Volvo 2001 electrical earthing point

[Dipper]

Is there a specific point on the 2000 series that is recommended as an earthing point for the electrical system or will any suitable bolt do? What do other owners use? Thanks in advance for suggestions.

 

[Tranona]

What are you trying to earth? The DC system does not require an earth, just a positive and negative. The negative for the engine systems (starter etc) usually goes to a convenient bolt on the flywheel housing, but it does not need to - on my boat it goes to an engine mounting bracket because that is convenient.

 

[Pete7]

Our 2003 had an earth connection from the gearbox bell housing bolt. Originally this went direct to the battery terminal, but I moved it to a new bus bar. However, whilst recently replacing the alternator I was shocked to see the tiny wire used by Volvo going to an engine mounting bolt. The positive wire from the alternator to the starter motor was undersized. I replaced both with 25mm wire, running the negative to the bus bar. You may still need a negative connection from the engine block for things like the temperature and oil pressure switches.

 

[Dipper]

What are you trying to earth? The DC system does not require an earth, just a positive and negative. The negative for the engine systems (starter etc) usually goes to a convenient bolt on the flywheel housing, but it does not need to - on my boat it goes to an engine mounting bracket because that is convenient.

I need to earth my brain! I've spent the last two days crawling round the back of my engine re-installing the saildrive after renewing the seal and I'm knackered. I meant negative terminal and you have answered my question thank you. I have two negative leads, one of which I have attached to a bolt on the flywheel housing and the other on an engine mount bracket so that sounds about right.

 

[Dipper]

Our 2003 had an earth connection from the gearbox bell housing bolt. Originally this went direct to the battery terminal, but I moved it to a new bus bar. However, whilst recently replacing the alternator I was shocked to see the tiny wire used by Volvo going to an engine mounting bolt. The positive wire from the alternator to the starter motor was undersized. I replaced both with 25mm wire, running the negative to the bus bar. You may still need a negative connection from the engine block for things like the temperature and oil pressure switches.

Thanks Pete.

 

[VicS]

I need to earth my brain! I've spent the last two days crawling round the back of my engine re-installing the saildrive after renewing the seal and I'm knackered. I meant negative terminal and you have answered my question thank you. I have two negative leads, one of which I have attached to a bolt on the flywheel housing and the other on an engine mount bracket so that sounds about right.

Woah
VP 2001 with sail drive rings an alarm bell for me regarding the engine earth / negative connection.

Are you sure the engine does not have an isolated electrical system. ie one in which the cylinder block is not used as the common negative connection.

With a sail drive I'd expect an isolated system with two-wire oil pressure and temperature sensors , an alternator with an isolated negative connection and an earthing relay which only earths the cylinder block to battery negative during the operation of the starter motor.

I have ringed these items in green on the schematic

 

[Dipper]

Thanks Vic. I took it all apart in October thinking it would be bleeding obvious how it went back but of course it isn't that easy 5 months later. I'll check the alternator again. That makes sense.

 

[VicS]

Thanks Vic. I took it all apart in October thinking it would be bleeding obvious how it went back but of course it isn't that easy 5 months later. I'll check the alternator again. That makes sense.

The alternator may not be the best indicator. It could have a separate (and insulated) negative terminal but still have a connection to the block , although if it does not have an insulated negative the engine obviously does not have an isolated electrical system.
Two-wire temperature and oil pressure sensors may be better clues but the best will be the earthing relay. A solenoid like , and sized lump mounted below the starter motor.

It's all to do with protecting the sail-drive from galvanic corrosion , or even electrolysis . Something which was done from the B version of the MD 2010 etc onwards by electrically isolating the sail-drive from the engine

 

[down...2 greens]

This is from my shaft drive 2001 - beefy negative connected to a bracket just beside the gearbox, but that might not be of much interest for a sail drive installation.

 

[VicS]

This is from my shaft drive 2001 - beefy negative connected to a bracket just beside the gearbox, but that might not be of much interest for a sail drive installation.

On a VP 2001 with an isolated electrical system that negative connection would be made to the earthing relay as shown in the schematic.