If you’re here, you are probably like me and dont fully understand the “pull-up” and “pull-down” details of wiring so I want to do a quick and simple “How to” write up that anyone should be able to do. It works for me and charges at target voltage. If this is in the wrong category or has already been written up please delete post.
To start you need a constant 5V supply from the ECU, im using an EMU black so i used one of the two 5V supply outputs
Use a resistor, GROK told me to use between 1k-2.2k ohm resistor so i used a 2.2k provided with the ecu.
Tie one leg of the resistor into the 5v supply near the ecu
Next pick an output that switches low, that would be any of the AUX outputs. i used AUX1
This part im going to explain the best i can without a written diagram to post
Wire your AUX output to the control pin on your alternator
Take the other leg of the resistor mentioned earlier and “T” it into your AUX output
The way this works, 5 volts will pass through the resistor and go to the alternator. Consider this 100% duty cycle
When the AUX output is activated it will pull the 5V signal to ground and the alternator will see 0V
You will need to invert the output. 60% AUX duty cycle will equal 40% alternator control. If you do not invert, the alternator will see less duty cycle when the ecu commands the charge rate to go up
You need to look up the frequency for your specific alternator. In my case an a 99 Miata it was 250Hz
The current issue which ive seen will be corrected in the next update is if the key is on but the engine is not running, the ecu will command full duty cycle at the alternator which is not good for it. In the mean time if you are making changes without the engine running remember to uncheck “invert output” while doing so. Then recheck it once the engine is running. An example of this NOT being a concern is if you are only keying on long enough to prime fuel before starting. In other words its not an issue unless its key on engine off for a while
I hope this helps someone