Battery cross over switch and charging

[All_at_Sea]

Hi , l have the usual cross over switch, off, 2, both and 1.

When this is on 1 or 2 is it only that battery that would be charging from the alternator? and what happens on both, which charges first or do they both get half each?

 

[madabouttheboat]

On 1 or 2 only that battery gets charged. On both, the two batteries act like one big battery and gets charged at the same time.

 

[RupertW]

It’s a great system if you are happy being the VSO (Voltage Sensitive Operator) and swapping between them as the battery needs it . The boring way is to buy an inexpensive VSR between the engine battery and the domestic battery (ies) and attach the alternator to engine battery only. That way the domestic battery gets automatically put onto Both whenever the engine battery is at a decent charged voltage.

For 10 years I had two different boats, one on each system and was equally happy with both, but only solo sailed the one with 1-2-B so there was no crew member to get it wrong and let the engine start battery get discharged.

 

[pvb]

For 10 years I had two different boats, one on each system and was equally happy with both, but only solo sailed the one with 1-2-B so there was no crew member to get it wrong and let the engine start battery get discharged.

And there's the main disadvantage of such an antiquated device.

 

[RupertW]

And there's the main disadvantage of such an antiquated device.

Yup - like a manual gear lever in a car it is perfect for its purpose but needs a skilled operator.

 

[VicS]

Hi , l have the usual cross over switch, off, 2, both and 1.

When this is on 1 or 2 is it only that battery that would be charging from the alternator? and what happens on both, which charges first or do they both get half each?

As more or less already said
When the switch is in position 1 no. 1 battery is in service and is being charged when the engine is running.
When in position 2 no. 2 battery is in service and is being charged
When in the "both" position both batteries are in service and are being charged.

If you have a VSR or diode splitter both batteries will be charged simultaneously irrespective of which is selected to be the "in service" battery.

The downside of this type of switch is that you have to be careful not to accidentally switch to the "off" position while the engine is running or you risk blowing the alternator diodes.

I'd suggest adopting a routine

When you are preparing to start the engine select the engine start battery.
Start the engine.
When the engine has been running long enough to recharge the starter battery switch to both, then to the services battery.( A simple voltmeter or ammeter will help to judge when this point is reached)..
Leave the services battery selected until you are next preparing to start the engine (Or leaving the boat)

There is one golden rule to add to the above:
THE SKIPPER IS THE ONLY ONE ALLOWED TO OPERATE THE BATTERY SWITCH

 

[Poey50]

Yup - like a manual gear lever in a car it is perfect for its purpose but needs a skilled operator.

It's a clever and witty reply but it isn't a good analogy. If you don't use the gear lever the car won't go far. Not so with the 1+2+both. It won't give you a pre-emptive warning. If you forget to change back from both to 1 or 2 then this might only be discovered when the engine won't start. This may be very unlikely but you have to remember every single time - the switch gives you no credit for the 2,000 times you remembered.

 

[lustyd]

The downside of this type of switch is that you have to be careful not to accidentally switch to the "off" position while the engine is running or you risk blowing the alternator diodes. ( but it should not be a problem with VSR or diode splitter fitted).

Donning my pedant hat for a moment, the switch is not relevant to this statement. If the alternator connects directly to the starter battery with a VSR then the switch makes no difference whatsoever, you just can't start the motor (depending how the switch is wired!). If the alternator is wired after the switch then the VSR installer probably needs shooting. The question from the OP is flawed because the presence or lack of a 12BO switch is not sufficient to draw any conclusions about operation. It's literally just a multi option switch.

 

[PaulRainbow]

The downside of this type of switch is that you have to be careful not to accidentally switch to the "off" position while the engine is running or you risk blowing the alternator diodes. ( but it should not be a problem with VSR or diode splitter fitted).

Donning my pedant hat for a moment, the switch is not relevant to this statement.

