1,2 Both Switch - When on Both do the 2 batteries even out on charge?

[RupertW]

We have the simple 12both setup. I use both for an engine start unless we've been anchored overnight in which case I'll use one battery overnight and use the other for starting the next day. Use both when engine is running. My last pair of identical leisure batteries lasted 10 years...possibly because mostly each only has to provide half the starting current.

I'm a 12both fan but I'd be very nervous if I didn't know whether my start battery could start the engine always by itself. I tend to do 1 for starting then swap over to 2 after 15 mins or occasionally do both if the engine hasn't been started for a while. With engine off it's always 2 and only 2.

 

[Tranona]

I'm a 12both fan but I'd be very nervous if I didn't know whether my start battery could start the engine always by itself. I tend to do 1 for starting then swap over to 2 after 15 mins or occasionally do both if the engine hasn't been started for a while. With engine off it's always 2 and only 2.

If you had a dedicated engine start battery it would always start the engine if it was charged - which it would be if you also had a split charging system. If you really wanted belt and braces you could have a parallel switch so you could also start from the house bank.

Can see no merit is a 12both switch when there are superior alternatives available.

 

[RupertW]

If you had a dedicated engine start battery it would always start the engine if it was charged - which it would be if you also had a split charging system. If you really wanted belt and braces you could have a parallel switch so you could also start from the house bank.

Can see no merit is a 12both switch when there are superior alternatives available.

Can see no advantage in a superior alternative when the simpler one works perfectly with nothing to go wrong, provided the user isn't silly. And in 25 years of the simple system I was silly once in the first season and learnt the simple lesson. I also admire your confidence in saying a dedicated start battery will always start the engine - of course it will if its in a good state and the engine is good too but eventually it will deteriorate (in my most recent case 12 years after we bought the boat).

That's why any decent system whatever it is, will allow the other battery bank or both to take over engine start with fiddling with wires.

 

[SteveGorst]

This is a very good explanation thanks for that. I have used a 12B for years without problem but obviously been lucky. I will now be avoiding the both setting and look into the alternatives for the future. I am assuming that as long as I do that one duff battery shouldn't drag the other one down.

 

[PaulRainbow]

We have the simple 12both setup. I use both for an engine start unless we've been anchored overnight in which case I'll use one battery overnight and use the other for starting the next day. Use both when engine is running. My last pair of identical leisure batteries lasted 10 years...possibly because mostly each only has to provide half the starting current.

Good plan, much better than the thought of having a dedicated start battery.

Oh, hang on..................

Motoring along, one battery catastrophically fails and drags the other one down. You are unaware, as you would be. You stop to anchor and as you turn the engine off all of the circuits go dead. Yo obviously can't start the engine. Let's call for help. Bugger, the VHF won't work.

What now skip ?

Me, i'm just going to isolate the dead engine battery and use my domestic bank to start the engine :encouragement:

 

[PaulRainbow]

This is a very good explanation thanks for that. I have used a 12B for years without problem but obviously been lucky. I will now be avoiding the both setting and look into the alternatives for the future. I am assuming that as long as I do that one duff battery shouldn't drag the other one down.

Yes, only use (both) for emergency engine starting.

 

[Tranona]

Can see no advantage in a superior alternative when the simpler one works perfectly with nothing to go wrong, provided the user isn't silly. And in 25 years of the simple system I was silly once in the first season and learnt the simple lesson. I also admire your confidence in saying a dedicated start battery will always start the engine - of course it will if its in a good state and the engine is good too but eventually it will deteriorate (in my most recent case 12 years after we bought the boat).

That's why any decent system whatever it is, will allow the other battery bank or both to take over engine start with fiddling with wires.

Makes you wonder why no new boats are built with such a system nowadays if the old style was so good! It was of course a reasonable response to the increased electrical demands as boats acquired better engines and more electronics, but quickly got replaced with better systems. But we are talking 40 odd years ago and things have moved on a bit since then.

 

[RupertW]

Makes you wonder why no new boats are built with such a system nowadays if the old style was so good! It was of course a reasonable response to the increased electrical demands as boats acquired better engines and more electronics, but quickly got replaced with better systems. But we are talking 40 odd years ago and things have moved on a bit since then.

