Help me understand ACR

suds1421

Seaman Apprentice
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Jul 6, 2018
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39
Good morning everyone,

I have a Four Winns I/O which came with a marine starting battery. I had a one year old deep cycle battery so I added a second battery with an isolator switch that allows to run off of battery 1, 2 or combined.

When we go out for the day I turn the battery selector switch to 1 or 2 and try to remember to use a different battery every time.

The reason for adding the battery was backup and try to avoid being stranded.

I'm looking at adding a stereo to the boat (the one in it is shot) that would run off of the deep cycle battery.

Help me understand how an ACR helps my situation. How does the ACR interact with the battery selector switch?
 

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dingbat

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Nov 20, 2001
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The only reason your flipping back and forth between batteries is for charging.

An ACR (automatic charge relay) keeps the starting battery at full charge then diverts the excess to house battery automatically.

The switch has on/off/both.

I turn the the switch on in the morning and off when I get back. Both is to combine batteries for those tuff, cold morning starts
 

suds1421

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Jul 6, 2018
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39
In looking at the diagram again, it looks to me like the purpose of the ACR is to charge both batteries whenever the alternator is charging?

This makes sense but in order to really take advantage of this system I'd need to separate house and starting loads. Currently the battery selector switch is connected to the large positive cable going to the motor and the "house" loads come off of the motor wiring.

I'd need to isolate those to the house battery to really have the advantage of the system pictured right?
 

dingbat

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In looking at the diagram again, it looks to me like the purpose of the ACR is to charge both batteries whenever the alternator is charging?

This makes sense but in order to really take advantage of this system I'd need to separate house and starting loads. Currently the battery selector switch is connected to the large positive cable going to the motor and the "house" loads come off of the motor wiring.

I'd need to isolate those to the house battery to really have the advantage of the system pictured right?
You are correct.
The only thing connected to my starting battery is the motor, chart plotter and vhf. Everything else is powered by house battery
 

suds1421

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You are correct.
The only thing connected to my starting battery is the motor, chart plotter and vhf. Everything else is powered by house battery

Thanks! The ACR would still help me without separating loads because it would ensure both batteries are getting charged. Boat is in storage but I'll have a look when I get it out and see how easy it would be to separate the house loads from the motor.
 

dingbat

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Thanks! The ACR would still help me without separating loads because it would ensure both batteries are getting charged. Boat is in storage but I'll have a look when I get it out and see how easy it would be to separate the house loads from the motor.

It only transfers the charge when the starting battery is fully charged and the line voltage exceeds x volts for a time period.

If demand is close to supply on the starting battery, you may or may not charge the house battery at any given time
 

Old Ironmaker

Captain
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Dec 28, 2015
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An ACR (automatic charge relay) starts

That helps. Learn something new everyday.

I always carry a fully charged good quality battery booster. Not just for our boat many times someone needs a boost out on the water. I've been caught with a dead battery because I had too many accessories on without the engine running. Luckily there was just enough juice to start the kicker when we were 10 miles offshore and not another boat within sight. .I buaght a battery booster the next day.
 

dingbat

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always carry a fully charged good quality battery booster.
I carry one as well, it’s called the house battery. Can’t forget it at home. Always charged when I go to use it ;)

Sizing the battery to the load is the key. I ran a starting and deep cycle for a number of years. Worked well until I added a backup chart plotter and upgraded to a 1kW sounder. After 6-7 hours of trolling the sounder would start acting weird and or shutdown.

Long story short, now running two grp. 27 deep cycles with an ACR. I can go 10 hours w/o an under voltage alarm. Simplified battery management tremendously
 

Mischief Managed

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I carry one as well, it’s called the house battery. Can’t forget it at home. Always charged when I go to use it ;)

Sizing the battery to the load is the key. I ran a starting and deep cycle for a number of years. Worked well until I added a backup chart plotter and upgraded to a 1kW sounder. After 6-7 hours of trolling the sounder would start acting weird and or shutdown.

Long story short, now running two grp. 27 deep cycles with an ACR. I can go 10 hours w/o an under voltage alarm. Simplified battery management tremendously

How do you recharge all that capacity?
 

briangcc

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2/3 bank battery charger would be my bet. Plug it in when you get to the dock and let it charge overnight.
 

H20Rat

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It only transfers the charge when the starting battery is fully charged and the line voltage exceeds x volts for a time period.
If demand is close to supply on the starting battery, you may or may not charge the house battery at any given time

ACR's only understand voltage, not state of charge of the starting battery. At least in my experience on my hard-to-start 1985 Ford 460 RV, the ACR will kick over to both battery banks a minute after starting the main engine, even if the engine was finicky and the starting battery is near dead.

My ACR has a minimum of 1 minute delay, and needs 13v. The required minimum to charge a battery is 12.9 volts, so unless the demand on the starting battery is equal or greater than the alternator, it is going to flip.
 

dingbat

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My ACR has a minimum of 1 minute delay, and needs 13v. The required minimum to charge a battery is 12.9 volts, so unless the demand on the starting battery is equal or greater than the alternator, it is going to flip.
Blues Sea add a battery spec
  • Closing voltage: 13/26V (2 min.) or 13.6/27.2V (30 sec.)
  • Opening voltage: 12.75/25.5V (30 sec.)
 

dingbat

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2/3 bank battery charger would be my bet. Plug it in when you get to the dock and let it charge overnight.
Well, you lost that bet.....lol

Apparently I’m one of the few that uses their boat
enough that the dedicated onboard charging system, aka alternator, does the job.

I’ll throw a charger on them maybe 2-3 times a year to top them off if I think about. Connect my vintage 1989 Craftsmen battery charger (6/12V - 2/10A) and forget about (sometimes literally, oops) it until the green light comes on.

Primitive by modern expectations but it works for me Currently working with battery date codes of 2010 and 2011
 

Mischief Managed

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Well, you lost that bet.....lol

Apparently I’m one of the few that uses their boat
enough that the dedicated onboard charging system, aka alternator, does the job.

I’ll throw a charger on them maybe 2-3 times a year to top them off if I think about. Connect my vintage 1989 Craftsmen battery charger (6/12V - 2/10A) and forget about (sometimes literally, oops) it until the green light comes on.

Primitive by modern expectations but it works for me Currently working with battery date codes of 2010 and 2011

Thanks for the reply.
 
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