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Thread: Alternator problem… again.

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  1. #1 Alternator problem… again. 
    club member Club Member element's Avatar
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    Seasons greetings...

    Fiat Twin Cam 2.0 version 1983. I inherited the car from my dad, he built it 2001-2002. It sat under a cover for 8yrs then I got it running and have been maintaining it this last 5 years. Initially the alternator worked then it stopped working and I replaced it with one from eBay. 2 yrs later this ‘new’ alternator stopped charging the battery. I took this alternator last yr to an auto electrics specialist in Glasgow & they overhauled it and I refitted it and all was well again.. I have barely driven it 20 miles this year (what with the incumbent elephant) but that red light has come on again on the dash. Sure enough when I put my meter on the battery when its running; it’s not being charged. Yet if I leave it to cool down and try the next day start the engine, car stationary – it is charging… when it’s hot it stops charging.
    So has anyone found a similar problem & if so how did they fix it? – Or shall I just replace it again for another one off eBay at £67?
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  2. #2 Re: Alternator problem… again. 
    frequent forum contributor Club Member stevejgreen's Avatar
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    Quote Originally Posted by element View Post
    Seasons greetings...

    Fiat Twin Cam 2.0 version 1983. I inherited the car from my dad, he built it 2001-2002. It sat under a cover for 8yrs then I got it running and have been maintaining it this last 5 years. Initially the alternator worked then it stopped working and I replaced it with one from eBay. 2 yrs later this ‘new’ alternator stopped charging the battery. I took this alternator last yr to an auto electrics specialist in Glasgow & they overhauled it and I refitted it and all was well again.. I have barely driven it 20 miles this year (what with the incumbent elephant) but that red light has come on again on the dash. Sure enough when I put my meter on the battery when its running; it’s not being charged. Yet if I leave it to cool down and try the next day start the engine, car stationary – it is charging… when it’s hot it stops charging.
    So has anyone found a similar problem & if so how did they fix it? – Or shall I just replace it again for another one off eBay at £67?
    Is it a Lucas one. It could be diodes failing, a fairly easy diy fix.
    MOC member since 05/97
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  3. #3 Re: Alternator problem… again. 
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    Contact the repairers and get them to fix it!
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  4. #4 Re: Alternator problem… again. 
    club member Club Member andyf's Avatar
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    Quote Originally Posted by HairyDave View Post
    Contact the repairers and get them to fix it!
    +1

    Also is it close to the exhaust manifold? It could be that a heat shield would help keep it cooler
    Mk2 SWB Marina Roadster with a 2.0L Pinto built in 1986
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  5. #5 Re: Alternator problem… again. 
    club member Club Member element's Avatar
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    Gave it some thought and I wonder - if it works when cold but when the engine is hot it doesn't - could it be the belt is slipping when hot? I have had trouble with belts - there's not a lot of room and there's only one size /type I can use. I fit them when it's cold (obviously ) but maybe I can try tightening it while wearing gloves when it's hot and see if that fixes it... worth a try... I know nothing about diodes - or indeed what make the alternator is. However I have plenty to be getting on with... Timing belt change, exhaust removal , make new gasket and refit, handbrake cable replacement... Just as well there's a lockdown!
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  6. #6 Re: Alternator problem… again. 
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    Its a possibility, but unlikely, usually A loose belt squeals on starting when the alternator puts the power back in the battery. My suggestion is to ring the 'reconditioner' and tell them your problem. A decent company will ask for it back to check it over. Did you ask for it to be reconditioned or for a 'first aid repair' where they fix what is wrong and nothing else? Good luck and a Happy Hogmanay!
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  7. #7 Re: Alternator problem… again. 
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    The diode pack is unlikely to be the fault, if a diode brakes down it does not repair itself depending on the underbody temperature. What you would get is a half wave rectification a mixture of AC/DC supply voltage to the battery. This would fry the battery which you do not say is happening. It is more likely to be the voltage sensor being affected by the temperature. This means that when it is cold it produces an output from the alternator providing the battery voltage is lower (it wont if it is not). And when the battery voltage is high, it cuts of the supply to the battery until the battery voltage is reduced. Then turns back on the output from the alternator. This also explains that when it is repaired and tested in a workshop the alternator is cold and their will be an output. I hope that this helps Stuart
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  8. #8 Re: Alternator problem… again. 
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    Hi , Also suggest checking / cleaning Alt connections also Eth cable connections from engine block to chassis - there could simply be a high resistance connection which is breaking down when heat expands the metal.

    Good luck and Best wishes to everyone for 2021 - better times are on the horizon !! Paul W
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  9. #9 Re: Alternator problem… again. 
    club member Club Member element's Avatar
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    Quote Originally Posted by d068795n View Post
    The diode pack is unlikely to be the fault, if a diode brakes down it does not repair itself depending on the underbody temperature. What you would get is a half wave rectification a mixture of AC/DC supply voltage to the battery. This would fry the battery which you do not say is happening. It is more likely to be the voltage sensor being affected by the temperature. This means that when it is cold it produces an output from the alternator providing the battery voltage is lower (it wont if it is not). And when the battery voltage is high, it cuts of the supply to the battery until the battery voltage is reduced. Then turns back on the output from the alternator. This also explains that when it is repaired and tested in a workshop the alternator is cold and there will be an output. I hope that this helps Stuart
    This sounds likely - where would I find the voltage sensor? - I imagine it isn't part of the alternator itself; if it is part of the charging circuit - I can maybe find it if I trace around the engine bay & hunt for it - if I knew what it looked like - presumably it is from the original donor Fiat Argenta?
    The alternator is earthed with a braided strap; it looks ok.

    When the repairer 'repaired' it - they also replaced the pulley, I believe they are a good business. Trouble is they are in Glasgow and it's an awkward haul to get there and back and then go back another day to collect it... Given the history of the problem - I surmise the fault doesn't lie with the alternator itself - I have had cars with no alternator problems over 10yrs+ yet this is a repeat of a repeat...
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  10. #10 Re: Alternator problem… again. 
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    My Alfa engined Roadster had a separate/remote voltage regulator despite if I remember it being a Bosch alternator. It looked like a slightly bigger version of the voltage stabiliser they use on Smiths instruments such as fuel and temp gauges. It's a sealed unit so non adjustable.
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