Battery Isolators: positive or negative and leakage?

[nigelmercier]

[1] The 12V isolator on my boat switches the lead to the negative busbar.

[2] Even when off, there seems to be about 1/3 Amp being drawn, possibly from the various sensors on the shunt.

Are [1] and [2] normal?

 

[VicS]

Some boats seem to have the isolator in the negative. I have no idea why!

1/3 amp excessive. There must be circuits wired to the battery side of the isolator.

You mention shunts. The one instrument that I can think of that is likely to be wired so that it is always connected to the supply is a battery monitor, (but with a single battery and simple isolator switch that probably need not be) In any event its current consumption will be very small compared with the 300mA observed.

The answer is to systematically investigate the cause of the current drain by disconnecting the various circuits that are connected directly.

 

[sailinglegend420]

Some boats have both a negative and a positive switch. This should totally isolate all loads if the negative isolator is the only wire going to the battery. If not there are other circuits connected permanently - these could be:

A Navtex or similar weather info receiver.
A radio cassette - which awlways draws current to keep the stations stored in memory.
Fire/smoke/gas alarms.
The bilge pump - there could be some current leakage to the water in the bilges.
Any other instruments that might be on STANDBY or fed by a charger.

To eliminate all current drain you need to find and isolate any other fuses that are in circuit with any of these devices.

 

[jwilson]

You may have a gas alarm wired direct to the battery, bypassing the switch. That was where I was told to wire mine, but as it draws about 1/3 amp it would well flatten the battery after a week with the boat unused, so I put it after the isolator.