The reason the more complex systems took over is simple - for charter boats and inexperienced owners they are far more foolproof. The simple switch is equally good functionally but doesn't forgive mistakes.

 

[lpdsn]

My last pair of identical leisure batteries lasted 10 years....

That's the key point. Why have two identical batteries to do two jobs that each have very different requirements.

 

[RupertW]

That's the key point. Why have two identical batteries to do two jobs that each have very different requirements.

You are right but in this system I do the same so I can charge them as one battery bank if both are low and all I have wasted is a little but if money have a deep cycle battery as a starter.

 

[lpdsn]

You are right but in this system I do the same so I can charge them as one battery bank if both are low and all I have wasted is a little but if money have a deep cycle battery as a starter.

I've just got a small, high CCA, battery as a starter. Cost me about £50 IIRC. I've a Sterling A2B so it gets first dibbs at the alternator output once the engine starts, after which the A2B starts stuffing as much as it can into the much bigger domestic bank. At the moment the solar output only goes to the domestics. I have thought of a small dedicated panel for the engine battery but it's never really got past page 12 of the jobs list. In extremis I could move the solar regulator output to the engine battery in about 15 mins but there's never been any need to do that, or indeed to use the link switch except for testing. Engine battery is now over 8 years old and works every time first time. Even the time I had blocked fuel pipes it allowed me to crank over the engine dozens of times before I gave up and sailed in. So no need for anything bigger.

 

[lw395]

The reason the more complex systems took over is simple - for charter boats and inexperienced owners they are far more foolproof. The simple switch is equally good functionally but doesn't forgive mistakes.

When 1b2 switches were the default option, boats were much simpler. Often no solar (certainly not fitted as standard), no shorepower, just a few instruments and lights. A fridge maybe.
In the old days, we used to quite often take the batteries home alternately for a good charge.
Boats have changed, but I don't see them failing to start any less often?

TBH, I think boats have moved on to the point where 'an isolator for each bank and one to link the two banks' is not always the right thing either.

 

[RupertW]

I've just got a small, high CCA, battery as a starter. Cost me about £50 IIRC. I've a Sterling A2B so it gets first dibbs at the alternator output once the engine starts, after which the A2B starts stuffing as much as it can into the much bigger domestic bank. At the moment the solar output only goes to the domestics. I have thought of a small dedicated panel for the engine battery but it's never really got past page 12 of the jobs list. In extremis I could move the solar regulator output to the engine battery in about 15 mins but there's never been any need to do that, or indeed to use the link switch except for testing. Engine battery is now over 8 years old and works every time first time. Even the time I had blocked fuel pipes it allowed me to crank over the engine dozens of times before I gave up and sailed in. So no need for anything bigger.

I don't disagree at all - it sounds like a good setup. For me the cheopo setup outweighed the small extra cost of a 55AH deep cycle compared to a similar starter battery cost. I rarely use mains except for fan heater and have a 15 year old £10 charger from Halfords which I only tend to use when visiting the boat when the tide is too low to start the engine. Both batteries lasted 12 years before I recently replaced them.

 

[ghostlymoron]

There's no reason why batteries shouldn't last for many years, especially the starter as it does a bit of work then is immediately recharged. The house battery is usually discharged to 60% or so and then recharged.
This is what does the damage and they don't last so long. It is also why it's not a good idea (IMHO) to alternate duties if you have two batteries as you risk both failing at the same time and having no standby to start your engine. Incidentally, the battery on my car is now 7yrs old and still seems ok although it is cranking for a couple of seconds at the moment rather than starting instantly due to current low temperatures.
My opinion of the 1 2 both switch is that it will work ok provided you remember to switch over to no 2 when the engine is not running, and back to 1 for starting, and to both when motoring. I would almost certainly forget to do this at some stage and know of two instances where competent persons have forgotten to do this and ended up with both batteries flat. I would always fit an automatic system.

I don't disagree at all - it sounds like a good setup. For me the cheopo setup outweighed the small extra cost of a 55AH deep cycle compared to a similar starter battery cost. I rarely use mains except for fan heater and have a 15 year old £10 charger from Halfords which I only tend to use when visiting the boat when the tide is too low to start the engine. Both batteries lasted 12 years before I recently replaced them.

