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Testing a alternator
adam1985 - 27/4/12 at 11:13 AM

Car is a 1.7 puma which has had 2 indicator stalks fitted ( half the lights stop working) and keeps blowing bulbs
Ive tested the alternator and here are the results

Across the battery
Engine off 12.6 volt
Engine on with heater, radio, screen elements, lights and hazards on 13.0-13.2 volts
Engine on everything else off 14.2 volts

Is my alterator duff?
Is there anything else to test?

Thank you for the help adam

coyoteboy - 27/4/12 at 11:17 AM

It's fairly high without load but not miles off, if you'd been over 14.5 I'd have been more worried.

adam1985 - 27/4/12 at 11:20 AM

What else could cause it to keep eating bulbs and control stalks?

theduck - 27/4/12 at 11:23 AM

Sounds like there is a short somewhere to me.

adam1985 - 27/4/12 at 11:28 AM

quote:
Originally posted by theduck
Sounds like there is a short somewhere to me.


That doesnt sound easy to fix what would i have to do route the cables back and inspect for damage

Alan M - 27/4/12 at 11:32 AM

You need to test amps too!

daviep - 27/4/12 at 12:45 PM

quote:
Originally posted by Alan M
You need to test amps too!


That's a good idea, can you explain how to do it please?

Cheers
Davie

Alan M - 27/4/12 at 01:37 PM

It can't be tested with a multimeter, as the wires are not sufficent. It is normally done using an ammeter with an amp clamp. Charging output is measured with an inductive amp probe clamped around the BAT (B+) wire that connects to the alternator. It can also be measured on an alternator bench tester. A lot of garages will have this equipment and some will know how to use it!

Alan M - 27/4/12 at 01:46 PM

Something like this:

www.youtube.com/watch?v=LriNo7PwwoM

coyoteboy - 28/4/12 at 04:49 PM

You don't need to test amps really, unless you suspect the alternator can't put out enough power for some reason (regularly flat batteries). If the battery voltage is fixed at 14.2 say and never gets any higher despite long runs then the alternator is producing enough power and limiting its voltage output to 14.2, at which point it's current output will be negligible (that required to run the engine and nothing more). If there had been a failure of its regulator circuitry and it was still throwing out power at full chat it would need to raise the voltage higher to get more current (and therefore energy) into the battery, so a long run would see battery voltage continuing to rise, cooking the battery and other parts.


Two things that tend to blow electronics and lamps are large fluctuations in power (to higher voltage or lower voltage) and ions disolved in water. Bad grounds, regulator breaking down intermittently or damp are my thinking. The latter is obvious,the former a bit harder to find, especially if it's short in duration (milliseconds) due to failing components. Personally I'd want a scope on the output of the alternator to see what it's producing in real time and I'd be checking all of my grounds over with a wiggle test.

I'm sure there's more to cover here but I'm starving any my head isn't working yet.