Battery switch position while charging?

[seaman-recruit]

I just purchased a 2001 - 2500SCR and the PO supplied a Maxum manual titled "Sun Cruiser". It mentions referencing the battery charger manual (not in my possession) for further information on operation of that system.

Before I closed the deal on the boat I had downloaded a 2700SCR manual for general reference off this web site. I ran across a statement in that document that says for proper battery charging use any battery switch position "except both" which I thought was strange since you would seemingly want both batteries being charged simultaneously.

Can anyone shed some light on this topic?

[Cymru]

There's a article I read when I had the very same questions. Here is the link.

http://continuouswave.com/whaler/ref...alBattery.html

It says the following about the BOTH position; Hope it helps.

In the BOTH position, the two batteries are connected in parallel. This has a number of implications. Unless the batteries have exactly the same state of charge, the combined voltage to the two batteries in parallel will sag to a voltage somewhat lower than the highest battery's terminal voltage. Current from the higher voltage battery will flow into the lower voltage battery and begin charging it. As long as the state of charge in one battery is higher than the other, the lower battery is more of a load than a source of power. Eventually, the batteries will reach an equilibrium, and they will both have the same terminal voltage. At that point they will both tend to supply current to loads that are attached to them, and they will both receive charging current furnished by the engine.

It would seem like operating in the BOTH position would be beneficial, but that is not always the case. Even thought the batteries will eventually rise or fall to the same terminal voltage when connected together, they will not necessarily become exactly the same. A battery (or any source of electrical engery) can be though of as having an internal resistance. The lower this internal resistance the greater the current it can supply. The internal resistance will also affect how the battery absorbs charging current. Even though they are connected in parallel, it is possible that they will supply unequal currents to the loads, and it is also possible that they will accept unequal currents from an the engine charging source.

If the batteries are significantly different in their age, their type of construction, and their state of charge, this unequal distribution of current can be more significant. To describe the situation in the simplest of terms, when two batteries are connected in parallel, they will probably tend to behave more like the weakest battery of the two than the strongest.

Paralleling the batteries can come in handy in some situations. For example, both batteries may be discharged to a point where neither alone can provide enough current to crank the starter motor, but combined in parallel they can turn the engine over.

If one battery is fully charged and the other is totally discharged, connecting them in parallel (by using the BOTH position) can cause very high currents to flow between the batteries. Extreme heat can be generated by the sudden charging of the discharged battery. Use caution in this situation. It is better to recondition a discharged battery by slowly re-charging it with an AC-operated battery charger.

The arrangement of the contacts of the typical OFF-1-2-BOTH permits the operation of the switch in the range of 1-2-BOTH without ever disconnecting the batteries from the load or the outboard charging circuit. This is important, as it is possible to cause damage to the charging circuit if the battery is disconnected while the engine is running. By choosing the path of rotation of the switch, it is possible to change from 1 to 2 without moving through the OFF position.

[seaman-recruit]

Thanks Cymru - exactly the information I was looking for.

[sabinaa]

Could someone please elaborate on this?

I just had a 2nd battery installed with a switch. When they then installed the stereo, they switched to battery 1 only. This worked for a day, and then battery # 2 went dead (it wasn't charging). With battery 1 only, the stereo would no longer work right. So we switched to ALL - and now the stereo works great, and the boat starts fine. We also noticed that now battery #2 is charging again.

Is it dangerous to keep the switch set to ALL? What else can I do to optimize / manage my power?

[seapuppy]

well...first off...welcome to the zoo...2nd off...the #1) side of the batt's sw. should be for starting the boat...the #2) side is for running the house items..ie..radio...lights..etc....now if it's all working on both...then that's fine as they should both charge...but be aware if one batt goes south....it's going to drag the other one down...but it should be the opposite from what your hooked up with now..


SP

[shrew]

Do you have a 2 bank battery charger? Is it connected directory to both batteries? The position of the switch shouldn't dictate whether the charger is charging batteries. That is, unless there is no charger or the charger isn't working or it's not connected to both batteries.

[biggerseagar]

Yes Ditto..........During my lay-up period in the winter I leave my two batteries in the boat hooked and with one of the shore power cords connected to a 110 outlet with the charger on. I put both isolaters switches on off mode for the winter. The batteries have stayed charged all winter long with this method. When the boat is in the slip on shore power the isolater switches are in the both mode. I guess what I am saying is that if you don't what your batteries charging turn your baterey charger off because your isolater switch has nothing to do with if they are charging or not. The isolater switch distributes the power to the whatever it is connected too .....frig, engines, lights, pumps, etc etc.

Roger

[seaman-recruit]

Another related question from the newbie. If you have a dual battery configuration with one cranking and one deep-cycle battery is it normal to keep the battery switch in the "both" position while underway to use charging from the alternator to both batteries? I don't know if that loads the alternator too much or if deep-cycles want a reduced current level from a charger, etc.

[ss3964spd]

Jim,

If the two batteries are of the same type, lead acid for example, you can put the switch in the Both position to charge both batteries. Ditto if you are using a lead acid and an AGM. From what I understand the only time there is an issue is if you're using a Gel type battery which, evidently, don't play nice with LA or AGM when it comes to charging.

Still, there are exceptions to running on "Both", like if one of the batteries is significantly discharged. In that case it's best to start the engine on the good battery then switch to the other - so long as the other has enough juice to run the engine.

Dan

[seaman-recruit]

Thanks Dan. In my case they are both LA so I should be good to go excluding noted exceptions.