I have had my iotawatt running for a year now, and normally look at the watts graph. I swapped over to looking at amps to get an idea of how close I get to using the max 150 amps that my panel can handle.
I have a 50 amp circuit for a car charger, and when the car is charging, it seems to take ~40 amps from both main inputs, so when i look at “total power” (main 1 + main 2), it looks like im using 80 amps… but that doesn’t seem right…

In the United States, a 200 Amp residential, split-phase service will provide 200 Amps per leg. One typically has a two pole 200 Amp circuit breaker with such a service, with 120 Volts between each leg and neutral, and 240 Volts between legs. So, you have 200A available at 240 volts, or 200A per leg at 120 Volts.

Thus, when your car is charging at 40 Amps/240 Volts, each leg is using 40 Amps of current. This leaves ~160 Amps per leg for 120 Volt circuits. However, most panels are designed to not use all 200 Amps of capacity to prevent overloading.

Thus, if you’re getting close to 200 Amps on either Main1 or Main2, you may need to rethink/reorganize the breakers and associated loads in your panel to balance things a little better.

Every amp that flows in on one of your phases must flow out on either the other phase or the neutral. For 240V loads they use both phases, and nothing would flow on the neutral. For 120V loads if all your loads on one phase equal the loads on the other phase then they “cancel out” and you’d have 0 A on your neutral.

So if you want to know how many amps your house is using you have to look at the max of phase 1 and 2, not the sum. In your case it looks like your charger is using 40 Amps and the rest of your house is using a negligible amount.

Look at it this way. If you put a CT on the other wire to your charger, it would read the same 40A. That doesn’t mean your charger is using 80A. It’s the same 40A going the other way to form a circuit. Same thing with your mains with respect to any 240V load.