Thread: Battery Charging voltage

I have Scan Gauge 2, 1 normal battery & run a small fridge.
The Scan Gauge usually tells me that I have around 13.5v.
Is that the amount of charge going to the battery?
Does that sound like it is correct?

I also run a scanguage, mine normally indicates a charge rate of around 13.9V in day to day use, if not used for a week or so it will up the charge to about 14.5V for a while and after a long run with a very full battery it will drop the charge rate as low as 12.9V.

Thanks all for your input. I checked the charge v again and is 13v whilst idling or accelerating and 14v whilst coasting. So it appears that it only charges when coasting. So the question is will it keep 2 batteries charged whilst towing a van?
Also running a Waco in the back seems to make no difference. I would rather charge my batteries fully than save 20c of fuel, if that's what is about!



Cheers

Mark

Hi Mark, it depends on the state of charge of your cranking battery and the type of battery isolator.

What isolator do you have?

I have installed a sidewinder isolator. IT seems to work ok.


Cheers

Hi Mark and like all standard type VSR isolators, that one will not work with 2013 and later D4's alternator variable voltage systems.

It will separate the cranking battery but when the motor is turned on, will not cause the BMS to charge the auxiliary and any house batteries, as the BMS will see the cranking battery is charged and lowers the operating voltage too soon to allow for any other batteries to be charged.

Originally Posted by drivesafe

Hi Mark and like all standard type VSR isolators, that one will not work with 2013 and later D4's alternator variable voltage systems.

It will separate the cranking battery but when the motor is turned on, will not cause the BMS to charge the auxiliary and any house batteries, as the BMS will see the cranking battery is charged and lowers the operating voltage too soon to allow for any other batteries to be charged.

Thanks, how does the Bms know the difference between the batteries when they are connected as I would think the two batteries would equalize their voltages whilst connected.


Cheers

Hi Mark and because ordinary type VSR isolators turn off almost as soon as the ignition is turned off, or soon there after, the batteries will not equalise so you can have a fully or near fully charged cranking battery, but low auxiliary and/or house batteries.

With your Prado, where it does not have a BMS, a simple diode type fuse tricks the alternator into running at 0.6v higher than it normally runs at, but the Prado had no real idea of the state of charge of the cranking battery.

In that setup, a standard VSR type isolator works fine.

A D4 has a regenerative charging system, which monitors the cranking battery and adjusts the alternators operating voltage according to the state of charge of the cranking battery and whether the motor is under load or not.

As the standard type VSR does not allow the batteries to equalise, when you turn the motor on again, the BMS sees the cranking battery is fully charged and sets the alternator operation in accordance to that and lowers the operating voltage shortly after starting.

This means any other batteries in the system will not be charged, if they are in a low state, which is exactly what is happening in your D4, and why it runs at 13v.

So while you are running around town, a standard VSR is fine, but the first time you use any power from you auxiliary and/or house batteries, while the motor is off, using a standard VSR in a D4 stops the auxiliary/house batteries from being fully charged if they are in a low state at the start of a days drive.

Well explained, thanks, much appreciated.



Regards

Mark