Self Excite an Alternator Without Any DC Generator, Capacitor Bank or Battery





Introduction: Self Excite an Alternator Without Any DC Generator, Capacitor Bank or Battery

About: Its all about life hacks, tools, scientific & creativity instructables ~ electron7m


This instructable is for converting a field excited alternator into a self-excited one.The advantage of this trick is that you won't have to power the field of this alternator with a 12 volt battery but instead it will power-up itself so that you can use it as a normal self-excited home generator.

Also, this method doesn't involves any additional components like capacitor banks, dc generators or a battery.Its just a simple trick with wires.

You can directly watch the step by step video.

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Step 1: Things Needed:

  1. an alternator
  2. a dc motor
  3. pulley and belt.
  4. multi-meter
  5. mobile charger
  6. 2 x laptop chargers
  7. crocodile clips
  8. 12V bike head lamp bulb
  9. Wooden Board 30 x 30 cm^2
  10. Vice

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Step 2: Mechanical Connections:

First we will do the mechanical connections and then we shall proceed with the electrical connections.

Take a DC motor of around 500W and connect a Pulley on its shaft.Now take a wooden board of 30 x 30 cm^2 and Mount the DC motor on one side of that board.

Take a vice big enough to Mount an alternator and place it on the other side of the wooden board.Use screws for mounting it properly on the wooden board and then Mount the alternator on it.

Take a belt to connect the pulleys of the DC motor and the alternator as shown in the picture.

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Step 3: Electrical Connections (Alernator):

Rotor (field) - The red and the blue wires of the alternator are of the brushes which are connected to the rotor (field) with the help of the slip rings.Red is for positive and blue is for negative.

Armature - the big long screw of the alternator is the main output positive terminal and it separate from any other screw on alternator.

Connect the positive red wire from the brushes to the main positive terminal (long screw) of the alternator.

*Note - in the second picture, the red wire is not directly connected to the main positive terminal of the alternator since the red wire wasn't long enough.The screw to which I connected the red wire was indirectly connected to the main positive terminal (the long screw) of the alternator so it worked the same.You can without hesitation connect the red wire from the brush to the main long screw positive terminal of the alternator.

Connect the negative blue or black terminal of the brush to anywhere on the body of the alternator since its at ground negative.

Outside power source - take a 5 volt mobile charger and connect its positive wire to the main positive terminal (long screw) of the alternator. Connect its negative wire(usually black) anywhere on the body of the alternator.

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Step 4: Electrical Connections (DC Motor):

You can use any mechanical rotating source to rotate the shaft of the alternator.

I have used a 100 volts DC motor because of which I had to use 2 laptop chargers.I connected them in series 20 volts + 15 volts making an overall voltage of 35 volts.

I used a 35V DC source because I didn't have a hundred volts DC source to run the motor at rated RPM and torque. Still i achieved around ~400rpm which was enough to self excite the alternator.

Step 5: Testing:

So anyways, after doing all the connections simply start you mechanical source (DC motor in my case).

After the entire system is in motion, simply disconnect the mobile charger & remove it.Your alternator is self excited now.

Take a multi-meter and connect its positive terminal to the main positive output of the alternator (long screw) and touch the negative terminal of the multi-meter to the body of the alternator it shouldn't get some voltage (~5V DC in my case).

At 1000+ rpm, an alternator generates 14.4V for charging batteries.The achieved RPM for my alternator was only ~400 because of which it generated only 5 volts DC but yes the self excitation project was successful.

So that was all for this instructable guys.

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    11 Discussions

    I think someone is self exciting themselves


    7 months ago

    This is B.S.

    Try using this as a small windmill and you will soon realize that it is not a "Self Excite" alternator!

    Why title/claim as "Self Excite" when you're using external power to get the excite?

    Your title is "Self Excite an Alternator Without Any DC Generator, Capacitor Bank or Battery" but you use a mobile charger??

    4 replies

    Yess but then the charger can be removed after it gets self excited

    Yes but it is not self excited at that point it is self fed in that once started producing current it no longer needs exciting

    I hate to be 'that guy' - but this is the principle by which the alternator normally works in your car. Once the field gets power and the alternator generates electricity, the system operates at a higher voltage than the battery, so it could be said the alternator is 'self exciting' at that point. You can actually pull the cable off the positive battery terminal once the engine is running and it will continue to run because the alternator is powering its own field coils. This is NOT recommended, however, because the power surge could possibly fry the expensive electronics in the car, and there's also the possibility of a spark which could ignite hydrogen gas generated by the battery.

    Yes you are right but the instructable is about making those connections yourself..

    Your title implies that any outside power source is un-needed which is obviously not the case.

    Also the procedure of removing the external source from the output terminal effectively removes the voltage reference that the electronic regulators need,instantaneously frying it!

    This may work on older alternators but it's instant death to modern day stuff.

    You would be better off using a permanent magnet 3 phase motorcycle alternator though some means of voltage control would be required.

    Perhaps I'm missing something here .

    You are supplying a voltage but more importantly a current to get it started and then it runs and produces a larger current.

    OK well that's exactly what is done by feeding a current through the pilot light . The pilot light feeds in the same but this is done with a diode in that line so that when the alternator starts producing current no more current passes down the pilot light and it goes out . Same thing as you have but just a better way because the pilot light tells you that the alternator is charging the battery.

    The pilot light needs about 100 milliamps usually and you will notice that LEDs often don't work because they don't pass enough current.