Adding 3rd battery What charger do I need

Mike,
Mike explained it very well.
Here's a little background.
Blue Sea originally recommended that a single bank charger feed the auxilary battery and that the starting battery would be maintained through the combined relay. But they didn't envision these Add-A-Battery kits being used for more than light instrumentation, such as a chartplotter/fishfinder/GPS/etc. They never used the kit, for example, as a link to combine a large capacity trolling motor bank with the rest of the charging system and they didn't envision the inequity in battery banks as applied to large audio systems. So, even Blue Sea has modified their recommendation to address what we have been doing for many years now.
If you followed the Blue Sea instructions, which is certainly understandable, then we can give you simple instructions for the mod so that a flip of the switch will give you total dual-bank isolation while in storage.

David

Quote:

---

Originally Posted by MLA

Mike,

Next time you are on the water with the engine running, pop your head in and look at the ACR to see if the green Combined light is illuminated. This means voltage from the alternator is passing through it and both batteries are combined and receiving a charge.

Next time the boat is back in its resting spot, like now i guess, plug in the charger, wait about 5 or so minutes and again look for the green light on the ACR. If its illuminated, then your system is not wired to the most optimal configuration. This light being on indicates thet the on-board charger is causing the ACR to combine the battery banks into one large battery.

When you have a dedicated stereo bank and dedicated starting bank, as you do, these banks are used in entirely different ways. They see different loads and different degrees of depletion. For this reason, they need to be recharged differently. This is the main reason for using a 2 or 3 bank charger as opposed to a single bank. A good 2 bank has the ability to monitor and charge the 2 banks differently. If yours is wired as I think it is, your 2-bank charger is working as a single bank when the ACR combines.

---

This makes since. I am headed to the lake now, so i will look at this, and then when i return home tonight and its in the garage i will check it again.

Thanks.

Something must be happening because I'm actually following this conversation. I tried this with a portable charger. At 13.8 volts the relay opened and charged both batteries and must see it as one large bank. Clipped the ground sensing wire and batteries isolated. I'm gonna buy the charger and a switch to interupt the ground sensing wire. On to chargers. Dual bank for me but I'll have two group 31 agm's on one bank. Prosport 20 or plus and someone mentioned the prosport 30. Which one? Thanks Gene

Quote:

---

Originally Posted by MLA

Mike,

Next time you are on the water with the engine running, pop your head in and look at the ACR to see if the green Combined light is illuminated. This means voltage from the alternator is passing through it and both batteries are combined and receiving a charge.

Next time the boat is back in its resting spot, like now i guess, plug in the charger, wait about 5 or so minutes and again look for the green light on the ACR. If its illuminated, then your system is not wired to the most optimal configuration. This light being on indicates thet the on-board charger is causing the ACR to combine the battery banks into one large battery.

When you have a dedicated stereo bank and dedicated starting bank, as you do, these banks are used in entirely different ways. They see different loads and different degrees of depletion. For this reason, they need to be recharged differently. This is the main reason for using a 2 or 3 bank charger as opposed to a single bank. A good 2 bank has the ability to monitor and charge the 2 banks differently. If yours is wired as I think it is, your 2-bank charger is working as a single bank when the ACR combines.

---

Gene,
Typically a Group 31 AGM is about 105 amp/hours. Two in parallel will be 210 amp/hours. A Group 24 starting battery will be about 65 amp/hours at minmum. So the collective amp/hours will be 275+. For proper desulphation after deep cycles I recommend a 30 amp charger. A 20 amp charger is lite. If you have an AGM starting battery also, so all battery chemistries are the same, then we use the Intelli-Power 30 amp.

David

I visited one of the largest battery shops in Denver today and it supprised me how little they know about what we are talking about. I spoke to the owner who claims to know it all. He did bring up a good point though about why I would want to shore charge my starting battery as all it's used for is starting and factory electronics and is charged up quickly by my alt. . My head unit and all amps are powered off of my house battery. What do you guys think about that. If so what charger would work good for charging 2 group 31 batteries wired in paralell (+ to+ and -to-). Could I use a dual bank 20 amp charger hooked to each battery giving each one 10 amps? I was following this last night but am lost today? Thanks
's

Ditch,

during the normal season when the boat is used on a regular basis, there will typically not be a need to recharge the main cranking battery on 99% of boats with properly configured dual battery setup. The real advantage to having and dual bank charger thats hooked to both the main and the house bank, is when the boat is put up for the winter. A quality marine on-board charger will maintain both banks during the off season.

