Keep in mind the negative side shunt setup has only one connection to the battery—only the battery negative post.
ALL other load negative sides, the trailer frame ground lead, and the negative from the converter and the solar charge controller MUST be on the other side (load usually) of the shunt.
The idea is to have all the current going into and out of the battery go through the shunt no matter what...that way the monitor can know how much current is going in and out of the battery and maintain its charge state information. Voltage is only a rough measure of battery state of charge. Monitoring current is a lot better.
My Airstream has two buss bars under the front bed. The negative battery terminal has a heavy cable that goes to the battery side of the shunt, nowhere else. The other side of the shunt (load) is a heavy short jumper that goes to the negative buss. All other negative wires land there. The positive buss gets all the positive leads through the Use/Store relay.
The one exception is my tongue jack, breakaway switch, and power WD jacks. They all get power off the positive battery post, through a 30-amp MRBF fuse on the positive battery terminal and these loads are grounded directly to the A-frame with a bolt and serrated washer so they are also on the load side of the shunt. The ground gets to the load side of the shunt through the frame ground connection to the negative buss under the front bed.
This way all load current and charge currents only go through the shunt before they get to the battery. On my rig I used color-coded marine-rated 4 gauge cables for all connections to the battery, shunt, and buss bars as well as the disconnect switch shown below. The switch is fed through an 80-amp MRBF bolted directly to the battery positive post to protect all the wiring.
Some high precision charge monitors literally count the number of electrons flowing in the circuit and their direction. It’s referred to as ‘coulomb counting’ and gives you super precise information on the exact charge level of the battery. Idea is that batteries store electrons, and it’s all about current, not voltages per se.
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.