Jim F Posted November 9, 2014 Report Share Posted November 9, 2014 I'm having an odd problem with the charging system on my TR5. When I start the engine the ignition light goes out as you'd expect it to do. However, after I've driven for about an hour the ignition light comes on when the rpm drops below 1,000. If I then let the engine cool for an hour or so and restart the engine the ignition light goes out immediately, (as you'd expect). I'm thinking I might have an alternator component that failing as the alternator temperature rises, but I'm guessing. I removed the alternator and had it tested but no problem was identified. The alternator is a "fiesta" alternative. Anyone experienced a similar problem? Advice welcomed. Thanks Jim Quote Link to post Share on other sites
Dick Posted November 9, 2014 Report Share Posted November 9, 2014 You might have a brush sticking. Easy to check. Quote Link to post Share on other sites
john.r.davies Posted November 9, 2014 Report Share Posted November 9, 2014 An obscure ignition light problem I had was due to poor engine earthing. Since then, I've had a length of starter cable bolted between the engine and the body shell earthing point. John Quote Link to post Share on other sites
RogerH Posted November 10, 2014 Report Share Posted November 10, 2014 Hi Jim, if it happens repeatedly then suspect the Alt diode pack. When it gets warm/hot things can happen. Either change the diode pack or the Alt. Roger Quote Link to post Share on other sites
littlejim Posted November 10, 2014 Report Share Posted November 10, 2014 have seen a similar symptom caused by the age of the bulb (old) in the indicator light. in that case changing the bulb stopped the problem. Quote Link to post Share on other sites
Jim F Posted November 11, 2014 Author Report Share Posted November 11, 2014 Gent, thanks for the feedback and Littlejim I like the old bulb theory! As I slept on the problem one other question came to mind - given that the light comes on at ~1,000 rpm after approx an hours drive and at that point the battery is fully recharged, (and therefore demanding little from the alternator), what is the "ignition light" sensing? Is the ignition light telling me that charging voltage from alternator is too low after an hours drive? Not sure this alters any of your suggestions but any answers will add to my understanding of alternators. Thx Jim Quote Link to post Share on other sites
graeme Posted November 11, 2014 Report Share Posted November 11, 2014 Jim, The lamp shows that there is a difference in voltage between the alternator O/P and the battery voltage. You would have to use a voltage meter to determine which side is higher. As Roger has suggested the diode pack is most probably the cause. Not sure how an old bulb could effect the system but would be interested in an explanation. Cheers Graeme Quote Link to post Share on other sites
RogerH Posted November 11, 2014 Report Share Posted November 11, 2014 Hi Jim, what does the bulb do? With ignition on but engine not running the battery has higher volts than the Alt so a voltage flows and the light glows brightly. With an old dynamo if the tick over is low then the dynamo output is low so a small voltage is sensed across the bulb and it glows dimly. At 1000rpm with an Alt that should not be the case as there is plenty of grunt. If the diode pack goes dicky then that would/could allow a path for the bulb voltage. Diodes (semiconductors) are susceptible to heat damage hence my suggestion. It could also be that the Alt is producing tooooo much volts and illuminating the bulb in reverse - this would be very bad if left to continue. A new diode pack is cheap - go for it. Roger Quote Link to post Share on other sites
littlejim Posted November 11, 2014 Report Share Posted November 11, 2014 (edited) Jim, The lamp shows that there is a difference in voltage between the alternator O/P and the battery voltage. You would have to use a voltage meter to determine which side is higher. As Roger has suggested the diode pack is most probably the cause. Not sure how an old bulb could effect the system but would be interested in an explanation. Cheers Graeme I have no idea either. But I happened to be there when the nice mans changed the bulb and the problem disappeared. he didn't charge anything either. the previous auto electrician we visited had offerred to replace most of the generating system but was booked out for a week. Guess it was based on the auto electrician's(AE) personal experience rather than any deep explanation based on physics. It was quite funny, after hearing the early description of the problem, the AE started walking away towards his bulb collection while my friend was still finishing his description of the problem, we thought he was giving us the big 'A'. But instead he produced the goods. Edited November 11, 2014 by littlejim Quote Link to post Share on other sites
LGFromage Posted November 11, 2014 Report Share Posted November 11, 2014 The replacement bulb probably had a higher resistance so required a higher residual voltage to make it illuminate. Interesting solution to the problem. I would not have thought of that but it is still worth checking/replacing the diode pack. Tim Quote Link to post Share on other sites
