volt meeter
- Thread starter john shaw
- Start date
darth sidious
New Member
Assuming you mean the ammeter (the gauge having 0 in the centre and ± 60 at the extremes)
It should read more towards the + side when the car is running. If yours is showing more towards the - side, it seems the alternator is not charging!
It should read more towards the + side when the car is running. If yours is showing more towards the - side, it seems the alternator is not charging!
With the engine on tickover the needle should be around the centre, possibly slightly towards discharge, then put the lights on and leave it idling it should show a more definate discharge. Leave it like that for a minute or so, then rev the engine to 1500/2000rpm and you should see the needle immediately swing over to show a charge, which will start high then gradually drop back.
DaveHerns wrote,...
Hello Dave,
I expect is has to do with the rpm that the alternator spins at while at idle, and the amount of current that it can return to the battery at that given rpm.
Modern cars demand considerably more current from their batteries so as to run all the electronic systems that the car contains, so naturally the alternators need to be capable of meeting that challenge.
Alternators that are capable of delivering far more current are readily available for Land and Range Rovers, so provided all the necessary brackets can be plumbed into the P6B engine bay, then I dare say it would be possible.
Ron.
Hello Dave,
I expect is has to do with the rpm that the alternator spins at while at idle, and the amount of current that it can return to the battery at that given rpm.
Modern cars demand considerably more current from their batteries so as to run all the electronic systems that the car contains, so naturally the alternators need to be capable of meeting that challenge.
Alternators that are capable of delivering far more current are readily available for Land and Range Rovers, so provided all the necessary brackets can be plumbed into the P6B engine bay, then I dare say it would be possible.
Ron.
Hello John,
The three devices which are the usual cause of alternator problems are worn carbon brushes or problems with either the voltage regulator or rectifier. If the alternator has seen in excess of 200,000 miles, then the slip ring may also be showing signs of wear....they become grooved like a record, but it is unlikely to be the sole cause of your current problem.
You can either take the alternator to an auto electrician and have it tested and the necessary parts replaced or you can buy the parts and do it yourself.
Replacing the brushes and the voltage regulator is quite easy while the rectifier will require you to do some soldering.
Given that your alternator is showing a constant discharge irrespective or engine rpm while at the same time the ignition light remains off, then it is unlikely to be the rectifier.
Is your alternator an 18ACR? Or better still, what is your engine number?
Ron.
The three devices which are the usual cause of alternator problems are worn carbon brushes or problems with either the voltage regulator or rectifier. If the alternator has seen in excess of 200,000 miles, then the slip ring may also be showing signs of wear....they become grooved like a record, but it is unlikely to be the sole cause of your current problem.
You can either take the alternator to an auto electrician and have it tested and the necessary parts replaced or you can buy the parts and do it yourself.
Replacing the brushes and the voltage regulator is quite easy while the rectifier will require you to do some soldering.
Given that your alternator is showing a constant discharge irrespective or engine rpm while at the same time the ignition light remains off, then it is unlikely to be the rectifier.
Is your alternator an 18ACR? Or better still, what is your engine number?
Ron.
darth sidious
New Member
john shaw said:
Is the red light coming on at all? Depending on which alternator you have (if you have 18ACR, no light = no excitation to the rotor = no charge! Could it be the bulb has blown? (if it does not come on at all)) The 11AC alernator can (so I am told!) charge without the light coming on (the rotor excitation is fed via a relay/control unit)
If the bulb is OK, then Sydney's advice is good about having the alternator checked. [Though I cannot quite agree with it being "unlikely the rectifier". Had a similar problem years ago with my old Peugeot 305D not charging. It might be, like it was in my case, that some rectifier diodes have blown and are 'leaking', but not enough to switch on the ign light (assuming that is working!) Then again, depending on which diodes have gone, I would expect the battery to discharge through the blown diodes, like mine did!]
Do they still produce brushes on their own? I am sure my local auto electrics say they now replace the whole regulator and that the brush springs are spot welded to the connectors, as it's cheaper! (I wonder for them, or for the customer!
)I am about to admit my sin and the possible blasphemy and/or treason here!
With all due respect to harvey and his mountains of P6 knowledge, I do question the ammeter reading centre 0 with the engine idling under no load (assuming ign light has extinguished, of course!).
To be fair, I can visualise the ammeter reading discharge with engine idling and lights on, but not under no (heavy electrical) load (which I assumed what was meant with "normal running") I certainly would expect it to show a slight movement/bias towards the + side under no load (after ign light extinguished), even at idle.
I await the lynch mob!
darth sidious said:With all due respect to harvey and his mountains of P6 knowledge, I do question the ammeter reading centre 0 with the engine idling under no load (assuming ign light has extinguished, of course!).
To be fair, I can visualise the ammeter reading discharge with engine idling and lights on, but not under no (heavy electrical) load (which I assumed what was meant with "normal running") I certainly would expect it to show a slight movement/bias towards the + side under no load (after ign light extinguished), even at idle.
I await the lynch mob!
The alternator will only charge as it needs to, so on tickover with no load other than what is required to keep the engine running, which would only be the supply to the alternator and coil, I'd expect to see the needle in the middle once the battery has been recharged after starting the engine in the first place. Assuming the ammeter is accurate, I'd have concerns that the alternator was overcharging at tickover if the ammeter was showing a constant charge, although having said that,the ammeters in the cars aren't precision instuments, rather just indicator.
darth sidious
New Member
I do bow to your wealth of knowledge and experience (what you don't know about a P6 just isn't worth knowing! ), but surely there would be a slight but noticeable (on the ammeter) current flow to the battery, even if the battery is fully charged and at idle. I am not meaning a lot of movement btw, I mean just a slight but noticeable movement to the right.
