Alternator Mystery

[rossco]

Ok last night went out and parked up then came back started all right noted battery red light did not come on so carried on.

Drove for about 30kms stopped for 3 minutes then tried to start up but no go, dim lights and no turn over. Tried jump starting but no go, left hooked up for about 1 minute then started up no problems lights dim on the way home
Now no charge to battery.
Checked leads, connections, fuses that the 10 amp under bonnet etc..

Questions
1: Why has the red light on the dashboard gone out, shouldn't it come on telling that the battery is not charging? ( checked bulb ok )

2: Why so sudden no warnings?

3: Is there any other fuses I have missed?

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[rustic]

Hi Rossco, I would think there is a faulty connection at the alternator however, this is how the alternator normally works when the regulator is on the alternator ..
The light on the dash is fed with 12 Volts at the dash, the other side of the lamp goes to the alternator, to generate a field at the coils in the alternator.
When the alternator is running the field coil becomes self generating producing its own 12 volts. Now the bulb on the dash now has 12 volts on each side and thus is extinguished.
Problems can be caused by a faulty bulb/ wiring, broken wire at the alternator or faulty alternator (regulator or bad connection, or bad earth).
You need to check the voltage at the alternator on the thinner wire with a multimeter. OR..
To by pass the bulb, you could place a 12 volt bulb ( say 2.2 Watt ) as follows:
Battery + ve>---------> 12Volt Bulb>-------->Field terminal on Alternator.
Bulb should do what it normally does on the dash. This will eliminate any faults with the vehicle wiring.
Hope this helps.
Don't use too high a wattage bulb, if you haven't got a 12 volt 2.2 watt
put 2x 5 watt bulbs in series, they will be dimmer but will pass the correct current.
Battery + ve>-------> 12Volt Bulb>-- 12Volt Bulb>------>Field terminal on Alternator.
Best regards, Rustic

 

[DJ38]

"Top post Rustic" :smile:
The above can be applied to most vehicles

 

[Terranosaurus]

I had exactly the same style failure on my old Mav a month or so back - only I didn't notice the red light wasn't coming on when I started it. Fortunately my battery was in pretty good shape and it was daylight so finished the days laning but on the way home in the dark I had to swap to a friends winch battery whilst he charged up my battery again on his truck as we completed the journey - new alternator problem solved.

As stated above I believe its when the regulator packs up that it happens this way, the link in the circuit is broken completely, when I used to run escorts with ACR alternators they would go through brushes and as the brushes got worn the curcuit would still be complete and the light would start to glow at high revs (IIRC) when the alternator just wasn't putting out full voltage.

 

[fusbblood]

just a thought check the earth strap from the engine to the body is sound. a quick check is to put a jump lead from the engine block to the neg terminal of the battery. Worth a try

 

[rossco]

Thanks rustic for that.
I get the feeling it's the regulator but once I get some time I'll do a check.
Have to recharge the battery first.

 

[mrogers]

Had something similar last night. Drove home no problem, but stopped in local petrol station to pick up some stuff, came out and car would not start or turn over. Luckily i was a 3 minute run away from home so went and grabbed wife kids and her car went back and jumpstarted.

When I got home a decided to check the battery with the engine still running. it read 12.4v which isnt good, even worse was when i revved it the figure dropped down to 10v. I carefully tightened the atlerantor belt adjuster and it went back up to 13.8v, revver again and it stayed around 13.6 - 13.9.

belt was obviously slipping but, it seemed quite tight (was a quiet but audible chirping sound comming from the belt).

my onlt worry is even though its now seems ok, it may be too tight, still a faint chirping sound.

I tried to replace the belt the weekend and no matter what I tried I could not get the adjust to slacken enough to get the friggin belt off. The PAS one took me an hour with a hammer, but the atlernator one would not budge with hammer, breakers bars or anything.

Just have to wait for her to snap i guess, got the belts and relevant tools in my boot just incase.

 

[rossco]

Hi it was the alternator that packed up and has been reconditioned new one to expensive.
Cost $500 or 180 pounds for recon or $750= 278 pounds for new one 8O

Mrogers you'll find 2 bolts under the alternator the you have to loosen to adjust the belts :wink:
If the noise is coming from the alternator possibly the bearing going.

 

[rustic]

Hi it was the alternator that packed up and has been reconditioned new one to expensive going.

I'm pleased you have solved the problem, in an earlier part of my career I designed an automatic electronic alternator tester for an alternator refurb company, so that's how I found out how they work. The more complex ones are when the regulator are not on the alternator.
Best regards, Rustic