SOC does not increase on Lynx Shunt using Orion DC to DC chargers

[Tyblood (Tom Toungblood)]

I am also having this issue of SOC going down when Orion is adding Amps. I have 2 30 amp units with 6 AWG wires running from the upfitter connection (through fuses) back to the Orion units, but no negative wires, using the chassis instead. To rectify this will I need to run 2 6 AWG wires (black) from the engine battery all the way back, or is there something else I need to do in the rear? I have the + and -s from the Orions going into a lynx distributor and then to lynx shunt and that goes to a chassis ground on the negative side, positive to the battery positive.

[pwfarnell]

The key is how is your chassis connected to your house battery negative, see my sketch in the link below, the chassis MUST be connected to the system/ load side of the shunt. If it connects to the house battery negative then it bypasses the shunt. It is all in the write up linked below.

Shunt / battery monitor not reading the correct SOC/ Amps, missing solar, decreasing daily or other misreading problems

This topic covers the SOC / Amps reported by BMV battery monitors, SmartShunts, Lynx BMSs and Lynx Shunts and will just be called shunt below. It is also assumed that the shunt is monitoring the domestic / house / cabin battery bank and not engine start / bow thruster / winch / caravan mover battery banks. The problems may be one or more of the following The SOC decreases daily despite the solar charger or other charger(s) working. The SOC increasing when discharging and falling when charging…

[Tyblood (Tom Toungblood)]

You are talking about the one with all the various connections on the negative side? I was editing my post while you wrote back (thank you) so there is more detail there. I will look at it again.

[Tyblood (Tom Toungblood)]

To be clearer, I have BattleBorn batteries, not Victron. They do have their own BMS. I am using a Cerbo GX to monitor.

[pwfarnell]

@Tyblood

I have the + and -s from the Orions going into a lynx distributor and then to lynx shunt and that goes to a chassis ground on the negative side, positive to the battery positive.

This is the key but it can be interpreted several ways. The way I read it, starting from the battery side of the Lynx shunt is

Battery + and - and ground to the battery input side of the Lynx shunt, Lynx Shunt then on the output side a Lynx distributor. If my interpretation is correct then the chassis ground is on tje wrong side of the shunt, it is on the battery side so any current flowing through the chassis to the batteries bypasses the shunt.

A drawing is always better than description.

[Tyblood (Tom Toungblood)]

Ok, my chassis ground and battery negative are connected together currently. Should the chassis ground come off of a negative in the lynx distributor?

[pwfarnell]

Yes, move the ground to the Lynx distributor. Then the negative current from the chassis to the battery will pass through the shunt and get counted.

[Tyblood (Tom Toungblood)]

Thanks. I am waiting on one piece of shrink tubing to make a new cable, fortunately I had enough 4/0 black wire.

[Tyblood (Tom Toungblood)]

Thanks again for your help. I had the chassis grounds from my mppt units and input side of my 2 30 Amp dc to dc chargers (Orion Tr Smart) going to a bus bar that then joined my Chassis ground at the negative side of the Lynx Shunt, which I hadn’t realized was on the wrong side of the shunt. I moved that with a longer 4/0 cable to a middle negative input on my second Lynx distributor (the other has the negative input from my Multiplus), and now the alternator power is showing up going in the3 right direction. Yay!

[pwfarnell]

Always nice when someone comes back to report “case closed”. Thanks.