 

[lw395]

There's no reason why batteries shouldn't last for many years, especially the starter as it does a bit of work then is immediately recharged. The house battery is usually discharged to 60% or so and then recharged.
This is what does the damage and they don't last so long. It is also why it's not a good idea (IMHO) to alternate duties if you have two batteries as you risk both failing at the same time and having no standby to start your engine. Incidentally, the battery on my car is now 7yrs old and still seems ok although it is cranking for a couple of seconds at the moment rather than starting instantly due to current low temperatures.
My opinion of the 1 2 both switch is that it will work ok provided you remember to switch over to no 2 when the engine is not running, and back to 1 for starting, and to both when motoring. I would almost certainly forget to do this at some stage and know of two instances where competent persons have forgotten to do this and ended up with both batteries flat. I would always fit an automatic system.

Fair comment, but I know of someone whose starter battery died (partly to be fair bleeding the fuel system gave it a hard time) so he switched to the house battery, which although it was fine for running the fridge etc, wasn't interested in starting the diesel.
In the limit, the 'system' isn't just about switches and batteries, it's about issue like how do you decide to replace the batteries, what limits do you set for discharge etc.

One of my aspirations is to have a system that's simple and obvious enough for people to come aboard and understand what they're working with.
I've seen some convoluted systems on boats, including one where the owner isn't sure what he's got.

 

[Tranona]

The reason the more complex systems took over is simple - for charter boats and inexperienced owners they are far more foolproof. The simple switch is equally good functionally but doesn't forgive mistakes.

What strange reasoning. They took over because - well they are superior. All part of the continuous technical development, as you note later. Boats electrics are more demanding and require better control systems.

Even experienced owners such as most of the contributors here appreciate the benefits as do charterers who may well also be experienced.

 

[lw395]

A cynic would point out that a good quality 1b2 switch seems to be a lot more expensive than several of the normal battery isolator switches....

 

[RupertW]

What strange reasoning. They took over because - well they are superior. All part of the continuous technical development, as you note later. Boats electrics are more demanding and require better control systems.

Even experienced owners such as most of the contributors here appreciate the benefits as do charterers who may well also be experienced.

You can't keep saying that modern systems are superior without any reasoning.

 

[geem]

You can't keep saying that modern systems are superior without any reasoning.

My thoughts exactly. Fit what you like out of personal choice. If 1b2 works for you then thats great. If you want automation then fit something that does it for you. For me the 1b2 works fine. I have 1000 amp hr of domestic bank. My batteries were 96% charged this morning. I never use the 1b2 switch as I have no reason. Both domestic and engine bank will start the engine. Solar, wind and towed does all the charging. The alternator is not really needed as we hardly ever engine. The solar, wind and towed charge both banks. The 1b2 switch is perfect for my set up and anything else would just be unnecessary.
We make water every other day using the generator for just half an hour. If we have had lots of cloud cover I just bank the chargers on. I can push 200 amp/hr in to the batteries if I needed to but I havent run the chargers for a couple of weeks now as we have had sufficient sunshine. There is no right or wrong but one system may suit your needs better than another depending on battery capacity, boat use, location, charging set up etc

 

[halcyon]

You can't keep saying that modern systems are superior without any reasoning.

Interesting statement, what is modern ? this pdf link is a 1982 system and goes someway to answering your question .... http://www.kddpowercentre.co.uk/data/P4000_82_lit.pdf

Times change and requirements change, back in 1972 when I started alternators were almost unknown and most boats had a dynostart, by 1982 you had small alternators, 30 amp if you were lucky, but bigger demand. Plus towed generators, solar panels etc. had yet to be invented for long range cruising yachts. but the basic idea was to split charging so prioritize engine battery and maximize charge by making use of how the a battery works.

Today you have engine battery, service bank, bow and stern banks, complex to do manually, easy to do automatically and show indication of battery level, but still only a expansion of the 1982 system, but there is still the future !!!

The bottom line is what I have always said, the optimum solution is what suits you.


Brian