The AC output from the alternator is directly related to the engine speed as the rotor is attached to the end of the crankshaft.
The AC current from the alternator supplies the Rectifier and is converted into DC current, which is in turn fed to the lead acid battery. The Zenor diode is mounted on the right footrest bracket which acts as a heat sink. The purpose of the diode is to regulate the flow of current to the battery. Excess current is converted to heat and dissipates through the alloy foot rest bracket where the Zenor diode is mounted.
A more detailed explanation of the charging components used is below:
There are a few ways to troubleshoot alternator coils. It is easiest to test it while still installed on the bike.
- Disconnect the wires coming from the alternator. (White/Green and Yellow/Green)
- Connect a voltmeter with a 1 ohm resistor in parallel to the wires. Make sure the voltmeter is switched to AC.
- The reading at the voltmeter with the engine revs at about 3000 rpm should no less that 9 Volts.
Rectifiers of this type (Silicon bridge connected full wave) should be handled delicately on removal or replacement. When tightening be sure not to twist the plates or internal connections will be broken.
It is possible to test a rectifier. If your rectifier should fail a modern type Solid State rectifier is recommended.
Testing a rectifier while still attached to the bike.
- Disconnect the wire from the center terminal at the rectifier.
- Connect a voltmeter with 1 ohm resistor in parallel. Connect red lead from meter to the bike frame, and the black to the center terminal. Switch the voltmeter to measure DC.
- Start bike and run at about 3000 rpm.
- The reading should be above 8 volts. If it is below you have a faulty rectifier.
- There are other test which can be performed. When I have figured them out I will post here!
In general the 2DS 506 type rectifiers are very reliable. The only problems I have had are with wires being loose on the terminals or coming right off.
This is how I would check the operation of a Zener Diode.
- Remove battery from bike, charge until it is fully charged, then replace and reconnect.
- Connect a meter between Zenor Diode terminal and feed cable. Positive wire from meter to the diode. Switch meter to amps.
- Connect another meter between the diode terminal and the footrest bracket (earth/ground). Red wire from the meter should go to ground. Switch meter to DC volts.
- Start the bike with meters connected.
- Ensure there is no current draw on the battery (lights are off)
- Increase engine speed slowly.
- Up to 12.75 volts on the DC meter there should be Zero amps on the current meter.
- Between 13.5V to 15.5V there should be 2 amps.
- The Zener diode must be replaced if the ammeter shows a reading before the volt meter reads 12.75V or if the voltmeter shows more than 15.5V before the ammeter reading has reached 2 amps.
Zener Diodes are not repairable, and must be replaced when faulty. It is critical that when refitting a Zener the contact between the heat sink and diode is good and clean. The diode nut must be torqued to 26 lbs/inch.
I am thinking about replacing my Zener diode and rectifier with a modern solid state system, which should be more efficient. I was waiting for something to go wrong but nothing has gone wrong with my system yet. In fact I have never had a problem with Commando charging!
The electrolyte level should be between the 2 level lines marked on the battery. If the level becomes low top up with distilled water.
Always check the battery level before or after charging to get an accurate measure. While charging the electrolyte level rises as the battery gets hot.
To check the electrolyte specific gravity, a hydrometer is required. Follow the instructions which came with the hydrometer.
For more information about the battery check the Technical Data section.