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  1. #1

    Dual battery wire question

    Doing a dual battery set up on my Yamaha VXR.
    I have a blue sea switch and ACR ( there mini add a battery kit). In the install diagram is showing a fuse wire for the ACR. I am using 6AWG tinned marine wire for the switch and batteries. I also have a few 12awg marine inline fuses with 30a fuses. Can I use the 12awg inline fuses for the ACR? To small? Or do I need bigger wire? Anyone have any advice?
    i do not have any inline fuses for 6awg.
    thanks


  2. #2
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Jetskibob View Post
    Doing a dual battery set up on my Yamaha VXR.
    I have a blue sea switch and ACR ( there mini add a battery kit). In the install diagram is showing a fuse wire for the ACR.

    I am using 6AWG tinned marine wire for the switch and batteries. I also have a few 12awg marine inline fuses with 30a fuses.

    Can I use the 12awg inline fuses for the ACR? To small? Or do I need bigger wire?

    Anyone have any advice?
    i do not have any inline fuses for 6awg.
    thanks
    I am not entirely understanding your configuration. You are using 6 AWG wire between each battery and the ACR unit, correct?

    Where exactly would you be connecting the 12 AWG wired fuse holders?

  3. #3
    Quote Originally Posted by K447 View Post
    I am not entirely understanding your configuration. You are using 6 AWG wire between each battery and the ACR unit, correct?

    Where exactly would you be connecting the 12 AWG wired fuse holders?
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  4. #4
    Click avatar for tech links/info K447's Avatar
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    Well, I would suggest using a much simpler wiring configuration. No round battery ‘switch’.

    Stock electrical system remains completely unchanged. Battery connects to factory wire harness and starter solenoid, etc.

    ACR ‘sensing’ terminal connects to the ‘regular’ battery positive post.
    Other ACR terminal contents to the ‘house’ or ‘auxilary’ battery positive terminal.
    This would use your 6 AWG wire, or whatever wire gauge the ACR instructions suggest.

    Second battery negative connects to first battery negative OR to the engine block. Also a heavy wire gauge, per instructions.
    ACR thin negative wire connects to main battery negative post.

    GPS and any other auxiliary electronic loads connect to the second battery positive terminal.
    These secondary load connections are the place to use inline fuses.

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    TimeBandit's Avatar
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    Quote Originally Posted by Jetskibob View Post
    Doing a dual battery set up on my Yamaha VXR.
    I have a blue sea switch and ACR ( there mini add a battery kit). In the install diagram is showing a fuse wire for the ACR. I am using 6AWG tinned marine wire for the switch and batteries. I also have a few 12awg marine inline fuses with 30a fuses. Can I use the 12awg inline fuses for the ACR? To small? Or do I need bigger wire? Anyone have any advice?
    i do not have any inline fuses for 6awg.
    thanks
    I believe you will be fine using 12AWG because ACR (as implied) will only operate during charging conditions, and the so-called charging “source”, aka the voltage regulator/rectifier, I believe has a 20 (or 30) amp fuse inline (see your fuse box). 12 AWG wire itself can handle twice that.

    On the other topic about the switch…
    I run a dual (LiFEPO4) system myself for years now … and while I don’t use an ACR, I DO indeed use the batt switch. The switch permits me to isolate "off" one of my batts for the purpose as a "trusted spare". Meaning, whilst out on the water adrift, fishing for hours, and powering my accessories (gps, sounder, FM radio, etc….), if I happen to somehow drain the batt I’m on and cannot start the ski, I can simply switch to the trusted good batt.

    Another reason for the switch (generally-speaking) is that most lead-acid dual systems consist of a starting batt and a deep-cycle batt - so it is imperative that one not start off a deep-cycle.

  7. #6
    Thanks for the reply’s

  8. #7
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by TimeBandit View Post
    I believe you will be fine using 12AWG because ACR (as implied) will only operate during charging conditions, and the so-called charging “source”, aka the voltage regulator/rectifier, I believe has a 20 (or 30) amp fuse inline (see your fuse box). 12 AWG wire itself can handle twice that.

    ... while I don’t use an ACR, I DO indeed use the batt switch.

    The switch permits me to isolate "off" one of my batts for the purpose as a "trusted spare". Meaning, whilst out on the water adrift, fishing for hours, and powering my accessories (gps, sounder, FM radio, etc….), if I happen to somehow drain the batt I’m on and cannot start the ski, I can simply switch to the trusted good batt.

    Another reason for the switch (generally-speaking) is that most lead-acid dual systems consist of a starting batt and a deep-cycle batt - so it is imperative that one not start off a deep-cycle.
    The ACR does precisely what you are using the mechanical battery switch for. The second battery supplies the auxiliary electronics, while the primary engine start battery remains well charged and ready to start the engine.

    Among the upsides to ACR is that the original factory electrical system remains entirely unchanged. With a mechanical battery switch the most critical wires in the electrical system, the main electrical system feed, is routed through the switch.

    If any of the extra cable connections work loose, or the big switch develops an internal problem (corrosion, vibration failure, etc) then the electrical system could go entirely dark.

