# Ecu controlled Alternators.



## bjfreeman (Dec 7, 2011)

This came up in the dc -dc topic but since is really does not relate to EV wanted to put it out there.
Did a little thinking about the 14.4. I have not back this up with reading the service manuals.
When the Vehicle is first started the ECU will speed up the engine enough to do a fast charge and set the alternator to charge 14.4 volts for a period, usually 5-10 min, if you let it just idle on its own.
After the fast charge to make up for the starting, the ECU will adjust alternator to charge at 13.6.

So it you check the voltage just after starting it will show a higher voltage than normal.


----------



## DJBecker (Nov 3, 2010)

Alternators on Hondas have long been controlled. On the older basic models the control was simply hooked up to the brake light circuit, which boosted the alternator output when slowing down. Later and more advanced models have a connection to the ECU. Presumably it does all of the obvious optimizations.

Even stand-alone, alternator voltage regulators chips are smarter than you might expect. The don't start charging until a minimum RPM is reached, and control the output based on the RPM and temperature. Specifically they increase the output voltage when cold, which usually has the effect of quickly restoring the charge lost when the car is off.


----------

