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minnmarker

Dual Battery with #6 wire?

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minnmarker

So here's the situation.  I bought a new pontoon which has #6 copper between the battery compartment and the helm station as part of the standard wiring.  Running additional wire will be difficult or impossible because of the under sheeting and other pontoon construction.  The factory said they will not run larger gauge wires for me.

I would like to put a battery in the helm station to run stereo amps (with probably #4 wire to the amps), and charge the battery off the outboard's alternator.  I think an ACR would be good but am concerned the wire won't handle the amperage if the stereo battery gets discharged much and then the circuit closes when I start the engine.  Does anyone know if the Blue Sea ACR, when in the charge mode, connects the batteries directly (no resistance between batteries) or if it just splits the alternator output, which is 60 amps (doable for #6 stranded I think)?

What would the current between the batteries be if the engine start battery was at, say, 13.2 volts (the highest I have seen) and the stereo battery was at 9.9 volts (the amps are supposed to cut out at <10 volts so it should not go lower)?

Can you think of any way else to charge the stereo battery off the alternator?

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minnmarker

One hour bump.  Any EE's out there?

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MLA

On some of those toons with the bottom closed in, the deck side caps (or rub rail if you like) detaches to access the cable raceway. 

The ACR is an electo-mechanical relay, and the house bank gets paralleled to the main. The ACR is not distribute on  demand, just allows charge from side A to pass through to side B when closed. The main should already be getting alternator charge. 

What size engine/alternator? One issue with house banks that get deeply cycled and smaller outboard staters, is the heavy load that house bank puts on them once you pull up anchor. I prefer a traditional 1/2/BOTH/OFF switch, and no ACR. Mount 2nd battery and switch back by original battery. Run my amp cables to helm. When the house bank is run deep all day at the party cove, simply turn the switch to main cranking bank, fire up engine and return to dock, plug up shore charger. The heavy load of that dead battery is never introduced to the stater. 

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minnmarker
1 hour ago, MLA said:

On some of those toons with the bottom closed in, the deck side caps (or rub rail if you like) detaches to access the cable raceway. 

The ACR is an electo-mechanical relay, and the house bank gets paralleled to the main. The ACR is not distribute on  demand, just allows charge from side A to pass through to side B when closed. The main should already be getting alternator charge. 

What size engine/alternator? One issue with house banks that get deeply cycled and smaller outboard staters, is the heavy load that house bank puts on them once you pull up anchor. I prefer a traditional 1/2/BOTH/OFF switch, and no ACR. Mount 2nd battery and switch back by original battery. Run my amp cables to helm. When the house bank is run deep all day at the party cove, simply turn the switch to main cranking bank, fire up engine and return to dock, plug up shore charger. The heavy load of that dead battery is never introduced to the stater. 

Thanks.  That is what I thought the ACR did but was not sure.

It is a 150hp Merc with a 60 amp alternator.  I cannot run the amp power supply cables to the helm as noted above.  The current between batteries should be less than between the battery and the amps (about 1,000 watts rms Class D total)?  I know what you mean with the deck side caps but they do not wrap around the stern or bow, and the battery compartment is on the port side and the helm is starboard.

I had the same setup on my "old" I/O pontoon with a 45 amp alternator and never had a problem with alternator strain - that I know of.  It was/is a big deep cycle Group 27 that never got very discharged.

So do you think with a voltage differential of about 3.5 volts max that there will be an over current situation?  Or will #6 be OK?

Edited by minnmarker

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MLA

Im missing what you mean by the voltage differential of 3.5V. There should never be a difference of voltage anywhere that greater then .5v. 

As to the 6ga helm BUS supporting a battery thats powering any more then a micro/pocket amp. Ill never do it. Its carrying 99% of the boats electrical loads. It was not designed to handle much more then factory options. 

Once the side caps are off, fishing across the boat under the floor between the joists, is a breeze.  

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minnmarker
3 hours ago, MLA said:

Im missing what you mean by the voltage differential of 3.5V. There should never be a difference of voltage anywhere that greater then .5v. 

As to the 6ga helm BUS supporting a battery thats powering any more then a micro/pocket amp. Ill never do it. Its carrying 99% of the boats electrical loads. It was not designed to handle much more then factory options. 

Once the side caps are off, fishing across the boat under the floor between the joists, is a breeze.  

3.5 is the max difference between the starter battery voltage and the lowest voltage of the stereo battery.  I'm assuming that a greater difference would result in a higher current between the batteries when the ACR circuit closes.

