Strange electrical with 405 SRDT
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  1. #1
    Fellow Frogger!
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    Default Strange electrical with 405 SRDT

    Strange thing this morning with my 405 SRDT ,when I switched it off the battery warning light came on. I switched it back to accessories position and the light went out but the accessories worked i.e. radio etc. I disconnected the battery for a while then reconnected it and the same thing. Everything works ok but the battery light does not show on accessories position or while waiting for the glow plug light to go out then when actually starting it shows momentarily then goes out when the alternator starts to charge as normal. Switch it off and remove the key and the light stays on.
    Anyone have a thought on this. any info would be appreciated.
    Regards Dennis.

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    maybe the diodes in the alternator are shot allowing ,current back through the warning light ,or you may have some wires shorting someplace .PUGS

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    Quote Originally Posted by pugwash View Post
    maybe the diodes in the alternator are shot allowing ,current back through the warning light ,or you may have some wires shorting someplace .PUGS
    Nope, it wasn't this with mine.- There is something strange in the dash. Pulling fuses didn't stop the radio turning itself on. I drove the car for about 18 months disconnecting the battery whenever the car was to be left overnight, but leaving it connected in carparks etc during the day. The car has been retired with extreme prejudice at 315,000 km

    If there is a closed retifier diode the alternator will whine and get hot, plus it won't be able to keep the battery charged with AC or cooling fans / lights running.

    Best of luck, but it won't be an easy fix.

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    1000+ Posts robmac's Avatar
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    Alternator field diode short, short in main winding if the 'star' point is used to to drive the charge light or short in the wiring in between.

    I guessing the first option.
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    Fellow Frogger! Bruce Llewellyn's Avatar
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    Quote Originally Posted by robmac View Post
    Alternator field diode short, short in main winding if the 'star' point is used to to drive the charge light or short in the wiring in between.

    I guessing the first option.
    Not sure if this can put power in downstream of the ignition service relay. From memory the alternator output lead goes to the hot side (starter cable) so is on the wrong side of the ignition switch circuits, so a closed retifier diode will simply flatten the battery.

    Unless there's a fault that allows the alternator field to be re-energised via the regulator power transistor. As far as I know the 405 alternator is a twelve pole claw type, so doesn't have any diodes in the field coil circuit, just a power transistor and some kind of zenner reference circuit. I'd assume that it won't regulate if it's failed in such a way as to feed current back into the car downstream of the ignition service relay.

    I think the star point is grounded in these alternators, and the six rectifier diodes feed the output terminal and the ground.

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    Get rid of the Valeo and fit a bosch from a Falcon (EL I think but might be EA) . Only a few minor things to do with the wiring and grinding a tad off the mounting bracket. Also have to make up a different bracket to fit on the top...easy, Reliabilty 2nd to none with the bosch and cheap as chips for spares at Wreckers.

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    Easiest way is to remove the alternator and take it to a auto electrician and ask them to bench test it.
    They should be able to test it on the spot and tell you if anything is wrong with it.

    I have seen faulty dashes cause this on other cars. But normally other parts of the dash will play up to. (lights/gauges not working or lights coming on when they shouldn't or dim lights.
    normally caused by a faulty plug. you could try fiddling with the plugs at the back of the dash to see if anything happens.

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    Quote Originally Posted by gromzx View Post
    Easiest way is to remove the alternator and take it to a auto electrician and ask them to bench test it.
    They should be able to test it on the spot and tell you if anything is wrong with it.

    I have seen faulty dashes cause this on other cars. But normally other parts of the dash will play up to. (lights/gauges not working or lights coming on when they shouldn't or dim lights.
    normally caused by a faulty plug. you could try fiddling with the plugs at the back of the dash to see if anything happens.
    The dashboard will eat your hand...

  9. #9
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    Quote Originally Posted by Bruce Llewellyn View Post
    Not sure if this can put power in downstream of the ignition service relay. From memory the alternator output lead goes to the hot side (starter cable) so is on the wrong side of the ignition switch circuits, so a closed retifier diode will simply flatten the battery.

    Unless there's a fault that allows the alternator field to be re-energised via the regulator power transistor. As far as I know the 405 alternator is a twelve pole claw type, so doesn't have any diodes in the field coil circuit, just a power transistor and some kind of zenner reference circuit. I'd assume that it won't regulate if it's failed in such a way as to feed current back into the car downstream of the ignition service relay.