I was always led to believe that an alternator will push (an albeit small-ish) current even into a fully charged battery, and that this was necessary to prevent large voltage spikes building up in the alternator windings. In a way, the alternator uses the battery to release/expend its pent-up energy slowly. (Sorry, electrical engineering background!)
Then again, our old P6 never had an ammeter, so this is merely conjecture on my part! :-S
In any case, I think we all agree that John's alternator is highly suspect!
), but surely there would be a slight but noticeable (on the ammeter) current flow to the battery, even if the battery is fully charged and at idle. I am not meaning a lot of movement btw, I mean just a slight but noticeable movement to the right.I was always led to believe that an alternator will push (an albeit small-ish) current even into a fully charged battery, and that this was necessary to prevent large voltage spikes building up in the alternator windings. In a way, the alternator uses the battery to release/expend its pent-up energy slowly. (Sorry, electrical engineering background!)
Then again, our old P6 never had an ammeter, so this is merely conjecture on my part! :-S
In any case, I think we all agree that John's alternator is highly suspect!
The alternator will always put a small amount of charge into the battery, because whenever the engine is running there is a discharge, so the regulator will allow just enough back in to replace what is being used. That's why if the alternator fails, the battery eventually goes so flat that the engine won't run, and conversely, when there is a high load the alternator would put back say 30 amps at 2000rpm, but it won't be putting that much back at the same speed if the load isn't there. Variatons in the accuracy of the ammeters in the cars mean that some will show a slight lean to one side or the other of centre at tickover, but taking into account the variations in load as well there's no guarantee there actually doing what they're indicating anyway.
Back to the OP, you'd have to think that if it shows a discharge under load, but doesn't show a charge when revved, that either the ammeter is faulty, or it isn't charging properly even though the light doesn't come on, so I'd be looking at the brushes initiall, as that's an easy first stop, and then checking the regulator. If it's an 18ACR all the parts are available.
Back to the OP, you'd have to think that if it shows a discharge under load, but doesn't show a charge when revved, that either the ammeter is faulty, or it isn't charging properly even though the light doesn't come on, so I'd be looking at the brushes initiall, as that's an easy first stop, and then checking the regulator. If it's an 18ACR all the parts are available.
darth sidious
New Member
harveyp6 said:
Hear hear!
ripvanwinkle
New Member
Hi
There is one more point to consider . The P6B charging system , in common with Jag E types and Aston Martins is weird . There is a LUCAS 3AW relay buried in the right hand door pillar which is an integral part of the ignition light and charging system . No relay , no light, no charge .!
This relay is fragile and prone to failure . It's also difficult to find a replacement relay , at least in N America. The 3AW looks like a flasher relay BUT operates at much lower current , you can't substitute a flasher relay as a replacement.
You can find a solid state replacement from high end Jag parts emporia , at a suitable premium price
Cheers
RVW
There is one more point to consider . The P6B charging system , in common with Jag E types and Aston Martins is weird . There is a LUCAS 3AW relay buried in the right hand door pillar which is an integral part of the ignition light and charging system . No relay , no light, no charge .!
This relay is fragile and prone to failure . It's also difficult to find a replacement relay , at least in N America. The 3AW looks like a flasher relay BUT operates at much lower current , you can't substitute a flasher relay as a replacement.
You can find a solid state replacement from high end Jag parts emporia , at a suitable premium price
Cheers
RVW
darth sidious
New Member
harveyp6 said:
On looking on the internet, I think Harvey's right.
http://drcwww.uvt.nl/~bogaard/manual/engielec/11accirc.gif Though this is for a +ve earth (ground) system, the same applies for a -ve earth (ground) system. The 4TR will let/control the current flow to the alternator excitation field, regardless if the ign bulb is working or not.
The 18ACR is more like modern alternators in that the regulator is within the alternator itself. The only downside here is that the ign MUST work, as it forms part of the excitation circuit!
And before anyone says anything, I am also astounded that there were +ve earth alternators at one time!
darth sidious said:And before anyone says anything, I am also astounded that there were +ve earth alternators at one time!
Yep, IIRC some early 1960's Jags had them and ISTR coming across them on Rootes cars as well, as well as quite a few others were out there I'm sure.
darth sidious
New Member
harveyp6 said:
Oh, I see. I had always assumed all alternators were -ve earth! :-S (arrogance of the not-so old, I suppose! :-S)
I wouldn't say they were common, but they were out there, and just enough of them to catch out the people who used to say "all cars with alternators are Negative earth!" one of whom could have been me probably back in pre-history when I was just getting used to getting rid of dynamos in favour of those new fangled alternator thingies. But at the time I was working on just about everything so there was always something to catch out the unwary.
It was only the AC alternators with the seperate 4TR's that were +ve earth and it's in the back of my mind that these had the black 4TR's and the -ve earth ones had red, but I may have dreamt that........
It was only the AC alternators with the seperate 4TR's that were +ve earth and it's in the back of my mind that these had the black 4TR's and the -ve earth ones had red, but I may have dreamt that........
darth sidious
New Member
Oh, I see.
Would be worth checking out about the 4TR colour on +ve earth cars!
Would be worth checking out about the 4TR colour on +ve earth cars!
tantus pedis
Member
Just to hijack another thread for my own purposes.... My alternator stopped charging last week. It's been 'looked at' and now charges including on the ammeter, but the red light still stays on. Regulator has apparently been replaced. Any suggestions?