Battery cable shunt caused corrosion?

[Flyview]

About 4 years ago I added a shunt to monitor current flow in my 2x parallel 12v 100Ah LiFePO4 setup in my camper. I had bolted one side of it straight to the negative battery terminal and the other end to the negative cable that went to chassis ground. I recently revamped the wiring by redoing the terminal ends with better crimp connections and replacing some wires with thicker wires. While doing this I noticed that the negative cable coming off of the shunt to the chassis was corroded. I had to cut off maybe 3-5" to get to clean wire. The little sense wires on the shunt are also rusting. I added a small length of wire from the battery to the shunt now. See attached pic.

I just replaced the batteries with 2x 140Ah TimeUSB units today and I don't want this to continue to be a problem. I'm worried about the cables rusting again or worse, causing damage to the battery.

Did this happen because I had bolted the shunt straight to the battery? Or a cheap shunt? Can someone explain what happened electrically?

 

[WindWizard]

Rust is caused by metal being exposed to air. If you cover up the metal with a dielectric synthetic grease like super lube then it should prevent the corrosion.

 

[Flyview]

Rust is caused by metal being exposed to air. If you cover up the metal with a dielectric synthetic grease like super lube then it should prevent the corrosion.

Then why has nothing else rusted? It all happened to what was connected to the shunt. The rust spreading down the battery cable is concerning. I believe it may be due to pairing different metals together combine with the current running through it speeding up the chemical reaction. This is usually done on purpose to prevent corrosion of one metal while sacrificing another, but I'm not sure what happened here.

 

[WindWizard]

Then why has nothing else rusted? It all happened to what was connected to the shunt. The rust spreading down the battery cable is concerning. I believe it may be due to pairing different metals together combine with the current running through it speeding up the chemical reaction. This is usually done on purpose to prevent corrosion of one metal while sacrificing another, but I'm not sure what happened here.

The dielectric grease will prevent it. Undo all of your connections and clean them up. Apply the dielectric grease to the exterior surfaces and no more rust. If air cannot get to the metal then it prevents rust from forming.

 

[Flyview]

I understand that. I guess I'm more so looking for an explanation of what happened rather than a solution. I'll be switching to a Victron battery monitor and shunt shortly.

 

[robbob2112]

dissimilar metal corrosion - take it all apart, clean connections, coat with no-ox-id special ... the rest - a thin coat of any other grease will prevent the corrosion.