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3-Phase Motorcycle Voltage Regulator Circuits

3-Phase Motorcycle Voltage Regulator Circuits

The post discusses a list of PWM controlled 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.

motorcycle alternator voltage stabilizer circuit

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.

PWM controlled motorcycle alternator battery charger 3 phase

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

MOSFET controlled shunt regulator circuit for motorcycle

The second design presented below is a Rectifier plus Regulator for a 3-Phase charging system of Motorcycles. The rectifier is full-wave and the regulator is shunt-type regulator.

By: Abu Hafss 

Motorcycle Battery Charging System

A motorcycle's charging system is different from that on cars. The voltage alternator or generator on cars are electro-magnet type which are quite easy to regulate. Whereas, the generators on motorcycles are permanent magnet type.

The voltage output of an alternator is directly proportional to the RPM i.e. at high RPM the alternator will produce high voltages more than 50V hence, a regulator becomes essential to protect the entire electrical system and the battery too.

Some small bikes and 3-wheelers which do not run at high speeds, only have 6 diodes (D6-D11) to perform full-wave rectification. They don't need regulation but those diodes are high ampere rated and dissipate a lot of heat during operation.

In bikes with proper regulated charging systems, normally shunt-type regulation is used. This is done by shorting out the alternator's windings for one cycle of the AC waveform. An SCR or sometimes a transistor is used as shunting device in each phase.

 Circuit Diagram

Rectifier plus Regulator for a 3-Phase charging system of Motorcycles

Circuit Operation

The network C1, R1, R2, ZD1, D1 and D2 forms the voltage detection circuit, and it is designed to trigger at about 14.4 volts. As soon as charging system passes this threshold voltage, T1 starts conducting.

This sends current to each gate of the three SCRs S1, S2 and S3, via current limiting resistors R3, R5 and R7. D3, D4 and D5 are important to isolate the gates from each other. R4, R6 and R8 help in draining any possible leakage from T1. S1, S2 & S3 should be heat-sinked and isolated from each other using mica insulator, if using common heat-sink.

For the rectifier, there are three options:

a) Six automotive diodes

b) One 3-phase rectifier

c) Two bridge rectifiers

All must be rated at least 15A and heat-sinked.

The automotive diodes are two types positive body or negative body hence, should be used accordingly. But they might be little difficult to contact to heat-sink.

Using Two Bridge Rectifiers

If using two bridge rectifiers, they may be used as shown.

Using Two Bridge Rectifiers

Bridge Rectifier

Automotive diodes

Automotive diodes

3-phase rectifier

3-phase rectifier

Bridge Rectifier


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

71 thoughts on “3-Phase Motorcycle Voltage Regulator Circuits”

  1. HI I want to build the second circuit that uses MOSFET and my alternator puts out around 90 volts at high RPM and I need a regulator that puts out around 15 at all RPM’s will the 555 timer circuit work the one that uses MOSFET like will it maintain a steady voltage?

    • Hi, yes it is supposed to maintain a steady voltage depending on the PWM adjustment, however the mosfet could get significantly hot, therefore a large heatsink will become mandatory for the application.

  2. Hi Swagatam,
    Forgot to mention that my DC generator is permanent magnet type. So i opine that the circuit built based on your last explanation should work perfectly i guess. Waiting for your expert suggestion please.


    • Hi Deepak, it doesn't make of a difference since the circuit will rectify any form of current applied across the bridge network according to me….whether it's a square wave signal sine wave signal or plain DC…all will be combined and presented across the (+) (-) output of the bridge

  3. Dear Swagatam,
    Your last explanation that states "PWM circuit could be corrected by replacing the three BJTs with a single powerful mosfet, and by connecting its drain/ source right across the output of the bridge network….this will solve the issue entirely" seems much simpler and sensible. Please update the design such that other members in this forum are also benefited. Thank you for your time and happy dipawali.


  4. Hi Swagatam,

    In both circuit diagram, the alternator AC output is directly connected to transistor 3055 collector. Will transistor work on AC? or diodes needs to be connected in series in between?


    • …the above PWM circuit could be corrected by replacing the three BJTs with a single powerful mosfet, and by connecting its drain/ source right across the output of the bridge network….this will solve the issue entirely. I'll try to update the modified design soon in the article…

  5. Hi Swagatam,
    Thanks for reply. I would be grateful if you could send the final working circuit made by Mr. AHMAD JAUHARI? My mail id is 'basanta.dhakhwa@gmail.com'. I have one more question. To handle the large current of 100A at 48V, i will need sizable capacity of both MOSFET and Diode right? So instead of using high amp MOSFET and power Diode, what if i use SCR which can be fired as required plus does the rectification at the same time. Please suggest.


