Trying to build a 12v stator

[DanielHowden]

I have a motorcycle project on the go and I would like to build my own 12v stator. If I make a single winding and rotate the rotor I can produce 6v, however, I would like to make 12v and I have repeatedly failed at doing this.

I thought that there needed to be a second winding over the first winding. I have tried this, winding both CW and CCW but I don't achieve any more than 6v.

I have tried linking the two windings up in series but no joy still.

Of course I may just have the connections in correct, if I have two windings on the same laminate and I joint the two windings together, I can then have three outgoing wires, two that are single and one that is double.

Any help will be very much appreciated.

 

[Nigel Goodwin]

Basically the more windings, the higher the voltage, so winding a single winding with twice the turns will double the voltage. If you're winding two separate windings, them wind them both the same way, and put them in series - essentially just a single winding.

 

[DanielHowden]

Thank you, I will go back and have another go.

 

[Nigel Goodwin]

I seem to recall, that there was something in these crude motorbike alternators that limited their output power, so their power output increases fairly rapidly as speed increases, but then flattens out once it reaches it's maximum output. This was to avoid blowing headlamp bulbs, on bikes where the headlamp is fed directly from a separate winding.

I appreciate your desire to convert it to 12V, 6V systems are absolutely rubbish

 

[DanielHowden]

Exactly!

So I has 10m of wire around the laminate and that gave me 6v, I now have a continuous run of 20m of wire around the laminate and I still get 6v. Im missing something - Im just not sure what it is.

 

[Diver300]

Are you measuring the voltage with a load?

 

[DanielHowden]

No, I'm not. Just measuring the output.

Would the strength of the magnets be a factor?

 

[Diver300]

The strength of the magnets will be a factor, but they can't really alter the difference between a winding and one with twice as many turns.

Have you got any photos?

What are you using to measure the voltage? Some multimeters won't read higher frequencies correctly.

Have you tried with a load like a small 12 V bulb?

 

[DanielHowden]

Hi, sorry for the delay in answering. Interesting what you say about the multi meter, I will try a bulb today. Here are two pictures, one of the windings I made, this is the latest one and the old 6v windings. For this latest winding, I used 0.5mm wire and I put 50 meters on it. If I spin the rotor as fast as my cordless drill will go I did get 9v out of this.

I'm just wondering if the windings need to be closer to the magnets and thats my problem?

 

[Diver300]

Some terminology. The winding are the copper wire. The armature is the thing that the copper wire is wound around.

The distance from the armature to the rotor magnets will have a big effect on the voltage. The closer the windings to the rotor magnets, the larger the voltage.

Also, the windings aren't very tidy. That in itself won't make any difference. However if you have shorted a winding, it will have a much bigger effect than the loss of the number of turns that have been shorted. For instance, if you have 1000 turns, and 100 are shorted, the voltage you will get is far less than you would get with 900 turns and no short.

I don't know if you've got a photo of the curved bit of the armature, the bit that is shaped to be close to the rotor. I can't see any evidence that the armature is laminated. It is also possible that the laminations are being shorted out somehow. If you have bolts that hold down the armature that go through the laminations they should be insulated.

There is an explanation of why shorted laminations makes a difference here:-

 

[DanielHowden]

Fascinating explanation and thank you for correcting me on terminology.

Your comments made me go back and check things - I found that I had continuity between the armature and the winding. I started again paying more attention to the insulation. This time I got to 17vac so very happy with that.

So moving forward, I have to turn the rotor fast to get up to or past the 12v I am looking for. If I introduced a second armature that same as the first, would I achieve 12v at a lower RPM?

 

[Diver300]

If I introduced a second armature that same as the first, would I achieve 12v at a lower RPM?

It should do. It depends on the phasing of the magnets on the rotor. You should measure the voltage from both windings, and then the voltage with them in series. Also swap the connections on one of the winding and see what the series voltage.

If you are lucky, you will get twice the voltage with two in series, and nearly nothing with the two in series when one is reversed.

What is it that you want to run from the motorcycle alternator? On alternators like that, the current is limited by the inductance of the windings. As the speed increases, so does the voltage. When you take current, the inductance of the windings will reduce the voltage. The effect of the inductance (the impedance) is proportional to the frequency, which is proportional to the speed. The overall effect is that as the speed increases the current never increases past a level that is set by the rotor magnets and the windings. The current is not much affected by the voltage at high engine speeds.

I changed a motorcycle from 6 V to 12 V without changing the windings. It was a Honda CG125 built in around 1982. It had a 6 V system, where the headlight and tail light totalled about 30W, so 5 A at 6 V. There was a ballast resistor that was put in circuit when only the sidelight was on at the front, which was to stop the sidelight and tail light burning out, which would happen if the full 5 A supplied to a sidelight and a tail light.

To get a 60 W 12 V head light to work reasonably well with the existing generator I had to do very little. Basically I just connected the headlight to the alternator. The headlight was the same current as the original. The lamp was a bit dim at low engine revs, but it was a 125 that did 8000 rpm at 60 mph and I found that there was a small lighting improvement at 30 mph by changing down from top (5th) to 4th so the revs went up a bit.

 

[DanielHowden]

That's a great story, this project I am working on will be a motorcycle I build, it will be kick start and the ignition coil is an AC version so I need to produce a reliable 12v at kick over speed so that I can produce a spark from the ignition coil.

 

[Diver300]

Battery powered ignition systems don't need 12 V to start. Vehicle battery voltages often drop well below 12 V when starting, so you only need about 8 V.

However, the ignition systems that are designed to run from the battery may need power for a lot longer than can be provided by a kick start.

The ignition systems on kick-start and pull-start engines will just store enough energy for one spark. On the CG125 the original ignition system had an armature coil much like the ones in your picture, a contact breaker and the ignition coil that the HT lead came from. The contact breaker would be closed until the spark was required. The current in the armature coil built up in half a turn of the engine, flowing through the contact breaker, and energy was then stored in the armature coil. When the contact opened, the current was diverted into the primary of the ignition coil, which transformed the voltage and produced the spark.

More modern systems have a capacitor charged from the armature coil, and that is where the energy is stored.

So both schemes have a store for just enough energy for one spark, in ways that can give out most of the energy into the spark, and be replenished in just one turn of the engine. That is quite different from the charging of a battery.

 

[DanielHowden]

I would be interested to know what you thought of this wiring diagram. Do you think I would need a capacitor in this setup?

 

[DanielHowden]

.

 

[Diver300]

I would be interested to know what you thought of this wiring diagram. Do you think I would need a capacitor in this setup?

View attachment 148176

I don't know enough about the internals of the ignition coil unit or the regulator / rectifier to be able to answer the question.

It looks like you have the battery the wrong way round.

 

[DanielHowden]

OK, no problem. I meant to say that the armature on current charging units are made up of laminates. The armature I have is old and made from a solid cast piece. Is there evidence that the laminated version performs any differently to the solid cast version?

 

[Diver300]

I don't have direct evidence on your motorbike as to the effectiveness of laminates.

However just about all electrical machines that involve changing currents (including the armatures of DC motors and the latest versions of your motorbike charging units) have had the manufacturers go to the expense of laminating, so there must be an improvement.

Shaded pole induction motors and most AC contactors have partial shorted turns which affect the timing of the magnetic field in the area of the shorted turn. That would only have an effect if laminations made a difference.