    Also, with a mechanical battery switch the user must remember to use the correct switch positions. Engine start the switch is set to main battery only. The switch would moved to the ‘both’ position while the engine is running. This setting charges both batteries with engine running.

    With engine shit off, the switch must be manually changed to the ‘house’ only position. The ‘Both’ and ‘Engine Start battery’ positions (with engine not running, but the auxiliary electronics in use) can result in a drained main battery, and potentially no engine start.

    The ACR does all this automatically. Engine charges both batteries, while the auxiliary electronics only draw from the secondary ‘house’ battery. No user switch actions required, no remembering which setting to use for what. No risk of draining the engine start battery.

    Your point regarding not using a deep cycle battery for engine start is valid, but it opposes the logic for having the switch. If you will not use the second battery for engine start, then no need to have the big switch interspersed between the batteries and the main power cable to the engine.

    Don’t allow the auxiliary gear to run down the main battery, then no need to be switching heavy cables to allow the other battery to start the engine.

    12AWG cable, as a single unbundled wire, can handle some current. But I would not expect it to tolerate 60 amps without notable voltage drop and some wire heating. Even 40 amps is a lot for 12 AWG, especially if voltage loss/drop is to be minimized.

    Some ACR units have an emergency override function that allows the user to force the two batteries to be combined for a short time just prior to and while the engine is cranked, should the main battery need help to get the engine cranked.

    During this special mode the current flow through the ACR can be higher than normal as the engine cranks, so heavier gauge wires from the ACR to each battery would minimize voltage drop, hopefully allowing a quicker engine crank and start up. Once started, the ACR can revert to normal operation, and both batteries begin to charge,

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  10. #8
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    K447, I think we are summarizing similar points given several different implementation scenarios … so it’s probably worth mentioning a few and how it pertains to the OP’s topic :

    As you have stated above, a dedicated starting battery hooked only to the starter circuit (and wiring harness), and a dedicated deep-cycle battery to power only accessories/lights is a common "boat" implementation. In this scenario, one could EITHER implement just a distro switch or just an ACR, or maybe both.
    True, just an ACR in this dual dedicated setup is the more elegant (or automatic) approach for sure, and that deems the distro switch the optional component. This is because, while the starting batt is technically receiving the stator charge… the ACR will intelligently relay the charge potential over to the deep battery, and the deep will never be able to start the ski. Technically, since each battery is permanently-purposed to their own circuits, you could wire the starting batt with 6AWG and the accessory deep batt with just 12AWG, and same 12 for the ACR union circuit.
    However, the nice advantage about still having the switch in addition to the ACR (as is with OP's Blue Sea "Add a battery kit"), is that one could still opt to combine or start off the deep batt in a emergency scenario. Not sure about other folks, but I like having options like this, and that might be why the kit includes both.

    How about this . . . As I stated above, my personal system is a dual starting** implementation, especially as my Lithium packs do not have Deep or Starting power characteristics, these can do both applications. Furthermore, I do prefer the option of starting from either or both batts. Thus a distro switch is certainly hard to avoid and desired. Starting. . . Yes. . . discharge amps can certainly surge above +60A… so for that, you'd need a distribution switch with heavy contact ratings. How would an ACR fit this application? Sure this dual starting setup requiring switch (manual or automatic) could indeed benefit from the addition of an ACR to make recharging more carefree, yet given that this distro switch already exist, the ACR can now be said the optional component. Both batts would be wired 6AWG (ground and switch poles), HOWEVER, and as I mentioned already, the ACR can be wired 12AWG as in the OP's scenario. Why? Okay, worst-case conditions. . . a heavily depleted battery (either), AND at WOT rpms = highest charging-power present. The stator and rectifier can only produce a finite amount of Power. This could be 260-300 watts (or about 20-ish amps at 13-ish volts) under those conditions at best. Thus, if one is concerned with what minimum "safe" AWG for the ACR circuit should be (as per the OP’s thread topic), one only needs to observe the AWG size selected in the OEM harness itself along the stator and rectifier charging circuits, as the ACR just "relays" this same circuit to the "other" battery.
    Also note that the ACR will not allow one battery to "dump" into the other, or contribute to starting amps, so it’s moot to expect anything over 20-ish amps across the ACR circuit - inline fuses for added protection.


    ** More specifically on my particular dual-start setup... which is essentially a single battery setup with “instant battery change-out” capability. I "manage" this so-called dual-single-battery implementation by : On odd calendar day outings, my switch is on “1” the entire day. My ski starts and recharges #1 batt like it’s the only battery in my ski. On even calendar day outings, my switch is on “2” the entire day. My ski starts and recharges #2 batt - you got it - like it's the only battery on my ski. Now…. if ever the day I find myself in a dead/weak battery scenario, I can instantly perform a battery exchange with the flick of a switch. Now, this may not be everyone’s preferred dual-batt implementation strategy, but it is mine, and it does have utility for what I use that specific ski for.

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    . . . next I wanted to address some of your points specifically :

    “The ACR does precisely what you are using the mechanical battery switch for. The second battery supplies the auxiliary electronics, while the primary engine start battery remains well charged and ready to start the engine. “

    Statement is too generic . . . cannot discern if you are implying both charging and discharging states, as the later does not hold true.

