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Old 08-03-2010, 04:00 AM   #1407
Gnarly Adventurer
Aivasovsky's Avatar
Joined: Jun 2008
Location: Istanbul
Oddometer: 155
Stator re-winding

Hi All!

Due to some charging problems i decided to work on alternator of my bike.
That way it would be a nice opportunity to learn the details about it.

The XT350 electrical system has two coils for charging, one for ignition and a small pickup coil to trigger the ignition.

The charging coils has branch from the middle of the coils which feeds the main lightning directly with AC voltage before being rectified(turn to DC) and regulated.
I guess this is for avoiding loss of power while rectifying.

The main cables from coils goes to reg/rect. unit which charges the battery, feeds the turn signals, park and stop lights.

There are some measurements below:

The wire diameter of the coils: 0.85mm (19/20 AWG)
Number of turns: 320
Number of turns side to side of the coil in each layer: 40 (38mm wide)
Number of layers: 8
Coil body height and width: 8mm x 23mm
Length of wire wound aroun each coil: 26 meters
The branch for main lightning is located at: 9 meters(or 17meters)
The number of turns after and before the branch: 97 / 224
The total resistance of each coil 1,7 ohms

I also attached the flywheel to a milling machine and made some more measurements while turning at 3000 rpm

I will name the ends of the coils as GND - MID- END
MID end is the branch between two main ends of the coils.

(all AC, open circuit measurements)
MID-END: 25V - 9A
GND-MID: 11V - 4A
GND-END: 35V - 3A

I made tons of measurements with different number of turns and different
diameter wires.. but couldn't get any significant output.

I tried 1mm wire but the clearance between magnets and the coil was very narrow, it scratched.
Less number of turns cleared but the voltage dropped a lot.

The last setup was with 0,95mm wire. (18/19 AWG)
300 turns, 8 layers, 30V, 3.7A

After satisfied the last results, i started to make measurements with the reg/rect. unit. At that point i found out that the unit was malfunctioning.

I went out and bought a china made cheap reg/rect. unit for 10 usd.
It worked like heavens.

I have 14 volts at idle.
When all the lights on, the voltage stays well over 12 volts at idle
and around 13 volts at mid. RPMs. I got more than 100Watts

I will keep you informed as soon as i got more detailed measurements

Best wishes,


2003 KTM 640 LC4e 18000km (High Flow top)
1993 Yamaha XT350 40000km
Rebuilding XT350 project pics:
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