Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Double Check
Hi
I noticed my sat nav screen was dull when I started the car yesterday, so decided to check out the battery etc due to cold weather.
Now I believe it is simply my battery that is on its way out (has been charged off the vehicle a month ago as when I left the boot open it drained the battery, so not a strong battery imho.
I have just been out and noted the following
Outside temp -2
Battery charge from cold (left overnight) 11.9v, too low I believe it should be around 12.6?
On starting car, alternator output showing 14.7v after approx 10 seconds
FBH cut in, no affect to output 14.7v
I then switched on the heated windscreen and heated rear window, plus turned on heated front seats, voltage reading 14v for approx 10 seconds, rising to 14.7v over the following 30 seconds approx.
Now before I simply buy a battery, am I correct in thinking the alternator is fine and working as it should?
Kind regards
Jay
13th Dec 2014 9:25 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Your battery testing technique is fine, as is the alternator output testing. However, the alternator output is a little low for a D3 in cold conditions with a poor battery as I would expect something like 15.2v.
The alternator may be ok and just a little worn but it could also be in a default mode (which is around 14.7v) or it could be leaking some power to earth. This final point could be checked by an amp clamp around the alternator lead with the engine off (or, with care, a regular DMM in series between the lead and the battery) - it should show zero current.
More stuff on current drains in my signature.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Thanks Robbie,
I do not have a clamp meter, so that way of testing is going to be problematic for me until I eventually get one - so will have to see if I am able to do the other method stated, but I will need to understand how this way is done correctly to be sure I fully understand.
Now I could not see this way of testing in your sig literature - so am I reading it wrong?
Thanks again,
Jay
13th Dec 2014 1:50 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
The +ve terminal on the battery has a branch on it that connects to 2 red leads. One goes to the battery junction box and one goes to the alternator/starter - this is the one you should check.
With the engine off if you disconnect this lead and place a DMM in series between the lead and the battery and it should be very close to zero amps as no current should be flowing. If it was flowing this would show that some battery energy is leaking through the alternator through to earth.
I said 'carefully' as this carries a small amount of risk to your DMM. In the unlikely event that you had a big short at the alternator it could blow the DMM fuse. Some use a test light or a fused lead to provide protection but in your case it you would have to have a minor drain otherwise the battery would already be flat. There are other methods, such as a resistance check, that can be used but we will not go into that for now. The joy of a clamp meter is the absence of risk and you do not have to disconnect anything.
Click image to enlarge
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Thank you Robbie,
I will check this out tomorrow and report my findings.
As always, your technical knowledge / help here is really appreciated.
Kind regards
Jay
13th Dec 2014 4:38 pm
UKJay
Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Oh,
In relation to the comment you made about Alternator possibly being in default mode, what / how does this happen?
Kind regards
Jay
13th Dec 2014 4:42 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
The D3 alternator is reasonably smart and is governed by commands from the ECM based on power, temperature, state of charge etc. Should this link fail it turns back into a dumb alternator that tries to produce a near-constant output. This is set at a lower voltage than available at peak output to avoid boiling the battery, as it would no longer have a clue what the conditions were.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Went out today and removed the lead from the battery terminal, removed the lead going to the battery box, then put MM in series (hope this is the correct way to check it, as never done this before).
Hopefully the correct way to check the potential current draw:
And the Reading on the DMM
If I have done this wrong, please advise so that I can understand where I went wrong. If I have managed to understand the instructions correctly, then am i right in assuming the Alternator is not drawing any current?
Kind regards
Jay
14th Dec 2014 11:14 am
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20857
Correct. Looks like it's just a tired battery (assuming no.battery drain from inside the car) My D3 Build Thread
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
I should have guessed that you had the later type of battery connection. Your technique for overcoming this extra hurdle is not, from a purists perspective, ideal from a safety point of view but it has given you a valid test. My only note of caution is that some cheap DMMs can read zero because they have failed or a fuse has blown, so always do a confidence check on your DMM afterwards if you have not seen it read above zero.
On the safety side it is ok to remove the alternator lead on its own, where this is possible, but always be careful with metal tools. As the battery junction box will be drawing some power and will draw a great deal when it 'wakes-up' it will spark when connected. It is traditional to do this on the negative lead so that tools are at the same potential as the surrounding bodywork and it also protects vehicles with a pyrotechnic device fitted to the positive terminal.
Apologies for not considering the later type of terminal bridge but your results suggest there is nothing leaking through the alternator to earth.
Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Thanks for the confirmation DM, it is appreciated.
Just one more question in relation to the possible Default mode of a D3 alternator - is this reversible if the alternator has decided to sit in default mode, or am I simply waiting for the alternator to now die and potentially take out the new battery?
kind regards
Jay
14th Dec 2014 11:45 am
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20857
That's not a pyrotechnic fitted to the terminal Robbie, just a fuse for the starter/alternator incase of.major short circuitMy D3 Build Thread
Member Since: 24 Aug 2013
Location: In The Mud
Posts: 432
Robbie wrote:
I should have guessed that you had the later type of battery connection. Your technique for overcoming this extra hurdle is not, from a purists perspective, ideal from a safety point of view but it has given you a valid test. My only note of caution is that some cheap DMMs can read zero because they have failed or a fuse has blown, so always do a confidence check on your DMM afterwards if you have not seen it read above zero.
On the safety side it is ok to remove the alternator lead on its own, where this is possible, but always be careful with metal tools. As the battery junction box will be drawing some power and will draw a great deal when it 'wakes-up' it will spark when connected. It is traditional to do this on the negative lead so that tools are at the same potential as the surrounding bodywork and it also protects vehicles with a pyrotechnic device fitted to the positive terminal.
Apologies for not considering the later type of terminal bridge but your results suggest there is nothing leaking through the alternator to earth.
Thanks Robbie,
I did look to remove simply the alternator lead, but it appeared to me like this can only be removed after the whole thing was off the battery terminal - as there looked to be a screw on the back side of the connection (nearest the battery side wall) - thus I ended up taking the battery feed cable off first, then the whole connector (if this makes sense). I may have been totally wrong on the method to removed only the alternator cable, but I will have another look to see for future reference.
Also, post test - I did check the voltage on the battery etc to ensure the fuse had not blown inside the DMM, as I assumed that this would hopefully show the DMM is not in fault showing a dummy zero current reading?
Regds
Jay
14th Dec 2014 11:54 am
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
I don't know as I am unfamiliar with how your DMM is laid out. The better DMMs have a completely separate circuit for amperage, including separate fused sockets, so a check via voltage would tell you nothing. Just do a quick amperage check on anything simple that is kicking around on your bench. You could even check what amperage your DMM is drawing from its own battery.Land Rover - Turning Drivers into Mechanics Since 1948
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