Any thoughts on why I'm seeing the 0 amps and a pegged indicator after engine start? Apologies, the plane is fairly new to me, and I haven't traced the wiring from the shunt yet.
You don't state what airplane, what alternator, what regulator, or any other information about your setup, so we have to guess.
There are three main ways of installing a shunt that indicate current:
- In between Alternator and Main Bus - this will show alternator output. So generally, this will be the sum of the current used to run the electrical bus on the plane and the charging current to the battery. Since it's obvious that the alternator is on and that your battery stays charged, this is NOT your setup.
- In between the main bus and the alternator/battery - this will show main bus load - IOW, what the airplane is using for current. Could be coming from the battery; could be coming from the alternator - we don't know - but it's what the airplane is using. Since you have stuff on (presumably - you don't indicate what's turned on when you took the picture) and we're seeing zero current, this is also probably NOT your setup
- In between the battery and the alternator, but NOT between the battery and the starter. This will show the battery current flow to the main bus when the alternator is off, and the alternator current flow to the battery when the alternator is on. This is my preferred setup, as it shows battery health (you already know alternator health by looking at the voltmeter).
Assuming you have setup #3, when the alternator is off, this setup will show the current flowing out of the battery, so in this case, your airplane is using 3A prior to engine start. Once the alternator is on and the battery is recharged from the starting losses, there will be 0 - 1A flowing from the alternator to the battery, hence the indication of "0". So #3 is consistent with what you're seeing, but the voltage levels and alarms are set very poorly - I'm assuming you just purchased this plane and didn't build it or do the setup of the D120 (again, you gave us essentially zero information).
I would suggest that you set the levels on the screen to be from some large positive level (current out of battery) maximum, but with a yellow starting maybe at 2A and red at 4A so that if your alternator isn't working and you're draining the battery, you're warned about it. And that you set the negative current to be yellow at some reasonable charging current once the battery is charged - say 2A, with a red at some high # that will be dependent upon the type of battery you have and the alternator maximum output. You may need to play with the levels until you find something that warns you when actual bad things (battery continuously taking too much current or battery outflow too high) are happening, but NOT false alarming just because you haven't flown in two weeks and are now doing the 3rd hot-start of the day and have drained the battery a lot so it's taking a lot of charging current for a few minutes until it's fully charged. This last issue ls particularly of interest if you have a lithium battery with very low internal resistance and will take all of the current your alternator can put out.
My $0.02.
