Make Before Break

[viva]

My boat manual says I shou"ld start with the battery switch on the "BOTH" setting, but as others have said previously I would rather start on "1" and then switch via "BOTH" and just use "2 when the engine is not running for domestic use I would therefore like to verify that my battery switch is of the "make before break" variety, and as access to the back of the switch is not easy can the electrical gurus please advise if the follow test is valid.

Switch battery to "2" (domestic)

Switch on cabin lights

slowly turn battery switch to "BOTH" and cabin lights should stay on -

 

[Burnham Bob]

sounds sensible to me - as long as you turn through the position marked 'both'. if you turn through off or 0 you will break the circuit. I do exactly as you do. 1 for starting, both for when the engine is running and 2 for when it's not. being a lifelong pessimist I also carry a rechargeable jump start booster pack that will get me started in case of a flat battery. never had to use it. the problem of breaking the citcuit with the engine running is blowing the alternator output ( i think the diodes burn out).

 

[Alan ashore]

If, as it appears from your post, your switch is a big rotary OFF-1-BOTH-2 switch designed and sold for the purpose, then it's surely going to be designed not to break the connection to "2" while switching between "2" and "BOTH".

If it's badly worn or damaged then it is possible that contact might be interrupted during any movement of the switch. If you have reason to suspect that, then your test would be useful I think, but I'd suggest putting a digital voltmeter across the output, as well as having the lights on, and I'd exercise the switch many times, switching between BOTH and 1 and between BOTH and 2.

A.

 

[elton]

Other than taking it apart and having a look, turn on the cabin lights, and turn the switch slowly through 1/1+2/2 and watch for the lights flickering. For absolute certainty, connect a storage oscilloscope to the lighting circuit, turn the switch, and carefully examine the oscilloscope trace. In the real world, turn it slowly and if you don't notice a flicker, assume it's make-before-break.

 

[Maine Sail]

My boat manual says I shou"ld start with the battery switch on the "BOTH" setting, but as others have said previously I would rather start on "1" and then switch via "BOTH" and just use "2 when the engine is not running for domestic use I would therefore like to verify that my battery switch is of the "make before break" variety, and as access to the back of the switch is not easy can the electrical gurus please advise if the follow test is valid.

Switch battery to "2" (domestic)

Switch on cabin lights

slowly turn battery switch to "BOTH" and cabin lights should stay on -

If your #2 / House bank is healthy why not just start on it, and stay there.... You can alternately fit a combining relay to charge the other battery so you never need to do anything more than trun the switch on when you get there and off when you are done...

If you need to use BOTH, unless you have a massive power boat diesel, then there is something wrong with the system, wiring or batteries.

But yes you can determine if you have a make before break by turning on the lights and moving between 1/BOTH & 2.. You may have a make before break that is also now worn so it is no longer make before break. I prefer to have some sort of a load on the system, in addition to the lights when testing this. An alt is a pretty hefty current source and a break may show up with a 40 or 50A charge but not with a 3A domestic lighting load..... Most marine battery switches produced in the last 20 or so years, by reputable brands, are make before break..

 

[awol]

I have never met a 1-Both-2 switch that wasn't make before break, but others may know better. I don't understand the point of ignoring the boat manual, though. Unless you have reason to believe one bank is heavily depleted, say after an all-nighter with lights, instruments and AP, starting on "Both" splits the starter current between the 2 banks and drops the voltage less, giving a marginally faster engine turn-over. Leaving the switch on "Both" while the engine is running saves you having to worry about the make/break function.

 

[VicS]

My boat manual says I shou"ld start with the battery switch on the "BOTH" setting, but as others have said previously I would rather start on "1" and then switch via "BOTH" and just use "2 when the engine is not running for domestic use I would therefore like to verify that my battery switch is of the "make before break" variety, and as access to the back of the switch is not easy can the electrical gurus please advise if the follow test is valid.

Switch battery to "2" (domestic)

Switch on cabin lights

slowly turn battery switch to "BOTH" and cabin lights should stay on -

I would not even has considered that there could be any interruption when switching between 1 and 2 via both.
However, doing what you suggest with the lights will confirm that there is not.

 

[ditchcrawler]

Nowadays many people have specialist starter batteries.I have a Red Flash AGM starter and 2 sealed marine as my domestic bank.I therefore always start on no1 and switch to no2 after 10minutes or so.Assuming that the starter battery is charged and the engine was easy to start (which is usually the case).When I am due to start the engine again I switch back to no1.In emergency I can start the engine on the no2 setting without switching.
My starter battery has done 7 seasons and my domestics 5 seasons so far and according to my battery monitor are still fine.