You are right about the 6 gauge being for the stock stereo and other factory loads but I think it is over engineered.  If I don't run the power Bimini at the same time the battery is charging it might not be a problem - but then again, it might, and I don't want any inaccessible wires melting!

Yes, I looked at fishing and plan to do that with the sub woofer line but it looks difficult to put a pair of large gauge wires between the batteries since they are on opposite sides of the boat.  Will take another look at doing that with some larger wires.  Good idea.  That's probably what I'll try to do.  Do you think #4 would be adequate?

Thanks for your help.

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jtrezon

I believe the OP said the new “house” battery would be located at the helm station.    In that case.... the new “house” battery should then supply both the helm power distribution as well as the stereo.  The #6 wire would then only be used for the charging current from the ACR...which I would think would be fine in this case.   The ACR would be located near the “starting battery”   

I would only assume the ground wire is also #6. I don’t know how toons are wired but a lot of metal to help with common ground.  The ACR does need a good common ground to both batteries.  

It is recommended to connect the start isolation circuit for outboards in this case (outboards typically utilize a single wire for both starter and alternator).  

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minnmarker
8 minutes ago, jtrezon said:

I believe the OP said the new “house” battery would be located at the helm station.    In that case.... the new “house” battery should then supply both the helm power distribution as well as the stereo.  The #6 wire would then only be used for the charging current from the ACR...which I would think would be fine in this case.   The ACR would be located near the “starting battery”   

I would only assume the ground wire is also #6. I don’t know how toons are wired but a lot of metal to help with common ground.  The ACR does need a good common ground to both batteries.  

It is recommended to connect the start isolation circuit for outboards in this case (outboards typically utilize a single wire for both starter and alternator).  

There are 2 #6 wires (ground, +) between the starter battery and the house buss (perhaps future battery).  Between engine and starter battery there is one wire.  I think it is a 2/0.  Ground is through the hull.

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minnmarker
19 minutes ago, jtrezon said:

I believe the OP said the new “house” battery would be located at the helm station.    In that case.... the new “house” battery should then supply both the helm power distribution as well as the stereo.  The #6 wire would then only be used for the charging current from the ACR...which I would think would be fine in this case.   The ACR would be located near the “starting battery”   

I would only assume the ground wire is also #6. I don’t know how toons are wired but a lot of metal to help with common ground.  The ACR does need a good common ground to both batteries.  

It is recommended to connect the start isolation circuit for outboards in this case (outboards typically utilize a single wire for both starter and alternator).  

Now that I think about it, perhaps I could use both #6 wires for the + and ground through the hull?

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MLA
20 minutes ago, minnmarker said:

3.5 is the max difference between the starter battery voltage and the lowest voltage of the stereo battery.  I'm assuming that a greater difference would result in a higher current between the batteries when the ACR circuit closes.

Still a little fuzzy on where the 3.5 is coming from. If you are running that house bank down to 9.3 (12.8 - 3.5 = 9.3), that house battery will be done for by mid season, not to mention placing a huge demand on the alternator every time you pull anchor and restart the engine. 

25 minutes ago, minnmarker said:

but I think it is over engineered. 

This is a rarity, especially in regards to accessories. 

28 minutes ago, minnmarker said:

Do you think #4 would be adequate?

Sticking with your plan on battery placement and the alternator's rated output, 4ga is likely good for even a 28ft pontoon. 

 

34 minutes ago, jtrezon said:

the new “house” battery should then supply both the helm power distribution as well as the stereo.  The #6 wire would then only be used for the charging current from the ACR...which I would think would be fine in this case.

I get where you are going. The helm loads are what I would call active loads. Meaning they only require more output from the alt, when they are in use. A house battery/stereo, can be a passive load. If you sit at anchor and run the house battery down, it will trigger the alt to go into high gear, once the engine is re-fired. At this point, the house battery is a liability, not a contributor to the helm . The helm supply cables may not have been intended to carry the potential of the alternator, because those helm loads could NEVER draw to the potential of the alternator. Adding a house battery and audio amp on to that helm cable, could be pushing it. Cable is cheap, and I aint met a toon I couldn't wire yet.  

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MLA
26 minutes ago, minnmarker said:

and ground through the hull?

Not sure what was meant by the lots of metal comment, but boats do not have a chassis ground plane like cars.  

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minnmarker
9 minutes ago, MLA said:

Still a little fuzzy on where the 3.5 is coming from. If you are running that house bank down to 9.3 (12.8 - 3.5 = 9.3), that house battery will be done for by mid season, not to mention placing a huge demand on the alternator every time you pull anchor and restart the engine. 

