jabbahutt
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 posted on 3/9/07 at 07:23 AM |
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testing alternator
Monday morning and time for a daft question which someone here is bound to find easy to answer.
with a multimeter what is the easiest way to test an alternator is working. I thought putting the probes across the battery terminals and seeing what
voltage I'm getting with engine running, expecting about 14v.
Is that the right to test an alternator or am I completely wrong and what voltage sjould I expect?
Thanks
Nigel
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RazMan
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| posted on 3/9/07 at 07:41 AM |
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Thats pretty much how to do it alright. To eliminate any other electrical problems you could disconnect the alternator completely and connect your
meter between the charge wire and earth. You should see between 14 - 15V at around 2000rpm.
[Edited on 3-9-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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02GF74
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| posted on 3/9/07 at 09:35 AM |
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quote:
Originally posted by RazMan
you could disconnect the alternator completely and connect your meter between the charge wire and earth. You should see between 14 - 15V at around
2000rpm.
^^^..... hmmm, I am pretty sre I have seen somethwere that you should never run an alternator disconnected from battery - will see if I can find the
reference.
.... and it may not work if the wire for the field current (charge lamp) is disconnected.
One of the haynes manuals goes into great detail in disgnosing the faults but the first test that should be carried out is:
1. all wires connected and connectors making good contact
2. is charge warning lamp fitted and working - it should be lit when ignition is on and engine is not running
3. is fan belt tension correct
4. does charge lamp go out when engine is running - may need to be breifly revved to about 2,000 rpm
5. when engine is not running, voltage across battery is about 12 - 12.5 V (any less that and battery is not fully charged); 6. when engine is
running, voltage should be as ^^^ says, 13.5 - 14.0 V. More than that and alternator is uwell.
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RazMan
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| posted on 3/9/07 at 09:53 AM |
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quote:
Originally posted by 02GF74
^^^..... hmmm, I am pretty sre I have seen somethwere that you should never run an alternator disconnected from battery - will see if I can find the
reference.
.... and it may not work if the wire for the field current (charge lamp) is disconnected.
One of the haynes manuals goes into great detail in disgnosing the faults but the first test that should be carried out is:
1. all wires connected and connectors making good contact
2. is charge warning lamp fitted and working - it should be lit when ignition is on and engine is not running
3. is fan belt tension correct
4. does charge lamp go out when engine is running - may need to be breifly revved to about 2,000 rpm
5. when engine is not running, voltage across battery is about 12 - 12.5 V (any less that and battery is not fully charged); 6. when engine is
running, voltage should be as ^^^ says, 13.5 - 14.0 V. More than that and alternator is uwell.
Quite right - what was I thinking! Of course the alternator needs to have the sensing wire conected to enable it to make any power at all.
Just ignore my muppetry 
[Edited on 3-9-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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02GF74
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| posted on 4/9/07 at 08:59 AM |
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re: ^^^..... hmmm, I am pretty sre I have seen somethwere that you should never run an alternator disconnected from battery - will see if I can find
the reference.
^^^ what I was referring to is running the alternator with the main battery/charge lead disconnected. Seems it is ok to run with all lead
disconnected.
From the green bible:
quote:
Do not connect or disconnect any part of the charging circuit - including the battery leads - when the engine is running. Run the alternator
with all connections made or with the unit disconnected
[Edited on 4/9/07 by 02GF74]
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