Car Alternator Regulators

Created: "Mar 2, 2011"
Updated: "March 4, 2015

As a Request from a guy wanting a Voltage Regulator to give: Much Higher Voltage Outputs from a Car Alternator,

So I designed up these Circuits below.

1) The Upper Circuit on the Schematic below is for a typical 14.5 Volt output to charge a 12 volt car battery. This one connects through the Ignition Switch and has No Warning Light.

2) The Middle Circuit on the Schematic below is also for a typical 14.5 Volt output to charge a 12 volt car battery. When car is off, No power goes through the Rotor Winding, as the Drive transistor is fully Off.

3) The Lower Circuit can be set to Higher Regulated Output Voltage Levels. But it still Requires a 12 Volt Battery to drive the Field Coil.

4)NEW: A Revised Circuit and PCB for the Higher Voltage Regulator.

NOTE: Adding a Diode in Series with a Zener will increase its voltage by 0.6 Volts. So a 12 Volt Zener with the Series Diode will be 12.6 Volts. So in these Circuits it will charge at 14.6 Volts.

Most car Alternators draw about 2 Amps on the field coil and the TIP121 Darlington Transistor is rated at 5 Amps.

From my Tests, it should be quite satisfactory without overheating. For added Safety, I Do RECOMMEND using a Small "Heatsink on this transistor".

Also be aware: The Alternator requires a Higher RPM, if it is to generate a High Voltage. EXAMPLE: For 100 Volts Output, you will require a Engine RPM of around 2000 to 2500 RPM.


The Diodes in Alternators can Vary in Voltage Ratings. Some may be as low as 30 Volts, while others may be 50 or 100 Volt Ratings.

If you DON'T Know which Diodes you have in your Alternator, I Suggest you REPLACE Them with Appropriately Rated Diodes.

Also, Definately Fuse the Output appropriately.

For BEST PROTECTION, Put your new Diodes External to the Alternator and add a Seperate Inline Fuse going into Each Diode.

And Remember: DIODES Require Suitable HEAT SINKS, if expected to operate at their Rated CURRENT! Also make sure these Diodes have a Good Air Flow for Cooling.

"Back to My HOME Page"

  Regulator Schematic

 Regulator PCB's.

  Revised, Higher Voltage Regulator Schematic.

  Revised, Higher Voltage PCB Artwork.

"Doug's Alternator/Regulator & Generator"

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