Adding a House Battery

Electrical and electronic topics for small boats
Beerspitnight
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Adding a House Battery

Postby Beerspitnight » Thu Apr 13, 2017 4:02 am

Hello--As the start to my short boating season slowly rises from the polluere depths of the coal bleak Chinese winter, I have started to think about my summer boat project. Last year, I spent a few days wet sanding, compounding, and waxing the hull. I detailed that experience here.

This year, I would like to add a house battery to power the current accessories that are installed on my 1989 MONTAUK 17, and any future accessories that I will add. I am slowly building up the electronics on the boat and currently have an audio system that I would like to power when the boat is not running. Next season, I will purchase and install a GPS and depth sounder unit, and a fixed-mount VHF radio.

Adding a House Battery:

I would like to move my current dual purpose battery to the console and add a deep cycle AGM battery. Perhaps I should replace the current dual purpose battery with an AGM starting battery, but I will look into that at a later date.

I currently have a BLUE SEA SYSTEMS ST Blade Fuse Box with Negative Bus. Electrical power is provided to this box via the dual purpose battery.

To add a battery, battery switch, and automatic charging relay (ACR) I would like to use the BLUE SEAS Add-a-battery kit 120A.

I observed in this recent thread that Divin'Ivan installed this kit. Perhaps he has some insights and/or tips to share about the installation.

The instructions that BLUE SEA SYSTEMS provides (placed inline below) shows the negative connection to a negative bus bar. Am I correct in assuming that I should use this negative bus bar in addition to the negative bus bar located in the BLUE SEA SYSTEMS ST Blade Fuse Box? If so, could someone provide a short explanation as to why?

The instructions also show a positive lead from the starting battery to the battery switch, and then from the battery switch to the engine. There is an additional positive lead that is shown running from the engine to the key start switch. May I assume that my boat's current setup has a positive lead going from the engine to the key start switch via the bundle of wires and cables that currently connect the engine to the remote control box? If so, would there be a reason to modify this specific connection?

The instructions also indicate that one could add an optional switch from the negative bus bar to the ACR to prevent current draw when in storage. If one were to want to install a switch for this purpose, what type of switch should one use?

The instructions indicate that one should connect the ACR directly to the battery positive terminals using appropriately sized fuses. The chart on the instructions correlates fuse size to charging amps. I am unsure where I can find the charging amps for the batteries that I will use. I do see the maximum charging voltage for the AGM battery that I want to purchase, but I do not see maximum charging amps. Where can I find this information?

That brings me to my final question for this post: I will need to replace the wires running from the starting battery to the battery switch, and from the battery switch to the engine. I have read enough on this site to know that I need to select and use a wire gauge large enough to provide the necessary amps to start the engine and that resistance increases with the length of a wire. I am nearly 7000 miles from my boat, so I am not able to measure the run of wire that will be required for this application. I can, however, complete this measurement when I return home in 62 days (who's counting!) My SUZUKI DF70 requires 512 cold crank amps. If my run of wire is 12' or less, can I use 4-AWG for this connection? Do I need to provide additional information for this calculation to be completed? Would any classic Montauk 17 owners know the length of wire that is required to complete this connection?

Although I learned a good deal about electrical wiring last season when I rewired the navigation lights, and installed a JBL marine amp and Bluetooth receiver, I still have a good amount to learn. As always, I appreciate the insight, knowledge, and guidance that is provided through this forum.
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1989 MONTAUK 17

jimh
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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 1:44 pm

I will reply to the many questions with individual posts. Please note the vendor's name is not BLUE SEAS but rather is BLUE SEA SYSTEMS.

The instructions that BLUE [SEA SYSTEMS] provides (placed inline below) shows the negative connection to a negative bus bar. Am I correct in assuming that I should use this negative bus bar in addition to the negative bus bar located in the BLUE SEAS ST Blade Fuse Box? If so, could someone provide a short explanation as to why?


Yes. You should NOT use the fuse panel negative as the main negative bus. It is not sufficiently sized. I explain further below

In the power distribution system you propose, there will be two tiers of electrical power, the PRIMARY and SECONDARY electrical power distribution systems.

