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Rectifier Help Needed

Discussion in 'General Electronics Discussion' started by Classicglory, Apr 1, 2015.

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  1. Classicglory

    Classicglory

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    0
    Apr 1, 2015
    Hi,

    I am converting a system which originall used a 2 diode rectifier and some awkward alternator coil and resistor switching to run the full alternator output through a bridge rectifier and then a voltage regulator circuit.
    This is the alternator setup....
    [​IMG]

    My question is.... How do I achieve the full output?
    Do I just connect to the top and bottom connections and leave the middle one unused?
    WIll this provide full wave output?

    Please help as I do not fully understand alternators...

    PS. not sure if it makes any difference but it is a Inductance alternator and not a revolving magnet alternator.

    Regards

    ClassicGlory
     
  2. Miguel Lopez

    Miguel Lopez

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    63
    Jan 25, 2012
    Gryd3 likes this.
  3. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    It would help if you would give more information on the alternator. Is it on a motor bike or car or is it in a power station to provide electricity for a town? How about a picture?
    Variable speed alternators are designed differently from fixed speed alternators but have similar circuitry.

    As Miguel has said, if you want DC, use a polyphase rectifier which has six diodes to get maximum output.

    What do you mean by an inductance alternator? All those I have seen have a rotating magnet, either supplied with a slip ring or with rotating diodes (brushless).
     
  4. Classicglory

    Classicglory

    3
    0
    Apr 1, 2015
    Ermmm yes, sorry a little more info should have been provided...
    Its a 1940's Motorcycle Single Phase alternator produced by Lucas.
    The model number is 1A45 and I believe that means its an inductance alternator (whatever that means) with a 45 watt max output. The later Lucas motorcycle alternators were all numbered with an RM number, which stood for Rotating Magnet. This early one was a step between the RM series and the even earlier Magnetos, which definitely used slip rings etc... I do not know anything about the internals of the 1A45 other than the drawing I provided though....
    Thanks to anyone who can help me....

    Classicglory.
     
  5. duke37

    duke37

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    769
    Jan 9, 2011
    Present day vehicle alternators are built with considerable leakage inductance which means that the current is limited and they will not burn out if shorted. The impedance of the inductance is proportional to frequency as is the generated voltage. These two cancel to give a current limit which does not depend much on speed. Some small motor cycle alternators do not have voltage regulators and depend on the correct load being applied.

    Magnetos that I have seen do not produce low voltage output, the slip rings are to output the spark voltage.

    Lucas produced much vehicle equipment and you may be able to find a web site which deals with this.

    If this alternator has 1940s rectifiers, then a considerable improvement will be achieved by fitting silicon diodes or even Schottky diodes
     
  6. Classicglory

    Classicglory

    3
    0
    Apr 1, 2015
    As I said this is an old device and originally was installed like the diagram at the bottom of this post...
    The terminal numbers on my coil wiring match the terminal numbers on the schematic.
    As far as I know there was no current limiting, and all that happened was that when the lights were switched out, the resistor in the headlight was switched into the alternator circuit to limit (dampen) the output voltage.
    This arrangement uses a rectifier with only 2 diodes (not 4). I want to use combined regulator rectifier which includes a bridge rectifier on its first stage and allow this to control the battery charging voltage.
    This will eliminate the headlight resistor and coil switching.

    So my question is:- Do I just take G2(G4) and (G1) outputs to the RR input or do I tie G3 and G1 together to one leg on the AC input of the RR and take G2(G4) to the other one.
    OR
    Am I barking up the wrong tree and need a completely different approach?

    Regards

    Classicglory

    [​IMG]
     
  7. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    I met a retired electrical engineer at the supermarket a couple of days ago. He said the Bantam alternators were very reliable. To get maximum output, first check that the magnets are OK which they will not be if the alternator has been dismantled.

    I would forget the centre tap and fit a bridge rectifier across the full winding. Feed into a capacitor to check the voltage at maximum revs and then use a buck converter to drop the voltage to 7V. You should get a considerable increase in power without dissipation in a resistor.
    For the headlight, you could use a current output converter to drive a led.
     
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