Is anyone here an electrical engineer?

[Telekinetic-Potato]

Was putting a battery shunt to monitor it in my dad's truck and noticed something that has been throwing me for a loop, if I connect the chasis ground to the battery side, it reads out the alternator amps and watts but if I connect it to the p side it gives me what I'm guessing is the battery info isolated... The readings go so fast I'm trying to find some kind of low pass filter for the monitor I have.

Also, it thinks the ground polarity is reversed but only when the car is running (regardless of how I wire the chasis ground) but isn't the voltage regulator supposed to make everything run DC?

This is confusing the total PHUCK out of me because what direction is the current moving in? 😂

[unending]

Alternators generate AC, not DC. The rectifier converts the AC to DC by allowing only the positive half of the AC voltage waveform to pass through while blocking the negative half. That creates a pulsating DC voltage that has to be stabilized by a voltage regulator in order to charge the batter and run DC circuits. So like you said you are connecting to the P terminal on your alternator, which could be the pulse, stator connection for tachometer. Thus you are getting the DC pulses that are used to measure RPMs.

[Telekinetic-Potato]

Ohhhh so there's always charging pulses and discharging pulses from the perspective of the battery negative? That's why my monitor keeps thinking I have the -b and -p flipped when it's turned on?

[unending]

By default alternators generate pulses of DC before the voltage regulator stabilizes the voltage. On some models of car, that voltage regulator may have been integrated at the end of the alternator, on others there will be a little box that is wired to the alternator before the battery terminal probably to the chassis and it does the job, but in a lot of modern vehicles the power-train control module (PCM) is responsible for regulating the voltage because of fuel efficiency goals. Modern PCMs determine when the alternator will charge or not charge to put drag on the serpentine belt. If the battery is full charged then they want to eliminate the drag of the alternator to increase fuel efficiency. If the battery needs charging, then they want to increase drag so it all becomes micromanaged by a computer chip. As to exactly what is happening on your car, I'm not sure. Just letting you know, pulses are normal from an alternator based on how they work. Everything else is more case dependent and more information is needed.