. The reason why you can do this is because the power generation voltage of the charge coil is proportional to the engine speed, and there are some models that can generate more than 12V with the charge coil for 6V depending on the engine speed. But it is originally a coil for 6V.If the RPMs are low, the voltage is low, and you can't charge a 12V battery

In order to charge 12V battery stably, it is effective to rewind the coil. As I mentioned before, there are 3 types of coils for moped class, ignition coil, charge coil, and lighting coil, but we need to rewind charge coil and lighting coil for 12V.The generated voltage of the coil is proportional to the number of turns of the copper wireSo if you simply wind the coil twice as many times as the 6V coil, the generated voltage will be 12V.

If you want the headlight and tail lights to be AC, as is common on 12V mopeds, you will need to rewind both the charging and lighting coils. On the other hand, if you want to use battery power for both the headlight and tail lamp, as is the case with midsize and larger models, you don't need a lighting coil. So I changed the circuit from lighting coil to headlight to battery.

When it comes to charging the battery with all the electricity generated, counting the number of turns on the charge coil and doubling that amount will double the amount of electricity generated. However, before disassembling, you need to know the power generation capacity of the 6V coil so you can be more specific about the number of turns. In the case of the motorcycle shown here, 7 at 1500 RPM idling..It was generating an AC voltage of 3V. I counted and unwinded the coils wound on the core one by one, and found that there were 187 coils.

Based on this number, the generated voltage per coil of this coil is 7.3V / 187 winding = 0.039V/It is one volume and 0.039V.

Next, if the voltage is 12V and the number of turns required is calculated, then 12V / 0.039V/One roll = 307.It turns out to be 9 windings, and I found that if I wind more than 308 windings, the generated voltage becomes 12V.

In order to charge a 12V battery, you need a voltage higher than 12V, so for example, if you want to make the voltage 15V, you only need 384 windings to satisfy the requirement.

POINT
  • Point 1: The amount of electricity generated by the AC generator is proportional to the number of turns of the charge coil.
  • Point 2: By knowing the generation voltage of the original charge coil and the number of turns of the coil, we can find the number of turns required for the conversion to 12V.

Make the wire diameter thinner so that it does not interfere with the flywheel.

06-9.jpg To double the number of turns, originally 0.The copper wire that was 84mm is now 0.The size is reduced to 6mm. As the voltage is doubled, the current value is only halved, so thin polyurethane copper wire can be used. The smaller diameter is effective in keeping the coil compact.

07-10.jpg To connect both ends of the charge coil to the newly installed 12V regulated rectifier, it is passed through an insulated tube and placed in the core. The copper wire drawn at right angles to the core is wrapped around the core so that there is no gap.

08-8.jpg After that, you just have to wind it without care. 187 times at 6V is more than 380 times, so you should check the copper wire with a marker pen after every winding. The density of the winding becomes high by bending the four corners of the core firmly. If the winding is not done properly, the copper wire will be too thin and the outer diameter will be too large.

09-5.jpg The number of turns is more than doubled, but the coil does not get bigger thanks to the thin wire diameter. If you want to increase the generation voltage, you can increase the number of turns, but since the charging voltage is controlled by the regulated rectifier, it will only increase the excess voltage, which is meaningless. Rewinding the coil itself is rather simple work, because the lighting coil is not wound and connected to the regulated rectifier for single phase AC.

The copper wire used to be enameled wire insulated with enamel varnish, but now it is generally polyurethane coated copper wire which is flexible and hard to break. If you double the number of turns, the coil becomes thicker, it may interfere with the magnet inside the flywheel, so be careful.

The best way to avoid this is to use a smaller coil wire diameter. As explained earlier, if the voltage is doubled to do the same job, the current only needs to be halved, meaning that the cross-sectional area of the copper wire can be halved. The enamel wire diameter of a 6V coil is 0.5 mm..84mm, but you can change this to 0.6 mm to reduce the volume of the coil. This diameter difference almost halves the cross-sectional area. Eliminating the lighting coil, which is double wound on top of the charge coil, is also effective in controlling the coil thickness.

When winding the new polyurethane copper wire, make sure that the copper wires are tightly packed together, just as you did with the unraveled stock coil, and count each coil as you wind it. This is just a steady process, so it's important to stay focused and not get bored along the way. If the coil is not thicker than the original one, you can add more coils, but be careful not to touch the inside of the flywheel.

Also, since the voltage generated by the charging coil will be 12V, you will not be able to use the bulbs, indicator relays, regulators, etc. from the 6V era. When the lighting coil is abolished and the headlight and the tail lamp are also lighted by the battery like this time, for example, the regulated rectifier for 12V Monkey of the carburetor age cannot be used because the AC power generation itself that lights the headlight and the tail lamp is gone. Here, I used the regulated rectifier for Kawasaki GPZ250, but it is necessary to switch to the circuit equivalent to the medium-sized motorcycle or more.

If you don't have the confidence to change the wiring on the body side even if you change to 12V, you can continue the AC lighting of the headlight and tail lamp by wrapping the lighting coil on the charge coil as well as the 6V coil, and in this case, you can use the regulated rectifier such as 12V Monkey.

If it is a moped 6V model with a simple coil structure and a small number of turns, it would not be difficult in principle to increase the generated voltage to 12V by doubling the number of turns of the charge coil. The other issues are the physical problem of avoiding contact with the flywheel, and the ability to design a circuit that incorporates a regulated rectifier. You need to read the wiring diagram in the service manual of the other model to understand how the charge coil and the regulated rectifier are connected.

I'm sorry that I can't explain this in general, because it depends on the circuit of the original vehicle and the regulated rectifier used to change the circuit to 12V. I hope you know that you can make 12V by rewinding the charge coil of 6V motorcycle. Next time, I'll show you how to make 12V without changing the circuit of motorcycle body.

10-6.jpg Once the coil is protected with sports bandage tape, which is suitable for winding under tension, it is restored to the stator base. What I'm soldering in this image is the ground wire for the source coil above.

11-5.jpg Changing a simple rectifier for 6V electrical to a regulated rectifier for 12V is more difficult than rewinding the coil. This is a specification change to eliminate the lighting coil and use all the rising current of the charge coil to charge the battery. With the engine performing at 2,000 rpm, the charging voltage is 13.1V, and thanks to the regulated rectifier, even if the amount of discharge increases, the battery can be charged at the corresponding voltage. The headlights and tail lights are also lit by the battery, so even when idling at traffic lights, the lights don't dim, making night riding a breeze.

POINT
  • Point 1: It is important to check the thickness of the rewound charge coil so that it does not interfere with the magnet on the inner surface of the flywheel.
  • Point 2: If you want to eliminate the lighting coil and use the battery to operate the headlight and tail lamp, you need to modify the circuit on the body side.
 
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