peejay4A Posted November 11, 2014 Report Share Posted November 11, 2014 (edited) I think I would do this. When the fault occurs measure battery volts with the engine running. If it's around 14v then the alternator is working but a voltage is being developed across the warning light which is sufficient to light it. That could be due to a high resistance between the bulb and its reference supply from the battery. The hr could be in the bulb, it's holder, the wiring or the ignition switch. Under these conditions it wouldn't light very brightly though. So if it's at full brightness the alternator fault is more likely. Edit: actually ignore what I said about a high resistance, that won't make any difference to the voltage across the lamp, only its brightness. Edited November 12, 2014 by peejay4A Quote Link to post Share on other sites
McMuttley Posted November 11, 2014 Report Share Posted November 11, 2014 My ign light also starts to glow when after a decent run, for example the oil pressure gets low on idle and the engine is happy to stall - someone in this thread told me that was normal ? ! Quote Link to post Share on other sites
RogerH Posted November 11, 2014 Report Share Posted November 11, 2014 Hi Austin, low rpm at tickle over may well cause the Ig light to come on especially with a dynamo. You could raise the tick over a little 900rpm. Roger Quote Link to post Share on other sites
TR NIALL Posted November 11, 2014 Report Share Posted November 11, 2014 My ign light also starts to glow when after a decent run, for example the oil pressure gets low on idle and the engine is happy to stall - someone in this thread told me that was normal ? !Are you sure it's not the Oil Pressure Light.You may have the Bulbs in the wrong Holders. Quote Link to post Share on other sites
Lebro Posted November 11, 2014 Report Share Posted November 11, 2014 (edited) I would expect the warning light to come on at a slow tickover with a dynamo setup, but not with an alternator. The purpose of the warning light differs between the two setups: Dynamo The lamp is connected between the dynamo main output, & the battary -via the ign switch. it will illuminate as soon as ign is turned on as the dynamo has no output. When engine is started, & revs taken above a slow tickover the dynamo will produce enough voltage to activate the "cut in" contacts in the regulator box, This connects the dynamo output to the battery, thus shorting out the warning lamp - which will go out. The "cutin" contacts will not normally open again unless the dynamo output falls to a low level, (causing the battery to start discharging into it) this can happen at slow tickover, & when it does, the warning lamp will come on - but not as brightly as before engine start. The charging will take place perfectly well if the warning light is blown, or not present. Alternator The lamp is connected between the alternator field winding -(slip rings) & the battery via the ign switch. It has to be there in order to supply initial current to the field winding to start the alternator producing an output. Blown or missing bulb means no charging. When started, the alternator will immediately give an output which is rectified: A. By some high current diodes to provide the main output, & B. some lower current ones to provide the field current. These latter diodes connect to the same point as the warning light, & so as the rectified voltage rises from the alternator, it equals the battery voltage, and the light goes out. The earthy end of the field winding is connected (via the slip rings) to the regulator, which adjusts the field current to give the correct output voltage. It is very unusual for the warning light to ever come back on again until engine is stopped. If it does, then I would strongly suspect the alternator is at fault, either the rectifier diodes (either set) or the regulator, or the slip rings. All are worth checking. By the way anyone who wishes to update their dashboard illumination lamps, & the two warning lamps with LED types (I have) will find that the IGN warning lamp will not pass enough current to energise an alternator. The fix is to solder a resistor across it, to increase the current. Bob. Edited November 11, 2014 by Lebro Quote Link to post Share on other sites
AndrewP Posted November 12, 2014 Report Share Posted November 12, 2014 Are you sure it's not the Oil Pressure Light. You may have the Bulbs in the wrong Holders. Agree ^^^ double and triple check this. Easy to do, just ground the oil pressure switch wire on the block by the sender and have someone look at the bulbs; its very easy to mix them up. Quote Link to post Share on other sites
graeme Posted November 12, 2014 Report Share Posted November 12, 2014 Are you sure it's not the Oil Pressure Light. You may have the Bulbs in the wrong Holders. Niall and Andrew, Assuming it is standard, McMuttleys TR3A does not have an oil pressure warning light, they were only fitted to six pot engines. Cheers Graeme Quote Link to post Share on other sites
littlejim Posted November 12, 2014 Report Share Posted November 12, 2014 As the light is showing the balance between the alternator and the battery do you reckon Jimf ought to get the battery checked, in case it is showing a battery problem? Quote Link to post Share on other sites
AndrewP Posted November 12, 2014 Report Share Posted November 12, 2014 Niall and Andrew, Assuming it is standard, McMuttleys TR3A does not have an oil pressure warning light, they were only fitted to six pot engines. Cheers Graeme The OP says it was a TR5. Not sure if they have both indication lights though. Quote Link to post Share on other sites
Jim F Posted November 12, 2014 Author Report Share Posted November 12, 2014 Gents, thanks for all the feedback. I have a few things to check out this weekend. Jim Quote Link to post Share on other sites
TR NIALL Posted November 12, 2014 Report Share Posted November 12, 2014 The Lights are On but no ones at Home. Quote Link to post Share on other sites
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