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Old 10-02-2020, 01:56 PM   #1
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City: La Conner, WA
Vessel Name: Agnus Dei
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ACR or not

Hi All,

Hope your summer of boating was fun and safe. We are done with summer adventures and now off season maintenance etc. begins.

I installed a new 50A charger last year and hooked it up to 1 battery bank. The boat had an ACR I’m guessing because the old charger/inverter from the dark ages only had one charger circuit. My question is why shouldn’t I hook the charger up to both battery banks
and do away with the ACR? It would never function if both batteries were being charged, no?

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Old 10-02-2020, 03:11 PM   #2
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It depends on the charger and whether it controls each output separately. My older ProMariner charger would control off the battery with the highest charge, which unfortunately was a group 24 generator battery instead of either of the 8D batteries that were also connected, leaving them always undercharged. I've since redone everything with a large house bank and common start battery for both main engines and the generator. I feed the charger and one alternator to the house bank, the other alternator to the start battery and use an ACR to combine them.

RC at has some great discussion about smart chargers and ACRs.

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Old 10-02-2020, 03:45 PM   #3
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Not necessarily. Think about ALL your charging sources when you think about the ACR, and what about when you are using alternators or, if you have it (or in the future) solar.

Typically, what you find is your house bank regularly needs the most charge amps and that is what your charging sources should be hooked to. The start batteries, while using a LOT of amps, use them for a short period of time and need relatively little charging.

Usually, the ACR is a preferred way to go in "modern times". There are some who are advocating that newer battery isolators can do the job because their techonology has caught up (older battery isolators used diodes that consumed a LOT of power.)

Check out Pacific Yacht Systems youtube videos and look for both ACR and isolator videos.

On NWD, we have a large start battery connected only to the twin lehmans. The start battery cannot power ANYTHING else on the boat (unless connected manually to the house batteries as described below.)

We have a very large (800 Ah in lead acid GC2 batteries) battery bank that our charging sources are connected to (alternators, AC charger, and soon the solar.) This puts all of the charging directly into the battery bank that always needs the most amps.

We also have a third battery, an independent start battery for our genset. It cannot be manually connected to any other battery. We could, in a pinch, manually remove it, and manually connect it to the engines to attempt to start them.

We have a ACR than connects the start bank to the house bank whenever enough charge voltage is present to charge. Our genset start battery is connected to the engine start by an echocharger, which is a low current version of an ACR.

The ACR and echocharger are all automatic, and activate when there is sufficient charge voltage. Both have smart profiles. We have no 1/2/both switches on board.

Our ACR allows us a manual (switched) cross connect to connect the house and start batteries in case of a start battery drain/failure. In case of an ACR failure AND a start battery failure, I would have to physically jump a connection between the ACR (about 4 inches apart.

In the engine room: this is an old photo. Ignore the breaker attached directly to the ACR, this was removed and properly routed... You can see half of the Echocharger to the left of the Xantrex ACR. The Echocharge exists to keep the genset battery charged / topped off / floated.

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Our lower helm overhead panel: Roughly center is the control panel for the Xantrex ACR. It shows green when charging voltage is present and the house/start batteries are connected for charging. It has a manual switch for me to manually connect the house and start batteries in the event of a dead start battery. There is a second manual switch on the ACR itself in the engine room.

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I don't know that I have the most advanced/best charging system. It may be that a more modern (like the modern Victron isolator) system would be better, but the concept is the same - the charging systems ALL input to one point, and charge the batteries to a common distribution, whether it is an ACR or a modern efficient (no diode loss) isolator.

All I know is this - I have a monitor for all three of my battery systems. I have no switches to regulate charging. I have no issues with them being automatically charged.

my 2c. FYI I inherited this system from my PO, and have only upgraded the size of my house bank, cleaned up the installation, and verified what I know about it. I've added a missing fuse at the hose bank, and am adding a house bank remote shut off switch.
"There exist minds that think as well as you do, but differently."
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Old 10-03-2020, 05:38 AM   #4
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The big fear with a single charger hooked to all the batts is if a single cell dies in one batt ,all may be boiled out with an overcharge.
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Old 10-03-2020, 10:39 AM   #5
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I prefer Smart ACRs, Echochargers and DC toDC chargers over standard ACRs. You are a lot less likely to shorten the life of dissimilar batteries.
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