Alternator/Charging issues.

[DoctorDubb]

Hey,

Ive been trying today to analyse a issue that i have with my charging system. Ive searched and searched the forums and im stumped. Heres how it goes:

Incident:
When i bought it the battery was completely dead. So i put my battery in and it ran for at least 40kms till i got home. The battery goes flat over time (less then a week - but testing lights and stereo - so not completely suprised). The other night i jumped started it then it started an ran, i removed the jumper cables it still ran fine. Leave it running for about 10 mins and then went for a drive about 2 km with my headlights on and when i got too my mates i stopped (left car running for 1 min). I then went to leave again and as i tried the car started to splutter and nearly die (i saved it by turning off headlights). Then i pulled back into the driveway and its running very rich and not very well at all. But still runs for about another 10 mins. Guess battery is flat so i leave it on charge there over night, the next day it drives home again fine and has started about 5-6 times since alright (can feel the battery is slowly dieing though).

HISTORY:
->CHG and BRAKE light are on in IGNITION and while running (well CHG light is connected to same cirucit as BRAKE).

->Tacho when turned key is turned to IGNITION proceeds and sits at 4000rpm (though i did notice last nite when at my mates place and it was spluttering the tacho goes to 1500-2000rpm occasionly). This has been a issue since i bought the car and dont know if this incidents are connected.

->'Home made' kill switch 'immobiliser' is hooked up to ignition circuit - bascially a latching relay from what i can see with a switch - dont see how this could be causing the problem though.

->Alternator looks 'new' and has correctly tensioned belt. It doesnt make any whining noises either.

->Turbo has been taken on and 'plated' i.e. a plate over the exhaust housing and removed the rest of the turbo as a temporary fix. So its effectively a NA for now but cant possibly be connected with electrical issues as i didnt move/change any wires.

->Hooked up the horn as it wasnt connect orginally when i bought the car - doesnt sound like that great (my girlfriend says it sounds liek a dieing cow) and is not very loud. This could be connected with the thin wire that was already in place (i just connected it back up).

Testing:
Took out BRAKE light diode - BRAKE light turns off and CHG light stays on - so definately CHG light is on not a fault with BRAKE light. - CHG light identified.

Then the plug n the back of the alternator is removed the CHG light turns off. Then tested the CHG light by earthing the (white/red - L wire) and this turns back on the CHG light. Then put a multimeter between this wire and ground and got a reading of about 170-180mA. Which i think is enough to start field coil of alternator - CHG light is working successfully.

Tested the battery without engine on: 12.3-12.4v
Tested the battery with engine on: 11.9-12.0V
Thought battery was problem (as it is relatively old - thought could have shorted cell) so changed with battery out of other car. Still had same voltages - Battery ruled out.

The next suspect was dodgy wiring. Testing with a multimeter and when the car is not running there is +12v on the BATT terminal and +12V on the SENSE wire (bottom of the plug). Funnily enough that is expected as they join to the same wire. - This rules out the FUSIBLE link between battery and alternator.

Then i made another wire up and earth the Alternator Casing to the Chassis. - Rules out dodgy EARTH wiring.

Then i removed the 'leak capacitor' that sits on the outside of the alternator from BATT to EARTH as i thought it could of possibly shorted. No luck still same voltages accross the battery. - Rule out leaking capacitor.

Checked wiring under dash, bit of a butchery from a dodgy stereo job but by all means not the worst i have seen. Check all the fuses of which non had blown. - Rule out fuse related issue.

Then the next suspect is the alternator (HITACHI - assume 65 amp). The reason i didnt think it was a problem as i was told it had been replaced by last owner and its the only thing that looks 'new' in my engine bay, otherwise i would of suspected it earlier. Plus if the battery was as dead as it was i wouldnt of charged it up that much when i jump started it the other day - so the alternator i thought must be doing at least something. So I removed the alternator. Now this suspect starts to make sense if the diodes are faulty in the rectifier of the alternator. If a diode had possibly short circuited then the AC voltage produced could be leaking into the electrical system and creating issues with the instruments like the tacho. This would also account for the low voltage reading accross the battery when the engine was running.