The PRIMARY power system involves the power at the source of the power, in this case from the battery or two batteries, the switch, and the primary load (the engine). The NEGATIVE BUS of the primary power must be capable of handling the total negative current, which will be a very high current because the engine starter motor will be drawing over 100-Amperes of current during engine starting. This primary negative bus should be large enough to handle that sort of current.

In small boats, however, it is often seen that the primary negative bus is omitted, and, in its place, the terminal post of the battery or batteries is used. (In fact, that is how my boat is wired.) Although as a general practice it is BEST if there is only one ring terminal connector on a terminal post, even the American Boat and Yacht Council (ABYC) seems to permit more than one ring terminal on a post. In that manner, the terminal post or posts of the battery or batteries can serve as the primary power negative bus, so long as you don't stack more than three or four (at the very most) ring terminals on those posts. Below is a sketch of my boat's primary power distribution, and you can see that the HOUSE battery has three connections at the negative post and the ENGINE CRANKING battery has four at its negative post:

Image

One of the connections to the battery negative is a 8-AWG conductor that feeds the battery negative circuit to the negative bus of the SECONDARY power distribution panel, which is also a product of Blue Sea Systems and has its own negative bus to which all the loads being powered by that panel have their negative circuits connected.

In my sketch the bus marked "Aft negative bus" is for connection of secondary loads that are nearby in the transom area, such as the negative circuits of:

--one of the navigation lamps,
--a sump pump
--a panel lamp associated with the control of that sump pump
--an isolated negative circuit associated with the engine trim gauge
--the negative circuit fed from the primary bus
--the negative circuit fed to the secondary panel
--and something I cannot remember right now :-)

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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 1:56 pm

The instructions also show a positive lead from the starting battery to the battery switch, and then from the battery switch to the engine. There is an additional positive lead that is shown running from the engine to the key start switch. May I assume that my boat's current setup has a positive lead going from the engine to the key start switch via the bundle of wires and cables that currently connect the engine to the remote control box? If so, would there be a reason to modify this specific connection?


Yes, that circuit is part of your engine wiring harness.

There is no need to modify that circuit. It is just shown in the schematic for clarity because of the involvement of the ignition key switch in the STARTING ISOLATION circuit.

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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 2:02 pm

The instructions also indicate that one could add an optional switch from the negative bus bar to the ACR to prevent current draw when in storage. If one were to want to install a switch for this purpose, what type of switch should one use?


That is an interesting comment about the quiescent current draw of the ACR device. I don't recall that being noted in prior versions of this drawing.

It will be a VERY GOOD idea to install a switch or some means of shutting off the quiescent current drain of the ACR when the boat is not in use, as otherwise there will be a drain on the battery or batteries. The switch can be any sort of switch, perhaps a toggle switch being the easiest to find. I would be guided by where the switch can most easily be mounted. I would avoid mounting it on the helm panel, and would prefer it close to the battery end of the circuit. I have two ideas:

--mount the toggle switch on the cover of the battery box, or
--don't use a switch at all, just pull out the fuse; use a fuse holder that accepts blade fuses and can be easily located.

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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 2:05 pm

The instructions indicate that one should connect the ACR directly to the battery positive terminals using appropriately sized fuses. The chart on the instructions correlates fuse size to charging amps. I am unsure where I can find the charging amps for the batteries that I will use. I do see the maximum charging voltage for the AGM battery that I want to purchase, but I do not see maximum charging amps. Where can I find this information?


The charging current Amperes will be determined by the outboard engine's charging circuit. Typically about 30-Ampere will be the maximum. If you have some really hefty AGM battery and an outboard that can supply 50-Amperes, perhaps use 50-Amperes.

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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 2:10 pm

I will need to replace the wires running from the starting battery to the battery switch, and from the battery switch to the engine. I have read enough on this site to know that I need to select and use a wire gauge large enough to provide the necessary amps to start the engine and that resistance increases with the length of a wire. I am nearly 7,000 miles from my boat, so I am not able to measure the run of wire that will be required for this application. I can, however, complete this measurement when I return home in 62 days (who's counting!) My SUZUKI DF70 requires 512 cold crank amps. If my run of wire is 12' or less, can I use 4-AWG for this connection? Do I need to provide additional information for this calculation to be completed? Would any classic Montauk 17 owners know the length of wire that is required to complete this connection?