    • Hi Deepak, All these circuits are perfect according to me, as you may see there's nothing complex or doubtful with their configuration, so please rest assured if you build them correctly and carefully these will work as per the expectations.

      for 100 amps only the bridge diodes needs to be rated at much higher above 100 amps (with heatsink), other diodes are not relevant to the 100 amp current so those can be ordinary 1N4007 type.

      SCRs are ideally high voltage low current devices, therefore not suitable for your application.

      By the way here's another article which you can refer, you can try any of the last two designs for your need


    • …if you are using mosfet then please go through the earlier comments on top for knowing which parts can be eliminated for mosfets.

  6. Hi Swagatam,
    Can this circuit be used for 48V battery charging with charging current up to 100 Amps. I have a DC battery charging diesel generator and the regulator has gone faulty in it. I wish to build this circuit if it can be replacement for faulty unit. Kindly please advise. And yes i want to use MOSFET instead of BJT for handling high current. Thank you.


    • Hi Deepak, yes definitely you can use it for your a 100 amp application by replacing the BJTs with high power mosfets capable of handling over 120 amps…and mounting them on large heatsinks.

    • Hi Deepak

      First of all, please clarify what is the type of the generator i.e. Permanent Magnet type or Field Coil Type. Both have different circuits.

    • Deepak

      As requested earlier, you should clarify the type of the generator you have. The above circuits are suitable only for a 3-Phase, Permanent Magnet Generator. If it is single phase Permanent Magnet Generator or Field Coil Generator then the regulators circuits would be different. This information is important so that anybody helping you will guide you on the correct track and of course, save time.

  7. Hi Swagatam,

    Sorry to take long time to post again, so I finally got it working. It turned out I miss connecting the output from the alternator to bridge pins, that's why it looked like it is not working. Now the output voltage measured is maintained at 15V max throughout engine RPM range and it is able to deliver 3A of current at 1K RPM, very nice design.
    I do have something in mind i would like to ask.

    1. Is the 47K preset value is crucial in the design, because I cant't find any 47K trimpot right now. So I'm using a 50K trimpot instead of 47K, is that okay? the final result is fine thou.
    2. What is the main consideration of using 1 ohm resistor between emitter and ground of the BJTs, can I remove it if using a mosfets?


    • That's wonderful Ahmad, thanks for updating the info!

      1) the 47K preset is not critical, in fact I have approximately assumed the value with respect to the 10K on the upper side….you can use any other value ranging from 22K to 100K

      The 1 Ohm is related to the max current handling capacity of the transistors, it's for safeguarding the transistors from getting completely shorted with ground.

      You can use Ohm's law for determining them for your transistors as per their max current rating.

      If the rating of the mosfets is greater than the alternator max current generating capacity, then it those resistors can be eliminated

  8. Hi sir thank you for your wonderful design,
    I am just concern if how can it be possible
    if i use an arduino mcu instead of 555 and what is the possible connection?
    Can I also use optocoupler to isolate the supply to arduino? TIA

    • Hi Em, thanks!

      you can replace the pin#3 output line with your Arduino output for achieving the same results.

      an opto coupler can be used.

    • Thank you very much sir,
      can i also used the part where you placed a zener diode?
      can I replace it by an arduino port so i can manage and fixed the output voltage? thanks 🙂

  9. but the opamp will provide around 12V output voltage swing with R1 = 10K (in the mentioned circuit), right?

    I don't realy sure about that short circuiting an alternator output could be equivalent to an open circuit as it is always brings down the engine rpm whenever I manualy short circuiting the output leads. I haven't had time and proper equipment to investigate it thou

    • yes when the opamp output is triggered high, the alternator is shunted to ground which switches OFF the opamp, and this ON/OFF switching continues rapidly sustaining a constant preferred voltage across the output

      right, open circuit means no current flowing while short circuit means full current flowing and shunted, how can both these conditions produce identical results? that does not make any sense

    • from what I get from the article, there's some sort of magnetic field created during shunting process which cancels the magnetic field from the permanent magnets thus no voltage generated in the stator. it could be true of false, need to prove it thou

