Battery Isolator Switch

[Thepipdoc]

I'm very new to boating and the boat I now own was previously berthed on a marina. When I took possession of the boat and the previous owner took me through the various aspects of the it, he sort of skirted around my question as to how I should use the battery isolator switches. He told me to always have the switch pointing to "BOTH" and to turn the domestic switch to "ON". This, I now understand may be fine when on a marina and hooked up to shore electricity, but potentially idiotic when on a swinging mooring - as I am.
The owners manual doesn't explain anything about the isolator switches and so far I’ve flattened one of the 3 batteries twice by leaving the fridge on overnight.
I have 2 engine batteries and one domestic battery.
I would appreciate it if anyone/everyone could give me the basics on how this switch should be used. How should I position the "main" switch to ensure I'm not left high and dry? Is it possible that one of the engine batteries is also supplying the domestic circuit? The reason I ask that is because when I first flattened the domestic battery, the starboard engine battery was also flat.
Thanks

 

[halcyon]

Can you expand on what boat, and what sort of isolator switches, as you say both?

Brian

 

[markdj]

The one two both switch has got to be the worst invention of the last 50 years as it is just a cheap way of charging batteries but sooo prone to improper use.

For proper use, set the switch to one, start the engine and after 5 minutes set the switch to both. After stopping your engine, set the switch to one or off.

From what you describe, your starboard engine charges your domestic battery but you need to use the 1 2 both to isolate the 2 battery banks when the engine is not running.

I would think that your domestic battery has had it unless your fridge has a low voltage cutout e.g. isotherm fridges cut out at 10.5v.

I'd suggest connecting your starboard engine starter to your port starter (pos. and neg.)
Change your starboard engine battery for another liesure battery to increase your capacity.
Connect your new leisure battery with your domestic battery (best to get a new one).
Get rid of your 1 2 both and domestic switch.
Fit a BEP battery cluster

http://bepmarine.web03.co.nz/Dual-Battery-Charging-Cluster-180-1464.html

available from Merlin Equipment.
Check your alternator outputs are connected either to each starter of the engine or one to engine battery and one to domestic - it doesn't matter.

Now, with this done, you will have an Engine battery switch, a Domestic battery switch, and an emergency parallel if at any time your engine battery fails, and more capacity for your domestic battery bank.

The BEP cluster senses when a battery bank is charging and combines the 2 sets of batteries while the voltage is above 13.8 volts. When the engine stops and the voltage drops to 12.8, it disconnects the 2 sets so the engine battery bank is completely isolated from the domestic bank.

If your alternators put out more than 125Amps combined, then you will require the Merlin Smartbank which uses their own smart box and heavy duty relays.

If you have a bow thruster battery then you will need another VSR which will give charge when available.

Hope this makes sense - you can certainly use your existing setup as mentioned but a better way is available.


Mark
www.boatdoctorni.com

 

[realslimshady]

make sure it's switched 'off' when you leave the boat-hey presto! no flat batteries...

 

[Thepipdoc]

Thanks very much for the constructive replie - perticularly Markdj's. The penny has finally dropped as to what the isolator switch is meant to be isolating!