Problem- Alternator or Battery

[mogindo]

Car dies today, no start.

I went out for a drive and the battery light came on. I turned back to the house and measured voltage at the battery terminals and it was 11.48V (red flag !!)

I couldn't get good reading at the alternator.

But when I took the positive cable off the battery terminal and the car died.

Well, I couldn't start it again after that.

Any pointers, I don't want to rush out to get new Red Top Optima not knowing whats going on.

Cheers,

[Tombie]

Taking the battery terminal off a running engine can:

Blow the alternator
Blow the ECU...

People who don't understand shouldn't mess with electronics :)

[Tank]

Jump start it with the main battery connected and a good earth, put a multimeter on the battery and read the voltage, then get someone to rev the engine above idle and see what the reading is. Or get it started and take it to an Auto electrician and get him to test the battery and alternator, regards Frank.

[mogindo]

I did have someone rev the engine and the voltage went up, and then the battery light went disappeared. But I still didn't believe it, so I tried to start it again, twice, and second time there was like a half a crank...no juice.

I can jump start it, but the mechanic shop is far away, so if the alternator is done then I wont make it.

BTW, I replaced to new alternator 6 months ago

[Tank]

What voltage reading did you get when you revved the engine should be up over 13 volts, if so check your battery leads are clean and tight, especially the earth where it attaches to the block. Take your battery out and put it on a charger and give it a boost for a few days, Regards Frank.

[mogindo]

So I jumped the car, and checked the voltage again at the battery, but it was already 11.04V (from 11.48v earlier) then at the car was running it seemed that the voltage continued to drop.

I checked at the alternator and it was 10.94V. I had one probe on the terminal in the back and the other to the body of the alternator. So I guess my reading was ok, but voltage not.

Seems that I will have to replace an alternator, which sucks as this one is 6 months old.

[djam1]

Did you buy a good quality alternator or a cheapie??
Might be a lesson here

[mogindo]

I don't recall what make was it, but I checked and I paid USD$ 269.00, so I wouldn't call it cheap, but I hope its not Britpart. I bought the ANR5425

[mogindo]

BTW, the battery warning light is not illuminated anymore.

[bee utey]

BTW, the battery warning light is not illuminated anymore.
The important thing to note is that a warning light needs to be on with the engine stationary and the ignition on, then go out as the engine runs. A major electrical fault in the alternator may cause the warning light to not come on at all. To test the warning light, disconnect the small brown/yellow wire from the back of the alternator and hold it onto engine earth while the ignition is on. The warning light should then be on. If this wire has fallen off the alternator may not work at all as the trickle of current flowing through the globe to the alternator is needed to excite (or "kick start") the alternator charging cycle. On rare occasions the warning light globe fails.

[mogindo]

Sorry I wasn't accurate in my statement.

The battery warning light comes on before ignition and then stays on for few seconds, then it goes off, just like normal.

However, since me alternator is not charging properly, I would think that the battery light would stay on for longer. Hmmm, initially the light came on and that prompted me to turn back home. I stopped reved the engine and the light went off. After that I started my investigation, because I didn't think that the light just came on randomly.

So if alternator wasn't functioning properly then I assume that the light would be on. Maybe my measurement at the alternator wasn't good. Maybe its just the battery. But the car wont turn without a jump.

[bee utey]

However, since me alternator is not charging properly, I would think that the battery light would stay on for longer.
Don't overthink things! The warning light goes out regardless of the alternator producing one amp or full output. It simply shows the difference in the voltage between the ignition switch and the internals of the alternator. It isn't "programmed" in any way, it is just a dumb light globe.

The reasons for an alternator not charging properly are many, including not enough revs, loose drive belts or a melted main power cable connector at the back of the alternator. You should check the alternator voltage at elevated revs if your battery has been flattened, say 2000 rpm. A flat battery at idle will not show a higher voltage.

[mogindo]

so if my battery is flat (and it is) then when I rev up to 2000rpm, I should see elevated voltage at the Alternator, correct? I read that the voltage at the alternator should be about 13V at high rpm.

