My '11 TDV8 had a new alternator almost a year ago as it wasn't charging properly. I seem to be having a much of similar symptoms again already so I was wondering whether it is the same thing or if there is something else in the vehicle that controls the excitation of the alternator that may be sending inconsistent signals, etc.

I may be getting confused by some of the IID Tool signal terminology and how they relate, e.g. Vehicle Battery Voltage, Vehicle Battery Current, Alternator Current & Alternator Load. Thos are the four parameters that I've been trying to use to diagnose things.

Most of the time my IID Tool shows around 13 volts with a very low battery current, e.g. 0A - 2A. When it shows the battery current increasing then the battery voltage does also but the voltage then drops back to 13-ish as soon as the current drops also.

It seems to show very little relations o the alternator current and alternator load which is why it is confusing me.

I've already put a brand new AGM battery on the car in case the told one was causing issues, even though it was changed along with the alternator last July.

Here are a few examples of the readings I've been seeing:

Battery Voltage Battery Current Alternator Current Alternator Load
12.9V 0.0A 47.0A 22.0%
13.7V 7.0A 59.0A 26.0%
12.8V -17.0A 34.0A 14.0%
12.8V -43.0A 0.0A 8.00%

Some days it spends most of the day around 13V and only goes up to 14.6V on occasions. Other times it starts at 14.6V and stays there for quite some time, i.e. 30 minutes or more, before dropping to 13V and staying around that figure.

I did some testing with either the AC on full or the defrost heating on full.

Battery Voltage Battery Current Alternator Current Alternator Load
13.0V 0.0A 59.0A 27.0%
13.1V 6.0A 63.0A 28.0%
12.9V -3.0A 119.0A 53.0%
13.0V 3.0A 126.0A 57.0%

On another occasion:

Battery Voltage Battery Current Alternator Current Alternator Load
14.1V 17.0A 66.0A 36.0%
14.6V 16.0A 60.0A 25.0%
14.1V 11.0A 64.0A 36.0%

Any and all suggestions welcome as I have absolutely no idea why it is so inconsistent.

AGM batteries don't charge at a constant rate like old lead acid batteries. If there is little electrical load they will charge at a lower voltage as this puts less load on the engine so saving you (a bit) of fuel. 2012 TDV8 Vogue (L322)

You should be seeing around 14.5V when the engine is running (I have an AGM battery on my 4.4TDV8 and this is the voltage i get through both the IID tool and using my multi-meter). The diodes inside the alternator prevent back current and convert the AC to DC, maintaining about a 14.5V output +-1V and are largely independent of shaft speed. The current is what the alternator varies depending on load and battery state of charge. The battery should be reading around 13.2‐13.5V if fully charged (which it should be after a run) without the engine running.

If you're having charge issues and battery charge is depleting, I'd be looking at the alternator cables running the charge circuit. It is known for failed spade terminals or cable breaks to cause issues, simply as a result of wear and tear. Of course, it is also possible there's a bad diode in the alternator.

I'd start by checking what voltage is reaching the battery and what is at the alternator (with no load so, all accessories turned off). A smart charger should also be able to do an analysis on battery condition, to confirm it has been fully charged. 2015 Range Rover Autobiography 4.4 SDV8

I’ve never seen a constant 14.5v on mine. Recently had the alternator checked by Glenrands and all was good. 2012 TDV8 Vogue (L322)

garyRR wrote:

You should be seeing around 14.5V when the engine is running (I have an AGM battery on my 4.4TDV8 and this is the voltage i get through both the IID tool and using my multi-meter). The diodes inside the alternator prevent back current and convert the AC to DC, maintaining about a 14.5V output +-1V and are largely independent of shaft speed. The current is what the alternator varies depending on load and battery state of charge. The battery should be reading around 13.2‐13.5V if fully charged (which it should be after a run) without the engine running.

If you're having charge issues and battery charge is depleting, I'd be looking at the alternator cables running the charge circuit. It is known for failed spade terminals or cable breaks to cause issues, simply as a result of wear and tear. Of course, it is also possible there's a bad diode in the alternator.