This is a rarity, especially in regards to accessories. 

Sticking with your plan on battery placement and the alternator's rated output, 4ga is likely good for even a 28ft pontoon. 

 

I get where you are going. The helm loads are what I would call active loads. Meaning they only require more output from the alt, when they are in use. A house battery/stereo, can be a passive load. If you sit at anchor and run the house battery down, it will trigger the alt to go into high gear, once the engine is re-fired. At this point, the house battery is a liability, not a contributor to the helm . The helm supply cables may not have been intended to carry the potential of the alternator, because those helm loads could NEVER draw to the potential of the alternator. Adding a house battery and audio amp on to that helm cable, could be pushing it. Cable is cheap, and I aint met a toon I couldn't wire yet.  

The 3.5 is the max differential between the starter battery voltage (usually 12.8 or so) and the helm battery (at the shutdown voltage for the amps - but I've never gotten it down that far).  I was just looking at worst case.

Anyway, I'm learning from the comments and discussion.  First option will be to see if I can run some larger wire (#4) between the batts using the skirt and "joist space."  Second will be using the #6 (for + and ground) to run between the ACR and house battery.  In both cases I would plan to disconnect the house loads from the starter battery.  Glad you have gotten the tune wiring done!  I think/hope the alternator is up to it (as long as the starter battery is fully charged).  I currently have the same loads on a 45 amp alternator.

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jtrezon

Don’t parallel the #6...if the alternator is only 60A It should be OK for charging the stereo battery through the ACR.   If you ever need a larger alternator, plan on increasing the wire size.  Cant agree more...a larger wire size will ultimately help your cause either way, but trying it out as is shouldn’t hurt.  

The ACR will keep your batteries isolated until the alternator voltage >13V.   A low voltage of <9.5V will also lockout the ACR from closing so I wouldn’t worry about any 3.5V difference l....the ACR is engineered to prevent that.  

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MLA
12 minutes ago, jtrezon said:

I wouldn’t worry about any 3.5V difference l....the ACR is engineered to prevent that.

Not when he's anchored. Operator can run a house bank as low as they want, and the ACR is not involved until the engine it re-fired. 

 

18 minutes ago, jtrezon said:

Don’t parallel the #6.

 I agree, because you would then need to run a proper gauge ground, that would be equal to the capacity of the two 6ga. As noted earlier, the Neg is usually the same length as POS. So if it takes two 6ga of that length to carry the load, it would take equal gauge of the same length to support the ground. Boats do not have a chassis ground plane to support a short ground, like in a car.  

14 minutes ago, jtrezon said:

A low voltage of <9.5V will also lockout the ACR from closing

This is part of why I dont like the OPs plan. A deeply cycled house bank can cause the ACR to bounce between open and closed. This can render your "stereo wired direct house battery system" useless, until the house bank finally recovers to the point of the ACR staying closed. 

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minnmarker

@MLA and @jtrezon Thanks for the advice.  I think I'll try the #6 between the ACR in the stock battery compartment and the battery under the helm and give it a try after listening for a while with the engine off.  If the wires get warm after starting the engine then disconnect it and run larger wires.  I never planned on running the stereo battery down to 9.5 volts, that is just worst case and was picked because the sub amp shuts down at that voltage so it can't get any lower.

One more question: When I do this would it be better to run the house loads (mainly nav lights) off the starter battery (and put the ACR under the helm in parallel with the house buss) or off the stereo battery (and put the ACR in the stock battery compartment and run the house buss right off the stereo battery)? 

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MLA

Well, the ACR is intended to only supply alternator charge to the house bank, from the main bank, when voltage levels permit. 

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minnmarker
42 minutes ago, MLA said:

Well, the ACR is intended to only supply alternator charge to the house bank, from the main bank, when voltage levels permit. 

Yes, but sorry, I don't understand your comment in the context of the question?

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Ronnie

ACR explained.

Just an FYI to add to the discussion.

What is an ACR, and how does it work?

What is an ACR?
An ACR parallels (combines) batteries during charging, and isolates them when charging has stopped and after battery voltage has fallen. An ACR is intended to keep a load from discharging both of the batteries.

 

How does an ACR work?
An ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR′s contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries.

 

Why do I need an ACR?
An ACR allows two battery banks to be connected so that they can share the output of a single charge source, allowing the user to charge more battery banks than the number of charging outputs. For example, an ACR can be used with a single-output charger, resulting in a simpler system at lower cost than a dual-output charger.

