Smartshunt connection

[Rasmus]

I have installed a Smartshunt on my boat. The shunt is meassuring the house battery. It is also configured to also show the start battery voltage (using the AUX-wire).

The batteries share common ground (both connected to the engine block. Both batteries are charged by a single charger using a BEP DVSR.

It all seems to be working - but…

When I draw power from the start battery I can detect a voltage drop on the start battery just as I would expect (no voltage drop on the house battery.

What I do not understand is that the data for Current, Power etc. is also affected. I would expect that all the data regarding the house battery remained unaffected when only drawing power from the start battery.

Am I missing something or is something not connected right?

Rasmus

[pwfarnell]

If the digital VSR is latched in the closed (connected) condition then both batteries will share the discharge.

The common ground must be on the load side of the shunt, not the battery terminal.

Have a read of this about SmartShunt wiring.

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…

[CharlieJ]

@Rasmus
By connecting the starting battery and the house battery to a common ground, you have not wired the SmartShunt IAW section 3.5.1 of the manual.

The negatives for all sources and loads are landed on the “To System Minus” terminal (over the VE.Direct port) and the negative for the battery or bank that you are monitoring Ahr consumption is landed on the “To Battery Minus” terminal above the Aux/B+ ports.

This trips up a lot of people!

[Rasmus]

Thanks a lot… I see the point.

As i was troubleshhoting I tried disconnecting the house plus terminal. To my big surprise the fridge, lights etc. was still on - and there was power for the engine. It seems like the house circuit and the engine circuit is connected somewhere! I have to dig i to that…

[pwfarnell]

As I noted above, depending on your DVSR settings this could still keep the 2 systems connected when you do not expect them to be.

[Rasmus]

I think that my DVSR is supposed to isolate the start battery when the start battery falls below 12,8 volts which it was when testing.

Also when disconnecting the start battery and only the house battery is connected then there are no lights, fridge etc.

I suspect there is a wiring problem somewhere…

[Rasmus]

Thank you both for helpfull answers…

I removed the direct connection between the minus terminals on the batteries. Both batteries are still connected to the engine ground but the house battery minus is connected at the load side of the shunt while the start battery minus is connected directly to the engine ground.

Furthermore I found out that a previous owner (perhaps?) had connected the main house cable to the start battery at the main switch…
This was corrected and it all makes sense now. The only times I detect a simultaneous voltage drop on both the house battery and start battery (when turning on lights etc.) is when the BEP DVSR is connecting the plus side of the house and start battery (it engages at 13.4V and disengages at 12.8).