I think you are confusing the recommendation of Suzuki for the Marine Cranking Ampere (MCA) or perhaps the Cold Cranking Amperes (CCA) rating for the BATTERY that should be used to start the DF70. It is unlikely that the DF70 will draw 512-Amperes of sustained current during engine starting. It may draw about 500-Amperes for a very small portion of a second when the starter motor is stalled at has not yet begun to turn, but not for long.

I suspect that on a MONTAUK 17 with the battery moved to the console, the distance between the battery switch and the engine is about 12-feet. Let's proceed on that basis. I will refer to my own article on power distribution at

http://continuouswave.com/whaler/reference/powerConductorSize.html#UsefulTable

in which I introduce the concept of pre-computed values of "Ampere-feet" (a term I have also invented) for power distribution at 12-Volts and three-percent voltage drop. From the table for 12-Volts (the most conservative approach) I find values for 4-AWG as follows:

4-AWG = 724.3 Ampere-feet

To apply this to our situation in the Montauk, we divide Ampere-feet by feet to get Amperes:

734.3-Ampere-feet / 12-feet = 60-Amperes

By the way, to be clear, the "12" feet is for the end to end length of a two way circuit, not the total wire length. So in this case there will be 24-feet of wire to make an end-to-end two-conductor circuit of 12-foot length.

Well, 60-Amperes does not seem like very much. But that is for only a three-percent voltage drop. We can be more generous and allow ten-percent voltage drop. This means we can scale-up the Ampere-feet by a factor of 10/3 or 3.3. Now we would have

4-AWG = 734.3 x 3.3 = 2,390-Ampere-feet

2,390-Ampere-feet / 12-feet = 200-Amperes

This tells us that if the starter motor is drawing 200-Amperes and is wired with 4-AWG for 12-feet end-to-end between battery positive and starter motor, we will deliver the 12-Volts with a ten-percent voltage drop, or 10.8-Volts at the starter motor.

Will that be good enough to start the engine? Yes, if the battery was close to full charge, its terminal voltage would be about 12.8-Volts, so you'd have about 11.6-Volts at the starter motor.

The real decision is with regard to how much margin you want to have to start the engine when the battery is somewhat discharged. If the battery is already down to 12.00-Volts and you lose ten-percent in the wiring, you may be approaching the limits. Also, we don't know how much the battery itself will sag in voltage under a 200-Ampere load. It is not going to stay perfectly at its open circuit terminal voltage. The nice feature of two batteries aboard is you can parallel them for engine start if needed, and that will give you more margin.

Another good basis for choosing wire for engine primary cables is to consult the engine maker. For example, Evinrude recommends using these wire sizes and these distances:

FEET      15–30 HP  40–300 HP
1 to 10 6-AWG 4-AWG
11 to 15 4-AWG 2-AWG
16 to 20 2-AWG 1-AWG


Going by their recommendation, you probably would use 2-AWG in preference to 4-AWG.

Also note that if you try to EXTEND the existing cables, you will have to use a very large wire size for the extension because the total resistance of the wire is what makes the voltage drop. The added section must be very much lower than the existing section in order that the total resistance is not excessive. There is not a quick way to calculate this; you have to look up the resistance per foot for each wire size and length of that wire in the total combined cable.

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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 2:39 pm

You might also want to read a little article I wrote on the general method of power distribution:

Boat Electrical Circuits and Wiring Practices
http://continuouswave.com/whaler/reference/boatWiring.html

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Re: Adding a House Battery

Postby jimh » Thu Apr 13, 2017 2:47 pm

Although I don't think you asked about STARTING ISOLATION, I recommend you install that feature. It will keep your boat electronics from rebooting during engine start if the engine start battery voltage sags. If I had an ACR with that feature, I would make use of it.

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Re: Adding a House Battery

Postby Beerspitnight » Thu Apr 13, 2017 10:58 pm

jimh wrote:Although I don't think you asked about STARTING ISOLATION, I recommend you install that feature. It will keep your boat electronics from rebooting during engine start if the engine start battery voltage sags. If I had an ACR with that feature, I would make use of it.


