I have a travel trailer with a AGM battery on the tongue and a 24V battery with a Orion 24/12-70 converter in the front compartment. They both feed a switch that allows me to choose which one will power the trailer’s 12v system. After the selector switch the trailer has a positive bus bar at the very front of the trailer. Then there is about 30’ of #6 wire to the back of the trailer where there is a fuse box and a AC/DC converter. It doesn’t matter which source I choose, AGM or Orion, they share 100% of the same path/wiring positive and negative.
With the AC/DC converter turned off and a small 12V load, approx. 3W. With the AGM battery selected I see about 0.05v of voltage drop, from 12.65v at the front bus bar to 12.60v at the rear fuse box. When I select the Orion I see about 1.5v drop, from 14.0v at the front bus bar to 12.5v at the rear bus bar. When I put a load on it, a fluctuating 6A to 8A and occasional peak at 15A. With the Orion, the voltage is completely steady and did not vary at all, 14V at the front bus bar and 12.5V at the rear fuse box. With the AGM battery under load dropped according to the amount of load, it got as low as 12V but the drop was consistent from front to back. I also have a Orion XS1400 that I tried in the exact same sicario, it performed exactly like the 24/12-70. 1.5v of voltage drop with 3W of current seems excessive, I was expecting to see the same amount of voltage drop as the AGM battery. The entire path from the bus bar to the fuse box and back on the negative to the battery/chassis ground is shared. No differences at all.
Why am I seeing this voltage drop? Is it normal?