It is relevant and VicS is correct, with a 1-2-B switch, alternator damage is likely if you switch to OFF with the engine running, because the alternator will be connected to the common terminal of the switch. Although damage is not certain, there may be enough loads turned on to save the alternator.

If the alternator connects directly to the starter battery with a VSR then the switch makes no difference whatsoever

The last part of VicS statement, which you quote above, states that it should not be a problem if a VSR is fitted.

If the alternator is wired after the switch then the VSR installer probably needs shooting.

Why ? Where would you connect it ?

The question from the OP is flawed because the presence or lack of a 12BO switch is not sufficient to draw any conclusions about operation. It's literally just a multi option switch.

Yes, it would be useful to know where the alternator is connected and if there is a VSR, diode, etc

 

[PaulRainbow]

The following basic schematic is from my website and shows how to connect a VSR to a system with a 1-2-B switch, depending on the exact installation additional fuses may be required:

 

[halcyon]

The following basic schematic is from my website and shows how to connect a VSR to a system with a 1-2-B switch, depending on the exact installation additional fuses may be required:

One point, a VSR for use with a 1,2 both switch should have it's power monitoring feed from the common output terminal, isolates the VSR with switch off and also stops battery drain.

Brian

 

[William_H]

One question I think the OP alluded to was regarding the charging of both batteries. A battery will take a charge current dependent on it's inherent voltage. (If they are forceably paralleled then they must have the same voltage. ) Each battery will take a charge current so assuming the total charge current is within the capabilities of the alternator total charging current will be twice that for one battery. (good)
One note of caution with this system. If you habitually start on both you get wonderful energetic start but this can cover up a failing battery. So in effect you lose your redundancy for starting if one fails and you don't know it until the second battery dies and you are stuck. So you should regularly if not always use just one battery for starting. But alternate as to which battery you start on. ol'will

 

[garymalmgren]

I removed the 1-2- both switch.
Fitted an inexpensive VSR.
There is no link between the start and the house battery except for the VSR.
The Start battery is charged up first and the the house battery.
With a small solar panel both batteries are kept topped up.
If (and this has happened) I have trouble starting on just the start battery I use jumper leads.

I know that this is a case of each to his own and am not promoting my set up as the bees knees, just as another way at looking at batteries and switches.

Gay

 

[lustyd]

because the alternator will be connected to the common terminal of the switch

You need to be less certain about things you don't actually know Paul. The alternator MIGHT be connected to the switch, it might not. It's entirely possible it's connected directly to the battery, bypassing the switch just like a charger often is. My point was that all of the advice on this thread is worthless unless and until we actually know how this specific boat is wired.

It's just a switch. All we can say for certain is that when the OP changes it the various contacts are joined and broken in a particular pattern. Once we find out how the boat is wired we can comment on the effect of those patterns. Until then though, you have no idea what the effect of that switch is. For all you know, the 2 position could be wired up to short the battery and cause a fire. It's unlikely, but it's a possible effect of the switch.

 

[halcyon]

One question I think the OP alluded to was regarding the charging of both batteries. A battery will take a charge current dependent on it's inherent voltage. (If they are forceably paralleled then they must have the same voltage. ) Each battery will take a charge current so assuming the total charge current is within the capabilities of the alternator total charging current will be twice that for one battery. (good)
One note of caution with this system. If you habitually start on both you get wonderful energetic start but this can cover up a failing battery. So in effect you lose your redundancy for starting if one fails and you don't know it until the second battery dies and you are stuck. So you should regularly if not always use just one battery for starting. But alternate as to which battery you start on. ol'will

The voltage you see is generated by the battery, alternators to not produce the charge volts. Current will flow through the lowest battery, easiest path, generating a lower voltage than the higher battery needs to except a charge. As the voltage rises with charge level, the voltage reaches a level that is adequate to start charging the higher battery, as levels equalize both start taking approximately the same charge. This was the theory behind the design of the VSR operation.