So i pull the alternator apart. Testing the field coil - has continuity and the field coil is not leaking into the magnet. Stator windings have continuity. Then i test the diodes on the rectifier. All test correct (diode test on multimeter as well as Ohm reading - '520-530' in one direction and 'open-circuit' in the other direction. Test connection for the SENSE and LAMP light and they have continuity to the voltage regulator.

So i reassmebled the alternator and then put it back in. Check connections and put battery terminals back on battery. Give it one more start in effort that something might have changed. Battery readings are similar but lower then before. Car not running: 12.1v and Running: 11.9v. Decide to call it a night and put the battery on charge.

The next day, after anaylsing it some more ive come to conclude the alternator is in someway faulty. I take it down to a auto electrician and they have 'confirmed' this (though i dont know how much face value to take this).

Now i did another measurement on the 'LAMP' signal and while the engine is running it reads 3V. Now when i take out the plug and then test the voltage on the plug with the same wire to the 'LAMP' it reads 12v. So i know that the 'LAMP' is receiving 12V in the dash, but something seems to be capping it at 3V when its running. From my understanding this has to increase to 12V in order to turn the lamp off?

So i take the alternator apart..again and check for resistance of the field coil = 4.3ohms so its fine. Bushes are still fine (easily push up and contact the copper rings) and so are the copper rings. There is no leakage from the field coil into the housing.

So i go out and buy three 400V 3A diodes as one of these may be faulty and at 25c each is a cheap fix. Put the alternator back in and no go still have the same problem. So i think the only connection of the 'LAMP' signal is through the regulator. Talk with the guys at another auto electrician place and this is the first thing they replace. So i take the alternator out AGAIN, and buy a $40 regulator and stick that in there. Put it back in the car and the problem is still there: Car not running: 12.5v and Running: 12.1v. .So its start raining and i call it a day.

Questions:
1) What could possible be capping the lamp at 3v if its not a faulty diode or faulty regulator?

2) Should i hook up a external 12V connection through a resistor and try it that way - i doubt it would make a difference though?

3) Any items/possible causes that i have missed?

4) Is there any mistakes in me analyising my faults?

So im now really stumped and any help would be greatly appreciated. As you see i do nearly all the work on my car myself as i want to learn. Apologies for the long post i just wanted to cover all my bases.

Cheers,
Steve

[oldcorollas]

this is a quickie, but.. if you have a beefy soldering iron, try to resolder the wire joins inside the alt.. as some of them may be dry, or have cracked from vibration.

the other thing might be that the wiring is just too dodgy...
perhaps hook up a seperate light for the ALT lamp, away from the original wiring... basically, temporarily redo the wiring including the main charging wire to the batt, and see if that helps...

to help diagnose diode issues, using a 10 LED battery voltage indicator, like the jaycar/DSE ones, can help.. iave had a few cases where one diodes solder has failed (both denso and bosch alts), and it results in the voltage being seen to cycle on the LED display.. even tho the multimeter says the voltage is constant

http://www.jaycar.com.au/productView...Max=&SUBCATID=

edit, when you checked the diodes.. did you unsolder them from the coils first?

[DoctorDubb]

Thanks oldcorolla, yeah the first time i didnt, but i tested the new ones i put in seperate from the circuit so not to introduce any weird circuit effects.

Thanks for the info on the diagnoising of the dodgy dioides, i was considering going out and buying a cheap oscilloscope and anaylsing the batt output as its really starting to annoy me . Should be quite easy to then see any dead diodes/dodgy connections.

I was thinking about redoing the ATL lamp wiring to a new line straight from a battery -> fuse -> resistor -> lamp. Should i be aiming at about 200mA to the field coil to initialise it? If so 12V/200mA = 60 Ohms resistor . 60 Ohms resistor dissapating power would be P=(0.2)^2 x 60 = 2.4W . Just found 5 Watt 56 Ohm which would be a bit more current but less power dissapation.

Any help is still appreciated.

[toymaz]

Dude, don't fuck around with the alternator, unless you know what you are doing. I assume its an internal reg, if not get a new ext reg or check the fuse under the lid of ext reg. Most toyotas have a charge fuse in the engine bay 7.5 amp. check it.
If your diodes are shot, the alt will whine or the charge lamp may be very dim.
cheers

[Norbie]

Charge light on -> alternator not working -> replace alternator or get it rebuilt by a pro.

Very simple, why the epic post? It's not like alternator rebuilds are expensive.