Battery selector only works on "All" and "Off".

[LakeMich2760]

Both my batteries finally died so I went and purchased two new group 31's last week. Figured this would be a good time to start a new habit of running a house battery while on the hook and turning off a starting battery. This way I'd still have juice to start engines if the house goes dead while running fridges and radio on water.

I went to my battery selector and off kills entire boat and all juices everything. But if I put it on battery 1 or battery 2 everything still has power and I can still start the boat. So it doesn't seem they are wired independently. Is this something worth having a tech look at and reconfigure, or just leave alone? I don't need to open a can of worms.

Boat is a 1999 2760 Commodore

[Muddy Blues]

I went to my battery selector and off kills entire boat and all juices everything. But if I put it on battery 1 or battery 2 everything still has power and I can still start the boat. So it doesn't seem they are wired independently. Is this something worth having a tech look at and reconfigure, or just leave alone? I don't need to open a can of worms.

Assuming you have 1 guest switch and 1 engine, then this is working correctly.

When the guest switch is in the battery 1 position, battery 1 is the sole power source and battery 2 is isolated. This way you can't drain battery 2 while on the hook. In this config, battery 1 is your choice for the house battery, and battery 2 is your choice for the starting battery (i.e. isolated just in case you drain the house battery). Vice versa for the battery 2 position. If you have the switch to ALL, then you are drawing from both batteries and you can drain both while on the hook.

If you have twins and two guest switches, the scenarios are more complicated.

[Chris_in_Texas]

So you have a twin and only a OFF/1/2/ALL switch on one battery? That is very strange. That is typically only used on single engine boats. It would be very much a can of worms to open and expensive to do correctly. Would like to see a few pictures of the battery switch box and or the layout in the engine room if you could.

I am not sure in 1999 how they did but in the newer mid 2000's in the smaller twin engine boats they used three batteries in two separate battery banks. One would start engine 1 and generator, one would start engine 2 and be the "house battery." They had two switches (OFF/ON) and then they had a momentary battery parallel switch with large relay at the helm. Two batteries would be in parallel on the house bank/engine bank. This way there was more ability to be on the hook, but typically you might kill this bank so that is where the parallel switch comes in.

Ideally for a twin engine cruiser you would want the following:
1) Single battery bank for main engine 1
2) Single battery bank for main engine 2
3) Larger bank either one or two batteries for the house battery.

If you had a genny then you would use either of the main engine batteries for starting that. You would also have a parallel switch that goes between the two engine batteries in case one dies.

Then you would want to use automatic charging relays (ACRs) to charge the batteries off of both engine alternators (older boats used battery isolator (2 inputs and 2 outputs). Newer boats don't use the isolators anymore and only have ACRs as there isn't any voltage drop across them. Then you would have a three bank battery charger as well for AC power. Each battery is separate from each other so no one battery can drain another. That way the house battery is the house battery only.

[LakeMich2760]

I have twin Volvo 4.3's and two batteries.

From what I understand asking around, there are three ways this can work:

1) Switch set to "all" utilizes both batteries
2) Switch set to "1" only utilizes one battery which will start both engines and run entire house. Second battery is not utilized.
3) Switch set to "2" only utilizes one battery which will start both engines and run entire house. Second battery is not utilized.

If that is truly how things work, then I'm okay with it. My biggest concern is not draining two batteries at once with house items while on the hook. I may have to dig deeper, but if its wired up like I've mentioned in this post, then while on hook I can move selector to 1 or 2 and achieve what I'm after. I have not yet tried to start both engines while selector is on just one 1 or 2 yet. Plan on that this weekend.

[stitchsc]

1) Switch set to "all" utilizes both batteries
2) Switch set to "1" only utilizes one battery which will start both engines and run entire house. Second battery is not utilized.
3) Switch set to "2" only utilizes one battery which will start both engines and run entire house. FIRST battery is not utilized.

I don't have twins but this is how my rig is set up and runs....

[gofast24]

My thoughts = if it were me I would have 3 batteries, one for each propulsion engine (then you could parallel both from the helm parallel switch) and a 3rd as a house battery, i.e. no connection between the engine starting batteries and the 3rd house battery. In our case we have two Group 34 AGM starting batteries (one for each engine and capable of paralleling from the helm) and a group 8D AGM house battery (really big guy) . Feel much better knowing with all the DC loads on the hook and gen not running that we cant kill either one of our engine starting batteries. Also, we have 3 battery disconnect switches, one for each of the three batteries for safety if something goes wrong with any one of them or to shut off if doing any wiring /service on the electrical system..

[kthurt]

My 2000 2760 is wired just as you describe. I do have a generator; hence, have no room for a 3rd battery....plus, I don't think I could even fit bigger batteries....I believe mine are 27s. I've had the boat 9 years and have never operated with the switch in All. This ensures you don't ever run both batteries down. I run either 1 or 2 and change the position about once a month. I have run deep cycle batteries for nearly the whole 9 years. They have always provided sufficient starting current and, being deep cycle, handle a significant draw down without deteriating the battery life. My current batteries (from Walmart) are 4 years old with not signs of end of life.

[LakeMich2760]

Yup, we have 95% the same boat. No generator here.

