Battery/alternator issues - do these voltages look healthy?

maxtaban

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Hi guys

I have a 2006 HSE (Jaguar 4.4 v8 engine). I occasionally get the odd HDC or DSC errors. Sometimes the car wont shift higher than gear 3. When these kinds of errors happen, I'll just pull over, turn it off, wait a few seconds then start it up again.

I've also noticed that sometimes the blower motor turns itself down (the speed), which I'm not worried/concerned about, just saying in case it rings a bell.

Whilst I was trying to park up today, the car shut itself off. I fired it up again and it shut itself off again. I turned off the AC blower and fired it up again, this time it was ok. Parked, did what I needed to do, came back to the car, and it started by fine. Tried not to run the AC blower on high after that as I didn't want to be stranded.

I took it to a garage who tested the battery and their tester said my battery only had 47 CCA and it needed to be replaced, although the tester settings only went up to 900 CCA, and mine is a 950 CCA AGM 105A Varta. They told me to go to their bigger branch so I went there and they tested it with a better tester (Midtronics MDX-651P AP) and it said the battery was at 12.1v with a measured 759 CCA. The machine says the battery is "GOOD, RECHARGE", with battery health showing around 30%. He measured the voltage with the car on and it was coming up as 13.2v.

I came home, a few hours later went out and popped the bonnet and without starting had around 12.15v across the terminals. A few seconds after starting I had around 12.89v across the terminals. I turned the blower fan all the way up and the headlights too. Got same, around 12.89v across the terminals. Then I turned on the high beam and fog lights as well. This time I got like 13.8v or so across the terminals. Measuring with a Draper digital multimeter with a good battery.

The battery currently on the car was fitted in May/June 2021. It was a brand new Varta 950 CCA 105AH AGM. I use the car around twice a week, usually for runs at least 15km (each direction).

I live in Qatar so car batteries usually last around 2 years here (as it's super hot here). Standard batteries usually last 2 years max. AGM ones usually last 2 years minimum, sometimes 3 years.

I'm thinking I might have an alternator problem. The shop I went to (reputable guys for batteries, tyres, etc, but not specialists) said that the voltage across terminals should be 14v minimum when the car is running. The Land Rover independent mechanic I spoke to here says that the voltage can be between 13.5v to 14v. Common knowledge says 14.4v is the target. There are plenty of happy people on these forums with 13.8v etc.

I'm not sure what the deal with my car is. Shortly after starting I got a reading of 12.8v. When I turned on everything I got 13.8v. The shop measured 13.2v. What's the deal here? Why so much fluctuation? If it was constantly 12.8 or 13.2 I'd say change the alternator, but the fact I saw it at 13.8 with everything turned on makes me hesitate. What are your thoughts?
 

joey

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Sounds like a bad battery to me.
 

bbyer

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The link below is to a pdf file in my gallery related to the alternator and more significantly, the internal regulator within the alternator.


The battery might be beat now, but my guess is that the regulator located within the alternator has failed.

When that happens, often rather than the alternator not generating any amps, the regulator defaults to a voltage of about 13.3 VDC. This default voltage is enough to make the alternator produce sufficient amps to power the spark plugs and maybe the headlights plus other stuff but not everything and certainly not enough to charge the battery. That can take at least 14 volts even in a hot country.

The engine start system only require about 11 volts for the engine to start and when the engine gets started, then the alternator will put out some amps, often enough to fool all the battery / electrical system checking tools. Also the red battery light on the instrument panel will not illuminate, (I do not think it ever does.), it is just that stuff does not work or works only intermittently. Also the computers seem to require at least a steady 13.5 volt feed even though they operate at 5VDC. I think they have poor voltage step down internals.

I learned all this when a replacement alternator I installed turned out to have a defective internal regulator. It took some fooling around to figure out the problem was the replacement alternator and hence a replacement for the replacement alternator was required. All has been good since and that was years ago.


Below is a link to where the previous file link is located plus there are four or five other alternator/regulator related files that may be of interest.

 
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Bethany

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Hi guys

I have a 2006 HSE (Jaguar 4.4 v8 engine). I occasionally get the odd HDC or DSC errors. Sometimes the car wont shift higher than gear 3. When these kinds of errors happen, I'll just pull over, turn it off, wait a few seconds then start it up again.

I've also noticed that sometimes the blower motor turns itself down (the speed), which I'm not worried/concerned about, just saying in case it rings a bell.

Whilst I was trying to park up today, the car shut itself off. I fired it up again and it shut itself off again. I turned off the AC blower and fired it up again, this time it was ok. Parked, did what I needed to do, came back to the car, and it started by fine. Tried not to run the AC blower on high after that as I didn't want to be stranded.

I took it to a garage who tested the battery and their tester said
It could be your voltage regulator . My 2001 D2 had weird issues. After the voltage regulator was replaced, all was good on the land of Oz.


The voltage regulator is part of the alternator, on the D2. I got a replacement for the VR and alternator brushes for $45 US. It sure was a lot cheaper than buying an alternator.
 
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I agree with Bbyer. The alternator voltages typically are well above 14v to charge the battery after starting and then reduces to mid-low 13 after running for a while.
 

drivesafe

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Hin Maxtabam, it is your alternator.

If your battery was the problem, even if it had a dropped cell, which yours has not ( going by the voltage before starting ), but with a dropped cell, your alternator Could easily run at up to 14.7v.

In your case, as your battery was at 12.1 when you started your motor, while high enough to start your motor, it is still that low that the alternator voltage should have risen to a high 14v exactly 30 seconds after you started your motor.

The LR3 has an exact 30 second time lag from when you first start your motor and when the voltage rises, and during this initial 30 seconds, the LR3 determines what the state of charge of your battery is, and then sets the alternator voltage according to what is needed.

Again, at 12.1v at startup, your battery is low and the alternator voltage should have risen.

As it is summer time over where you are now, the voltage should have been in the high 14v and in winter, the low 15v.

My guess is that your alternator is on its way out.
 

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