Switching from Engine to Domestic battery

[dt4134]

You know, these posts just reinforce my view that the old-fashioned 1-2-Both switch has no place on a boat in the 21st century! It was introduced by boatbuilders in years gone by as the cheapest possible way of providing the ability to isolate a starting battery and allow charging of a second battery.

But the inherent problem with a 1-2-Both switch is that it's far too easy for the switch to be turned to the wrong position (or left in the wrong position). Apart from blowing the diodes in the alternator, the real danger is that using domestic electricity will flatten the start battery if the switch is left in the wrong position. Today, there are much better and simpler solutions which offer no chance of getting it wrong!

The easiest solution is to have two simple on/off switches - one for the start battery, one for the domestic batteries. The alternator feeds the start battery. When the engine's running, a VSR automatically connects the charge to the domestic batteries. When the engine stops, the VSR automatically disconnects, isolating the domestic batteries. There's nothing to go wrong. When you arrive at the boat, turn on the 2 switches; when you leave the boat, turn off the 2 switches. VSRs are incredibly reliable, so there's no reason not to use one.

Some people fit a third switch, to connect the domestic batteries to the start battery if the start battery is found to be flat. However, it isn't necessary really, because with the set-up I've described the start battery shouldn't ever get discharged.

I'm of pretty much the same opinion. If in the future I buy a boat with a 1-2-both switch it'll be one of the first things I'll replace.

For a start, the requirements for a battery to start the engine are very different from the requirements of a domestic battery or batteries.

I've two circuits, one with an engine starter battery connected to the starter (surprisingly enough) with its own isolation switch.

The second circuit connects the domestic battery bank to the domestic load, again with its own isolator switch.

I've an isolator switch that allows the domestic to be used to start the engine. This would normally be done with the starter battery isolated. I'm most likely to be using the domestic to start the engine when the starter battery has serious problems, so most likely it would be counter-productive to include it in the circuit. However, just in case, I've got it set up so both can connect to the starter. Haven't had to do either since I got the above properly set up.

I also use an alternator to battery charger (Sterling) to charge the batteries directly. Not cheap but I reckon it'll pay for itself eventually by extending the life of my batteries.

A big advantage is that if some confused crew member accidentally turns any switch to off all you need to do is turn it back on. No smoke. No sparks.

 

[sailorman]

How can that prevent someone leaving the switch in the wrong position?

it stops inadvertent switching dunit

 

[pvb]

it stops inadvertent switching dunit

Yes, but it doesn't stop someone leaving the switch set to "Both" when it shouldn't be, and finding the start battery is flat when it's next needed...

 

[sailorman]

Yes, but it doesn't stop someone leaving the switch set to "Both" when it shouldn't be, and finding the start battery is flat when it's next needed...

Skippers responsibility
i have a dual sensing relay + a 1 2 both the latter is an easy way to use either bank or if needed both

 

[VicS]

Skippers responsibility

Absolutely. The person I crewed for always insisted on switching batteries himself.
It was years and years before he allowed me to do it.. and even then looked over my shoulder!

 

[pvb]

Absolutely. The person I crewed for always insisted on switching batteries himself.
It was years and years before he allowed me to do it.. and even then looked over my shoulder!

Further proof - if proof is needed - that the 1-2-Both switch is an unnecessarily complicated contraption.

 

[VicS]

Further proof - if proof is needed - that the 1-2-Both switch is an unnecessarily complicated contraption.

Well no that's where you are wrong. I left out one bit of info as it was irrelevant to the " skippers responsibility" comment

The boat in question has separate isolators for the batteries. T'would have made life a lot less complicated IMO if it had been fitted with a 1,2,both,off switch.

 

[pvb]

Well no that's where you are wrong. I left out one bit of info as it was irrelevant to the " skippers responsibility" comment

The boat in question has separate isolators for the batteries. T'would have made life a lot less complicated IMO if it had been fitted with a 1,2,both,off switch.

I give up!

 

[halcyon]

Yes, but it doesn't stop someone leaving the switch set to "Both" when it shouldn't be, and finding the start battery is flat when it's next needed...

Going back to 1980 ( sorry ) the reasons for the VSR design was :-

1) people changing rotory 1,2 both switch to both, or from bank 1 to bank 2 because bank 1 was going flat, but it resulted in flat batteries either way.