You would have to consult the particular charger manufacturer about combining the main and house outputs of a 2-bank charger. Many have dedicated main and house outputs, more amps going out on the house side as its typically the one that will be run down. Some sense the level of each bank and distribute on demand. Not sure how that might work with the 2 house batteries wired in parallel. You could go with a single bank, or put in a simple ON/OFF switch in between the 2 house bank batteries and open the switch for charging.

Great advise MLA. I bought a bass pro dual bank 20 amp charger. Their tech told me they are made by promariner. I just wired it to each of the house batteries wired parrell. . Their tech pulled out the instruction sheet and the manifacturer says it's ok to do so. Works great. Bass pro stuff has such a great return policy. I've never had an issue. Even when it's past warrenty. Thank you guys

Quote:

---

Originally Posted by MLA

Ditch,

during the normal season when the boat is used on a regular basis, there will typically not be a need to recharge the main cranking battery on 99% of boats with properly configured dual battery setup. The real advantage to having and dual bank charger thats hooked to both the main and the house bank, is when the boat is put up for the winter. A quality marine on-board charger will maintain both banks during the off season.

You would have to consult the particular charger manufacturer about combining the main and house outputs of a 2-bank charger. Many have dedicated main and house outputs, more amps going out on the house side as its typically the one that will be run down. Some sense the level of each bank and distribute on demand. Not sure how that might work with the 2 house batteries wired in parallel. You could go with a single bank, or put in a simple ON/OFF switch in between the 2 house bank batteries and open the switch for charging.

---

Gene,
I'll give you one scenario to consider with a manual dual battery switch. You are at rest for a long period. You run down your stereo bank. Before starting you combine the two banks with the switch. The two banks rapidly attempt to equalize.
It is a short distance and time back to the ramp and trailer. Much of it is through a no wake zone at low rpm. You are sitting at idle for a long time at the ramp while a guy and his girlfriend are arguing about getting the boat loaded on the trailer. The starting battery is discharged and you have not burned enough gas to restore it via the alternator. That justifies charging the starting battery with the AC shore charger.
Now an ACR minimizes the rapid equalization scenario.
Most Promariners are 'distribute on demand' so you have not diminished it's current capacity to the collective stereo bank when wiring one charger bank to each battery bank.
Don't forget that batteries can self-discharge several percent per month over the long winter.
Use a dual bank charger in the dual bank mode. Two identical batteries in parallel on one bank should be considered as one larger battery. There is no upside in dedicating the entire charger solely to the stereo bank.

David

David if i'm getting you correctly your telling me to wire one bank to the starting bank and one to the stereo bank. When the starting bank is full it'll send the 20 amps to the stereo bank instead of just 10 amps. I do have an acr which if i kill the stereo bank I still dont switch to both. I tried sending you a pm but your box was full. My 10w6v3s sound great. Very noticable improvement. Set lp and hp like you recommended and it flat pounds. Even the wife was impressed. She wouldn't be though if she knew what it cost Thanks, very happy. Gene

Quote:

---

Originally Posted by EarmarkMarine

Gene,
I'll give you one scenario to consider with a manual dual battery switch. You are at rest for a long period. You run down your stereo bank. Before starting you combine the two banks with the switch. The two banks rapidly attempt to equalize.
It is a short distance and time back to the ramp and trailer. Much of it is through a no wake zone at low rpm. You are sitting at idle for a long time at the ramp while a guy and his girlfriend are arguing about getting the boat loaded on the trailer. The starting battery is discharged and you have not burned enough gas to restore it via the alternator. That justifies charging the starting battery with the AC shore charger.
Now an ACR minimizes the rapid equalization scenario.
Most Promariners are 'distribute on demand' so you have not diminished it's current capacity to the collective stereo bank when wiring one charger bank to each battery bank.
Don't forget that batteries can self-discharge several percent per month over the long winter.
Use a dual bank charger in the dual bank mode. Two identical batteries in parallel on one bank should be considered as one larger battery. There is no upside in dedicating the entire charger solely to the stereo bank.

David

---

Gene,
"David if i'm getting you correctly your telling me to wire one bank to the starting bank and one to the stereo bank. When the starting bank is full it'll send the 20 amps to the stereo bank instead of just 10 amps."
The above is true. A single bank from this particular charger does have the ability to send a majority of it's collective amperage capacity to the bank most in need.
You do need to make certain that the ACR is frozen open while you are AC shore charging so that the charger can operate as two discrete banks and so that the ACR will NOT close/combine thereby circumventing the dual bank isolation.

David