  10. Hi, can I use the schematic for shunting 2 alternator output in the same connection. I have alternator with stacked windings, that is another winding on top of first windings so I have 2 set of pole in one alternator

    • Hi, I am not quite sure about it, if it matches the shown the three phase winding then probably you can try configuring them in that manner and see the effect

    • Hi, you did mention the transistor can use IRF540 instead of shown BJTs. I'm a bit confused with instruction on place 1K resistor across gate and ground, can you email me simple illustration on how to do this (1K resistor placement). And where should the G D S pins go in the shown schematic, I really need to build this regulator as my RR always failing (dunno why but I suspect due to high operational temp from the RR itself in such a confined space. wewh)

      • It is not difficult, just replace the D with the collector, G with the base, and S with the emitter of the existing BJTs.

        connect 1K across all the G and S of all the fets. the 100 ohm from the 555 pin3 can be eliminated and pin3 directly connected with the diodes (optional though)

    • is the diodes at the G pins still required or it's okay to omit it.

      I'm planning to build it this weekend, I will keep you posted for the result on my configuration

    • I think the diodes could be eliminated, and the gates joined together with pin3 of the IC, and in that case you could even skip the recommended 1K resistors across G and S of the fets, those won't be required now.

    • If the mosfet replaced with IRF840, is the component values still the same or is it have to be modified again? my seller sent me the wrong mosfet, he sent me IRF840 instead of IRF540. Will the IRF540 survive with slightly higher voltage on high rpms? I'm reading 100-110 volts in high rpm in open circuits AC.

      About the stator current measurement, I cant read the amperage with 2 probe type multimeter. It's reading zero but the resistor connected between one of the probe and stator lead is getting hot (1.2 ohm 5 watt). Connecting the probes directly to the leads also can't have fixed reading, briefly connecting and disconnecting the the probes do have some reading and the engine getting slightly stalled when the probes connected directly to the leads.

    • no changes would be required in the circuit even with an IRF840…

      you can use the same circuit…you can try using a moving coil type meter and add a shunt resistor across its terminals for measuring the alternator current. this shunt resistor value and the meter reading together can be calculated for understanding the approximate current from the alternator.

      for your present meter it should be in the AC range for reading the current

    • Hi, I have built the circuit in a bread board and tested it. But it's not working as expected. Maximum voltage regulated is only about 10v at peak 10K rpm, it should be about 100v at peak rpm when not connected to anything.

      I tried to check if the PWM function is working by connecting a light bulb to one of the mosfet and it is not conducting in response of the pwm adjust trimpot, the bulb is dimly lit on one full side of trimpot and fully off on the other side. While the other mosfet is like alwas conducting no matter how much I turn the trimpot (the bulb is lit dimly thou).

      What did i do wrong with the circuit, is this type of shunting not suitable for this, is it better to use the SCR version of regulator?

      I'm pretty much confused now

    • I think your 555 circuit is not working or has some fault, you can check it separately with a bulb across its pin3 and ground…and by increasing the 10nF capacitor to 100uF, this will slow down the frequency and allow you to see the bulb illumination period in response to the PwM pot setting clearly.

      because if the PWM works then the transistors will conduct according to its dutycycle and control the alternator current accordingly.

      By the way I also have two more similar concepts using SCRs and a single mosfet which you can refer to through the search box.

    • It could be the 555 circuit, I will check the circuit again this weekend or next week after ramadhan is over.

      The one using mosfet have updated diagram which use BJT instead of mosfet, can I just replace the BJT with a mosfet?

      Actually I'm much more interested building the one with the SCR as it is a parallel type regulation and it will prevent the stator from creating very high voltage. What modification should be made if I want to use mosfet instead of scr, It's more efficient and less heat generated in the mosfet (i think)

      check out this link below, it tells a story about shunting permanent magnet alternator (most motorcyle is using this type of alternator)

    • Mosfet is good because these are designed to handle high current and lower voltages whereas SCRs are opposite with their specs. Since for a motorcycle alternator the voltage gets restricted to 14V but current is much higher, therefore mosfets look a better option.

      However in the linked article, the following line looks controversial:

      "Shorting stator coils yields the same behavior of magnetic drag (magnetic reluctance) as open circuiting them, thus no Power is consumed and no drag is felt"

      by the way you can try the last circuit from this article, you can replace the BJT with a mosfet, but remember the minimum optimal triggering gate voltage is 10V :


      How can a short circuited alternator output could be equivalent to an open circuit output??