The above works with FLA batteries and normal size alternators, increase size and regulation voltage and things change. You get a rapid conversion of active material in the outer layers, causing a rapid increase in the voltage generating a surface charge, but it also reduces the charge, as you all see, extending charge time, reduces charge level, increases water loss.

Starting and using one battery for service power supply was a second reason behind the VSR design. Starting causes a low voltage and spikes, with the growth of electronic, sat nav, radar etc, it was causing resets and memory loss. So there was a reason why we used a separate engine start battery.

Brian

 

[PaulRainbow]

One point, a VSR for use with a 1,2 both switch should have it's power monitoring feed from the common output terminal, isolates the VSR with switch off and also stops battery drain.

Brian

It's a dual sensing VSR.

Besides, if you isolate the VSR when you turn the isolator off you also prevent charging of all batteries by solar power or a single output mains charger.

 

[PaulRainbow]

You need to be less certain about things you don't actually know Paul. The alternator MIGHT be connected to the switch, it might not. It's entirely possible it's connected directly to the battery, bypassing the switch just like a charger often is. My point was that all of the advice on this thread is worthless unless and until we actually know how this specific boat is wired.

It's just a switch. All we can say for certain is that when the OP changes it the various contacts are joined and broken in a particular pattern. Once we find out how the boat is wired we can comment on the effect of those patterns. Until then though, you have no idea what the effect of that switch is. For all you know, the 2 position could be wired up to short the battery and cause a fire. It's unlikely, but it's a possible effect of the switch.

If the alternator is not connected to the common terminal it is incorrectly wired. I'm aware that we don't actually know details of the OPs setup, which is why i said "it would be useful to know where the alternator is connected and if there is a VSR, diode, etc "

If the alternator is wired after the switch then the VSR installer probably needs shooting.

Why ? Where would you connect it ?

 

[vyv_cox]

Hi , l have the usual cross over switch, off, 2, both and 1.

When this is on 1 or 2 is it only that battery that would be charging from the alternator? and what happens on both, which charges first or do they both get half each?

Before this thread descends to the usual fight between electrical specialists, here is a proven way to manage a 1,2,both,off switch.
Rule 1 - never use Both.
Leave the switch on the domestic bank, in my case 2, always. A domestic battery bank is perfectly capable of starting a small yacht engine. The bank will then charge when the engine is running and on solar when it is not.
Leave switch 1 as an emergency starter. Occasionally, dependent upon your use of the boat, switch to it, start the engine and charge it for 30 minutes, then switch back to 2.
I have been using this regime for 25 years and never had a failure to start or any flat batteries. We run a fridge 24/7 throughout the season in Greece, so our demands are fairly high.

 

[halcyon]

It's a dual sensing VSR.

Besides, if you isolate the VSR when you turn the isolator off you also prevent charging of all batteries by solar power or a single output mains charger.

Dual solar regulator, far better, unless big solar system, VSR relay consumes to much of solar output. Mains charger?, just wire power / sense lead to battery with mains charger on, no problem.

Brian

 

[PaulRainbow]

Dual solar regulator, far better, unless big solar system, VSR relay consumes to much of solar output. Mains charger?, just wire power / sense lead to battery with mains charger on, no problem.

Brian

So, we have a dual sensing VSR, somehow connected to a 1-2-B switch, which miraculously isolates the VSR when the switch is set to off. We then fit a dual solar controller, so we can't have an MPPT controller.

No idea how your mains charger is connected, your description doesn't make sense. If it's a single output charger you can't charge both banks if the relay is isolated. If it's dual output it charges both banks but costs more and duplicates the function of the VSR that's somehow isolated.

So how is the mains charger connected ?
How is the VSR connected to the 1-2-B switch so that it is isolated ?
If all other charging sources are dual output, why even fit a VSR, why not low loss splitter, it only has to split the alternator charging ?

Personally, i'll stick with #10 for most installations. If there is a big solar array and the domestic bank is on a higher voltage charge regime than the engine battery would like, i'll use something different to a VSR, i'd also use something different to a 1-2-B switch