    I think the star point is grounded in these alternators, and the six rectifier diodes feed the output terminal and the ground.
    If the alternator is built without field diodes how does the field excite?

    http://www.google.com.au/url?sa=t&rc...DBds9oDjqbv9RQ

    Field diodes are small diodes, usually in potted enclosure near the main diodes. You wouldn't normally see field diodes without pulling the machine apart.

    The reason faulty field diodes cause issues is because the machine fails to fully excite. This causes the charge indicator lamp to flicker or fail to extinguish.

    The star point cannot be grounded because it effectively shorts out the main diodes. The star point, with respect to earth will however, generate an AC voltage which is frequency proportional to engine revs, this is sometimes used for other functions in the vehicle ECU.
    Last edited by robmac; 25th November 2012 at 04:58 PM.
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    Thanks for the interest. I had hoped that it may be simple and it probably is if one is educated in electricals and familiar with this particular system. I think it is off to the Auto Electric man. There is an honest trader in the business in Orange so I will talk to him tomorrow. I will convey the answer to the problem when it eventuates.
    Regards Dennis.

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    I had the alternator checked by an Auto Electrician today and it was indeed a diode that was causing the unusual reactions of the charge light. Also the output was only about 10 volts and it was declared kaput!!! They dont try to fix them because they cant get parts they tell me. Incidentally the Bosch alternative would appear to be non viable because the 405 SRDT alternator is a one off with a very unusual mounting.
    There are some available in GB for 80 pounds plus postage but they look Chinese, anyone had any experience of these? Local new original equipment items appear to be worth more than I paid for the car.
    If anyone has one suitable for a 94 SRDT 405 I could be interested.
    Regards Dennis.

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    had mine brought back from the dead by an old tradesman at KIRRA ,Caravell imports quoted me about $400 a t the time cost me $250 had to have the slip rings replaced and bearings ,and yes i think the ford one fits a petrol motor but the diesel one is a different animal ,try Lam Lam in bris was advertising here on parts for sale a while ago ,mine was also saturated with power steer oil as i had a leak in the low pressure pipe from the steer pump directly above it, try french connection in melbourne 0393354008 i have one off an s1 MI 16 that looks close although it has a different width belt and the electrical connections are a bit different, you could possibly swap the pulleys has to be someone on here more in the know PUGS

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    Thanks for all the suggestions etc. I got hold of a new Valeo for $440.00 (Gulp) but at least it should be OK. Interestingly I bought the car for $750 with about 8months rego and almost new tyres with 335000km on it and it has been very good . Seems better value than $440 for an alternator. I think I am getting old.
    Regards Dennis

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    http://www.nationwideautoparts.com.a...5%20ALTERNATOR


    Nationwide have a unit available. But you are probably better off with the valeo.
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  15. #15
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    Robmac. Thanks for the info but I have ordered the Valeo. I have it on pretty good authority that the DIesel one is a one off and the others do not fit however the info on the one you reported says Petrol/Diesel which sounds a bit suss. My source is a long time 405 SRDT owner and parts supplier and has always put me on the right track.
    Thanks to all contributers to this thread , we all learn by them.
    Regards Dennis.

  16. #16
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    Quote Originally Posted by robmac View Post
    If the alternator is built without field diodes how does the field excite?

    http://www.google.com.au/url?sa=t&rc...DBds9oDjqbv9RQ

    Field diodes are small diodes, usually in potted enclosure near the main diodes. You wouldn't normally see field diodes without pulling the machine apart.

    The reason faulty field diodes cause issues is because the machine fails to fully excite. This causes the charge indicator lamp to flicker or fail to extinguish.

    The star point cannot be grounded because it effectively shorts out the main diodes. The star point, with respect to earth will however, generate an AC voltage which is frequency proportional to engine revs, this is sometimes used for other functions in the vehicle ECU.
    Interesting. It seems to have two rectifiers...one for powering the field. Not what I'm used to with older external rectifier types.

  17. #17
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    Just a quick finale to my story . I fitted the Valeo alternator today (gee it is easy when you know how it all goes together) and all the problems are solved , including a strange noise (reverberation) on cold start then disappeared when it warmed up. All warning lights working as designed. Very good result.
    Regards Dennis.

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