4.06. Alternator

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Contents

4.06.02 Function of the Alternator

The 4.11. Wiring Diagrams help you to understand the function of the charging circuit.


Image:binmke_xs650sh_alternator.jpg

Picture: The alternator on a 1981 XS650SH. The alternator can be accessed by removing the sidecover panel on the left side of the bike.


The alternator consists of a Stator, a Rotor and Brushes.


The Rotor

The rotor is the spinning part inside the alternator. It consists of two iron parts pressed together. Inside is a coil of copper wire. This wire has a paint insulation and its resistance is about 5 Ohm. One end of this coil is connected to the outer slipring - another to the inner slipring. There is no electrical connection to the iron parts of the rotor.


Checking the rotor:

To check the rotor you need to remove the coal brushes. Make a drawing for the cable colors and position of the brush holder if you are not sure about the assembling position.

With a multimeter you check the resistance. Use a low range on the Multimeteres dial (i.e 200 Ohm, not the Megaohm range - it will give no precise reading). The resistance between the sliprings must be about 5 Ohm. It is reported that it will work even with under 4 Ohm, but it might be an indicator for some damage. There must be no connection (infinite Ohm) between each of the sliprings to the iron parts.

The rotor of the XS is a weak point of the electrical system. Most the charging problems have their cause in a damaged rotor. The insulation of the coil seems to get weak and brittle after many years and short circuiting the coil. This makes the resistance drop.


The Stator

The stator delivers an alternating current. This is rectified (making direct current) by the rectifier.

See 4.05. Rectifier


The Rotor and the Stator - how it works together

The rotor builds up an magnetic field and inducts the coils (3 coils) of the stator. If the output of the stator gets to high then the Voltage Regulator interrupts the circuit to the rotor. The magnetic field stops and as well the output of the stator goes down. If the Voltage is to low then the rotor gets the voltage (regulator switches on) from the battery, builds up a magnetic field and the stator delivers current again.


The Voltage Regulaor

The purpose of the voltage regulator is to keep the voltage under 14 Volt.

It controls the electrical current from the battery to the rotor. Since there is no permanent magnet inducting the stator the XS can not be started without a battery. No battery = no initial magnetic field from the rotor = no electrical current to get a spark from the ignition.

--herbs 17:16, 2 Jul 2005 (CEST)


4.06.03 Repairing the Stator

I ve been able to fix the stator of my '79 XS650.

Before you disassemble everything - remove the left engine cover, start the engine in the dark and check for sparks from the stator. Failure may occur under vibration.

Get the rotor and the stator out and check everything visually. The insulation paint get brittle with the time and it is possible that two of the three coils touch. It is also possible that a previous owner damaged it when pulling the rotor off i.e.

Remove the rotor, then the stator, clean it carefully. Check the stator visually. The three coils are soldered together at the end - open this connection and measure each coil separate. Try to move and bend the coils with the ohmmeter connected to check if they touch under vibration or pressure. Broken coils can be soldered. If its a short circuit you can bend them apart and isolate with epoxy glue.

When the three coils are separated at the end and you still measure some ohm between two coils then you may also connect a charged battery and check if certain spots of the stator get hot or deliver sparks.

On [4.11.09. Damaged Stator] you find a sketch what helps you to imagine the problem.


This was the scenario on my bike:

The stator gives not enough current, thats why the regulator switched on and applies to much current to the rotor (from the charged battery). I think this was the reason why the rotor overheats and fails after getting too hot..


"...Rotor ok. Cabling ok. Electronic regulator. Stator seemed to be fine. At idling I got about 11 Volt for charging - too less. Revved it up and at +2000 it squeezed out slightly over 12 Volt.

I had two rotors burned down.

After endless research I located the trouble: The Stator consists of three coils. On one end these coils are connected together. The other end of these coils end in the three white textile-insulated wires what are going to the rectifier.

The coils have this kind of brownish epoxy-insulation paint on, like a tranformator.

This insulation was getting porous or somehow old and two of the coils had contact there.

You wont find that with an ordinary ohmmeter.

To measure it: You can poke out the point where the three coils are soldered together - open it and then you are able to measure the single coils if they are electrically seperate. If two of them touch, you might be able to find the weak point - seperate them and insulate it with epoxy glue. Then you can connect the three again and glue them too. Keep in mind that the vibrations and temperature can cause such a problem temporary. The effect of this fault was:

The stator didnt supply enough Voltage to the regulator. Therefore the regulator gave to much current to the rotor. When the battery was fully charged on cruising i.e - the rotor got too much current from the battery and burned down..."


Also check:

Your rotor has about 5 ohm? The diodes are ok?


4.06.04 Measuring the Rotor

CAUTION! Every time you measure small resistances you should first check what resistance value your multimeter shows when the measurement wires are short circuited!

Very seldom it is zero. Especially with the cheap multimeters. The higher price ones might have some zeroing adjustment. And then when you measure the rotor resistance directly from slip ring to slip ring, at least another brush disconnected, you sould subtract this short circuit resistance value from the one that the meter displays.

For example: Measurement wires short circuited - 0.4 ohms The meter shows 5.2 ohms slip ring to another The resistance of the rotor is 5.2 - 0.4 = 4.8 ohms

I also once discussed with Ken about this issue. The resistance measurement of the multimeter uses very low voltage and current to get the resistance. There can be some phenomenas in XS650 rotor that show only when you use the real voltage ( >12 V) and the real current (> 2 amps).


--herbs 15:08, 13 Sep 2005 (CEST)


4.06.05 Rotor rewind & Repair

In the US (or out of the country I suppose) call Custom Rewind at 1-800-798-7282. They also have a new website: Custom Rewind They do great work for around $100.00 US funds.

--CLAY November 11, 2006


4.06.10 Brushes and how to change them

wire routing limits travel of brush when brush is worn out to stop wire end inside of formed brush from damaging rotor slip ring

Image:xsbrushes.jpg

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