    In addition, a manual switch does offer a total disconnected state which can be very useful and safely to isolate power during extended layups and/ or maintained actions.


    “If any of the extra cable connections work loose, or the big switch develops an internal problem (corrosion, vibration failure, etc) then the electrical system could go entirely dark. “

    True. Yet one bad ground can render the same.

    “Also, with a mechanical battery switch the user must remember to use the correct switch positions. Engine start the switch is set to main battery only. The switch would moved to the ‘both’ position while the engine is running. This setting charges both batteries with engine running.

    With engine shut off, the switch must be manually changed to the ‘house’ only position. The ‘Both’ and ‘Engine Start battery’ positions (with engine not running, but the auxiliary electronics in use) can result in a drained main battery, and potentially no engine start. “


    Very true. We humans are creatures of habit, so there's going to be some discipline needed.

    BOTH - Glad you mentioned this. While the switch does indeed have a “both” position, I find that as “bad practice” to leave it in that position other than for transitional or very short durations - to include no dual charging. Not only does this lend one to the mistake of possibly forgetting and draining both batts, if one batt is defective or internally grounded, one could risk fire hazard even with 6AWG.


    “Your point regarding not using a deep cycle battery for engine start is valid, but it opposes the logic for having the switch. If you will not use the second battery for engine start, then no need to have the big switch interspersed between the batteries and the main power cable to the engine.”

    It only seems opposing due to your intentional ‘absolute’ stance to that notion. Common-sense still applies . . . as one would not routinely start off a deep battery as this would prematurely stress it beyond it’s intended application. However, one could indeed start off of it (been there did that on my boat) “if” the dire circumstance deem necessary - especially given human safety at risk.

    “12AWG cable, as a single unbundled wire, can handle some current. But I would not expect it to tolerate 60 amps without notable voltage drop and some wire heating. Even 40 amps is a lot for 12 AWG, especially if voltage loss/drop is to be minimized.

    Some ACR units have an emergency override function that allows the user to force the two batteries to be combined for a short time just prior to and while the engine is cranked, should the main battery need help to get the engine cranked.

    During this special mode the current flow through the ACR can be higher than normal as the engine cranks, so heavier gauge wires from the ACR to each battery would minimize voltage drop, hopefully allowing a quicker engine crank and start up. Once started, the ACR can revert to normal operation, and both batteries begin to charge ”


    Correct. Logic sounds right with 12 AWG & 60 amps in general, but this does not associate with the 12 AWG on the OP’s ACR tie-ins. This Blue Sea ARC shouldn’t be exposed to starting amps.

    The mfr docs does not state if this Blue Sea kit ACR has this capability. However, if it does (and one intends to use this feature), I cannot disagree with you insuring the right AWG is used.

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    Click avatar for tech links/info K447's Avatar
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    We are indeed working from similar understandings.

    An important aspect of my suggestions is that the original factory wiring to the battery remain 100% intact. The heavy OEM battery cables, OEM battery configuration remain entirely unchanged. Neither of the original OEM battery cables are removed, extended, intercepted or otherwise altered. They just connect to the engine start battery, same as factory.

    This is the core of my ‘it should just start, same as factory’.

    An ACR fits within this restriction, as the wiring for the ACR is added to the factory configuration, merely connecting to the same original battery posts as the factory cables.

    The added/new wiring to the ACR from each battery should be sized to handle the maximum possible current (through the ACR). If that is just the maximum output of the charging system, that defines the minimum AWG. The wires on each side of the ACR should be the same AWG.


    There is a specific case where the ACR can flow more amps that the charging system alone provides. A deeply discharged second battery. When the engine starts and the ski begins running at speed, the ACR will combine the two batteries. The start battery may be very healthy and well charged, so when the ACR links the batteries together the main battery can flow significant current into the secondary battery. It is helped by the charging system and the combined current flow across the ACR into the second battery can exceed the charging system output.

    Perhaps unintuitively, some ACR/combiner systems purposely use rather long connecting wires of modest wire gauge. The idea is that the extra series wire resistance will impose a limit on the battery to battery cross current.

    The other approach is to use wire gauge larger than what the charging system ampacity alone would infer. While the engine is running just let the main battery flow current through the ACR and it will fairly rapidly raise the charge level of the depeted secondary battery. The main battery charge level will decline somewhat but it is not going to go flat. It is directly connected to a running engine that is pushing charge current as much as it can.


    Many(all?) ACR will automatically disconnect the second battery if the charging system voltage (which is also the voltage at the main battery) cannot stay above some minimum charge voltage level. Roughly 13.0 to 13.5 volts, somewhere in that range, as sensed by the ACR. Wire gauge is a factor in the voltage drops and what the senses voltage is.

    Each time the voltage sags too low the ACR (re)isolates the secondary battery. And keeps it isolated for some duration. Maybe several minutes delay before trying again to link them and see how the main battery voltage (charging system) handles it.

    This prevents a hugely depleted or perhaps damaged second battery from overburdening the charging system.

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