Renogy DC-DC Test Results-UPDATE 4 (Better!)

S Davis wrote:
So I just retook the readings for my 50 amp Redarc

Batteries at 80% 12.5 +-

13.8 volts truck idling
28 amp draw at under hood breaker

25’ 1/0 DLO both positive and negative to Redarc

13.6 volts into Redarc

14.4 volts out to batteries @ 24 amps

I remember in a past test how the truck's voltage fell off once I reached a certain demand on the truck battery by increasing the load on the inverter clamped to the truck battery (truck idling). It held its voltage near 14v up to a point, then the dash voltage needle started to tremble and then it fell off to the left. The truck's system can only take so much! I expect it is not linear.

I wonder what the numbers would be when output is 50 amps at 14.4v. What about the higher demand pulling the truck's battery voltage down where that may not be linear?

I am thinking the 24 vs 28 amps at half rating might not be just 50 vs 58.3 amps. You would need the house batts down to more like 50% instead of 80% going in to test for that.

The input watts use the voltage at the DC-DC end after voltage drop from the truck's end, but that truck voltage comes down too.

We have been looking at the efficiency of the DC-DC, but there is also the non-linear ? efficiency of the alternator. Efficiency of these electronic things seems to be somewhere on an "efficiency curve". What if the curves for the DC-DC don't match the shape of the curves for the alternator, so you don't get what you expect just from calculating voltage drop etc for the DC-DC unit?

Guys who know these things will be able to confirm or deny this whole notion and perhaps explain more how it actually works.