Adding a 3rd battery or, a higher amp alternator? Which is best? Both isn’t the answer! CPAP

[RupertW]

Adding a VSR to a simple installation that uses a 1-2-B switch removes the risk of user error. It also saves having to run up and down companionway steps changing switch positions (depending on where the engine panel and the switch are located, of course).

It doesn't add any failure points. If the VSR fails, you're just back to where you were before you fitted it.

I agree with all of that - assuming somebody is capable of bypassing the VSR. And I suspect VSR failures are very low - I’ve had mine for 10 years and it was probably already that old when I bought the boat.

As always I would agree if you said something like “1-2-B switches work but they risk flattening the engine battery if you make a mistake just once whereas a VSR will protect you. And if you do really prefer not to have a VSR one tip is to switch from 1 through Both to 2 once the engine battery is charged. That way you won’t end up switching the engine off in Both and draining all batteries by forgetting to switch to 2.”

 

[pvb]

I have similar 2+1 battery arrangement. You should fit a charge splitter/diode battery isolator to keep house and starter batteries apart unless the alternator is feeding in current.

Some time ago YM suggested a Voltage Sensitive Relay (VSR) rather than a diode isolator because the resistance of a diode isolator causes a big voltage drop when charging. VSR isolates batteries until it senses voltage rise.

Low-loss splitters avoid the voltage drop associated with conventional diodes.

 

[PaulRainbow]

I agree with all of that - assuming somebody is capable of bypassing the VSR. And I suspect VSR failures are very low - I’ve had mine for 10 years and it was probably already that old when I bought the boat.

Failures are very low in my experience. If it does fail, there's no need to bypass anything, the system just reverts to how it was without the VSR.

As always I would agree if you said something like “1-2-B switches work but they risk flattening the engine battery if you make a mistake just once whereas a VSR will protect you. And if you do really prefer not to have a VSR one tip is to switch from 1 through Both to 2 once the engine battery is charged. That way you won’t end up switching the engine off in Both and draining all batteries by forgetting to switch to 2.”

I agree with all of that , it's one way of safely using the switch, without risking all of the batteries.

Another way of using it is how Vyv Cox uses his. The bank of batteries are for everything, the small, single battery is a reserve battery. This is favoured by many in the States. It does have the advantage over the other method that you don't have to change over from 1 to 2. Vyvs idea of starting and running on the single battery from time to time ensures that a) the battery is sound and b) it gets its charge topped up.

The thing i don't agree with is using the switch on the "both" setting, because it's possible to end up with no power under certain failure conditions, or user error, but if people want to use that method it's up to them, as i keep saying.

 

[lw395]

The trouble with charging in 1 or 2 is that many sailing yachts don't do enough engine hours to keep the batteries anywhere near fully charged if you charge this way. Of course these days it's easy to get around that with £20 worth of solar panel. But that wasn't the case when most 1B2 switches were fitted. In those days, switching from B to 1 or 2 was just part of what you did after stopping the engine, often after needing to go below to shut up the oil pressure buzzer.

 

[pvb]

The trouble with charging in 1 or 2 is that many sailing yachts don't do enough engine hours to keep the batteries anywhere near fully charged if you charge this way. Of course these days it's easy to get around that with £20 worth of solar panel. But that wasn't the case when most 1B2 switches were fitted. In those days, switching from B to 1 or 2 was just part of what you did after stopping the engine, often after needing to go below to shut up the oil pressure buzzer.

Starting a boat engine uses so little battery capacity that the start battery can be considered recharged in next to no time. An automatic system recognises this, whereas many boat owners don't. As for having the engine panel inside, it does make you wonder what people were thinking about in olden times!

 

[PaulRainbow]

Starting a boat engine uses so little battery capacity that the start battery can be considered recharged in next to no time. An automatic system recognises this, whereas many boat owners don't. As for having the engine panel inside, it does make you wonder what people were thinking about in olden times!

Won't be long, just going down below to check the oil pressure.............

 

[lw395]

Starting a boat engine uses so little battery capacity that the start battery can be considered recharged in next to no time. An automatic system recognises this, whereas many boat owners don't. As for having the engine panel inside, it does make you wonder what people were thinking about in olden times!

I think some engine start batteries lose more charge to 'self discharge' than they actually use starting the motor.
Depending on what the alternator voltage is, you might need something like an hour's running a week.
Back in the dark ages before I bought my first solar panel, I was perpetually taking batteries home to charge.
To be fair they were never the newest of batteries.

 

[geem]

I think some engine start batteries lose more charge to 'self discharge' than they actually use starting the motor.
Depending on what the alternator voltage is, you might need something like an hour's running a week.
Back in the dark ages before I bought my first solar panel, I was perpetually taking batteries home to charge.
To be fair they were never the newest of batteries.

Agreed. If you have a separate solar panel for the engine battery there is no need to have a VSR or use a 1-2-both switch in both setting. I have my alternator output permanently set to charge the domestic bank.

 

[grandpaboat]

Far be it from me to defend Paul’s statement but many of us run off solar power 24/7. That’s what battery banks are for and I don’t know any other way of using solar.

In my opinion that would be running on battery power which is recharged by solar power. I know I'm being pedantic!