The post discusses a simple 3 phase motorcycle voltage regulator circuit which may be used for controlling the battery charging voltage in most two wheeler. The idea was requested by Mr. Junior.

Technical Specifications

hello my name is junior live in Brazil and work with manufacturing and recovery regulator rectifier motorcycle voltage and would appreciate a help u, I need a three-phase mosfet regulator circuit for motorcycles, entreda voltage 80-150 volts, correte Maximum 25A, maximum consumption of the system 300 watts,

I await return

The Design

The proposed 3 phase motorcycle voltage regulator circuit for motorcycle may be witnessed in the diagram below.

The schematic is rather easy to understand.

The 3 phase output from the alternator is sequentially applied across three power transistors which basically act like shunting devices for the alternator current.

As we all that while operating, an alternator winding could get subjected to huge reverse EMFs, to an extent which could get rip of the insulation cover of the winding destroying it permanently.

Regulating the alternator potential through the method of shunting or shorting to ground helps to keep the alternator potential under control without causing adverse effects in it.

The timing of the shunting period is crucial here and directly influences the magnitude of current that may finally reach the rectifier and the battery under charge.

A very simple way of controlling the shunting time period is by controlling the conduction of the three BJTs connected across the 3 winding of the alternator, as shown in the diagram.

Mosfets could also be used instead of the BJTs, but could be mush costlier than the BJTs.

The method is implemented by using a simple 555 IC PWM circuit.

The variable PWM output from pin3 of the IC is applied across the bases of the BJTs which in turn are forced to conduct in a controlled manner depending upon the PWM duty cycle.

The associated pot with the IC 555 circuit is appropriately adjust for obtaining the correct average RMS voltage for the battery in charge.

The method shown in the 3 phase motorcycle voltage regulator circuit using mosfets can be equally implemented for single alternators for getting identical results.

Peak voltage adjustment

A peak voltage regulation feature may be included in the above circuit as per the following diagram, in order to maintain a safe charging voltage level for the connected battery.

A quick review of the designs reveal that the BJTs are incorrectly positioned, which would never allow them to shunt both the halves of the alternator current.
However the designs could be modified appropriately in order to correct the aforesaid issue, as shown below:

Finalized Circuit Diagram

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