THIS AUCTION IS FOR THE CIRCUIT BOARD INCLUDING ALL THE COMPONENTS - UNASSEMBLED

The NB miata has the alternator control inside the ECU. When you install an aftermarket ECU like a Megasquirt or a Speeduino, there is no way to control the alternator correctly. I designed this board because because of 2 reasons. The 1st reason it that I couldn't get the software PWM alternator control in the Megasquirt firmware working right. I played with it for a while but it either didn't charge at all or only charged over 18V. No matter what I tried, I just couldn't get it right. When the fuse on my MS3 Pro finally blew, I decided to call it quits and design this pcb. The 2nd reason is that the programmed injector dead time is directly related to battery voltage, meaning that if you have voltage swings - something the Megasquirt most definitely has - than your injector dead time changes accordingly. I do not want my mixture going out of wack whenever I open my windows or turn on the headlights.

For the little time and money it takes to build the circuit, I see no point in spending hours trying to get software pwm right. The output is proved to be rock solid to within 0.2V over the entire rpm band. Once installed and adjusted, you don’t have to worry about it ever again.

I designed this for use with a DIY Megasquirt, hence the dimensions are 20*100mm, but you can use it with any other brand of ECU. The board also has an extra output to control the low battery light.

The board has 5 pins:

• 12V

• GND

• Field: this is the output to the alternator field wire (pin 1O on a ’99-’00 NB and pin 3M on a ’01-’05 NBFL)

• Disable (optional): When you ground this pin, the alternator stops charging. I use a general purpose output to disable the alternator while I’m cranking (<600rpm) and when tps > 99%. (to gain a tiny bit of hp at full throttle). If this is not desired, leave disconnected.

• LowBatt (optional): This output goes to the low battery light (pin 1Q on a ’99-’00 NB and pin 3U on a ’01-’05 NBFL) and triggers it when voltage goes below 12.8V. If this is not desired, leave disconnected.

Assembly instructions can be downloaded below.