Hi Blackburn,
Good question.
Exmil109 will know a lot more about this than I do. But here is what I do know.
In terms of my particular battery (Odyssey Extreme AGM type deep cycle battery) 14.8v is good.
Standard lead acid battery though, 14.4v is generally regarded as max, I think?
The Autobooks test for the 4TR is to warm the system up for minimum 8 minutes, runnning the engine with the ALTERNATOR at 3000rpm, and turn only the side/tail lights on (2A load). Test the current from the alternator output, which should be less than 10A. And test the voltage across the battery, which should be between 13.9 and 14.3v. But this is on the basis of the original transistor type 4TR, which was adjustable. Autobooks solution, if the voltage was outside these limits (and stable), was to adjust the voltage back to within the limits. Of course adjustment is not possible with the modern PCB replacement.
Also there is no mention of whether the voltage might be expected to be higher under more load. But there must be a reason for having a fixed 2A load together with the stated voltage range, during the test.
I found a Lucas test while looking into this. And they say roughly the same, except that the ENGINE should be at 3000rpm, rather than the alternator. But they still don't say what would happen if you increased the load above 2A.
The Lucas fault diagnosis manual is more comprehensive than Autobooks, and has additional tests on other parts of the system, so I will try and upload it, in case it is useful for anyone looking at this post in future (Page 34 for 4TR test).
Good question.
Exmil109 will know a lot more about this than I do. But here is what I do know.
In terms of my particular battery (Odyssey Extreme AGM type deep cycle battery) 14.8v is good.
Standard lead acid battery though, 14.4v is generally regarded as max, I think?
The Autobooks test for the 4TR is to warm the system up for minimum 8 minutes, runnning the engine with the ALTERNATOR at 3000rpm, and turn only the side/tail lights on (2A load). Test the current from the alternator output, which should be less than 10A. And test the voltage across the battery, which should be between 13.9 and 14.3v. But this is on the basis of the original transistor type 4TR, which was adjustable. Autobooks solution, if the voltage was outside these limits (and stable), was to adjust the voltage back to within the limits. Of course adjustment is not possible with the modern PCB replacement.
Also there is no mention of whether the voltage might be expected to be higher under more load. But there must be a reason for having a fixed 2A load together with the stated voltage range, during the test.
I found a Lucas test while looking into this. And they say roughly the same, except that the ENGINE should be at 3000rpm, rather than the alternator. But they still don't say what would happen if you increased the load above 2A.
The Lucas fault diagnosis manual is more comprehensive than Autobooks, and has additional tests on other parts of the system, so I will try and upload it, in case it is useful for anyone looking at this post in future (Page 34 for 4TR test).
Hi rob1miles,
It is possible!
The Lucas guide (my earlier post today) says in the notes on Pg34:
3.
A high reading indicates a faulty 4TR unit.
A correct reading denotes a high resistance
in the sensing circuit which must be located
and remedied.
Which is a bit confusing!
But I think they are referring to note 2. above it, and talking about the repeat test across the + and - terminals of the regulator? What do you think?
It could also be a typo. It depends where the sensing wire is picking its voltage from. I seem to recall moving the sensing wire further from the battery to fool the alternator to push the voltage up as my battery was on its last legs. I think it will try to get 14.5 (or whatever) at the sensing wire so if there's reistence between that and the alternator output it will push the volts up which could put the out put above 14.5. The whole sensing wire thing was a evolutionary blind alley, i think it caused more trouble that it solved, now alternators just sense internally. The idea was to stick the sensing wire on the battery and get the correct voltage there.
Hi rob1miles,
Thanks.
I guess in my case it must be the permanent +ve feed, which ends up at + on the regulator. Comes from the the starter solenoid, along with the +ve alternator output lead, and then on to the +ve terminal of the battery. I will check it and the Lucas test out in the morning.
Thanks.
I guess in my case it must be the permanent +ve feed, which ends up at + on the regulator. Comes from the the starter solenoid, along with the +ve alternator output lead, and then on to the +ve terminal of the battery. I will check it and the Lucas test out in the morning.
ExMil109
Active Member
I agree that 14.8V is on the high side, but not extreme. A wet cell battery might gas a bit, I'm not familiar with the sealed cell batteries but I think only the gel cell types need to be charged around 14.2V.
As per Rob's post, the 4TR senses the battery voltage from its + terminal and will increase the output voltage if there's a resistance between the + terminal and the battery. So all the regulator connections need to be clean and tight. The 4TR is fed via the field relay, so if that is past its best (contact resistance) then that will also give a higher output voltage.
A good test would be to run a direct feed from the battery straight to the + terminal on the 4TR, bypassing the relay. If that makes a difference to the voltage then the relay is on the way out...
BTW, that Lucas test manual is a great reference for the older Landy electrics - makes a nice change from plugging fault code readers into OBC ports!
