Adding 3rd battery What charger do I need

[ditchsnake]

Yes I have been following the other threads but still can't figure it out. I've got 2 group 31 agm batteries. They are a year old and will buy a new one for starting. One start and one stereo. I keep them isolated with the factory supra acr. I'm going to get a promariner prosport 20 amp charger. Do I just need a dual bank charger? One for the starting battery and one for the two stereo batteries wired together. These maintain batteries but what happen when my system reaches 13.8 and the isolator opens. Won't the charger see this as just one giant battery and not two isolated. Or do I need to get a 3 bank charger? And if so, how do I keep the two stereo batteries isolated from each other.

[EarmarkMarine]

A 3-bank charger will give you no more isolation than a 2-bank charger when using only two banks. So a 3-bank charger is a waste in this case.
Yes, the ACR can 'combine' from the higher shore charging voltage which leaves you with one big bank and no charging isolation between the two banks.
There are several methods to correct this.
1) add a Blue Sea 5511e dual circuit manual switch to force isolation. In this application you will modify the Blue Sea instructions to obtain the desired result.
2) add a small manual disable switch to the ground of the ACR which fixes it to 'open'.
3) add an AC triggered relay that interupts the ACR ground when AC power that supplies the charger is sensed.
4) add a simple On/Off battery switch between the ACR and starting battery to force isolation.
5) switch the ACR over to a solenoid that is controlled by the ignition.
6) and so on....

David

[ditchsnake]

David you are two damm smart. "and so on" LOL. I understood #1. And thank you for your reply. At least I'm not a total idiot because I could at least see the problem. Could I set the acr I have now to off to keep it manually isolated?

[EarmarkMarine]

David you are two damm smart. "and so on" LOL. I understood #1. And thank you for your reply. At least I'm not a total idiot because I could at least see the problem. Could I set the acr I have now to off to keep it manually isolated?

Well, there truly is other methods also. The easiest is method #2 which is to add a standard marine or automotive SPST On/Off switch (a standard 15 amp switch is more than sufficient) to the ground wire of the ACR. Flip it 'Off' when you place the boat on the trailer and flip it 'On' when you splash the boat.

Now your question, "Could I set the acr I have now to off to keep it manually isolated?", suggests that your existing ACR is accompanied by a high current switch. However, BEP, Blue Sea, etc. have different wiring schemes. Rarely would setting the existing switch to 'Off' create any isolation because the ACR is typically positioned on the battery side of the switch. It's no extra trouble to change on an initial installation. Rather than change it after the fact, it could be easier to just follow method #2.

David

[ditchsnake]

Now I understand number two. That will be an easy and cheap fix. If I understood all of them I'm propably just kill myself. LOL

Well, there truly is other methods also. The easiest is method #2 which is to add a standard marine or automotive SPST On/Off switch (a standard 15 amp switch is more than sufficient) to the ground wire of the ACR. Flip it 'Off' when you place the boat on the trailer and flip it 'On' when you splash the boat.

Now your question, "Could I set the acr I have now to off to keep it manually isolated?", suggests that your existing ACR is accompanied by a high current switch. However, BEP, Blue Sea, etc. have different wiring schemes. Rarely would setting the existing switch to 'Off' create any isolation because the ACR is typically positioned on the battery side of the switch. It's no extra trouble to change on an initial installation. Rather than change it after the fact, it could be easier to just follow method #2.

David

[bhowell]

Prosport 30


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[mmandley]

WOW im glad my system is so much simpler.

I have the Pro Sport 20.
Side A goes to the house battery + -
Side B goes to the Stereo Bank + -

On my ACR I just leave it on ON

Put the boat in the garage plug the charger in.
Pull the boat out, unplug the charger.

On the lake, Do my thing and never have to touch anything..

[EarmarkMarine]

Mike,
Two things must be in place before you have true isolated dual bank charging. First, the Blue Sea relay must be wired in such a way (opposite side of the switch from the batteries) that it will be isolated from the batteries by the manual Blue Sea dual circuit battery switch. Second, the switch must be turned 'Off' when the boat is on the trailer and turned back 'On' when the boat is splashed. Shore charging dual bank isolation does not happen automatically.

David

[mmandley]

Mike,
Two things must be in place before you have true isolated dual bank charging. First, the Blue Sea relay must be wired in such a way (opposite side of the switch from the batteries) that it will be isolated from the batteries by the manual Blue Sea dual circuit battery switch. Second, the switch must be turned 'Off' when the boat is on the trailer and turned back 'On' when the boat is splashed. Shore charging dual bank isolation does not happen automatically.

David

Explain to me why it wouldn't charge like this?

On my battery charger it has separate leads for plus and minus, these are connected right to the banks, not through the ACR.

When the boat is in the water it does work as intended from the Alternator to the ACR and batteries. I have voltage read outs for both banks.

On my LSV i had a single charger and i had to open circuit breakers i installed in order to isolate the ACR in order to charge both banks.

I just want to make sure my wiring is correct other wise at the very least i know my Golf Cart batteries are super sweet, because they have more then 12hours play time and still read 12.4V sitting idle. With out the boat running.

[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.