I'd start by checking what voltage is reaching the battery and what is at the alternator (with no load so, all accessories turned off). A smart charger should also be able to do an analysis on battery condition, to confirm it has been fully charged.

garyRR wrote:

You should be seeing around 14.5V when the engine is running (I have an AGM battery on my 4.4TDV8 and this is the voltage i get through both the IID tool and using my multi-meter). The diodes inside the alternator prevent back current and convert the AC to DC, maintaining about a 14.5V output +-1V and are largely independent of shaft speed. The current is what the alternator varies depending on load and battery state of charge. The battery should be reading around 13.2‐13.5V if fully charged (which it should be after a run) without the engine running.

If you're having charge issues and battery charge is depleting, I'd be looking at the alternator cables running the charge circuit. It is known for failed spade terminals or cable breaks to cause issues, simply as a result of wear and tear. Of course, it is also possible there's a bad diode in the alternator.

I'd start by checking what voltage is reaching the battery and what is at the alternator (with no load so, all accessories turned off). A smart charger should also be able to do an analysis on battery condition, to confirm it has been fully charged.

Mike Edwards wrote:

garyRR wrote:

You should be seeing around 14.5V when the engine is running (I have an AGM battery on my 4.4TDV8 and this is the voltage i get through both the IID tool and using my multi-meter). The diodes inside the alternator prevent back current and convert the AC to DC, maintaining about a 14.5V output +-1V and are largely independent of shaft speed. The current is what the alternator varies depending on load and battery state of charge. The battery should be reading around 13.2‐13.5V if fully charged (which it should be after a run) without the engine running.

If you're having charge issues and battery charge is depleting, I'd be looking at the alternator cables running the charge circuit. It is known for failed spade terminals or cable breaks to cause issues, simply as a result of wear and tear. Of course, it is also possible there's a bad diode in the alternator.

I'd start by checking what voltage is reaching the battery and what is at the alternator (with no load so, all accessories turned off). A smart charger should also be able to do an analysis on battery condition, to confirm it has been fully charged.

I've tried a battery condition tester and it said it was a healthy battery that was charged to 95% (12.57V). The cranking test came back at 10.84V and the 2,500 rpm test said the charging was 'low', showing 12.66V loaded and 13.08V unloaded.

It's a new battery that has only been on there a couple of weeks

If it was a bad connection, or a bad diode, I'd expect the charging voltage to either be consistent or all over the place. However, it isn't. It sits at 13V and goes up to 14.6V when it feels like it.

It can stay at 14.6V for a while or sit at 13V. I haven't seen it vary from those two voltages, aside from when it is transitioning between the two, during my testing.

I have numerous electrical problems that may or may not be related, plus plenty of dash warnings about low battery - please start engine warnings.

My concern over the battery charging is that it behaves differently at the same point across multiple repeated journeys under the same conditions.

Where would I find the charge diagnostic chart?

Here

https://www.fullfatrr.com/gallery/albums/u...gnosis.pdf

It does sound like the battery charge monitor needs a reset - it should be done on battery change and they can be damaged by connecting jump leads / chargers directly to the battery negative post.

It’s hasn’t been jumped in the year I’ve had the vehicle.

The IID Tool battery reset function has been used after each new battery installation.

Not even sure where some of the components are located in the link you supplied. It’s all rather confusing.

All you need to know is the measured voltage at the battery not the system reported voltage, the alternator output percentage (PWM duty %) - you've already reported that as 'alternator load' plot those points as per the instructions, see what the outcome is and follow the pinpoint tests. At this stage, you don't need to worry about the components, just carry out the test(s) as specified, the results will give you an indication of the causal part.

It could well be a historic fault with the battery charge monitor - what is your typical journey cycle? time / distance / type (fast road, urban, stop-start traffic etc.) it typically takes 7 miles driving, not idling, to put back the charge you took out of the battery just from starting the car.