Saildrive corrosion: galvanic isolation and grounding

[nigelmercier]

According to the wiring diagram in the owners manual all positive connections and all negative connections, starter included, go to the battery via the isolators.

Ignore the last bit in my previous post, I have found a more recent photo. In the original battery installation, the battery negatives were looped before going to the shunt. When I updated the batteries and wiring, I connected the domestic batteries with a delta connection, and ran a separate wire to the shunt for the starter battery. However, I have known for some time that there is a small leakage bypassing the isolator.

 

[mjf107]

Ignore the last bit in my previous post, I have found a more recent photo. In the original battery installation, the battery negatives were looped before going to the shunt. When I updated the batteries and wiring, I connected the domestic batteries with a delta connection, and ran a separate wire to the shunt for the starter battery. However, I have known for some time that there is a small leakage bypassing the isolator.

Not sure what you mean by a delta connection in this context. But I definitely don't like the idea of a leakage current that is unaccounted for even if its small, especially as your experiencing corrosion problems. Volvo suggest an insulation value of 100k ohms for the engine saildrive interface, so this would suggest 0.12mA as being accetable leakage current. So how small is your small.

 

[nigelmercier]

Not sure what you mean by a delta connection in this context. But I definitely don't like the idea of a leakage current that is unaccounted for even if its small, especially as your experiencing corrosion problems...

The terminals of the three batteries are connected in a delta configuration, in other words three coupling wires instead of two.

The leakage I refer to is bypassing the main negative isolator (a small current flows when it is off), not related to the saildrive isolation.

 

[mjf107]

The terminals of the three batteries are connected in a delta configuration, in other words three coupling wires instead of two.

The leakage I refer to is bypassing the main negative isolator (a small current flows when it is off), not related to the saildrive isolation.

Maybe I did't explain to clearly, I quoted the Volvo value as an example as an acceptable leakage level that could be applied to a healthy installation.

 

[nigelmercier]

Just heard back from my nominated Volvo Penta dealer:

The page that you have "linked" to [the Volvo Penta blurb saying that saildrives have a patented isolation system] refers to the later style of saildrive and not your 120S version. Isolation bush and design features are not applicable to your set up ...

So now we know, not all Volvo Penta saildrives are meant to be isolated.