I did not ask about start isolation, but I will do so. The wiring schematic provided by BLUE SEA SYSTEMS indicates that one needs to install a run of 18-AWG from the ACR to the start key switch and install a 2-Ampere fuse in-line.

[Nota Bene: I recommend using 16-AWG for the conductor. In general wiring on a boat, 16-AWG is about as small as you want to go for mechanical reasons.--jimh]
Last edited by Beerspitnight on Fri Apr 14, 2017 5:06 am, edited 1 time in total.
1989 MONTAUK 17

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Re: Adding a House Battery

Postby Beerspitnight » Thu Apr 13, 2017 11:01 pm

Thank you for your detailed response, Jim.

I look forward to engaging in the project.

I have read your articles on power distribution. I have also searched the present forum and the previous forum for insight. I find comfort in having specific questions answered by informed individuals, especially when it comes to electric systems.

Best,
1989 MONTAUK 17

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Re: Adding a House Battery

Postby Beerspitnight » Fri Apr 14, 2017 6:47 am

jimh wrote:
The instructions indicate that one should connect the ACR directly to the battery positive terminals using appropriately sized fuses. The chart on the instructions correlates fuse size to charging amps. I am unsure where I can find the charging amps for the batteries that I will use. I do see the maximum charging voltage for the AGM battery that I want to purchase, but I do not see maximum charging amps. Where can I find this information?


The charging current Amperes will be determined by the outboard engine's charging circuit. Typically about 30-Ampere will be the maximum. If you have some really hefty AGM battery and an outboard that can supply 50-Amperes, perhaps use 50-Amperes.


Can you offer a suggestion on an appropriate in-line fuse holder for the following connections:
--Starting Battery positive to ACR
--House Battery positive to ACR
--Battery switch (positive) to Primary Distribution Panel

I found an inline BLUE SEA SYSTEMS MAXI fuse holder on West Marine rated for 60A, but each unit costs $20! Perhaps I am searching for the wrong fuse holder?
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Re: Adding a House Battery

Postby jimh » Fri Apr 14, 2017 8:17 am

The $20 cost of the MAXI fuse holder is a bit expensive, but that is the appropriate type fuse holder for the high-current fuses that are needed. Use them for the two fused conductor between the ACR terminals and the battery terminals.

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Re: Adding a House Battery

Postby jimh » Fri Apr 14, 2017 8:32 am

For the fuse shown in the Blue Sea Systems diagram for the conductor that feeds the positive circuit from the main battery switch to the "accessory" power panel, I would not use a fuse. Use a circuit breaker. The circuit breaker should be sized according to two elements of the circuit:

--the size of the conductor feeding the "accessory" panel (what I would call the secondary power distribution panel), and

--the total current load anticipated to be powered by the "accessory" panel

Since the batteries are in the console of the boat and the "accessory" panel is just a few inches away, the conductor won't be long enough to worry about voltage drop, and the conductor size can be selected just based on current. It is probably already in place as part of the original boat wiring, and I would expect it to be 8-AWG.

I also expect that there is already a circuit breaker for this circuit; that would be the usual practice of Boston Whaler. So you do not need to add any other current protection; just use the conductor and circuit breaker that Boston Whaler provided.

If for some reason the circuit breaker is not there, then use an appropriate circuit breaker, and choose the current rating to be appropriate for the panel capacity. If you have a six-circuit panel, then 30-Amperes is probably about right; if you have a 12-circuit panel, then 50-Amperes may be more suited.

The Blue Sea Systems part would be

https://www.bluesea.com/products/7183/2 ... _Mount_50A

or

https://www.bluesea.com/products/7181/2 ... _Mount_30A

You can also buy (what appears to be an identical) circuit breaker from Amazon for about half the price of the Blue Sea Systems branded product. Search Amazon for the term "Bussmann CB185-30 Surface-Mount Circuit Breakers, 30 Amps." (That is where I bought the circuit breaker I use.)

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Re: Adding a House Battery

Postby Beerspitnight » Tue May 02, 2017 6:55 am

I ordered the majority of the materials necessary for me to move the "starting" battery to the console and add a "house" battery to the console.

