| Author | Message | ||
     Bill Coburn Moderator Username: bill_coburn Post Number: 1465 Registered: 4-2003 |
My car used mostwise daily usually on medium to long trips has always had the battery replaced at the slightest indication of grunting and probably been replaced every three years. I have had the alternator overhauled professionally twice yet occasionally the charging light comes on as a glimmer - nothing more, while driving. In the dark on a deserted road this affects my bowels. The battery 'condition' meter reads the max, there is never the slightest electrical problem - just this slight glimmer. My sparky tells me it is a very small short somewhere and inter alia 'not worth the effort to find and fix it'. Could I have some more consoling/reassuring words please? | ||
| James Feller Prolific User Username: james_feller Post Number: 253 Registered: 5-2008 |
the most consoling words I can give you Bill is speak to Richard Treacy! I had exactly this happen in my Turbo for a while only to find eventually the Alternator burnt out after it to was 'rebuilt'. RT steered me in the right direction. Take his advice and get rid of the 'rebuilt alternators' and never worry about iffy alternators again. J | ||
| James Feller Prolific User Username: james_feller Post Number: 254 Registered: 5-2008 |
or the other issue that may cause a batt light flicker is a loose or stretched alternator belt. Ive had both cars, the Rolls and Bentley, lose the alternator belts completely thus the light came on immedialtey. The Bentley did get the 80klms home but wasnt to happy with no alternator charging.....so if its an old stretched belt Bill or indeed an alternator about to burn out, speak to RT, both times he helped me straight out of the proverbial so my bowels remain fine and no quivering ensues....  J | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1466 Registered: 4-2003 |
James/ The only thing round here that is loose or stretched is me so there!! Actually if you are suggesting a new alternator, they are I think no longer available. My problem is not unique as I have discussed both the flickering light and the associated alimentary canal effect with, I think, three other owners. I will ask RT when I see him again. He at the moment is out performing the Scarlet Pimpernel and putting a new standard to peripatetic!! Good to here from you from time to time, the roll call sometimes rivals the membership of the League of Nations so a familiar face or any other bit of the anatomy is always re-assuring! The best!! | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1467 Registered: 4-2003 |
And as I was saying, it would seem that the glimmering light does not say 'I am not charging' because it would seem it is! And I have managed to catch the thing when it is glowing and the legendry Greg is at hand and he has assured me that the ergs are pouring out and furthermore the battery on such occasions is fully charged. On two occasions when someone has noticed the glimmer, I have advised that it indicates that as the car has been standing or the bottle cooler has been open too long hence it has not dropped to its optimum temperature for the Cliquot to be drunk!! | ||
| David Gore Moderator Username: david_gore Post Number: 1177 Registered: 4-2003 |
Bill, have you considered the possibility of a diode malfunction in the alternator? I had a similar experience a few years ago on a lesser and much abused vehicle not long before the rectifier in the alternator failed completely. | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1468 Registered: 4-2003 |
David thanks I'll mention it to my elec man who is on personal terms with God in this field but he may be fallible. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 148 Registered: 6-2005 |
The circuit for the ignition lamp and choke solenoid which is used for the Spirit and Spur is different to that of the Shadow. It uses a resistor across the ignition lamp to provide a current bypass so that sufficient current is available to operate the choke solenoid delay. This current will depend on the voltage of the battery and alternator and will be at a maximum when the alternator is delivering its maximum voltage. The ratio of the resistance of the bypass and that of the choke solenoid delay will determine the voltage across the bypass and it is possible that this voltage could be enough to cause the lamp to faintly glow. If the glow only occurs during normal running rather than idling this is a likely cause. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 149 Registered: 6-2005 |
Bill, Further to my previous post, if the condition is in fact a marginal one the solution may be as simple as changing the lamp. John | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1469 Registered: 4-2003 |
Thanks John worth a try! | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 150 Registered: 6-2005 |
Bill, Looking again at the lamp circuit (see below) it's hard to see how enough voltage could be produced across the bypass resistor to light the lamp however dimly during normal running. This resistor has to be low value compared with the choke solenoid delay resistors so is unlikely to have more than 2 or 3 volts across it. So unless the lamp can glow a little on such a low voltage I'm afraid it is more likely that the 'A' output of the alternator is dropping, so the alternator should be tested. I would still replace the lamp on the off-chance. John  | ||
| Jeff Young Prolific User Username: jeyjey Post Number: 104 Registered: 10-2010 |
If that diode fails, then the lamp will light dimly from the (backwards) voltage difference of around 14V from the alternator to a "ground" of around 12V from the battery positive terminal. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 151 Registered: 6-2005 |
I have just tested a 12V/5W lamp on 2.8 volts and it does produce a faint light which would easily be seen in a dark car at night. It is certainly worth trying another lamp, better still if you can select one with a slightly higher resistance. I am now leaning towards my first thoughts but Jeff's suggestion is also valid. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 152 Registered: 6-2005 |
Bill, after a good night's sleep I realised that the purpose of the diode in the diagram is precisely to prevent the problem you are having and Jeff's observation about it failing (short circuiting) is spot on. In the failed condition up to 2.5 volts could be across the lamp whereas it would normally be much less. So the diode should be replaced, the trick will be finding out where it is on your car. | ||
| John Kilkenny Prolific User Username: john_kilkenny Post Number: 153 Registered: 6-2005 |
Bill, I notice that in one version of the charging circuit diagram (M06 Charging Circuit) the diode is not present whereas in another (A4 Complete Wiring Diagram in Colour) the diode has been included. This suggests that the diode was added as a later modification to correct spurious operation of the ignition lamp. It is possible your car may not have this diode. John | ||
| stan Seymour New User Username: rollanut Post Number: 8 Registered: 7-2012 |
Hi Bill, Measuring from the positive output pole of the alternator to earth gives me just 13v.. My belief is that that should read 14.2v ,OR BETTER!! Is that correct?? Is there a remedy?? Have I "done a diode?? Rumour says a Mitsubishi alternator (with commensurate output) is an admirable substitute... ANY comments on that R=Nut | ||
| Jan Forrest Grand Master Username: got_one Post Number: 456 Registered: 1-2008 |
Most car manufacturers set the 'gearing' on the alternator to give maximum voltage/current output at 2K rpm. Whether Crewe did this I couldn't say as this equates to around the legal speed limit on UK roads for a RR/B. However at this rpm the voltage should be around 14.8 volts. Anything significantly under or over this indicates a fault - usually in the diode pack or the regulator respectively, although the brushes and/or slip ring can also be likely candidates. In Blighty most car spares shops and auto electrical specialists will check out an alternator for free or for a very nominal charge. Note: a failed or failing battery can drag the alternator output down by a volt or three if there is a dead cell soaking up most of the current. | ||
| Robert Lavallee Unregistered guest |
can anyone tell me what who makes the alternator on a 87 Silver Spur? (21380)} (Message approved by david_gore) |
