Alternator voltage output/Battery charge voltage

SteveSAS

Hi All,
Just posting this for people who replace their battery with non standard one.

The alternator in the 370z and many modern cars have a variable voltage output which is controlled by the engine ECU.

The charging system is matched to the battery model from factory.

Replacing with non standard battery may lead to shortened battery life due to overcharging.

Normally when car is started voltage is set to 14v and battery is charged until the ecu sees its fully charged via current sensor on earth lead.
Once battery is charged the voltage drops down to 13v where it floats.
This helps increase battery life by reducing fluid loss or something like that.

And sometimes you will see the voltage go higher than 14v which I think is used to de-sulfate the battery or something of that nature. don't quote me on this as i am no battery expert.

Anyways, I replaced my old original battery with a smaller one to help reduce weight in car but it seemed to over charge and lasted only 6 months.

SOLUTION

You can set the voltage to float full time at recommend float voltage by battery manufacture.

This is done by taking control of the PWM signal to alternator and setting voltage.

I have currently installed LifePo4 12.8v 40ah 900cca battery in my 370Z and set the voltage to 13.8v float (13.5v for Pb). 1/2 the weight with more capacity as well.

PWM is 12v at 10kHz at 45% duty cycle.

Hope this helps a few people.

Thanks!
Steve S