Variable Voltage Alternator: Can it be configured to be OFF?

[RoverLander]

The question is: Is there a paramater somewhere in the D4 3L system (a 2016 model in my case) that allows the variable voltage alternator function to be switched on or off? On would vary the voltage depending engine load/battery condition. Off would make voltage be regulated to a steady 14.7v (approx) at all time regardless of engine load.

Background:
When I first purchased the car the voltage varied. I can see this as my Tyre Pressure Monitor has a voltage display.

Then after about 12 months the starter battery failed. LR replaced the battery under warranty. However when I got the car back it ran at a constant 14.7V. Ie Variable voltage alternator seemed to be off. The car ran like this for 5 years with no battery problems. I was happy with this as I think it kept the battery in good condition.

I then recently had a new battery installed by LR. When I picked it up the service guy mentioned that they had reset the system for the new battery (or words to that effect). Now the variable voltage is back with voltage ranging from 12.3 to 14.9 depending on engine load.

I'm going to go back to the dealer to ask them to disable the variable voltage function again. I wonder what they will say? Does anyone here know?

[shack]

Try turning the headlights on

[DiscoJeffster]

You can’t disable it. They would have told the system you have a new battery and it will now know it’s capacity.

I believe if you remove the voltage sensing wire off the back of the alternator it defaults to maximum, but probably also flags an error on the dash.

There is nothing wrong with the variable voltage system. It monitors the charge of the battery and current draw of the vehicle to suit.

[RoverLander]

Try turning the headlights on

I may have already turned the headlights on a couple of times in the last 6 years of driving the car??? [biggrin] It makes no difference.

[drivesafe]

There is nothing wrong with the variable voltage system. It monitors the charge of the battery and current draw of the vehicle to suit.
While new vehicles have modern cranking batteries, which are designed to last longer in STOP/START equipped vehicles, having a constant voltage of around 14v and higher, applied all the time, will dramatically extend the battery’s lifespan even further.

[scarry]

While new vehicles have modern cranking batteries, which are designed to last longer in STOP/START equipped vehicles, having a constant voltage of around 14v and higher, applied all the time, will dramatically extend the battery’s lifespan even further.

Off topic,there is a diode some use on Toyota vehicles to bring the voltage up to around 14V,or just over.
Will this affect the alternator,overheat it or shorten its life?
TIA

[drivesafe]

Off topic,there is a diode some use on Toyota vehicles to bring the voltage up to around 14V,or just over.
Will this affect the alternator,overheat it or shorten its life?
TIA
Hi and unfortunately the diode does not work with Land Rovers, but if it did, it would not effect the alternator’s lifespan but would increase the lifespan of ANY batteries being directly charged by that alternator.

EDIT, and the higher voltage would decrease the drive time needed to recharge the batteries. In other words, the batteries would recharge faster with a diode fitted.

[RoverLander]

Can anyone advise what circumstances could result in the scenario I descibed above. Ie Variable voltage and Fixed Voltage and then Variable Voltage. Each time when in to a dealer to change the battery.

Do dealers change charging profile if there is a known problem with a battery going flat prematurely in a car? If so how.

[Tombie]

No they don’t.

The BMS is intelligent to know if the batteries capacity is reducing and will profile accordingly.

Once reset with a new battery the vehicle knows to run the right profile.

[DiscoJeffster]

Can anyone advise what circumstances could result in the scenario I descibed above. Ie Variable voltage and Fixed Voltage and then Variable Voltage. Each time when in to a dealer to change the battery.

Do dealers change charging profile if there is a known problem with a battery going flat prematurely in a car? If so how.

I can only assume the previous time your battery was replaced, the BMS wasn’t reset so it treated your new battery as a dying battery [emoji2369][emoji2369][emoji2369]
Maybe that’s why it behaved as you describe

[josh.huber]

Can anyone advise what circumstances could result in the scenario I descibed above. Ie Variable voltage and Fixed Voltage and then Variable Voltage. Each time when in to a dealer to change the battery.

Do dealers change charging profile if there is a known problem with a battery going flat prematurely in a car? If so how.

I recently put in a new battery in reset the BMS, reset of the BMS tells the ECM that the battery is brand new that is all. The negative terminal in the car has a shunt in it and can monitor current into and out of the battery.

After a BMS reset, is it a bit frustrating but normal to see the battery sitting as low as 12.3 while driving and while the car makes it's decisions on the battery capacity, it also monitors the battery for loss with the car off.

After about a week it'll normally settle down and go back to a reasonable 13.6v charge rate and bump up a bit under brakes. I've got dual batteries and a fridge that's permanent. Mine sits around 13.8v all the time..a bit higher if the crank battery got low.

[josh.huber]

I can only assume the previous time your battery was replaced, the BMS wasn’t reset so it treated your new battery as a dying battery [emoji2369][emoji2369][emoji2369]
Maybe that’s why it behaved as you describe

This is correct. Before my first battery died, it charged at 14.9v (which is too much). I put a new battery in and it was the same. I read on here about the reset and then it went back to doing it's thing.

[RHS58]

How does the BMS cope when a Traxide DBS is connected to the main battery?

[josh.huber]

How does the BMS cope when a Traxide DBS is connected to the main battery?

The same, however... If you use the traxide as intended, it will drain the cranking battery a little bit over night.. Which the BMS sees and ups the charge rate for. Which is perfect. I did some experiments a while back with my Traxide on IGN mode (isolates battery's at 12.7) the charge rate was much lower and the aux battery never recovered in my drive distance.

[DiscoJeffster]

How does the BMS cope when a Traxide DBS is connected to the main battery?

It doesn’t know about it. It just sees the second battery as additional current draw from the vehicle and it’s accessories. As part of that, it will instruct the alternator as required.

Unfortunately, and this is why Traxide is perfect for our vehicles, as it doesn’t know you have a second battery, it treats the second battery as an accessory and accessories don’t have specific voltage needs unlike batteries. So if your main battery is fully charged but your accessory is low, the vehicle may choose a lower voltage slowing the secondary’s recharge. The way Traxide works to use both batteries together means they both receive good charge current. I am ignoring that the system will level itself Eg a higher voltage starter would leak capacity to the second battery once connected together to establish equilibrium, but that goes away once the alternator is active, so there are many scenarios to consider.

[drivesafe]

It doesn’t know about it. It just sees the second battery as additional current draw from the vehicle and it’s accessories. As part of that, it will instruct the alternator as required.

Unfortunately, and this is why Traxide is perfect for our vehicles, as it doesn’t know you have a second battery, it treats the second battery as an accessory and accessories don’t have specific voltage needs unlike batteries. So if your main battery is fully charged but your accessory is low, the vehicle may choose a lower voltage slowing the secondary’s recharge. The way Traxide works to use both batteries together means they both receive good charge current. I am ignoring that the system will level itself Eg a higher voltage starter would leak capacity to the second battery once connected together to establish equilibrium, but that goes away once the alternator is active, so there are many scenarios to consider.
Doesn't quite work the way.

If the batteries are separated, meaning the isolator is off, then regardless of whether the cranking battery is in a higher or lower state of charge to the auxiliary battery, the batteries will not be connected together again, until the motor is already started, and the alternator is running and the voltage at the isolator rises to 13.2v or above ( 13.6v or above for lithium batteries ).

But if the isolator is still on, both batteries are likely to be at the same charge level, but this time, when you start the motor, both batteries will be supplying the starter motor energy required. Thus reducing the load on the cranking battery and because this happens on almost every start, the auxiliary battery actually helps to extend the operating life span of the cranking battery.

So Traxide isolators do not draw down the cranking battery when you need it, they actually assist it.