Below is a list of items that purchased. I post this list for reference purposes and for possible critiques.

Please note that I purchased more shrink butt connectors, spade connectors, and fuses than I need for this application.

The first number is the quantity ordered:

13 feet - 2/0-AWG Battery Cable, Black, Sold per Foot up to 50'
ANCOR

13 feet - 2/0-AWG Battery Cable, Red, Sold per Foot up to 50'
ANCOR

1 - Common 150-Ampere Bus Bar - Four 1/4"-20 Studs with Cover
BLUE SEA SYSTEMS

1 - "Add-A-Battery" Dual Circuit System
BLUE SEA SYSTEMS

3 - In-Line Fuse Holder
BLUE SEA SYSTEMS

4 feet - 4-AWG Battery Cable, Black, Sold per Foot up to 100'
ANCOR

4 feet - 4-AWG Battery Cable, Red, Sold per Foot up to 100'
ANCOR

1 - 16 AWG; 100' Spool, Black
ANCOR

1 - 16 AWG; 100' Spool, Red
ANCOR

1 - 285 Series, Thermal Circuit Breaker, 50A
BLUE SEA SYSTEMS

2 - MAXI In-Line Fuse Holder
BLUE SEA SYSTEMS

2 - 50-Ampere Maxi Fuse
BLUE SEA SYSTEMS

4 - Easy-ID Glowing Fuse, 10-Ampere
BLUE SEA SYSTEMS

6 - 2-Ampere ATO/ATC Fuses
BLUE SEA SYSTEMS

1 - Toggle Switch, Off/On, SPST
BEP MARINE

1 pkg - Heat Shrink Butt Connector, 16 to 14-AWG Wire, Blue, 25 Qty/Pkg
ANCOR
1

1 pkg - 16 to 14-AWG Wire Spade, Blue, #6 Screw Size, 6 Qty/Pk
ANCOR

4 pkg - 8-AWG Terminals, Red, 3/8" Hole Dia., 3 Qty/Pk
ANCOR

2 - Battery Box, Fits Group 24
WEST MARINE
1989 MONTAUK 17

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Re: Adding a House Battery

Postby jimh » Tue May 02, 2017 8:03 am

There is a corollary to Murphy's Law for electrical installations:

Any wire cut to length will be too short.

I am not sure what you mean by the term "wire spade." I hope you bought Ring Terminal Connectors.

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Re: Adding a House Battery

Postby Beerspitnight » Tue May 02, 2017 8:10 am

jimh wrote:There is a corollary to Murphy's Law for electrical installations:

Any wire cut to length will be too short.

I am not sure what you mean by the term "spade connector." I hope you bought Ring Terminal Connectors.


That quote is soothing; I am glad I am not alone.

I did buy ring terminal connectors. See: "4 pkg - 8-AWG Terminals, Red, 3/8" Hole Dia., 3 Qty/Pk"

The spade connectors are listed below for your reference. I purchased them to connect the toggle switch to the ACR.
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Re: Adding a House Battery

Postby jimh » Tue May 02, 2017 8:12 am

For the large battery cable, did you buy 2-AWG or 00-AWG (which is sometimes called "two aught")?

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Re: Adding a House Battery

Postby jimh » Tue May 02, 2017 8:17 am

The terminals you show are called fork terminals. Generally they are not recommended for wiring on boats. I believe the concern is for vibration, which might cause the retaining screw to become loose, and the fork terminal could fall off. At least with a ring terminal the connection is captivated by the retaining screw, even when a bit loose. Fork terminals might be used with some terminal strips where the screw fasteners have their threads jammed at the end so the screw is very difficult to remove from the terminal (said to be captivated in the terminal). The American Boat and Yacht Council (ABYC) recommendations might have something to say about use of fork terminal versus ring terminals. If I find something, I will post it.

Also, ring terminal will stack up on a single terminal post much better than fork terminals.

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Re: Adding a House Battery

Postby Beerspitnight » Tue May 02, 2017 8:20 am

jimh wrote:For the large battery cable, did you buy 2-AWG or 00-AWG (which is sometimes called "two aught")?


