Switching from Engine to Domestic battery

[ianat182]

I have just the two batteries and the usual 1,2,all off Battery switch on my boat with a newish Volvo Penta 2010A engine and instrument panel/ignition. This week I went for a sail after starting the engine using the Engine battery,but found that the Domestic battery was very low on voltage. Would it have been safe to have switched to the Domestic battery from the Engine one whilst the engine was running?
I remember there used to be dire warnings about destroying the diodes or something on my old engine which used a dynastart, not an alternator.
There was not enough voltage on the DOM battery to re-start the engine to change it if I had stopped it running. Probably will have to replace the DOM battery anyway soon.

ianat182

 

[sailorman]

I have just the two batteries and the usual 1,2,all off Battery switch on my boat with a newish Volvo Penta 2010A engine and instrument panel/ignition. This week I went for a sail after starting the engine using the Engine battery,but found that the Domestic battery was very low on voltage. Would it have been safe to have switched to the Domestic battery from the Engine one whilst the engine was running?
I remember there used to be dire warnings about destroying the diodes or something on my old engine which used a dynastart, not an alternator.
There was not enough voltage on the DOM battery to re-start the engine to change it if I had stopped it running. Probably will have to replace the DOM battery anyway soon.

ianat182

the switches make the nxt position before breaking the previous as long as "switched through" not from Batt 1 > off.
when the engine is running switch to both

 

[Hoolie]

No problem if you turn to or through "both". Disaster only if you turn to "off"

 

[VicS]

I have just the two batteries and the usual 1,2,all off Battery switch on my boat with a newish Volvo Penta 2010A engine and instrument panel/ignition. This week I went for a sail after starting the engine using the Engine battery,but found that the Domestic battery was very low on voltage. Would it have been safe to have switched to the Domestic battery from the Engine one whilst the engine was running?
I remember there used to be dire warnings about destroying the diodes or something on my old engine which used a dynastart, not an alternator.
There was not enough voltage on the DOM battery to re-start the engine to change it if I had stopped it running. Probably will have to replace the DOM battery anyway soon.

ianat182

With a 1/2/off/both switch. Always switch via the "both" position if the engine is running, when changing batteries. If you switch to the "off" position you may blow the diodes.

When the engine is not running it does not matter. via the off position might be preferable except that all power supplies will be interrupted.


As an analogy consider a motorway, BMWs all belting allong nose to tail at 90mph. Suddenly a barrier drops across the road. Nowhere for them to go. Massive pile up.

Same with your electrons all belting along the wires. Open a switch... nowhere for them to go. Massive voltage surge

 

[ianat182]

Thank you gents, very clear now!

ianat182

 

[Stu Jackson]

It all depends on how it's wired.

In another post active now I posted a link to switch wiring diagrams. The latest thinking is to avoid using the switch as the charging selector, rather send the alternator output to one of the battery banks and using a VSR to automatically charge the second bank.

http://c34.org/bbs/index.php/topic,6604.0.html

 

[William_H]

Switching to a flat battery

You are right to be concerned. You will have a battery happily being charged by the alternator at around 14volts and you then either whack a flat battery in parallel or change to a flat battery via the batteries in parallel. (don't go via off) There will be a fair bit of current flowing from engine battery/alternator into flat battery.
Though really this should not do any harm to the switch as the current will be less than starter motor current which the switch should be able to carry.
If you are really concerned get a headlight globe or similar ie 50watts with 2 leads and clips. With switch on engine battery only connect this between the +ve of the engine battery and +ve of the domestic battery.
That will give a max 4 amps into a dead flat battery which won't be such a shock to the system and after a while there will be enough charge in the dom battery to not matter if you switch to both.
Although it does sound like dom battery is dead so may just pull the engine battery down if in parallel.
good luck olewill

 

[johnphilip]

charging regime

Some years ago we chartered a boat with the typical 1-2-both-off switch. On handover to us the yard told us to turn to both in the morning and domestic overnight once moored. Simples. Once you have good condition batteries in each use this makes sense. Trying to remember to fiddle with the switch every time you use the engine for a few minutes is not on, this is realistic.

 

[ianat182]

Thanks for the pointer Stu, I'll have a readup of that item.

Olewill,I think the DOM battery is on the way out but thought I'd double check before dumping it. The charging voltage on the 'Both' setting is about 14 volts measured on the instrument panel gauge; I've also got to get a new multimeter at that has gone TU for some reason too!
Thanks for your advice.

ianat182

 

[ghostlymoron]

I've never been able to figure out just how a 1-2-B switch works! They seem a recipe for disaster to me relying as they do on correct positioning every time. But just to put my mind at rest could someone explain how they work controlling both battery charge selection and output.