Will I also see elevated voltage at the battery terminals at 2000rpm?

(when I reved up last night, I didn't see more voltage at the battery)

I am not, over thinking, but also try to learn in the process, so thanks to all you guys for advices and opinions.

(luckily I called my mechanic and he still has the old original alternator, one I replaced with the new one. On;y because I wanted to fix jummpy tacho, but it didn't help. I think that old alternator is actually still good.)

[bee utey]

so if my battery is flat (and it is) then when I rev up to 2000rpm, I should see elevated voltage at the Alternator, correct? I read that the voltage at the alternator should be about 13V at high rpm.

Will I also see elevated voltage at the battery terminals at 2000rpm?

(when I reved up last night, I didn't see more voltage at the battery)



If the voltage is significantly higher at the alternator than the battery then the connecting cable is faulty. There should be no more than 0.1 volts difference at full power. A big difference would mean you need to fix or duplicate the cable from the alternator to the battery.

[mogindo]

My voltage at the alternator was lower than the battery !

[Tombie]

My voltage at the alternator was lower than the battery !

That's likely because when you pulled the terminal off the battery the regulator backed off.

[mogindo]

Well dumb me, for taking the terminal off. Grrr, Thanks Tombie, I am learning a lot form this.

Now, how do I reset the regulator?

Will putting a fully charged battery reset the regulator?

I have a feeling that its the battery is dead, but the alternator is fine. Batt is at least 4 year old Optima red top and Alt is $265 six months old.

[bee utey]

You can't reset a regulator. It either works or is stuffed. There is no "computerese" involved in the regulator. It is strictly analogue.


My voltage at the alternator was lower than the battery !

Yes but what was the voltage with the engine running at 2000 rpm and the battery connected???? Is the drive belt tension correct?

[mogindo]

Belt is not making any noises so I assume its correct tension.
i think i ran about 1500prm and the voltage at the alternator was 10.98V and at the battery 11.04V. It seemed that the battery voltage was dropping though the longer the car was running.

I ran it for about 10 minutes like this.

So what if I put new battery in. Will that make the Alternator charge more and regulator increase its band. Where is it anyway?

Thanks man for help.

[mogindo]

Well, I was just thinking that my reading on the alternator may not have been done correctly. I measured the voltage with the main lead connected, sounds right to me, but I already made one mistake....

[THE BOOGER]

There are a few things that can cause your problem but the most likely is your got a dud alternator, we had one go a few months ago no light on the dash just noticed the head lights got dimmer. Luck it is a diesel so doesn't need electrics to run, I take it yours is a v8. try with your old alt that will probably fix it if it was still ok:)

[mogindo]

My is tdi 300

I just got another jump and started the beast.

Measured voltage at the Battery 11.40V and Alternator 10.69V

I reved up the engine to 2000rpm and the voltage at the alternator did not change a bit, 10.69V. So hmmm....?? I would assume even on busted alternator the voltage would go up a bit. If its it the regulator (which I may have screwed up according to Tombie), then where is it? I have been searching online I couldn't find anything.

I will try to get that "spare" alternator in by the end of the week, problem is that my mechanic where I left the alternator is 50km away (crap)

Cheers guys for all the help.

[THE BOOGER]

this is the regulator Land Rover 90 110 Defender Alternator Voltage Regulator 200TDI 300TDI | eBay (http://www.ebay.com.au/itm/LAND-ROVER-90-110-DEFENDER-ALTERNATOR-VOLTAGE-REGULATOR-200TDI-300TDI-/160958820535?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2579e4b0b7)
much cheaper than a new alt, there should be a thread on here about changing them

[mogindo]

I just installed my old Mirelli alternator, (my mechanic sent it with the currier yesterday). All in order 13.49 Volts

Thanks to all guys for help. The ****ty alternator that went out was some no-name piece of sh*t for for $269 buck lasted 6 months.

Yeah, if any asks why I replaced the alternator in the first place?....Jumpy tacho. It didn't help.

[THE BOOGER]

For the tacho check the terminal on the wire and wire for breaks as that is the weak point :)