Great to know! I'll start doing the same thing this weekend. They should both charge via the shore power batt charger no matter if switch is on 1, 2 or all it seems.

Thanks!

[tlc118]

While I only have one engine my setup is the same.
When I'm home, plugged in to shorepower, I run the fridge (12v) with the charger (to maintain the batteries and the fridge) with the selector on "ALL", with each battery supplying half the power to the fridge.
When we go to the lake I'll switch to one battery, alternating 1 or 2 each trip.
The Charles charger is wired up to both batteries directly, so it doesn't matter where the switch is.
I believe the alternator only charges through the switch.

[Seven]

I had the same setup on my last boat with single engine. I would switch between battery 1 and 2 each week.
I would not recommend deep cycle batteries, dual purpose batteries are designed for this configuration. My Volvo manual actually stated not to use deep cycle batteries because they do not provide enough amperage while cranking to run the computer. Doing so could fry the computer. You are probably okay when the batteries are new but when they get older or run down they may not provide enough voltage to the computer. I rather not risk the $$$ for a new cpu to have an extra hour or two on battery.
Get yourself some good agm batteries and they work great for both starting and deep cycle. I had optima's not the deep cycle models and they were awesome. Also get a remote voltage gauge if you do not have one to keep track of voltage so you don't run them down too much.

[gofast24]

I had the same setup on my last boat with single engine. I would switch between battery 1 and 2 each week.
I would not recommend deep cycle batteries, dual purpose batteries are designed for this configuration. My Volvo manual actually stated not to use deep cycle batteries because they do not provide enough amperage while cranking to run the computer. Doing so could fry the computer. You are probably okay when the batteries are new but when they get older or run down they may not provide enough voltage to the computer. I rather not risk the $$$ for a new cpu to have an extra hour or two on battery.
Get yourself some good agm batteries and they work great for both starting and deep cycle. I had optima's not the deep cycle models and they were awesome. Also get a remote voltage gauge if you do not have one to keep track of voltage so you don't run them down too much.

From experience, I doubt that low voltage while cranking one engine will cause the ECU unit to fail, maybe just not supply enough current to do it's start/run function to get the engine going (electric fuel pump, injectors, gauge loads, etc). Agree with the AGM batteries. I now have 4X AGM, 2X group 34 (engine starting), 1X group 8D (house) , and 1X group 24 for the gen set. Our Charles battery charger takes care of the 2X starting and 1X house batteries (switch set to AGM on the back of the charger) and the gen set takes care of itself via built in battery charging system when running (no way to set it to AGM or flooded) but it is doing fine after 4 years. i would definitely have a separate AGM battery just for house loads, I wouldn't like having one of your two engine starting battery's (if you have two) to also supply the house loads! With all of our DC house loads off of shore power or on the hook without gen running the big 8D can drop to 50% discharge voltage (12.4 VDC) in 3 to 4 hours with the audio cranking!

[Chris_in_Texas]

While I only have one engine my setup is the same.
When I'm home, plugged in to shorepower, I run the fridge (12v) with the charger (to maintain the batteries and the fridge) with the selector on "ALL", with each battery supplying half the power to the fridge.
When we go to the lake I'll switch to one battery, alternating 1 or 2 each trip.
The Charles charger is wired up to both batteries directly, so it doesn't matter where the switch is.
I believe the alternator only charges through the switch.

Be careful on the "ALL" position for long term, its not good to do. If one battery goes bad the other will follow as you are paralleling them. As an example if one cell shorts out it will pull the other battery down to it and keep it there as well. The other battery can actually supply full current into the shorted battery and bad things can happen if the "bad" one would overheat. It will also start to generate huge amounts of hydrogen off-gas during that situation as well and things can go boom. This is why its smarter to use large 6v batteries in series if you need a capacity increase instead of paralleling them up with two 12v. Obviously that will only work to a point and at some point for a large bank you will both have to parallel and series them.

If you are plugged into shore power then the charger will supply 100% of the power to the fridge, leave the selector in the 1 or 2 position only. The output voltage will increase on the charger, taking over for any loads that are "on" while its powered up to its rated capacity. The only reason to leave it on position 1 or 2 would be that way if AC power goes out, it will run the fridge it until it AC power is restored.

You are correct the charger should be wired on the battery side of the switches. And the alternating between 1 and 2 is correct as well as it keeps them both exercised. If on the charger full time make sure that you check the fluid levels as well if they are flooded cells. The chargers can tend to boil them off sometimes, and that can be due to the above if other things are running the voltage will increase on the charger which depending on how long thats for can slightly overcharge the batteries causing the boil down.

[gofast24]

Agree, regarding boil out that is why I switched to all 4X AGM batteries, old flooded batteries used as a core charge rebate when buying the AGM's. Question = If the vessels battery charger is connected to the "bat" side of the switches what difference would it make whether switch(s) were set to 1/2/ or all, they would all be receiving a charge from the "house battery charger and it would provide power to any ancillary loads drawing current?

[tlc118]

Thanks Chris for the advice. I am running two group 31 AGM batteries. Boil off was one of the reasons I upgraded to AGM.
While the Volvo AND Mercury both say not to run deep cycle, everyone's in our group actually came with deep cycles installed.
A couple of them were new boats, direct from dealers.