Shamrock GS
|
| posted on 19/4/08 at 02:59 PM |
|
|
Alternator testing
Is there any way to test if an alternataor is working?
Mine was working fine until last week and suddenly nothing. I have checked the wiring and it seems ok but dont want to replace the unit and find its a
problem somewhere else in the circuit.
Thanks
Gary
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
|
|
|
|
|
big_wasa
|
| posted on 19/4/08 at 03:11 PM |
|
|
what alternator is it ?
|
|
|
britishtrident
|
| posted on 19/4/08 at 03:43 PM |
|
|
If it has the standard Lucas/Bosch 3 bladed connector block first stop is always the connector block -- the large spade terminals tend to arc (they
carry a big current) and fritz the alternator reculator.
Sometimes just cleaning them up with nail board and giving the connector spades a slight squeeze is enough.
After that do a voltage check --- if you don't get more than 13.2 volts across the battery with headlights on and engine at 2000 - 2500 rpm the
alternator is on the fritz.
You can check for blown diodes by checking for reverse current through the alternator when the ignition is off -- diodes usually aren't easy to
fix.
However 9 times out of 10 it is just the brushes or the regulator pack -- if so for spares try.
http://www.alternatormart.co.uk
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
daviep
|
| posted on 19/4/08 at 05:46 PM |
|
|
Very simple to test alternator independently of the vehichle wiring, you need a volt meter, a 12v test lamp and a piece of wire(and some crimps) .
1: Remove all wiring from alternator
2: Check alternator is correctly earthed
3: Connect 12v test lamp between battery positive and the warning light terminal on the alternator
At this stage the test lamp should light if it does proceed to step 4. If it doesn't connect the test lamp between battery +ve and the
alternator casing (it should light) to verify the alternator is correctly earthed. If it is correctly earthed then there is a problem with the
alternator.
4: Connect a wire (heavyish if possible) between battery +ve and the output (large) terminal of the alternator, nothing should happen
5: Start the engine, the test lamp should go out now to indicate the alternator is charging, if it stays lit again problem with alternator. If it goes
out the alternator is working correctly which can be verified by checking battery voltage. In this case there is a problem with the vehicle wiring.
Sorry this is so long winded.
Davie
|
|
|
Shamrock GS
|
| posted on 19/4/08 at 07:09 PM |
|
|
Fantastic - very clear instructions
Thanks
G
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
|
|
|
britishtrident
|
| posted on 19/4/08 at 07:42 PM |
|
|
quote:
Originally posted by daviep
Very simple to test alternator independently of the vehichle wiring, you need a volt meter, a 12v test lamp and a piece of wire(and some crimps) .
1: Remove all wiring from alternator
2: Check alternator is correctly earthed
3: Connect 12v test lamp between battery positive and the warning light terminal on the alternator
At this stage the test lamp should light if it does proceed to step 4. If it doesn't connect the test lamp between battery +ve and the
alternator casing (it should light) to verify the alternator is correctly earthed. If it is correctly earthed then there is a problem with the
alternator.
4: Connect a wire (heavyish if possible) between battery +ve and the output (large) terminal of the alternator, nothing should happen
5: Start the engine, the test lamp should go out now to indicate the alternator is charging, if it stays lit again problem with alternator. If it goes
out the alternator is working correctly which can be verified by checking battery voltage. In this case there is a problem with the vehicle wiring.
Sorry this is so long winded.
Davie
That procedure won't test the alternator --- what it will do is identify a wiring fault -- testing the wiring by substitution.
Also if the warning light goes it out --- it dosen't follow the alternator is charging many alternator faults won't show up this way.
Even if the warning light goes out and a reasonable charging voltage is shown across the battery the alternator can still be U/S.
|
|
|
02GF74
|
| posted on 19/4/08 at 07:57 PM |
|
|
^^^^ well although it may not guarantee the alt is working, if it faislthe above simple test, then it will show up the alternator as duff.
|
|
|
daviep
|
| posted on 19/4/08 at 10:04 PM |
|
|
Yes sorry as pointed the correct way to test an altenator is to remove it from the vehicle and strap it to your test bench. Everybody has one of these
in their garage don't they???????
quote:
That procedure won't test the alternator --- what it will do is identify a wiring fault -- testing the wiring by substitution
That's true how ever if you know the wiring is good and the battery still isn't charging then you can be reasonably sure the fault lies
with alternator.
It's a far moe comprehensive check than sticking a voltmeter on to the battery and then talking crap about diodes which is of no use to
anyone.
Davie
[Edited on 20/4/08 by daviep]
|
|
|
:{THC}:YosamiteSam
|
| posted on 21/4/08 at 07:05 AM |
|
|
quote:
Originally posted by daviep
Yes sorry as pointed the correct way to test an altenator is to remove it from the vehicle and strap it to your test bench. Everybody has one of these
in their garage don't they???????
quote:
That procedure won't test the alternator --- what it will do is identify a wiring fault -- testing the wiring by substitution
That's true how ever if you know the wiring is good and the battery still isn't charging then you can be reasonably sure the fault lies
with alternator.
It's a far moe comprehensive check than sticking a voltmeter on to the battery and then talking crap about diodes which is of no use to
anyone.
Davie
[Edited on 20/4/08 by daviep]
i got my brother to replace the diodes once in my pinto'd dax - they are a common cause of alternator failure - first sign is light stays on
to be honest if you know its the alt that is duff - an exchange one is only around £35 new (well recon) not worth repairing
|
|
|
