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Thread: Alernator charging problem.

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  1. #1 Alernator charging problem. 
    frequent forum contributor Club Member element's Avatar
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    Among many other components, a few years ago I had the alternator repaired and it has been fine until recently. Fiat engine. The usual check is to put a meter on the battery terminals with the engine off and then with it running and you should see a voltage of 12/ 12.8 with the former and some 13.7/14.2 with the latter.
    I checked it and got 12.6 first and 13.75 next. All well and good. However, when out on the road I have begun to notice the red bezel light glimmering while driving, then it comes on full after a few miles. Sure enough I stop outside my house, switch off and then try to turn the ignition on and the battery is flat! I jump start it with another battery then put it in the garage overnight with the battery charger on all night. The next day its fine and fully charged. I check and get a good cold voltage and she starts instantly. I check the volts when it is running & they're up in the 13.8 region. I take her out and again the same thing - the current drops off and the battery is flat - so I put it back in the garage on charge again.
    So clearly there is an issue with the charging circuit. I am planning to find and rewire the alternator to battery feed as I suspect maybe there's a poor connection in it which drops off during the vibration of driving. Am I missing something? Is there another explanation? - the battery wasn't under excessive load, no lights, no wipers just ordinary running. It is a good battery.
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  2. #2 Re: Alernator charging problem. 
    frequent forum contributor Club Member greyV8pete's Avatar
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    First check the ignition warning light bulb is tight in its holder. Better still re0ace it with a new one! If it blows or goes open circuit the alternator wont sense any current in that circuit and wont charge the battery. Next check all connections, especially earths and recheck any connections that you have recently disturbed! If that fails then best pop the alternator out and have it checked out on a test rig, if you can find anywhere that can do this anymore! :-(
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  3. #3 Re: Alernator charging problem. 
    frequent forum contributor Club Member Gareth's Avatar
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    I've had that before. The alternator was duff. Ok when cold but circuit breaking down when warm. Have you tried measuring output when the engine is hot?
    Gareth.
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  4. #4 Re: Alernator charging problem. 
    frequent forum contributor Club Member element's Avatar
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    Ok, food for thought there.. I checked the wiring and find it all looks good except for a thin wire coming from the back of the alternator; I imagine this will go to the red bezel light (ignition warning lamp). I had thought that the alternator was always charging the battery whenever the engine was running.. perhaps not then. It wouldn't surprise me if the alternator is playing up; it is 36 years old... I'm not sure whether I'd be able to source a 'modern' alternator replacement that will fit this engine? I'll check it again now cold, start up check again then a few times in a short drive to get the engine hot then list all the figures and go from there..
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  5. #5 Re: Alernator charging problem. 
    frequent forum contributor Club Member element's Avatar
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    I can hardly believe my eyes... !

    https://www.ebay.co.uk/itm/192355490153
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  6. #6 Re: Alernator charging problem. 
    frequent forum contributor Club Member element's Avatar
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    Ok, when I think about it.. I believe I bought the alternator as a replacement when the old one died completely; I may have bought it from this above supplier about 3 years ago; can't remember, have an invoice somewhere but atm can't find it. So I didn't get the alternator refurbished - instead I replaced it. It's thus likely not that old after all.

    I measured the vols across the battery cold; 12.71v I then started it up and the same measure was 12.44v so it wasn't charging at all. Switch off and the measurement was 12.6v.

    There's 2 wires coming from the back of the alternator; a thick one and a thin brown one. The thin one in its circuit actually goes with the thick one to the starter motor but doesn't connect to it; it turns off and joins to another wire somewhere (limited vision atm). The thin one goes through 2 old push block connections and it has another joint wrapped with insulating tape. I suspect this is the weak link and I'll replace it with a single good new wire throughout and see if this improves the situation. If not - it's only a few quid for a spool of wire and my time; compared to splashing out on a(nother) £110 alternator.
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  7. #7 Re: Alernator charging problem. 
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    The thin wire from the alternator always goes to the bulb on the dash . In your case it appears to go via connectors that may well due to the age of the wiring now be be corroded. This wire as greyv8pete correctly states is vital to charging. That dash bulb is the load that excites the diode pack into charging.

    I would separate the thin wire from places it joins and ensure that it has very low resistance with an ohmmeter . You will then soon identify the part that has high resistance that either needs cleaning up because of green corrosion or replacing as its corroded and also gone very rigid due to overheating.

    Very unlikely to be anything else. Incidently, the correct method to test the alternator is to put the headlights and heater on and anything else that pulls a current load and ensure that the alternator gives at least 13.8 v but less than 14.7 v . You may have to run at a faster idle e.g. 1500rpm to achieve this.
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  8. #8 Re: Alernator charging problem. 
    frequent forum contributor Club Member element's Avatar
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    I plan to cut and solder a new wire from as close to the alternator as I can right through to as far as I can define the thin wire; thus replacing it as best I can and see whether this makes a difference; I expect it is as you suggest - old and corroded at the joints.. a bit like myself!
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  9. #9 Re: Alernator charging problem. 
    frequent forum contributor Club Member kahawi's Avatar
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    A ‘quick-n-dirty jury-rig’ test:- Run a loose wire from that ‘thin’ one on the alternator (disconnect the other end) via a 12-volt 6-watt bulb, (not LED) direct to the battery ‘live’ (or via cigarette lighter socket)? It should light up bright.

    Fire up the engine and see what volts are heading into the battery, try a few revs under load, lights, heater etc. Temporary ‘Ignition' bulb should now be out, or very dim if all is working, then you can get loom/wire tracing!

    Don’t rule out bad/dodgy earth between alternator and bracket, engine to chassis etc.
    Last edited by kahawi; 27-07-2019 at 09:50 AM. Reason: Added do not use LED bulb
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  10. #10 Re: Alernator charging problem. 
    frequent forum contributor Club Member element's Avatar
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    Ok, the results are in..
    I rewired the ‘thin wire’ from the alternator to the red bezel on the dash direct (over the windscreen not around the engine bay). Measured the cold volts and they were 12.67v then I switched the ignition on and as normal, the red bezel lit up. I turned the engine on (red light went out) and checked the volts with it running; 13.68v, gave it some rev and it maxed around 13.84v.
    I then turned the headlights on and instantly, the red bezel it up bright. I checked the volts and they were 12.31v lights on and engine running; no charging happening.
    I could remove the alternator & take it to a place in Glasgow (Shandon Electrical Ltd) which refurbished the starter motor for me (they did an excellent job); I’m sure they could resolve the problem. Likely cheaper than a new £110 one from Ebay. That is – if it is the alternator that is at fault; I don’t see anything else that could cause this problem; the alternator must be faulty.
    The earth strap engine to chassis is fine, the alternator is bolted direct on the arm to the engine; that can't be the problem.
    Last edited by element; 27-07-2019 at 04:40 PM.
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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