Interaction of Solar and Alternator

BFL13 wrote:
With the monitor for your ammeter, it is easy to do some tests parked in the sun.

With the batts near full, just turn everything on in the camper and get as many amps draw as you can, say minus 20 amps. Now with no solar, turn on the engine and see what the amps do. Might be minus 5, so charging is 15 amps. Wait a few minutes and those amps will taper as voltage falls to 13.x. Might then only get 8 amps charging.

Same with solar and no engine on. Now you get your 4 amps solar, so amps go to minus 16.

Now turn on engine and see what happens to the amps.

If the charging amps go above the draw the diff still works with a few positive amps showing.

Funny. I was outside doing just that.
Disconnected solar and with the fridge running on DC I was -21.2 amps. Voltage was 12.0 at that point.
With truck on it came up to -8.2.
Truck plus solar -5.6 (scattered clouds today).
Solar alone -18.5

This tells me the truck is pushing roughly 13 amps back when the battery is around 12 volts. I'm fine with that.

With the fridge off, truck and solar together were showing 7 amps, but the voltage was back up around 13.2.

I'm still perplexed wrt my previous experience while driving, but at that point there was no negative load on the camper battery - just the solar and truck amps flowing in, and I don't know what the battery voltage was. It must have been high enough that it could only make the 4 amps.