As per Rob's post, the 4TR senses the battery voltage from its + terminal and will increase the output voltage if there's a resistance between the + terminal and the battery. So all the regulator connections need to be clean and tight. The 4TR is fed via the field relay, so if that is past its best (contact resistance) then that will also give a higher output voltage.
A good test would be to run a direct feed from the battery straight to the + terminal on the 4TR, bypassing the relay. If that makes a difference to the voltage then the relay is on the way out...
BTW, that Lucas test manual is a great reference for the older Landy electrics - makes a nice change from plugging fault code readers into OBC ports!
Hi ExMil109,
Thanks.
14.8v not a bad thing for my particular battery, but does indicate that possibly the 4TR is struggling to keep the voltage down, which can't be good in the long run. I will also try the direrct feed, as you suggest.
Relay is a new one.
I thought the Lucas manual was a good find too. All sorts of interesting things in there. Came from the Rolls Royce Owners Club of Australia!
Thanks.
14.8v not a bad thing for my particular battery, but does indicate that possibly the 4TR is struggling to keep the voltage down, which can't be good in the long run. I will also try the direrct feed, as you suggest.
Relay is a new one.
I thought the Lucas manual was a good find too. All sorts of interesting things in there. Came from the Rolls Royce Owners Club of Australia!
Hi,
Rain stopped play for a day here in Cumbria!
After much sanding of 50 year old contacts, I reduced the resistance between battery +ve and regulator + from 0.2 Ohms to 0.0. However voltage, fully loaded, still up at 14.8v. It is the same if I do the direct feed from the battery +ve terminal.
I guess that means it is the regulator?
I had a further thought of taking the permanent +ve feeding the regulator/field coil (via the relay) direct from the +ve alternator output instead. More like the situation in the modern alternators, where the regulator is integral. Any reasons against this?
Wonder why they didn't do this originally, and avoid the potential problems with resistance in the sensing circuit on route to the battery.
(Using the permanent +ve at the alternator output is effectively what they did when revising the wiring for the Japanese regulator).
Rain stopped play for a day here in Cumbria!
After much sanding of 50 year old contacts, I reduced the resistance between battery +ve and regulator + from 0.2 Ohms to 0.0. However voltage, fully loaded, still up at 14.8v. It is the same if I do the direct feed from the battery +ve terminal.
I guess that means it is the regulator?
I had a further thought of taking the permanent +ve feeding the regulator/field coil (via the relay) direct from the +ve alternator output instead. More like the situation in the modern alternators, where the regulator is integral. Any reasons against this?
Wonder why they didn't do this originally, and avoid the potential problems with resistance in the sensing circuit on route to the battery.
(Using the permanent +ve at the alternator output is effectively what they did when revising the wiring for the Japanese regulator).
ExMil109
Active Member
Taking the + feed direct from the alternator will be fine. The theory behind connecting this as close to the battery as possible is to compensate for any resistance in the cables, but this will be minimal in most cases and, as you say, later alternators are machine-sensing anyway.
I think it means the regulator is spot on (14.4V is what it is aiming for). What it may mean is that 0.4V is lost between the regulator - and earth somewhere - more sanding of old connectors! I find earth issues are a common problem with old Land Rovers, not helped by the electrolytic corrosion where aluminium meets steel.
Hi ExMil109 & rob1miles,
Thanks again for your thoughts.
What I was thinking, with taking the +ve feed to the regulator from the alternator output, was that the regulator would then control the field coil to keep that point in the system at 14.4v. Then if there is a 0.4v loss in the system, that would result in 14.0v at the battery? Land Rover's objective seems to have been to keep 13.9 to 14.4v at the battery, whatever else is going wrong in the system. But that is asking a lot of the alternator and regulator. Better to have a more stable alternator output, and rectify any faults if the charge to the battery is affected beyond the limits?
I have found a possible cause? There seems to be some leakage in the Ignition/starter solenoid circuit somewhere. 140mV in them even when the ignition is switched off. So I am going to check that out.
But it's good to have got to the point where it is working, and it is only 0.4v adrift (less than 3% error!).
Thanks again for your thoughts.
What I was thinking, with taking the +ve feed to the regulator from the alternator output, was that the regulator would then control the field coil to keep that point in the system at 14.4v. Then if there is a 0.4v loss in the system, that would result in 14.0v at the battery? Land Rover's objective seems to have been to keep 13.9 to 14.4v at the battery, whatever else is going wrong in the system. But that is asking a lot of the alternator and regulator. Better to have a more stable alternator output, and rectify any faults if the charge to the battery is affected beyond the limits?
I have found a possible cause? There seems to be some leakage in the Ignition/starter solenoid circuit somewhere. 140mV in them even when the ignition is switched off. So I am going to check that out.
But it's good to have got to the point where it is working, and it is only 0.4v adrift (less than 3% error!).
