Voltage Regulator Problem 12V

Discussion in 'The Projects Forum' started by doug08, Nov 7, 2012.

  1. doug08

    Thread Starter Member

    Jan 30, 2011
    I have an inverter generator that I made which uses a GM 10SI alternator(One Wire). Needless to say the regulator became faulty. I decided to remove the v-reg and use the attached circuit instead(the upper circuit). All components are as described, tested as NOT faulty, and wired properly. I live in a remote area where parts are not readily available, hence why I am making one. I removed the old v-reg and ran a wire from the diode trio which use to connect to it, and the wires from the field(brushes), and a ground wire. I connected the circuit up as follows: diode trio output to the top rail of the schematic, the remaining field wire to the collector of the trans with the diode, and the ground wire. Nothing happened. So I also connected the battery and trio output together and tried it again.....and as soon as the engine started the alternator was putting out a lot of voltage/current. It was reading 16.4V. Too high. I did not have a 13v zener, so I used 2 in series. 9.1V & 3.6V.

  2. JDT

    Well-Known Member

    Feb 12, 2009
    OK, so your alternator definitely works, then!

    The voltage rating of the zener diode is going to be quite critical. If it's too low then the zener will conduct,and the 2N3904 will switch on with the normal standing battery voltage - and switch off the field current - before the alternator is operating.

    If the zener voltage is too high the alternator will attempt to overcharge the battery. A high current will flow and the battery will boil!

    A better circuit would have a voltage reference, op-amp or comparator and a voltage feedback chain with a potentiometer so that the correct voltage can be carefully adjusted.

    BTW Expect the transistor that drives the field to be switching, probably at the AC ripple frequency - which can be quite high - kHz. The diode across the field winding is essential.
  3. Audioguru


    Dec 20, 2007
    I suspect that you have one or both transistors connected with the collector and emitter pins swapped. Look at the pins on the datasheets.
  4. doug08

    Thread Starter Member

    Jan 30, 2011
    No, I have been doing electronics for a very long time. I double and triple check to make sure the pinout is correct. I also verify it with a very good component tester. It tells me the pinout for any transistor connected to it.

    Can anyone suggest another circuit to use?