 

How many ACRs do I need?
To combine two battery banks, one ACR is needed; to combine three battery banks, two ACRs are required. 

 

What are some features of ACRs?

What does “Dual Sensing” mean?
A dual-sensing ACR will sense an active charge source on one or both batteries and not solely on a designated battery. The ACR will operate if the measured voltage on either of the terminals is of a level to initiate a connection or disconnection.

 

How does an ACR differ from a battery isolator?
Battery isolators use one-way electrical check valves called diodes that allow current to flow to, but not from, the battery. ACRs use a relay combined with a circuit that senses when a charging source is being applied to either battery. ACRs are more efficient than battery isolators because they create little heat and consume minimal charging energy.

 

Will an ACR manage the charge of my individual battery banks?
An ACR does not direct the charge to the battery that “needs it the most” or has the lowest terminal voltage. If there is a charge present on either battery, indicated by a high enough voltage, the ACR will combine the batteries.

 

What Charge Sources will an ACR work with?
An ACR will work with all charge sources, including an alternator, AC charger, or solar panel. However, low current charge sources might not produce the voltage rise required to force the ACR to combine.

What else do I need to know about my ACR?

What are the minimum number of connections I need to make my ACR work?
Three: One wire to each battery, and one for a ground (GND) connection. For safety reasons, remember to disconnect the negative battery connections before beginning any ACR installation. See this article for more information on selecting the right fuses for Blue Sea Systems ACRs: See Selecting the Appropriate Fuse Rating When Installing the 120A SI ACR

 

What does “Undervoltage Lockout” mean?
As a safety feature, some ACRs prevent combining into a severely discharged battery. A dual-sensing ACR will monitor the voltage on both batteries and will not connect if either battery is below the undervoltage lockout level. Use caution when combining into a battery with extremely low voltage, because this might represent a faulty battery or a problem elsewhere in the system.

Why doesn't my ACR automatically combine every time my engine is running?
For an ACR to automatically combine the batteries, voltage and time thresholds must be reached. Although these numbers vary somewhat from one ACR product to another, if ACR terminal voltage is greater than 13.0V for 2 minutes, the ACR should combine.

 

Why didn't the ACR disconnect when my engine was turned off?
The ACR will not disconnect until the low voltage threshold is reached to isolate the circuit. It may take several minutes for the voltage of the batteries to drop to this level. Since the ACR incorporates a delay, additional time (up to 2 minutes) is required before the ACR disconnects.

 

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minnmarker

I must not have worded my question very well...  I know what an ACR does.  Where to put it in the circuitry is the question.  Buss before the ACR (starter battery side) or Buss after the ACR (stereo battery side) is the question.  I don't think it makes any practical difference unless I drain the stereo battery (so I would not have lights).

Oh well.

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Sparky450

Why not leave the #6?  I believe # 6 wire is rated at 60 amps. Yes you will have voltage drop on 25'.  You could put a manual disconnect in for the House battery somewhere right by the battery. This way if you do happen to run the house battery down so low, that the alternator would work to hard, you can simply use the disconnect to eliminate the house battery and charge it on the lift. Your stereo and everything else would still work off of the starter battery for the return trip back. If the battery never goes that low, then you would not need to disconnect the house battery

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Falko

So when the ACR engages, it is a direct connection between the two batteries and alternator. The lower charge battery will demand slightly more juice. #6 should be good to 50A-60A, so I think you are all set. If you are worried, you can always install a re-settable 50A breaker before that line to protect it. That would also give you an easy way to disconnect that battery. I'd run my lights off the house battery in the event you are ever sitting out in the evening with the engine off but want marker lights on, no need to worry about draining the starter battery. I'd put the ACR as close to the charging unit and starter battery as possible as it reads those for control.

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minnmarker
1 minute ago, Falko said:

So when the ACR engages, it is a direct connection between the two batteries and alternator. The lower charge battery will demand slightly more juice. #6 should be good to 50A-60A, so I think you are all set. If you are worried, you can always install a re-settable 50A breaker before that line to protect it. That would also give you an easy way to disconnect that battery. I'd run my lights off the house battery in the event you are ever sitting out in the evening with the engine off but want marker lights on, no need to worry about draining the starter battery. I'd put the ACR as close to the charging unit and starter battery as possible as it reads those for control.

I think that will be my plan except undecided about which battery to run the lights off.  I never have sat out in the dark - because of skeeters!  The 50 amp breaker is a good idea - just in case.

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