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

Originally Posted by 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.

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.

Originally Posted by DiscoJeffster

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.