Adding a third battery and second switch question...

[PaulyB]

I currently have two Group 31 AGM stereo batteries and one group 24 house battery. I have a Group 29 Acid battery sitting not being used. I can get about 6-7 hours out of my stereo right now before my batteries are drained. I would like to change my group 24 house battery to my spare group 29 battery that isnt being used. I have drawn a schematic and am wondering if anyone could tell me if it would work the way I would like it to. Since the 3rd battery is a lead filled not AGM battery, I dont want to combine it with the stereo batteries. I am wondering if I can connect my House battery to a blue seas switch at the "common" connection, connect the "battery one" post to the "common" post on my stereo switch, and connect my starter circuit on the "battery two" post and it work as if when I have it on 1 it will send power from my house battery to the common post on the stereo battery switch, and when I have my house battery switch on battery 2 if it will send the power to my starter circuit only. Then I can turn the stereo switch to off and be running off my house battery... I have attached two files to show what I am talking about for reference.


Current set up

Proposed set up.

 

[PaulyB]

I think I solved my own question... I am just going to leave the Battery hooked straight to the starter circuit and have an On/off battery switch connected between a battery cable going from the Starter battery to the common post on the the House circuit switch....

 

[txav8r]

Your probably going to find your start battery depleted at some point using it as a backup. If you want to use it to supplement your setup, Using an ACR or VSR would be a better way to get a little extra during the day. But you have safeguards with that setup that will keep two very different battery banks from combining based on voltage tolerances. In your proposed setup, you have no safeguards. And you have two vastly different battery banks with one lead acid bank and one bank of AGM's.

 

[David Analog]

I don't see the need for the extra complications. Why not just a single dual battery switch or a dual circuit battery switch plus an ACR/VSR?
I would want to service the batteries while underway throughout the day and before any stay at rest. I would want to protect my stators. I would want a safety power cut-off when in storage. A very simple scheme will accomplish all these goals.
Mixing the two banks of dissimilar chemistry while underway doesn't bother me. There's only a fractional difference between the optimum voltage levels that these two types are intended to see. And that is a minor sin as compared to any scenario with two banks off one boat charging system, which is automatically flawed out of the gate. It's not as serious as the importance of having a shore charger with different settings for each bank. The boat charging system is a blunt device anyway where as the smart shore charger should be very precise.
Keep in mind that the exact same chemistry batteries (type, size, age, etc.) used separately for stereo deep cycling and starting will not have the same internal impedance for very long because they are used so differently.
I'm not sure what indicator you are using for "....batteries are drained". It should not be when the audio system shuts down. It should be when the batteries reach a 50% depletion level as measured which is 12.0 volts.

 

[Julian]

I would think your current setup at top would be the best. No chance of depleting your starter battery at all. The next best option would be to have a house/starter setup where you have a 2 bank isolated system with ON/OFF/COMBINE in the event your ever needed power from your house batteries to start the boat. On/Off would turn on/off both banks, and combine would provide that emergency option.

Like this (just with two batteries on the left and using the switch on the upper right)

 

[PaulyB]

I don't see the need for the extra complications. Why not just a single dual battery switch or a dual circuit battery switch plus an ACR/VSR?
I would want to service the batteries while underway throughout the day and before any stay at rest. I would want to protect my stators. I would want a safety power cut-off when in storage. A very simple scheme will accomplish all these goals.
Mixing the two banks of dissimilar chemistry while underway doesn't bother me. There's only a fractional difference between the optimum voltage levels that these two types are intended to see. And that is a minor sin as compared to any scenario with two banks off one boat charging system, which is automatically flawed out of the gate. It's not as serious as the importance of having a shore charger with different settings for each bank. The boat charging system is a blunt device anyway where as the smart shore charger should be very precise.
Keep in mind that the exact same chemistry batteries (type, size, age, etc.) used separately for stereo deep cycling and starting will not have the same internal impedance for very long because they are used so differently.
I'm not sure what indicator you are using for "....batteries are drained". It should not be when the audio system shuts down. It should be when the batteries reach a 50% depletion level as measured which is 12.0 volts.

I don't see the point of the VSR... It costs almost 100 dollars and there isn't enough benefit. The stators don't have enough output to charge my house batteries at all while my system is running so why waste the money? For the most part all I do is go to a sand bar at my local lake and hang out for 8 hours playing music. I have voltage meters installed in my boat so when the two house batteries get down to 12.0v, I know to turn my radio off. All I want is enough reserve power so if I am at a sand bar for 8 hours playing my stereo, I can switch the house batteries off and play off my starter battery for the last hour or so. I always have a jump pack, but I don't think I would run the starter battery down in an hour anyway. I also carry a generator on days I know I will be out for a long time, so I can hook up my on-board charger and charge my batteries if I need. I figured for 25 dollars (the cost of the switch) I could make this work the way I would like. I have plenty of leftover 1/0 guage cable from when I installed my stereo last year. Just for reference I don't know if you have seen my thread... https://jetboaters.net/threads/i-love-it-when-a-plan-comes-together.5016/

I would think your current setup at top would be the best. No chance of depleting your starter battery at all. The next best option would be to have a house/starter setup where you have a 2 bank isolated system with ON/OFF/COMBINE in the event your ever needed power from your house batteries to start the boat. On/Off would turn on/off both banks, and combine would provide that emergency option.

Like this (just with two batteries on the left and using the switch on the upper right)

I already have the Off, 1, 2, 1+2 switch, so essentially I would just be adding the on/off and it would work the same way, the only difference would be that with the start circuit left hooked straight to the battery, I could turn the battery switch off and my electronics (bilge pump and Garmin) would still have power...