Info Manual

Another Motorcycle Voltage Regulator

This is a circuit for regulating the output voltage on small engines. This circuit will work on engines that were originally equipped with a shunt type of voltage regulator. It is common on motorcycles, skidoos, ATVs and other recreational vehicles. This circuit was tested out on a Suzuki GS400E motorcycle and seems to function fairly well.



The above picture in comparison with the other voltage regulator posted here SCR regulator was, this one uses differential amplifier to detect battery voltage and control SCR .This has a number of advantages over using a zener diode to directly trip the gate of the
SCR.

 These are:
1)If the battery voltage is forced above 13.5V, the circuit limits the current into the gate of the SCR 
preventing damage to the regulator when changing the battery 
2)The circuit is more stable over temperature. 

The main drawback is that the circuit is leaky. The differential pair should be connected after the ignition
switch to prevent the battery from draining when the engine is not used for a long period of time. This
connection is shown as MONITOR in the schematic. The output of the bridge rectifier ties to the battery at
the BATTERY connection.

With the differential pair, the base input for Q2 is connected to a voltage reference consisting of D1 and
R9. The base input for Q1 is connected to a voltage divider that monitors the battery voltage. When the
voltage on the base of Q2 is higher than the voltage on the base of Q1, Q1 will turn on shunting all of the
current from R5 to ground. When the voltage on the base of Q2 is lower than the voltage on the base of
Q1, then Q2 will turn on. This will shunt the current of R5 through the limiting resistors to the gates of the
SCR. The SCR will turn on and short out the phase. Since the stator voltages are AC, the SCR will reset at
the end of the cycle when the voltage reaches 0.