This charging system wiring seems odd

[30boat]

It's not really that hard and the cost is hard to beat...

 

[halcyon]

When you buy your voltage sensing relay don't be tempted by the cheap, allegedly 180 amp ones on ebay and elsewhere. Durite 140 amp ones appear to be good.
Merlin who make the Smart Gauge battery monitor and the Smart Bank controller do not sell their relay separately but this page http://www.smartgauge.co.uk/more_relay.html shows the comparison between theirs and a so called 180 amp relay.

In passing, the deciding factor is alternator size, back in 1980 when we introduced VSR's alternators maxed out at around 30 amp, so we used a 30 amp relay. In the 80's we supplied 1000's and most appear to be still working talking to the current owners, a worry with re-engining with high output alternators and the owner not contacting me. Today alternators fitted to boats are much larger, so over time VSR relay have grown to match demand, it's all about contactor specification and the design of the control system.

Brian

 

[William_H]

So whilst slightly off thread- how can I tell on my boat that the starter battery is getting the initial charge then the house battery is getting the charge
Other than running the house batteries to zero then seeing if the engine starts
I am worried that I might flatten the start battery by mistake if I use too much electric on the house battery

The simple way to determine what battery supplies what is to turn on cabin lights, diconnect +ve of domestic battery. Lights should go out. If not disconnect engine battery +ve lights should go out. Disconnect domestic battery +ve try engine start. is it normal? if yes disconnect doestic battery +ve.

Or alternatively attach a volt meter. (Digital multimeter) to terminals of domestic battery. Crank engine over. Does voltage fall with engine actually cranking. If yes then domestic battery is helping start engine.
Turn on lots of lights and other domestic load. Is voltage of domestic battery falling? If so is voltage of engine battery the same and also falling?

Attach the multimeter to the domestic battery. If possibloe fit another to the engine battery. Start the engine and note engine battery voltage rising to 13.75 or more. Note if domestic battery rises at the same time or a little later. A little later will indicate a VSR doing its thing. Time delay may only be a second or 2 however. Or conect your multimeter on low volts between the engine battery pos and domestic battery +ve Start engine. There should be firstly a negative difference as engine cranks. Then a pos difference as engine battery is charged until VSR cuts in when difference should be zero.
good luck olewill