 

[blackbeard]

In line with johnphilip's post:
Assuming both engine and domestic batteries are OK and have some charge in them:
all I do is to select "both" when about to start the engine and leave the switch there until engine has stopped, when I select the domestic battery. That way, neither battery has to give all the current needed to start the engine so it's kinder to the batteries (though I admit it won't make much difference, as engine start current is well within capabilities for either), and both are being charged all the time the engine is running.
Of course if one bank is flat I will start it on the other, then move the switch carefully and directly to "both" (and then, perhaps, to the flat one)(might be a good idea to keep an eye on volts)
and if one bank is defective, just use the good one and replace the defective one asap

and of course start the engine on one bank or the other from time to time just to check that I can!

 

[VicS]

I've never been able to figure out just how a 1-2-B switch works! They seem a recipe for disaster to me relying as they do on correct positioning every time. But just to put my mind at rest could someone explain how they work controlling both battery charge selection and output.

they are basically a change over switc . You select which battery you want in circuit. no 1 or no2. The selected battery is then the one in use and ( unless there is some form of split charging system) it is the one being charged.

the switch also has a "BOTH" position in which both batteries are connected and of course an "OFF" position in which neither are connected.

With the basic system

Select the battery designated to use for starting.
Start the engine.
Keep the battery selected until recharged
Then change to the other ( house) battery by turning the switch via the "both"

You can of course at any time start with, charge, or use the "other" battery or indeed both in parallel .. depending upon circumstances or personal preferences

 

[fastjedi]

I wouldn't have it any other way...... no diodes to drop voltage / no VSR to go wrong.

As already said, we start and charge on 'both' to get the most out of the alternator and discharge on 'domestic'.

I've not moved the switch when running the engine since I accidentally overshot on the way from '2' to '1' and ran the engine for 5 minutes disconnected from the batteries ... no damage was done (Phew!)

 

[sailorman]

I wouldn't have it any other way...... no diodes to drop voltage / no VSR to go wrong.

As already said, we start and charge on 'both' to get the most out of the alternator and discharge on 'domestic'.

I've not moved the switch when running the engine since I accidentally overshot on the way from '2' to '1' and ran the engine for 5 minutes disconnected from the batteries ... no damage was done (Phew!)

it helps in that case to have permanent feeds to bilge pumps, radio ect. the current has somewhere to go

 

[VicS]

I wouldn't have it any other way...... no diodes to drop voltage / no VSR to go wrong.

As already said, we start and charge on 'both' to get the most out of the alternator and discharge on 'domestic'.

I've not moved the switch when running the engine since I accidentally overshot on the way from '2' to '1' and ran the engine for 5 minutes disconnected from the batteries ... no damage was done (Phew!)

Some would say that a better alternative to the 1,2,both,off switch is to simply use separate isolator switches for each battery!

 

[chewi]

With a 1/2/off/both switch. Always switch via the "both" position if the engine is running, when changing batteries. If you switch to the "off" position you may blow the diodes.

When the engine is not running it does not matter. via the off position might be preferable except that all power supplies will be interrupted.


As an analogy consider a motorway, BMWs all belting allong nose to tail at 90mph. Suddenly a barrier drops across the road. Nowhere for them to go. Massive pile up.

Same with your electrons all belting along the wires. Open a switch... nowhere for them to go. Massive voltage surge

I doubt most people wire this option up, but my 1-Both-2 -off switch has a field current connection so that if I switch to OFF the field current is broken which prevents the surge that blows the diodes.
I know I should avoid OFF anyway while the engine is running, but I wired it so nobody else blows it up by accident.

 

[Stu Jackson]

I've never been able to figure out just how a 1-2-B switch works! They seem a recipe for disaster to me relying as they do on correct positioning every time. But just to put my mind at rest could someone explain how they work controlling both battery charge selection and output.

You could try reading the link I posted. See Reply #6 on page 1. Also this one: http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg30101

 

[pvb]

I've not moved the switch when running the engine since I accidentally overshot on the way from '2' to '1' and ran the engine for 5 minutes disconnected from the batteries ... no damage was done (Phew!)

I've never been able to figure out just how a 1-2-B switch works! They seem a recipe for disaster to me relying as they do on correct positioning every time.

I know I should avoid OFF anyway while the engine is running, but I wired it so nobody else blows it up by accident.

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.

 

[sailorman]

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.

the Vetus switch has a positive locking catch system to avoid that happening. the perko type are poor quality

 

[pvb]

the Vetus switch has a positive locking catch system to avoid that happening.

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