I purchased 2-AWG:
ANCOR
Battery Cable, 2/0 Gauge, by the Foot

Regarding your comment about the fork terminals, noted with thanks.
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Re: Adding a House Battery

Postby jimh » Tue May 02, 2017 8:27 am

Beerspitnight wrote:I purchased 2-AWG:
ANCOR
Battery Cable, 2/0 Gauge, by the Foot


You bought 00-AWG cable, which is significantly larger than 2-AWG. ANCOR uses an odd notation, "2/0" which is a representation of "two aught", for 00-AWG. Compare with their notation for 2-AWG battery cable at

http://www.ancorproducts.com/en/product ... tery-cable

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Re: Adding a House Battery

Postby Beerspitnight » Tue May 02, 2017 8:33 am

jimh wrote:
Beerspitnight wrote:I purchased 2-AWG:
ANCOR
Battery Cable, 2/0 Gauge, by the Foot


You bought 00-AWG cable, which is significantly larger than 2-AWG. ANCOR uses an odd notation, "2/0" which is a representation of "two aught", for 00-AWG. Compare with their notation for 2-AWG battery cable at

http://www.ancorproducts.com/en/product ... tery-cable


Ok, well, I wonder if that cable will fit through the engine cowling?
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Re: Adding a House Battery

Postby jimh » Tue May 02, 2017 8:36 am

Re terminals, the ABYC standard is for use of a ring terminal or a captive fork terminal. The "captive" part of a fork terminal means the ends of the forks are bent upward slightly to better retain the terminal on the screw fastener. The image you posted (above) shows fork terminals with the ends of the fork bent up, so they are captive fork terminals--all the better.

There are also fork terminals that snap over the terminal post, like the ones shown in this image:

Image

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Re: Adding a House Battery

Postby jimh » Tue May 02, 2017 8:39 am

Beerspitnight wrote:Ok, well, I wonder if that [00-AWG] cable will fit through the engine cowling?


You might consider using the original engine battery cables and just joining them to the 00-AWG extension cable. The problem is where to make the connection and how to weather-proof the connection. Wire of 00-AWG is going to be rather big and heavy--not to mention expensive.

One approach will be to use a small terminal junction with two isolated posts, and join the two cables using ring terminals. Since this will be more or less a permanent connection, coat the terminals with liquid black vinyl insulation, sometimes called liquid electrical tape. Then mount the terminal assembly in some manner that keeps it from physical damage and avoids being exposed to spray.

I think--without doing all the calculations--that by using 00-AWG as an extension cable you won't have a problem with voltage drop for engine cranking.

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Re: Adding a House Battery

Postby jimh » Thu May 04, 2017 12:24 pm

Let's do the math on the 00-AWG as extension cables. The Ampere-feet for 00-AWG for 12.0-Volts and 3-percent is 2310. Let's figure the length of the 00-AWG extension will be 10-feet (which sounds about right to me). This suggests we could have 231-Amperes of current and only have 3-percent voltage drop. Note that 3-percent of 12.0-Volts is only 0.36-Volt. So at 231-Amperes of current in 10-feet of 00-AWG, we only drop to 11.64-Volts. That will be where the original engine battery cables will connect.

We can also compare with the recommendation of the outboard maker, who suggests that for 15-feet length (which I use to compare with 10-feet of extension cable and 5-feet of original cable) we should use 2-AWG. The Ampere-feet for 2-AWG at 12.0-Volts and 3-percent is 1151. For 15-feet that means the current must not be more than

1151-Ampere-feet/15-feet = 77-Amperes

to maintain 3-percent drop. We just figured out the 00-AWG is good for 231-Amperes, while the recommended 2-AWG is good for only 77-Amperes, if we want to hold to 3-percent drop from 12.0-Volts. That sounds to me like the 00-AWG is going to have plenty of "headroom."

Let's revisit 00-AWG at 77-Amperes:

2310-Ampere-feet/77-Amperes = 30-feet to get three percent voltage drop.

We are only going to have 10-feet, so that means at 77-Amperes the voltage drop will be now down to only

(3-percent/30-feet) x 10-feet) = 1-percent