Because the BMS on the Essential system acts on the negative side of the batteries (ground control), the negative (or chassis) from the tow vehicle with the alternator is at a slightly different voltage than the negative output of the lithium system. This creates a design challenge since shorting the negative output of the lithium system to the tow vehicle chassis would damage the BMS.
In a van conversion or coach, the issue of having two different negatives is easily resolved by routing the output of the lithium battery through the Orion 12/12 DC converter. The negative output of the Orion converter can then be tied to the chassis and all positives for the DC loads get re-routed to the positive output of the Orion. If the total DC load is more than 30A, multiple Orion converters can be connected in parallel. Inverters, or anything else that can have their negative isolated from the chassis will just connect directly to the output of the lithium battery system without going through the Orion converter.
In trailers, the issue of having two different negatives is solved differently. In this situation, the Orion converter goes on the input side of the lithium system, thus isolating the trailer from the tow vehicle’s chassis. When this is done, the Orion converter has to be modified so it’s output voltage is 14.2V instead of the factory 12.0V. This is accomplished by carefully tuning a potentiometer inside the converter that is accessible when the cooling fan is removed. This design will limit alternator charging current to 30A, but it will protect the BMS from having it’s input and output short circuited.