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Zener diode and rectifier

Discussion in 'Norton Commando Motorcycles (Classic)' started by pierodn, Aug 31, 2015.

  1. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi All.
    Please, Could you please explain to me what they are and they work?
    Can the zener diod burn or go out?
    In case, what happen?.
    Thank you.
    Piero
     
  2. lrutt

    lrutt

    Joined:
    Jan 16, 2008
    Re: Zener diod and rectifer

    Rectifier takes the AC waveform from the alternator which would measure 0 volts DC, flips part of it over so that the AC humps are all on the positive side of the line and now you have a DC type component. Looks like a series of boobies from the top.

    So now you have this lumpy looking waveform. The Zener will take that lumpy waveform and smooth it out some. Zeners can come in different voltage levels depending on the output you want. Ours is roughly 13v to allow the battery to charge and run the lights etc. Any excess voltage is bled off to the ground and dissipates in the form of heat. That is why the Zener is mounted on that big aluminum Z plate. It is a very rudimentary voltage regulator. but it works.

    Yes, any of the parts can burn out. It can blow open which it then does nothing, or it can short which will then cause smoke to be released from the wires and the electrical system will shut down until the smoke and wiring is replaced and a new Zener installed.
     
  3. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    Re: Zener diod and rectifer

    This sketch is not pretty, but a picture is worth a thousand words.

    Rect&Zener.jpg

    I hope this helps.

    Slick
     
    Last edited: Jun 25, 2018
  4. 84ok

    84ok

    Joined:
    Aug 10, 2014
    Re: Zener diod and rectifer

    first thing to check is all wiring for clean solid connection, if the zener fails, electrical stuff (lights etc) can burn out from too much juice including the batt

    a zener can fail for many reasons (could just be a loose connection), if it does, which you need to determine and confirm first, you then need to find out why, then fix, starting with basics, cheap and easy stuff first,

    otherwise you can end up replacing good parts until you may get lucky,

    what problem are you having? charging? overcharging? blowing fuses? something else?
     
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    But, hopefully, the fuse will (or at least should) blow before that happens (unless of course somebody has fitted a 35A continuous fuse in place of the 35A blow fuse)? :roll: :wink:
     
  6. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi Les,
    Please, could you explain the differences from countinuos and blow fuse?
    Thank you.
    Piero
     
  7. 84ok

    84ok

    Joined:
    Aug 10, 2014
    if a fuse is blowing, which one?
     
  8. 84ok

    84ok

    Joined:
    Aug 10, 2014
    it just means you have to use the right fuse otherwise that alone can cause problems, too big you can have a fire, too small and it can blow for no reason other than that
     
  9. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    Lucas rated their auto fuses using the "fusing" or "blow" amp number, so a 30mm glass 35A Lucas fuse as specified in manuals and handbooks has a continuous rating of 17A and will blow(fuse) at 35A.

    Any other type of non-Lucas fuse available nowadays is likely to be marked with the continuous amp rating (such as blade fuses etc.) and thus blow at double the marked amp rating, therefore the nearest equivalent continuous rated (blade etc.) fuse will be either 15A (30A blow) or 20A (40A blow).

    http://www.groups.tr-register.co.uk/nen ... 20BUSS.pdf

    SOME Lucas type fuses are marked with both ratings:
    [​IMG]
     
  10. Rusty bucket

    Rusty bucket

    Joined:
    Sep 18, 2014
    Re: Zener diod and rectifer

    Thanks guys for the explaination quoted above and the prior explaination. I've been wondering about these diodes and want to pick a few up for my road kit. Is there an easy way to test them with a multimeter?
     
  11. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    Rusty Bucket wrote:

    ". Thanks guys for the explaination quoted above and the prior explaination. I've been wondering about these diodes and want to pick a few up for my road kit. Is there an easy way to test them with a multimeter?"

    The multimeter, using the Ohms function, can only determine if the diode (either a common diode or a Zener) conducts in one direction, and blocks current in the reverse direction. If it conducts both ways it is shorted; if it does not conduct in either direction, it is open circuited. The diode must be out of the circuit for this test. The test is done by reversing the multimeter's + / - leads on the diodes conductors.

    Special test equipment is necessary to test if a Zener diode "avalanches", or suddenly conducts at the Zener reference voltage. This assumes the Zener is not in a functioning circuit. It it is, then the voltmeter on DC voltage scale, should read the Zener reference voltage if all parts of the circuit are working properly and the circuit is energized.

    Slick
     
  12. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    The high 35amp blow is fitted to a lot of British tin boxes in ALL the fuses and is too much when the vehicle gets old, the fuse doesn’t blow, but the wiring harness burns out, as I found to my cost
     

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