Bad Alternator? Voltage drop?

[beale187]

hi guys

Hoping someone can offer some advice or suggestions.

I'm having minor electrical problems and on occasion the vehicle won't start without the battery being jumped, but I don't think the battery is the problem, it's still under warranty and is only 18mths - 2yrs old.

Here's the run down;

Charged the battery last week using a 7 stage charger, reconditions, desulphation etc. Drove around for 4 - 5 days, no problems.

Day 6, started noticing my heated seats weren't reaching their normal temp, the headlights flicker when I wind the window up / down, getting a noise coming from my radio which increases with RPM and the cluster has ever so slight flicker. Also once or twice the alarm went off when I started the engine, even though the car was unlocked.

Pulled out the voltmeter and got the following readings immediately after charging the battery (again..)

Car off, Battery reading: 12.65V
At Idle, Battery reading: 13.35V
At Idle, Alternator Case to negative terminal on Battery: 0.02V
At 2,000rpm, Battery reading: 13.25V
At 2,000rpm and under load (Lights, A/C etc.. all on), reading at battery: 13.15V
At 2,000rpm and under load, Alternator Case to negative terminal on Battery: 0.13V
Parasitic draw test which was 0.02amps

There is zero clearance between the alternator and the fan assembly in a 4motion so before I pull the front bar off and put the lock carrier into the service position to start inspecting the alternator, is there anything I have missed??

[weonarok]

I'd be looking at all connections/terminals including battery, fuse links and especially engine to chassis/battery the earth cable for a loose bolt as I suspect being only two years old connections shouldn't be dirty or corroded.

If it's still under warranty why are you stuffing around with it yourself? [emoji848]


"You don't know what you don't know"

Cheers dave

[beale187]

Pulled every fuse in the cabin and under the hood last night and they're all good. But I did notice this.


Ground cable is rubbing a screw head on my Forge CAI. Even though I don't think this is causing a short, it's process of elimination so I pulled CAI out and put the stock box back.

Woke up this morning, unlocked the car, went to start... Nothing... Reds on but no other noise. Then for some reason my alarm starting going off... Put the voltmeter on and it was reading 12.36V, surely enough to crank. Put the jump pack on anyways, car started straight away. Didn't even have to reset the clock.

[beale187]

I'd be looking at all connections/terminals including battery, fuse links and especially engine to chassis/battery the earth cable for a loose bolt as I suspect being only two years old connections shouldn't be dirty or corroded.

If it's still under warranty why are you stuffing around with it yourself? [emoji848]


"You don't know what you don't know"

Cheers dave

Thanks mate, I'll jack it up and start checking the ground connections.. Just to clarify the Battery is still under warranty, not the car it's 13yrs old. Battery is holding charge, cleaned the posts and terminals everything appears good battery wise.

btw "You don't know what you don't know", haha love it

[weonarok]

Ok. So if car is that old then it's bound to be a bad connection.

I know this may sound stupid but check the actual cable connections at the battery.
The reason behind my thinking is that if the battery voltage is fine but won't start you are then probably connecting your jumper leads to the cable terminals, therefore bypassing a bad battery connection.

I have seen this happen to my sons Lux and was told by a NRMA road techie that his starter motor was shot.

$300 later didn't fix it and all it was a dirty connection at the battery.


"You don't know what you don't know"

Cheers dave

[Bora Sport]

If it is of any assistance I believe that an alternator has to produce at least 13.8volts to charge the battery. I have had to replace the alternator 3 times on my Bora.

[weonarok]

If it is of any assistance I believe that an alternator has to produce at least 13.8volts to charge the battery. I have had to replace the alternator 3 times on my Bora.

I would have thought the same but he did say that his battery was 12.65v and 12.36v standing, so his alternator must be charging to maintain these voltages.

Also, if the alternator detects that the battery is fully charged the voltage will drop off to avoid over charging. I think a battery at 12.5v (from memory) is considered to be 100% SOC.

After continuous short runs my battery gets down to 11.9v and still starts (diesel). An overnight boost with a 240v charger every couple of weeks brings it back up.

I would also see what the voltage is at the battery post only, and then the positive cable terminal and body earth while cranking. If will pin point your issue.


"You don't know what you don't know"

Cheers dave

[h100vw]

Regulators are set to prevent over voltages. The current varies depending on the load. Lights and fans on, more current output. And vice versa. Dont confuse offload voltage with the ability to start the engine. A high resistance in circuit could drop enough to prevent a start.

[beale187]

Ok. So if car is that old then it's bound to be a bad connection.

I know this may sound stupid but check the actual cable connections at the battery.
The reason behind my thinking is that if the battery voltage is fine but won't start you are then probably connecting your jumper leads to the cable terminals, therefore bypassing a bad battery connection.

My bad Dave, forgot to mention first thing I did was clean the posts and cable terminals.

[beale187]

If it is of any assistance I believe that an alternator has to produce at least 13.8volts to charge the battery. I have had to replace the alternator 3 times on my Bora.

That's a bunch of times!... How did you determine it was the alternator?

[Bora Sport]

Well it is 16 years old now and over 400,000 kilometres. The battery went flat and an auto electrician told me the alternator wasn't charging enough to stop it from going flat.

[beale187]

So I went home last night, walked down to my VW lawn ornament (spare Bora) and ran a couple of tests on it and came up with this.

Car off, Battery reading: 12.40V
At Idle, Battery reading: 14.40V
At 2,000rpm, Battery reading: 14.28V
At Idle but Under Load: 13.90V
At 2,000rpm and under load (Lights, A/C etc.. all on), reading at battery: 13.80V

All readings substantially higher than my daily drive.

Then i got talking to a buddy here at work who's a LAME and he told me something I didn't know. That is, if a battery has a good resting reading, say of 12.2V - 12.6V it can still fail to produce enough AMPS to crank the starter motor if for example it has a dodgy cell.

Unfortunately my voltmeter does not have the functionality to test / measure CCA (Cold Crank AMPS) for my battery. The Delkor battery I was using (which is 2yrs old) has a CCA rating of 500. So I threw in the SuperCharge Battery from my donor vehicle which is rated 600CCA. Turn the key, car started first time no prob and all the other symptoms disappeared also....

I'll run with that for a couple of days and see how it goes, though I still suspect there more to it than the battery.

[beale187]

Well it is 16 years old now and over 400,000 kilometres. The battery went flat and an auto electrician told me the alternator wasn't charging enough to stop it from going flat.

Holy crap 400,000kms! That's phenomenal, if it gets to 1/2mil I reckon you send it back to Wolfsburg and they can mount it in VW HQ lobby. Incredible.

[Euro Remaps]

I would try making an extra earth lead from the battery to the engine and connect it to the mounting bolt on the starter motor and see if that makes any difference...i spent months with issues relating to possible starter motor,altenator, battery and ignition switch problems that turned out to be the earth lead and its been fine ever since...

[beale187]

Quick update.. Installed another battery with a higher CCA last Friday and have had no issues since. Also removed the battery and tray to check the ground terminals, they were tight but gave them a quick clean up anyways.


But then... Last night driving home I hear an ever so slight "click" noise and my cluster starts flicker and headlights dim. So it definitely sounds like a bad earth somewhere else. I'll pull the front off this weekend and take a look at the cables to alternator.