  11. Can 7812 ic handle the power from alternator after rectifier? When the engine start i measure the output voltage of alternator is 14volt AC. Anyway I'll try to do your suggestion.

    • if the supply is a rectified DC and is below 35V then the 7812 will be able to handle it easily, because here the load is a 555 iC circuit whose requirement is not more than 50mA

  12. Julian, the IC is to be connected with an attached battery…if you connect it with an alternator directly then obviously it will blow off.

    alternatively you can try using a 7812 IC regulator between the 555 supply and the alternator or the battery.

  13. Sir, I've tried this circuit. Pwm ic 555 exploded when linked to the alternator and the engine started, what's the problem? pins 4 and 8 on my pcb circuit connect directly to the 3 phase diode cathode. Im using TIP 35 for transistor. Thanks for your help.

  14. Interesting circuit, thanks for sharing. However, I'm not sure if the regulator would work since the alternator works from 1,000RPM to 10,000RPM, hence the frequency of the AC signal is not constant, therefore the PWM signal would not switch the power BJT on time in the whole alternator bandwidth. Also, how can the PWM signal control the average output voltage if you do not have a zero cross detection circuit?

    Instead of the 555, I would rather recommend an MCU to add zero cross detection and auto regulated output voltage across the entire alternator bandwidth.

    • the above circuit allows a safe maximum voltage to be set for the battery, it's not meant to stabilize the voltage, here the shunting of the excess voltage is adjustable as preferred by the user and controls the excess voltage above the set value from entering the battery.

    • Thanks for the reply.

      Could you please explain how the user can adjust the shunting of the excess voltage?

      Please correct me if I'm wrong: the 100K trimpot adjusts the duty cycle of the PWM signal, which triggers the TIP3055 and sends _part_ of the sine wave generated signal to ground. Nevertheless, the adjustment would not work for the entire generator bandwidth, since the PWM signal does not change its frequency. The output voltage should be set at 14.5v to properly charge the battery, however the load also changes if the battery is charged or discharged, turning on and off the headlight would also change the load. A motorcycle voltage regulator should keep the voltage within 13.5v and 14.5v at any given engine RPM.

      Please be as detailed as possible in your explanation, I would really like to understand your design, since I'm struggling to design a voltage regulator circuit for permanent magnet motorcycle generator (the one used here).

      Thanks again.

    • as I mentioned in the earlier comment the circuit is not designed to produce a constant voltage across the battery terminals, it's designed only to allow the user to choose how much voltage and current needs to be shorted or shunted to ground…this shunting magnitude is variable through the 100K pot.

      frequency parameter is immaterial here…rather the pulse widths decide for much long the transistors need to conduct and short the alternator power to ground which in turn determines how much average voltage is allowed to reach the battery for a safe charging.

      The second circuit is even more sophisticated as it ensures that a peak voltage not higher than the zener diode value is allowed to reach across the battery terminals under any circumstances.

  15. Hi Mr. Swagatam.
    I am newbie on electronics.
    Can you explain further how to adjust the PWM pot at the circuit of battery charger above? TIA.

    • Hi Tia, the PWM decides the average output voltage across the bridge rectifier.

      so you can measure the output voltage with a volt meter and simultaneously adjust the PWM pot until the right voltage reading is achieved….

  16. Dear Sir

    If we use MOSFET instead of BJT what is the mosfet part number. And what are modifications to do. I'm going to build this circuit because my bike's R/R fails every time and have to charge the battery manually. I thank you very much for your help.

    • Dear Prabuddha, you can try IRF540 instead of the shown BJTs.

      only one change will be required in the circuit, you'll need to put resistors across the gate and ground of each mosfet, the values could be 1K for these resistors

    • first try without heatsink, if you see the transistors getting considerably warm in that case you can think of putting separate heatsinks for all three of them

  17. Dear Sir

    Could you please supply a rectifier circuit with detailed part numbers because my bike rectifier and regulator comes as a single unit

    Thank you

    • I doubt if 6 x 1N5408 would do the job because they are just 3A diodes. Depending on the electrical system of a bike, they should be capable of bearing at least 10A. And according to my experience the rectifier section needs a good heatsink.

  18. Hi Swagatam

    How will this circuit regulate the battery charging voltage? The transistors should shunt when the input voltage reaches the threshold voltage, particularly 14.4 – 14.7V.

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