2) forgetting to select both postion, or other bank to charge, resulting in flat domestic battery.

3) selecting off with engine running.

4) as the engine and domestic power supply are both on common output from 1,2 both switch, starting the engine caused very low voltage to electronic equipment, plus power spikes from the starter motor, resulting in system reset.

The VSR gave clean start to electronics, secure power reserve for engine, auto switching. Another important feature was secure battery charge feed to engine battery. even if there is total failure in the split charge system. With electronic ( diode, MOSFET, SM echo charge ) split charging, system failure can cause lose of charge to engine battery.

But as with all things boaty, it is what the owner ( skipper ) feels happy with.

Brian

 

[Kerenza]

When I required my system, I wired the alternator to the starting battery via a breaker, just as in a (Motorsport) car.The engine can't start without the breaker on and it also feeds the field on the alternator to protect it if switched off.
The intelligent shore power charger is also connected to the starting battery. The domestic battery is connected to the starting battery via a vsr with 100 A cable so gets charged only when there is sufficient power available.
Permanently on circuits such as bilge pumps, gas alarms etc. are fed via their own breakers from the domestic battery.
The main switch panel is fed via a 150 A fuse from the output of the 1 / 2 /both switch.
Off position isolates the panel. 1 feeds it from the starter battery. 2 feeds from the domestic battery. Both position effectively parallels the two batteries giving the option to start with assistance from the domestic bank or in case of complete failure of the starting battery, to use only the domestic battery after suitably isolating the starter battery.
I've never had to use anything other than position 2.

 

[onesea]

The easiest solution is to have two simple on/off switches - one for the start battery, one for the domestic batteries. The alternator feeds the start battery. When the engine's running, a VSR automatically connects the charge to the domestic batteries. When the engine stops, the VSR automatically disconnects, isolating the domestic batteries. There's nothing to go wrong. When you arrive at the boat, turn on the 2 switches; when you leave the boat, turn off the 2 switches. VSRs are incredibly reliable, so there's no reason not to use one.

Some people fit a third switch, to connect the domestic batteries to the start battery if the start battery is found to be flat. However, it isn't necessary really, because with the set-up I've described the start battery shouldn't ever get discharged.

All being good I am having me boat rewired as above, I have sailed with various systems. 1,2,Both Various breakers types of knobs and dials..

I can assure you all the owners I was comfortable with watched you switch them on and off...

That's why I have gone for VSR system I am not bothering with breaker No 3. I will either shift the batt's round or use jump leads, but there is no reason this situation should occur....

With this system it is near impossible to do damage. I have no shore power connection when this luxury is available (over night only normally) I will just have small cheap batt charger (1 or 2 amp) for the domestics, to keep them topped up.

Eng Batt will start engine, every thing else will be powered by the other battery. Simplesss.

If I want to leave the bilge pump on (or anything else for that matter) I have to options by pass and leave connected to domestics or leave domestics breaker on and switch every thing else off...

Further proof - if proof is needed - that the 1-2-Both switch is an unnecessarily complicated contraption.

You sound just like my father he kept his 19 50's?/ 60's switches/ breakers on all the boats he owned, I know understand why.

 

[Graham_Wright]

Is it not possible to protect alternator diodes with a resistive load permanently connected?

If so, what sort of load is required to limit the surge output? Presumably a resistor or filament lamp (less reliable) would suffice. A diode would avoid the battery discharging through the lamp or a connection to the "ignition" switch could achieve the same result.

When a battery is fully charged the alternator output is minimal so a zener could maybe offer the protection. Selected for 20 v, it would only conduct on the spikes.

 

[VicS]

Is it not possible to protect alternator diodes with a resistive load permanently connected?

If so, what sort of load is required to limit the surge output? Presumably a resistor or filament lamp (less reliable) would suffice. A diode would avoid the battery discharging through the lamp or a connection to the "ignition" switch could achieve the same result.

When a battery is fully charged the alternator output is minimal so a zener could maybe offer the protection. Selected for 20 v, it would only conduct on the spikes.

Maybe.

But the load required would probably depend upon the magnitude of the (charging) current that you would interrupt by opening the isolator.

Some alternators do I believe have built in surge protection but it is usually said that it may work once but it is likely itself to be damaged by the surge and not be effective a second time around. I don't know if that is true or total balls.

The answer is not to open the isolator while the engine is running or wire a foolproof system like that which our American cousins favour