Revamp Your Motorcycle's Charging System for 12v DC: Stator Winding Help

[bkrame429]

I need help building a charging system for a motorcycle that has been converted to a 12v DC EFI system (formerly carbureted with a CDI ignition). The original full wave system was designed specifically to produce high voltage for the ignition system (32 gauge wire with thousands of turns). My goal is to rewind the stator to achieve 12v DC charging capability through a full wave rectifier/regulator connected to a battery. The system features a permanent magnet rotor that spins on the outside of the stator.

My questions are:
Does my winding scheme make sense? (picture attached)
Is it critical that all poles contain the exact same amount of windings?
I know it is difficult to predict output without physically trying (or knowing the magnetic strength of the rotor) but are there any estimates for the number of turns required/wire gauge? From reading it appears that you would want the largest gauge possible that would yield a minimum voltage of 20V AC to allow for conversion to 12V DC. This would provide the most current?

Any help on this would be appreciated.

 

[Tom.G]

I was peripherally involved in a few of those many years ago. We ALWAYS farmed them out to a specialist shop as they had all the information readily at hand!

These search links return many hits for shops and for Do-It-Yourself. Also try the links without the '+near+me' on the end (more DIY hits):

https://www.google.com/search?&q=motorcycle+armature+rewinding+near+me
https://www.google.com/search?&q=motorcycle+stator+rewinding+near+me

A quick glance at your photos gives the impression there may not be enough Iron in the stators to get a lot of current. That's another reason to farm it out, they will be able to roughly estimate the current available for charging/lighting/accessories. Some, if you also give them the rotor, may be able to give an accurate estimate.

I would occassionally run across riders that had added so many lights to the bike that there was not enough current left to fully charge the battery. The other motorcycle shops were happy to sell them the lights and then keep selling them replacement batteries.

Cheers,
Tom

 

[Baluncore]

My questions are:

1. “Does my winding scheme make sense? ”.
If all poles line up with stator as shown, then yes, it seems OK for a single winding.

2. “Is it critical that all poles contain the exact same amount of windings?”.
Not needed if it is a single series winding with a bridge rectifier. But if a 90° two phase, or 120° three phase wound as a Y star it would only need to be close to equal. Avoid delta winding for beginners.

3. “I know it is difficult to predict output without physically trying (or knowing the magnetic strength of the rotor) but are there any estimates for the number of turns required/wire gauge? “.
There is no quick way to guess accurately. For a fixed geometry and magnet, voltage is proportional to RPM and number of turns. There will need to be some battery charge regulator.

Note that at high RPM = high voltage and high frequency AC, the current may be limited by the resistance of thinner wire which generates heat in the winding, and/or by the inductance of the winding which does not generate heat in the winding.

4. “From reading it appears that you would want the largest gauge possible that would yield a minimum voltage of 20V AC to allow for conversion to 12V DC. This would provide the most current?”.
It is a compromise and will depend on the regulator. You must decide minimum RPM to charge battery, or keep the lights on. That may be just above idle RPM, so filament lights dim slightly when idle is slow.

First experiment to find the number of turns needed to provide charging voltage at selected low RPM. Then increase wire diameter to fill the available winding space. That will yield sufficient voltage with maximum current = optimum power.

 

[bkrame429]

1. “Does my winding scheme make sense? ”.
If all poles line up with stator as shown, then yes, it seems OK for a single winding.

2. “Is it critical that all poles contain the exact same amount of windings?”.
Not needed if it is a single series winding with a bridge rectifier. But if a 90° two phase, or 120° three phase wound as a Y star it would only need to be close to equal. Avoid delta winding for beginners.

3. “I know it is difficult to predict output without physically trying (or knowing the magnetic strength of the rotor) but are there any estimates for the number of turns required/wire gauge? “.
There is no quick way to guess accurately. For a fixed geometry and magnet, voltage is proportional to RPM and number of turns. There will need to be some battery charge regulator.

Note that at high RPM = high voltage and high frequency AC, the current may be limited by the resistance of thinner wire which generates heat in the winding, and/or by the inductance of the winding which does not generate heat in the winding.

4. “From reading it appears that you would want the largest gauge possible that would yield a minimum voltage of 20V AC to allow for conversion to 12V DC. This would provide the most current?”.
It is a compromise and will depend on the regulator. You must decide minimum RPM to charge battery, or keep the lights on. That may be just above idle RPM, so filament lights dim slightly when idle is slow.

First experiment to find the number of turns needed to provide charging voltage at selected low RPM. Then increase wire diameter to fill the available winding space. That will yield sufficient voltage with maximum current = optimum power.

Thank you for the information, this is very helpful.