Alternator or battery, and how far can you get with a dead alternator?

[terravista]

Our 3 litre petrol auto Avalon has started showing the battery charge light intermittently.
There appears to be no common timing relating to engine temp or speed.
The regulator was changed by the RACQ 5 months ago, and I assume the brushes were checked the same time.
Yesterday, the light came on, and the battery showed a 12.9 volt charge. I kept driving for 10k and the light went off. It came back after another 10k, and stayed on for 60k till I got home.
I again checked the battery, and it had 13.2 volts.
When the charge light is not illuminated, it charges around 13.8 to 14 volts.
Does this sound like a faulty alternator?
Does anyone know how much distance one should expect from no charging, and only relying on the battery for power?  We had a similar problem years ago with a Toyota Camry at the end of a Nullarbor crossing, and we drove for around 200k on the battery, but that flattened the battery completely by the end.
Does it sound like that although the charge light is on, the alternator is still charging, but not enough to turn the charge light off?
Is the charge light related to the regulator, or further down the system at the battery?
I am just after sufficient information so I don't sound like a complete sucker when I go to an Auto Electrician. I recently replaced an A/C condensor that alleged experts (little devils of a red appearance) said had a big leak, and all it needed was a 40c O Ring.
Cheers and thanks
Ian

[gonfishen]

i had the same problem with my Disco it was an alternator issue and it needed to be rebuilt $300 from memory

[Jon]

Sounds like a dodgy connection, either loose or corroded.
In my experience failed electrical components do not usually fix themselves.

[oldtrack123]

Hi Ian
Intermittent faults are often difficult to locate.

[1]Does the battery voltage suddenly drop a little when the light comes on?
[2] How long does the light stay on for?
[3]when light comes on,switch your headlights on
 [a]Does the light stay OFF
Does the battery voltage drop?
[4]is it an external or internal regulator?

 I would suspect alternator or regulator trouble or could be a bad connection with the alternator external field connections.
 You would need your vehicle wiring diagram to see just where a bad connection may be.

 repair cost could be are rewind of rotor or stator[$300plus]

Peter

[dno]

If it were me,wait till the light come's on stop with the car still running and make sure the light is still on lift the bonnet check again that the light is still on, and then tap the alternator with the handle of a screw driver or something. Then check if the light's gone off on the dash. if the light's gone out it's more than likely brushes and will need replaceing ...

[terravista]

Hi Ian
Intermittent faults are often difficult to locate.

[1]Does the battery voltage suddenly drop a little when the light comes on?
[2] How long does the light stay on for?
[3]when light comes on,switch your headlights on
 [a]Does the light stay OFF
Does the battery voltage drop?
[4]is it an external or internal regulator?

 I would suspect alternator or regulator trouble or could be a bad connection with the alternator external field connections.
 You would need your vehicle wiring diagram to see just where a bad connection may be.

 repair cost could be are rewind of rotor or stator[$300plus]

Peter

Thanks Peter
1 & 3 I haven't noticed if the voltage drops with a light on. I started the car, and the light stayed off, so I gave up.
2 & 3. The light stays on for times between a flicker, a few seconds, a minute, 5 minutes, and yesterday, an hour. It stays off for the same time  frames.
4  It is an internal regulator, which was replaced 5 months ago.
I will try and see where the connections are, and check them.
Cheers
Ian

[terravista]

If it were me,wait till the light come's on stop with the car still running and make sure the light is still on lift the bonnet check again that the light is still on, and then tap the alternator with the handle of a screw driver or something. Then check if the light's gone off on the dash. if the light's gone out it's more than likely brushes and will need replaceing ...

Thanks.
When I got home yesterday, the light stayed on, so i hit the alternator a few times with a lump of wood, but it didn't make any difference. I also beat up the battery terminals, with no result.
Cheers
Ian

[terravista]

Sounds like a dodgy connection, either loose or corroded.
In my experience failed electrical components do not usually fix themselves.

Thanks Jon.
I have checked for loose connections on the alternator and battery, but will look further for the earth grounding.
Cheers
Ian

[terravista]

If anyone else has similar problems and finds this post by searching, I finally had the opportunity to stick a multimeter on the battery while the light was on. and it was reading 18.2 volts.
A slight overcharge from the alternator.
According to the RACQ, it is a faulty regulator, which failed in less than 5 months, but apparently the Bosch units are not too good, and Toyota replaced them as OEM's a few years ago with Denso units.
All now is well.
The RACQ guy also said you could probably rely on an hour or so of driving with a dead alternator, or broken belt, as long as you minimise battery usage by not using lights, wipers, A/C and fans , radio's etc.
Cheers

[danielhobby]

in the early eighties i had a nissan 720 dual cab that i drowned the alternator in in a large mudpond at big river state forest having some some fun(yep...i know).anyway i took of home and drove with out stopping(daylight) and i got four hours out of it till i got home  on sunday arvo,bump started it monday morning and drove it  another sixty km to the auto elec to get it fixed.todays cars use so much more battery i know so its not totally relevant but this was my experience.