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Comprehensive GL1000 Charging System Troubleshooting

This Tech Tip is provided courtesy of Ray Proebstl of Munich, Bavaria, South Germany. Ray is a professional educator in the field of electronics. He is a long-time avid GoldWing enthusiast.

Here are the components of the GL1000 charging system, this diagram was part of a complete wiring diagram to be found here

Typical Problems:

Undercharging: the battery is only partially charged and starting the bike after a week or two is impossible, the starter won't spin.
Overcharging: battery electrolyte is "boiled" dry and electronic components fail.

Battery Theory:

A lead acid cell has a typical voltage of 2 Volts (without load). Depending on how it is charged, the voltage goes from 1.8V (deep discharge) to 2.4V (fully charged). Like almost any automotive battery, the GoldWing battery has 6 cells, typical voltage 12V. A good charging system supplies a maximal voltage of 14.4 Volts (6 x 2.4 V). If you charge a battery with 14.4V, the charging process automatically stops, when the battery has also reached 14.4V. If you charge it with a higher voltage, the battery fluid will be electrically divided into hydrogen and oxygen, coming up as bubbles and leaving through the breather tube. This gas mixture is highly explosive! Finally, when all the fluid is gone, the battery is dry, with only acid residue remaining in the cells. That is why you must not add acid only when the battery fluid level is low, but only distilled water!

This means: you cannot effectively charge a battery with a voltage less than 12V or higher than 14.4V.

Testing the Battery:

Go to a garage or shop where they sell automotive batteries, they usually have special devices (load testers) to check the battery. It is not possible to make reliable tests with a normal gauge/multimeter.

Alternator Theory:

The GL1000s have a 3-phase-AC-generator located on the left side of the engine above the clutch in the rear engine cover. The alternator is maintenance free, You would have to pull the engine to get access to it. It consists of a stator with 18 coils and a rotor with six magnets. The eighteen coils on the stator are actually only three coils, each divided into six parts. In wiring diagrams the three phase generator is therefore shown with three coils only. They are connected to form a Y, the ends of the Y are the yellow wires coming out from the rear engine cover.

I call them A, B and C, but they are electrically equivalent. These stator coils are isolated and not connected to ground.

Testing the stator coils for continuity:

Unplug the 3-wire stator connector.
Using a normal ohm gauge or multimeter, set it to measure small resistances (lowest ohm range)
Check the resistance between:
- wire A and B
- wire B and C
- Wire C and A
You should always have about the same reading, which is typically between 1 and 2 Ohms.
Any resistance value greater than this on any of the wire pairs means that phase has failed and the stator must be replaced.

Testing the stator coils for ground faults:

Switch to a high ohm range on your multimeter and check the insulation of the coils by measuring the resistance between A and ground, B and ground, then C and ground.
Use a reliable ground point such as the rear engine cover.
You should get infinite resistance (or anything around 10k Ohms or more). The more the better.

If both continuity and ground tests are satisfactory, your stator is healthy.

Rotor theory:

A rotating magneto field creates AC voltage in the stator coils. The stronger the magnetic field, the higher the voltage. The faster the rotation, the higher the voltage. The GoldWing rotor has six permanent magnets and is connected to the crankshaft by a chain. That means: The output voltage of the stator is low at idle and maximal at 8000 rpms, because the magnetic field cannot be controlled and is always constant. (Automotive alternators have a rotor with a so-called field coil, which is nothing else but a magnet with variable strength. Automotive alternators reduce the magnetic field in the rotor with rising rpm, therefore the output voltage is constant.)

Testing the rotor is not practical. The rotor magnets may have become weak by age, vibration and heat. Measuring the magnetic field is very complicated. You can test the magnets indirectly by measuring the output voltage they create in the stator. More about this method later.

Charging system:

It consists of a 3-phase rectifier unit located to the left of the battery:

...and a regulator unit under the left "false tank" half:

The rectifier unit transforms 3-phase AC to DC by the help of six diodes. With the stator producing various voltages, depending on engine rpm, the DC coming out of the rectifier is also not constant. It can go up to 100V at 8000 rpms! What can be done now? Honda engineers found a very simple but primitive method: They installed a regulator unit, which drains current from the stator coils when the voltage gets too high, thus causing the voltage to drop (a "shunt" regulator).

Testing the charging system:

Attach a DC voltmeter to the battery terminal while the engine is running. (Or use the DC 20V range of your multimeter). The battery voltage should not drop below 12V when idling, and should be between 14 and 14.5V at 3000 rpms. It should never exceed 15V. You can additionally test the current with an additional ammeter, see picture below.

If the voltage is always too low, either the rectifier unit is damaged (probably) or the regulator unit (sometimes). A third, not very probable, possibility is the rotor magnets, which might have aged (see above).

Rectifier theory:

A rectifier is an electrical device that converts alternating current (AC) to direct current (DC) through the use of diodes. Diodes are passive semiconductors which allow current to flow in one direction only. They can be tested with a diode tester or Ohmmeter. A three-phase generator requires six diodes to make DC. There are cheaper ones with only three diodes, but these are not used in GoldWings.

Test the rectifier diodes as shown here::

Regulator theory:

The more load you put on a generator, the more its output voltage collapses. Honda engineers put a variable load in the shape of a regulator on one coil of the stator. This regulator shunts current to the ground, thus simulating heavy load. If all lights are off, battery full and the engine revs at 8000 rpms, the shunted current is maximal. All lights on, empty battery and engine idling, it is minimal.

In my eyes it is not the best solution to regulate a voltage, but for sure it works. Negative aspects are: The alternator always is under full load. High currents produce heat and stress to electronic components. Fuel efficiency is slightly decreased. The future will bring better regulator units.

Testing the Regulator:

Additional information:

The ground wires in the harness are green. Make sure there are no loose connectors between wires and good ground terminals everywhere. Discolored connectors (brown or black) or corroded connector metal is an indicator for a bad connection. Sometimes connectors cannot be properly repaired, cut them off and solder new connectors to the ends.
If a connector isn't pulled often, you can also eliminate it by soldering the wires together. This is often recommended for the 3-wire stator connector if it has been overheated, distorted or badly oxidized.
Connection terminals can be coated with a smear of dielectric grease to retard oxidation.
Replacing a failed stator unfortunately requires engine removal.

Ray Proebstl - Munich, Bavaria, South Germany

email Ray at: monaco2010@gmx.de

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