What Base does
Base is the duty cycle that should, on its own, bring battery voltage to the target voltage you've set. The ECU uses it as a starting point. Alternator control runs in closed loop, so the ECU (for example a Nexus R5) then adjusts the actual duty up or down to hold the target voltage. That's why the duty you see in the logs won't always match Base exactly.
Why it's worth getting right
A closed loop controller only has to make small corrections when its starting point is good. If Base is far off, the controller spends its time chasing large errors. That can mean a voltage dip or overshoot when the electrical load changes, such as when fans or lights switch on.
How we set it
- Get the engine warm and running with a typical electrical load.
- Log battery voltage and the alternator duty the ECU is actually using.
- Once the voltage has settled on target, note that duty and set Base as close to it as you can.
- Recheck with the load changing. Only small corrections should be needed.
For LS swaps, the small Bosch and large Yazaki alternator adapters and the Nexus Rebel LS Bosch alternator harness make the connection simple. The full setup is in alternator control and alternator control wiring.
