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  1. #1
    Join Date
    May 2016
    Location
    Barnsley
    Posts
    68

    LED alternator warning light

    Hi all,

    So, finally got LS3 running properly this week (ropey Omex connector to camshaft position sensor) then realised I wasn't charging battery through alternator.

    After some digging around I eventually worked out it's because I'm using an LED for the battery warning and not a conventional bulb which draws more amps.

    Being a wiring duffer, does anyone have a get around for this and what/ where can I get the bits to get around it? I'm using CBS 16mm chrome bezel LED's which I think look great - but only if they work....

    Cheers, Bence

  2. #2
    Join Date
    Aug 2009
    Location
    Birmingham
    Posts
    587
    Quote Originally Posted by Bence View Post
    Hi all,

    So, finally got LS3 running properly this week (ropey Omex connector to camshaft position sensor) then realised I wasn't charging battery through alternator.

    After some digging around I eventually worked out it's because I'm using an LED for the battery warning and not a conventional bulb which draws more amps.

    Being a wiring duffer, does anyone have a get around for this and what/ where can I get the bits to get around it? I'm using CBS 16mm chrome bezel LED's which I think look great - but only if they work....

    Cheers, Bence
    You could try running a resistor in series, this should cause more current to be drawn.

  3. #3
    Join Date
    Dec 2008
    Location
    Newcastle upon Tyne
    Posts
    1,857
    Bence,

    You are right in that the use of an LED, in place of a conventional filament bulb, will be causing the problem. A resistor in series would increase the total resistance and therefore reduce the current flowing to the alternator.

    I believe that some on this forum have used an LED successfully in this situation and hopefully they will post to share their experience.


    Regards,
    Ian
    Pilgrim Sumo Mk3; IVA Apr. 2014; RV8 3.9 EFi ; Cosworth T5; Granada Donor
    Phase Two underway - Conversion to Japanese

  4. #4
    Join Date
    Feb 2014
    Location
    bristol
    Age
    38
    Posts
    205
    Think it's something to do with the LED only being one way, whereas a normal bulb is 2 way, the charging light goes out when the two voltages equalise across the bulb which they can't do over a one way LED. The quickest fix i think is a proper bulb hidden behind the dash with a jumper off to the LED.....

    ....I think! 😬

  5. #5
    Join Date
    Jun 2003
    Location
    Brackley, Northants, England.
    Posts
    821
    Come on Daryn, this is pre school playgroup electrics. Ian is right you need a resistor in PARALLEL with the LED to increase the current.

    The Alternator needs a small excitation current to get it to start producing some current to charge the battery and this is normally provided via the so called ignition light. An LED with it's series resistor won't provide enough so a resistor of around 47R in parallel with the LED should sort it. I use that value on my car with a LED. Bear in mind it will dissipate around 4 watts when not charging so I used a 25W metal clad type resistor bolted to a piece of aluminium that I already had for other purposes behind the dash. A normal 5W resistor could get hot enough to melt any wiring that touches it.

    LEDs normally only have a small reverse voltage rating so I put a cheap 1amp diode (1N4006) in series with the connection to the Alternator. This ensures that current can only flow into the Alternator. It also prevents any high voltage spikes from damaging the LED by reverse voltage.

    I assume you are using a 12V LED indicator with internal resistor. If not you'll need to put a resistor in series with the LED as you probably know.

    HTH

    Denis

  6. #6
    Join Date
    May 2016
    Location
    Barnsley
    Posts
    68
    Thanks for the comprehensive reply Denis,

    No being in the least bit electrically or electronically biased, the terminology amounts to the the sum total I can see with my eyes closed....

    In answer to your latter question, yes it's a 12v LED from CBS so assume with internal resistor. The 47R resistor and 1amp diode, while much appreciated advice on, you may as well be talking Hebrew to me!

    Any chance you can add a simple schematic and part numbers/ sensible description that I can order the rocket ship components by?

    Sorry for being a duffer but simply, I'm a duffer, at least with wiring....

    Cheers, Bence

  7. #7
    Join Date
    Jun 2003
    Location
    Brackley, Northants, England.
    Posts
    821
    Bence...
    PM me your Email address and I'll put something together for you .
    Denis

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