Jump to content

Help how can i diagnose whats wrong with my alternator


Recommended Posts

 

Firstly Sorry for long post but need to give all the info as it may also help someone diagnose my problem

 

I have 2 Lucas A127 65 amp alternators which are from my land rover defender tdi(200)

 
to give a quick summary: one of these actual alternators has been on the car for last 6 years and has been charging both my batteries in the car (I  have a National Luna dual battery split charge system installed)
The alternator has been giving a good charge everyday of 14.2volts approx,although it would not hold that voltage steady when i put a bit of load on with lights heater it could go down to maybe 13,8volts which i realised is a bit weak.
I have a Madman monitoring system in the car which give instant live time display of coolant temp,oil temps ,exhaust gas temp, oil pressure etc BUT more importantly with connection to this matter ,battery voltage so i can accurately see the battery charging  voltage all the time and all these parameters are alarmed with low and high settings.
 
Last week i had to replace a power steering pump / alternator mounting bracket which was easy BUT after putting it all back together i cannot get a charge on the alternator its sticking at 12.6 volts with a fully charged battery.
As i say i never had ANY problems with charging at 14.2 volts before this  current  bit of work and would start vehicle on the button all day long even on coldest days  Battery is fairly new 5 months ago( last one lasting over 9 years-showing vehicle has been keeping a good charge).
 
I have checked the wiring to the alternator which is only 2 wires ,the main battery positve wire goes  to the B+ post, and warning light cable to the D+ post of the alternator.
After not getting a charge I have done a voltage drop test on the alternator positive lead and it came back good at @0.2 v same with the negative connection from the alternator casing to the negative post on the battery.
 
Thinking i must have damaged the alternator somehow i took it out and did the following (stripped down )tests.
 on this alternator AND the spare one that i had lying about as a spare .
1) test on the rotor windings from the earth of the claw magnet of the rotor to each slip ring and both ended up open circuit (OL). Also the slip rings are in good condition no obvious wear.
next tested the resistance between the slip rings and it came back as 3.1 ohms .my workshop manual gives a value of 3.2ohms 
As far as i can see this all in spec???
 
2) Next the stator windings (which had the rectifier(s) unsoldered and removed ) testing between each pair of the 3 windings i got values of 0.2 ohms on each of the 3 pairs.
.my workshop manual gives a value of 0.15ohms 
 
test on the stator windings from the earth of the magnet of the stator to each of the pair of 3 phase windings and all ended up open circuit (OL). 
 
As far as I can see this all in spec??? 
 
3) rectifier:I tested on the diode setting from B+ post to the 3 top diodes  and they all came back open circuit(OL) then swaped leads arounfd and tested the same 3 diodes and had readings of 0.54 volts(+/- 0.01volts)
Then used the bottom earth point on the rectifier to check the other diodes and the all came with rhe same results.
I even had a spare 3rd rectifier that i tested also with same results
I cant be 100% on my testing at the correct points on these diodes as i have tried to reasearch where they are it comes back that there are 9 diodes 6 from the stator windings and 3 which come from the rotor windings.
I will put some pictures of where i am testing these below.
 
Lastly could not test the voltage regulator so replaced with new one (twice !,once on each alternator) and still the alternator when fitted to car produces no charge and charge lite constantly lit.Had the 2nd alternator (which gave allexactly the same readings as first) bench tested and is showing no charge with charge light constantly lit.
 
I am completely stumped why for a start has the alternator come to give problems ONLY after removing its mounting bracket for repair .
How sturdy are they? Is it usual to be easily damaged inside by slight knocking about whilst working around them?
Remember the 2nd alternator( identical results) has been  BENCH tested and also shows no charge.
 
