This is application is used with single-phase alternators.
capacitor alternator 
The alternator is driven by the engine and makes the rotor rotate. The rotor is remanently magnetized and creates a rotating field.
The capacitor makes sure that current (that lags 90° behind the induced voltage) goes through the stator’s secondary winding. The current will make sure that voltage is generated in the rotor’s primary winding and that a direct current is immediately rectified thanks to the rotating diodes. The direct current in the rotor takes care of the rotating field and the generation of voltage in the stator’s windings.
When the generating set is charged with a load, a reverse magnetic field is created in the stator, which is absorbed by the rotor’s secondary winding. The produced voltage in the rotor’s secondary winding is rectified by the rotating diode. That voltage intensifies the direct current of the rotor’s primary winding. The combination of two direct currents is called the ‘compound effect’. This helps the alternator to start loads with high starting currents.
Checking the capacitor
We recommend you to measure this with a multimeter, which has a function to measure the capacity. The measured capacity may not exceed the capacitor value with more than 5%.
Solving a problem
If you have a problem with your capacitor-assisted alternator, you can find your problem in this table.
No voltage without any loads during start Connect 6V DC to one of the capacitors during 1 second The generating set builds up voltage and the voltage remains available, even when the battery is removed Not enough remanent magnetism
Check the capacitor’s voltage (10 to 15V on the secondary winding when the capacitor isn’t connected)
The generating set builds up voltage but the voltage is too low when the battery is removed Check if there is no interruption in one of the capacitor’s circuits
The generating set builds up voltage but the voltage disappears when the battery is removed Diodes are broken
Voltage too low
Voltage too low Check the speed Right speed Interruption of the stator’s secondary winding
Rotating diode (rectifier) is burned
Short circuit in the rotor’s primary winding, check the resistance value
Speed too low Increase the speed
Voltage too high Reduce the speed   Speed too high
Correct voltage when no loads but too low with loads     Speed too low with loads
Check the speed
Engine overloaded
Short circuit in the rotor’s primary winding
Check the resistance value



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