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#1 Alternator Light again
Posted: Wed Nov 18, 2020 6:54 pm
by colin gray
Hi all, I have the old charging light flicker on my series 3 2+2 it is almost unperceivable in daylight but very noticeable in the dark. I have very healthy battery voltage when running at around 14v and to be honest it has been this way for quite some time but I feel I should really attend to it now.
Historically I have fitted new Brushes and Diodes in the BUTEC but could not source the field winding Diode at the time, I also replaced the small while diode pack on the back of the Alternator at the same time. This work was done as charging failed completely due to the Brushes and the Diodes were done just while I had the unit off the car.
So.. should I just start by cleaning all the connections up again or do I take the Butec to an repair centre if I can find someone who will actually do it?
Are there any particular connections that would give this symptom?
The flicker does not get brighter with revs but it does get faster not sure if that is significant?
Thank you
#2 Re: Alternator Light again
Posted: Wed Nov 18, 2020 7:55 pm
by madjack4
Bin the big useless butec unit and fit a modern unit or spend your life fixing it life's too short
Regards
#3 Re: Alternator Light again
Posted: Wed Nov 18, 2020 8:05 pm
by MarekH
Cleaning the connections (including the grounding of the alternator, control box and battery terminals) sounds very sensible.
All the light is telling you is that the voltage going around one leg to the red light is different to the voltage coming around via the other leg for a short instant rather than persistently. The alternator is obviously spinning faster at higher rpm.
Charging at 14v is good, but the voltage is "wrong" (only) some of the time, so a simple multimeter may not be telling you the whole story and an oscilloscope is really needed to see the source of the mismatch.
I might have to think about this a bit. Perhaps a strategy of moving the location of the idiot light or jumpering some of the connections with known good wiring may help isolate it.
(The white box on top of the Butec is the field diode pack.)
kind regards
Marek
#4 Re: Alternator Light again
Posted: Wed Nov 18, 2020 8:42 pm
by MarekH
Think about this:- the control box works as it is switching the field voltage either full on or off and is regulating the voltage. Since the flickering is related to alternator speed, I'd either look at how a diode connection can leak to earth or, as you have new brushes, at how they misconduct on perhaps one segment of the commutator.
I have spares, but am not near you.
kind regards
Marek
#5 Re: Alternator Light again
Posted: Wed Nov 18, 2020 9:13 pm
by colin gray
MarekH wrote: ↑Wed Nov 18, 2020 8:42 pm
Think about this:- the control box works as it is switching the field voltage either full on or off and is regulating the voltage. Since the flickering is related to alternator speed, I'd either look at how a diode connection can leak to earth or, as you have new brushes, at how they misconduct on perhaps one segment of the commutator.
I have spares, but am not near you.
kind regards
Marek
Hi Marek, so do you keep new parts for the BUTEC or do you have a range of used spares and would you be prepared post at all?
If I clean all the connections first and then if no improvement is found start looking at the commutator etc?
I did wonder if the small Diode inside the unit that is between the field windings was a potential issue too so there is plenty to check. I have replaced the Field Diode block on the outside last time the unit was off the car.
Other work I have in mind is to convert to a Vacuum advance as I am running blanked off currently. Are you aware of anyone that has the expertise to drill a new ported Vacuum point to facilitate this or is it case of just have a go with the relevant guidance on the web. I did see someone that offers this service but they are in the USA.
Thanks
Colin
#6 Re: Alternator Light again
Posted: Wed Nov 18, 2020 10:50 pm
by MarekH
I have a couple of Butecs and control boxes in the loft. Other than that, I generally don't stock anything like that as any decent old time alternator shop can repair these easily. Postage is going to be expensive.
Because your symptoms follow alternator speed, I think that is where your problem is.
The s3 came with vacuum retard originally.
To convert to advance, you need to blank off the bottom left of the carburettor and take a feed from the manifold. Ported vacuum is simply ordinary manifold vacuum but with the signal thrown away when the throttle plate is shut and much diminished in other circumstances.
The reason people seem to think they prefer it to ordinary manifold vacuum is that having zero vacuum advance when the throttle is shut, means that the ported signal cuts in sharply as the throttle is cracked open.
It also means your engine is running needlessly retarded when standing at idle, causing it to heat up just when coolant flow and airflow are at their lowest.
You can check out my previous posts on the topic, including some tables explaining what "wide open throttle" really means and how and when and how much ported vacuum differs from manifold vacuum.
The only advantage I can see is that engine braking is better with ported vacuum versus manifold vacuum.
The cut-in effect thus probably happens to some extent when you change gear also, because of the momentary low engine load when you are declutched as you change gear. Put bluntly, you don't get more advance, you just force yourself to always have a sharper cut-in and cutoff of the same advance, so your seat of the pants perception of how good it must be is enhanced because of the inefficient retarding of ignition in the interim.
kind regards
Marek
#7 Re: Alternator Light again
Posted: Thu Nov 19, 2020 10:39 am
by malcolm
I've had exactly the same flickering for 5 years now. Battery charges fine so I ignore it, rightly or wrongly!
#8 Re: Alternator Light again
Posted: Fri Nov 20, 2020 6:33 pm
by colin gray
malcolm wrote: ↑Thu Nov 19, 2020 10:39 am
I've had exactly the same flickering for 5 years now. Battery charges fine so I ignore it, rightly or wrongly!
That is what I have been doing but have decided it can not be right so feel I should try to sort it out at long last, we will see where it leads. Maybe I can find a shop to go through the BUTEC properly.
#9 Re: Alternator Light again
Posted: Fri Nov 20, 2020 6:38 pm
by colin gray
MarekH wrote: ↑Wed Nov 18, 2020 10:50 pm
I have a couple of Butecs and control boxes in the loft. Other than that, I generally don't stock anything like that as any decent old time alternator shop can repair these easily. Postage is going to be expensive.
Because your symptoms follow alternator speed, I think that is where your problem is.
The s3 came with vacuum retard originally.
To convert to advance, you need to blank off the bottom left of the carburettor and take a feed from the manifold. Ported vacuum is simply ordinary manifold vacuum but with the signal thrown away when the throttle plate is shut and much diminished in other circumstances.
The reason people seem to think they prefer it to ordinary manifold vacuum is that having zero vacuum advance when the throttle is shut, means that the ported signal cuts in sharply as the throttle is cracked open.
It also means your engine is running needlessly retarded when standing at idle, causing it to heat up just when coolant flow and airflow are at their lowest.
You can check out my previous posts on the topic, including some tables explaining what "wide open throttle" really means and how and when and how much ported vacuum differs from manifold vacuum.
The only advantage I can see is that engine braking is better with ported vacuum versus manifold vacuum.
The cut-in effect thus probably happens to some extent when you change gear also, because of the momentary low engine load when you are declutched as you change gear. Put bluntly, you don't get more advance, you just force yourself to always have a sharper cut-in and cutoff of the same advance, so your seat of the pants perception of how good it must be is enhanced because of the inefficient retarding of ignition in the interim.
kind regards
Marek
Thanks Marek, I will check out the Vacuum posts. I do have an advance unit ready to fit and I do not mind where the vacuum comes from as long as it all works fine.
I may just look for a shop that can go through the Alternator locally and leave that to them, I will hopefully know that is not the problem if it persists.
Cheers
Colin