Am i testing all the diodes (and correctly)?   I only see 6 of them but what is that black rectangular component with letters "DIET" on and could this also be a diode 
 
Just to say this is me wanting to understand what is wrong rather than just bung in a new rectifier /regulator or complete alternator. Im in South Africa and often drive long distances without any support or backup so need things working or at the very least to understand how to diagnose and fix

20180618_182411_resized_by_AVG_Image_Shrinker.jpg

20180618_182428_resized_by_AVG_Image_Shrinker.jpg

20180618_182435_resized_by_AVG_Image_Shrinker.jpg

20180618_182511_resized_by_AVG_Image_Shrinker.jpg

20180618_182515_resized_by_AVG_Image_Shrinker.jpg

20180618_182520_resized_by_AVG_Image_Shrinker.jpg

20180618_182551_resized_by_AVG_Image_Shrinker.jpg

20180618_182628_resized_by_AVG_Image_Shrinker.jpg

20180618_182652_resized_by_AVG_Image_Shrinker.jpg

20180618_182707_resized_by_AVG_Image_Shrinker.jpg

20180618_182720_resized_by_AVG_Image_Shrinker.jpg

20180618_182735_resized_by_AVG_Image_Shrinker.jpg

20180618_182740_resized_by_AVG_Image_Shrinker.jpg

Link to comment
Share on other sites

Does the charge light on the dash show with ignition on but engine not running? This sounds like a case of no power to the stator windings... Can you test the voltage of the wire from the light where it attaches to the alternator? If that circuit isn't working you won't get anything out of the alternator - I suspect a broken connection or wire upon removal and its not something you mentioned testing. It's not just a telltale

Ian 

Link to comment
Share on other sites

hi there yes the light goes on as soon as ignition goes on and stays on when engine fires up.

I did test the voltage on that wire and if i test the wire by taking it of the alternator D-+ terminal  i get 12.6volt (battery voltage)from that wire to earth with ignition on but engine not running.BUT if i leave it on the alternator D+terminal and make a break in the wire with a chocolate block i am only getting 1.4 volts when connected to earth???

 

what i cant understand is  was working before removal of alternator braket and was not knocked about severely at all  AND the other spare alternator tested with the same results but was bench tested and also came up as broken??

 

if i thought that the charge light circuit was broken i would have take a wire with a test bulb straight from D+ alt and straight to battery + but the alt is coming back broken on a test bench??

Link to comment
Share on other sites

19 hours ago, lo-fi said:

Does the charge light on the dash show with ignition on but engine not running? This sounds like a case of no power to the stator windings... Can you test the voltage of the wire from the light where it attaches to the alternator? If that circuit isn't working you won't get anything out of the alternator - I suspect a broken connection or wire upon removal and its not something you mentioned testing. It's not just a telltale

Ian 

 

17 hours ago, justustwo said:

hi there yes the light goes on as soon as ignition goes on and stays on when engine fires up.

I did test the voltage on that wire and if i test the wire by taking it of the alternator D-+ terminal  i get 12.6volt (battery voltage)from that wire to earth with ignition on but engine not running.BUT if i leave it on the alternator D+terminal and make a break in the wire with a chocolate block i am only getting 1.4 volts when connected to earth???

if i thought that the charge light circuit was broken i would have take a wire with a test bulb straight from D+ alt and straight to battery + but the alt is coming back broken on a test bench??

As lo-fi says it isn't a tell-tale as such, it actually supplies volts to the alternator in order to get it generating itself. Only when it is up and running will it present its own 12v onto that terminal and that is what extinguishes the charge lamp (12v at both ends, one from the alt and one from the battery).

Are you absolutely sure that you are connecting the warning lamp to D and not W???

5b291933ca4c4_ScreenShot2018-06-19at16_54_19.png.cc415e6fd9020e73d0b28bc97a24ec72.png

Link to comment
Share on other sites

46 minutes ago, western said:

charge light staying on with no ign switched on is due to dead diodes in rectifier pack, 

That is not possible on a 200TDI as the charge light circuit has a diode to prevent the alternator back feeding the light and switched power circuit.

Link to comment
Share on other sites

55 minutes ago, Red90 said:

That is not possible on a 200TDI as the charge light circuit has a diode to prevent the alternator back feeding the light and switched power circuit.

seen it on Discovery 200tdi, maybe they haven't got the diode.

Link to comment
Share on other sites

sorry to everyone for not updating but have taken the spare alternator to a friend who is is long standing auto electrician for the police dept and he is going to take  a look.

.At least when i did go through with him he confirmed that it was not on the car that the problem was coming from but from the alternator itself.

still not got any real clues as of yet but as soon as i do will update

Edited by justustwo
spelling
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy