Battery or cabling/connection issue?

[PaulRainbow]

What kind of bolts are on the battery terminals?

The bolts are immaterial, they don't conduct electricity.

 

[jimbo]

You need to compare the voltage at the board with the battery voltage displayed by the Victron monitor, and confirm both with a multimeter, with as much load as possible on the system.
If the previously observed discrepancy is due to a bad connection or contact there will be little or no voltage difference while there is little or no load but its magnitude will increase as the current draw innreases.

Ok thanks, will try it again later when the batteries are depleted with fridge, water pump, shower drains etc going to see what the difference is then.

 

[jimbo]

You fully charged in the evening and then left shore power disconnected overnight so that these were the resting voltages?

The Victron shunt should be right next to the batteries, so I'm surprised there's that much voltage drop already - the whole point is that it should read the exact same.

The corrosion may not be obvious - that's why you test with fly leads; just a long wire with crocodile clips at each end.

They were resting voltages but will see what they read after a full day's sailing when the batteries are not full. The shunt is within a meter and the readings were within .08 of a volt. The solar panels were pumping in quite a few watts depending on the cloud cover so difficult to get an exact simultaneous reading. Unfortunately, the jump leads on board are only 2m in length and won't reach the board.

 

[B27]

This afternoon, I'll be looking at a friend's boat.
This morning I'm looking for some wire and bits'n'bobs to sort out extra long test leads!

'Resting voltage' of a battery can be misleading, the voltage with a known current going in or out is much more reliable.

Long leads should allow us to measure the voltage drops directly, rather than inferring them from two inaccurate measurements.

 

[KompetentKrew]

The bolts are immaterial, they don't conduct electricity.

Surely it depends on the arrangement? Before being aware of how poorly stainless steel conducts I used a stainless steel nut as a spacer on a longer bolt. An "innocent" washer could easily be overlooked.

 

[PaulRainbow]

Surely it depends on the arrangement? Before being aware of how poorly stainless steel conducts I used a stainless steel nut as a spacer on a longer bolt. An "innocent" washer could easily be overlooked.

Most busbars and terminal posts have stainless nuts, bolts and washers, the terminals are supposed to be in contact with the busbar and/or each other. Using stainless fixings as spacers is different.