mad-butcher
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| posted on 4/9/09 at 07:28 AM |
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Checking an alternator can someone please confirm
Hi All
Picked up a nice Pajero 2.8 TD for £500 to replace my transit as a trackday tow vehicle, the paj had a fault in the electrics which was draining the
battery, previous owner had fitted a new battery and had paid good money to allegedly have alternator serviced all to no avail so gave up and flogged
it to me, ( no probs just disconnect battery when not in use.) I suspected the glow plug relay as it's a known issue, not that.
decided to read mr haynes and they give an apparently simple way of checking the alternator.
would appreciate if someone could confirm
Can someone confirm the following is correct,
disconect the negative lead from battery now put one side of a bulb to the battery negatine now connect the other side of the bulb to the battery
negative lead, the bulb should light indicating a drain, now disconnect (carefully) the alternator feed wire,(1) if the light goes out this indicates
the alternator is up the creek (2) if it stays lit start pulling fuses to find the affected circuit, mine is the (1) option.
Sorry it's a big post
tony
[Edited on 4/9/09 by mad-butcher]
 
Rescued attachment passenger side.jpg
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t16turbotone
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| posted on 4/9/09 at 07:52 AM |
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Sounds good to me....Mr haynes spends a lot of time and money on his publications. And 99% of the time hes accurate and correct
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zetec
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| posted on 4/9/09 at 08:12 AM |
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It will depend on how much the drain is. Better to use a ammeter with a low range if you have one.
" I only registered to look at the pictures, now I'm stuck with this username for the rest of my life!"
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daviep
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| posted on 4/9/09 at 08:17 AM |
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That will definately work depending on how big the current draw is, bulb might not be very bright if it's just a trickle.
Watch out for things which are also permanently live such as clocks and radios as these may draw enough to light a bulb.
Regards
Davie
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daviep
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| posted on 4/9/09 at 09:42 AM |
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quote:
Originally posted by zetec
It will depend on how much the drain is. Better to use a ammeter with a low range if you have one.
Be careful using an ammeter as most have a 10 amp max, if you accidently switch on the ignition and something which draws more than 10A is switched on
such as heater plugs or lights then you may knacker your multimeter.
You could always put a small fuse in line with the meter if you have one.
Regards
Davie
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mad4x4
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| posted on 4/9/09 at 11:42 AM |
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Usually I do this :
To Check the Altenator:
Connet Multimeter across battery with engine off - Take reading
Start Engine and the take second reading, If Alternator is charging then the voltage will go up.
To check for a current drain when off :
either Remove the negitive lead and connect the Multimeter in Series (as an ammeter) this should give you the current draw. Watch though any large
current draw bigger than 10 A will pop the fuse.
Simiarly to check the alt is not draining disconnect then check to see it the neg still sparks when you remove it.
Or how I do it take of the neg battery and watch for a spark. between the terminal and the lead any spark indicates a current draw. Then working
though the fuse box eliminate circuits (pull fuses) until you find the ones that cause the current draw.
^^ I know the above is a bit "Heath Robinson" but seems to work. A favorite failure used to be the boot light staying on when the boot was
shut....
[Edited on 4/909/09 by mad4x4]
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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mad4x4
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| posted on 4/9/09 at 11:45 AM |
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quote:
Originally posted by t16turbotone
Mr haynes spends a lot of time and money on his publications. And 99% of the time hes accurate and correct
?? you sure
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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britishtrident
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| posted on 4/9/09 at 12:55 PM |
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quote:
Originally posted by daviep
quote:
Originally posted by zetec
It will depend on how much the drain is. Better to use a ammeter with a low range if you have one.
Be careful using an ammeter as most have a 10 amp max, if you accidently switch on the ignition and something which draws more than 10A is switched on
such as heater plugs or lights then you may knacker your multimeter.
You could always put a small fuse in line with the meter if you have one.
Regards
Davie
Most DMMs have a 10 amp internat fuse -- easy enough to replace --- 13 amp plug fuse fits.
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LBMEFM
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| posted on 4/9/09 at 08:41 PM |
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I would believe anything that you old me daviep, now pleeeeease stop pointing the gun at me. Phew! 
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02GF74
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| posted on 5/9/09 at 07:46 AM |
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^^^ wotthey say is all good - will cause no damage.
the haynes usually go in to greater detail in testng the internals of an alternator which requires a bit more knowledge.
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