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Testing alternator
pointy - 12/8/08 at 03:54 PM

All,

How (and I know there will be lots of tutting) do I check my alternators output using my newly aquired Multimeter?, and what should the output read...
Then Once/if that is ok is it simply a point of touching the terminal on the battery (pos and Neg) and ensuring the battery is receiving 12volts.

Lay-mans terms is fine

Andy


Paul TigerB6 - 12/8/08 at 04:02 PM

Check the battery voltage before starting the car. The voltage should be a bit higher than this when you start the car up - probably go from about 12.8V up to around 13.8 - 14 volts with the engine running


BenB - 12/8/08 at 04:04 PM

Put the multimeter onto volts reading.
Attach the clips to the battery terminals.

Normal readings would be as mentioned (ie 13ish fully charged engine off, going down to 10v (ish) when cranking, going up to 13.8-14v when charging...


02GF74 - 12/8/08 at 04:12 PM

^^^ wot he says.

now in layperson terms:

1. ensure multimeter is set for voltage reading, scale to be 20 V.
2. ensure red and black probes are connected correctly to multimeter.
3. touch black probe on battery negative (labelled -)
4. touch red probe to battery positive (marked +)
5. read voltage off multimeter display.

For a healthy and charged battery you would expect at least 12.5 V.

Start engine, blip the throttle so that ignition lamp, if fitted, goes out and repeat steps 3 to 5.

this time you would expect to see around 13.5 V or as high as 14.0 V.

^^^^ and wot he said too; you gotta type quick on this site!!!

[Edited on 12/8/08 by 02GF74]


pointy - 12/8/08 at 04:25 PM

Thanks all,

Got 12.8 with battery off of car
Will now fit battery and try when running.

I love this site .
No ridicule or titters just Cos I is fick

thanks again Off to test.
Andy

[Edited on 12/8/08 by pointy]


pointy - 12/8/08 at 04:55 PM

Help,

Car running showing 12.3 volts,..
Now if I put pos lead from meter on large terminal on rear of alternator and neg on smaller terminal should i see an output from the alternator and should this also be 14v ish ?

Also Small red wire from rear of alternator goes to cut out switch should this not go straight back to positive side of battery?

Andy


theconrodkid - 12/8/08 at 05:55 PM

just go red to+ and black to earth for output voltage on battery,if its not getting up to 14 ish volts check at alternator output term (big wire) and check again


02GF74 - 13/8/08 at 08:33 AM

quote:
Originally posted by pointy
Help,

Car running showing 12.3 volts,..
Now if I put pos lead from meter on large terminal on rear of alternator and neg on smaller terminal should i see an output from the alternator and should this also be 14v ish ?

Also Small red wire from rear of alternator goes to cut out switch should this not go straight back to positive side of battery?

Andy


this was explained in my post. to measure alternator output with engine running you measure voltage across battery 'coz that is what the alternator should be connected to.

I don't know about your coloured wires nor can advise with any confidence regarding the big/small terminals since would you believe, there is more than one type of alternator, and you do not say what make/model it is.

I will make a guess from the details you have given it is a Lucas type.

On the rear will be a slot where a connector goes and there are 2 wide 7.9 mm spade connectors - these are joined together and a smaller 4.7 mm spade.

The 4.7 mm spade is for the ignition lamp. One end of lamp connects to positive terminal of battery via the ignition switch, the other to this spade.

Either one of the larger spades, or both, can be connected to the postive terminal of the battery; usually this is done by connecting to the starter solenoid terminal as it is more convenient as there is a screw post there.