I feel like a dope...because I installed a second battery in my first boat and can't remember a few things. One, what gauge wire do I use

Second...where do I ground or connect the black lead on the second battery? I thought I took some good notes...I guess not that well

This is from AskJackrabbit.com. Question was asked by a guy with a 34' Silverton with regard to wire and fuse size.

Jack Rabbit: Sizing wire for starter cables is not so easy. The usual ABYC tables are set up to size wire for continuous use. With a starter, you have a very high current for a second or so, and then no current at all until next time you start the engine. Your engine manual may specify the expected starter current, or it may specify the CCA rating needed for the start battery which is much the same thing. The ampacity rating of 2/0 wire is 330A and that of 4/0 is 445A, i.e. the maximum continuous current that the wire can handle without overheating. Your starter motor might take 500+A for a brief time. The safe approach is to put on at least 2/0 cable for any starter circuit as even though this has a lower ampacity than the expected current, there is not time for it to heat up significantly. Be careful about repeated attempts at starting.

Any fuse you put in a starter circuit is going to have to be able to handle this high current for a short time. I would use an ANL fuse rated at about 125% of the expected starter current - you can get these fuses rated at up to 750A. Don't put fuses in any negative cables, they should always be on the positive side.

With a 500A load, 2/0 cable will give a 6.7% voltage drop in a 20 ft round-trip circuit. Using 4/0 cable will bring that drop down to 4.2%.

The starter circuit should have the same gauge wire throughout its length. That means from the start battery to the battery switch, and on up to the starter (positive), then from the engine block back to the battery bank (negative). As there might come a day when you start the engine from the house bank, the cable from the house bank to the battery switch should also be the same gauge, as should the negative cable from the house bank to the engine block.

This is a sizing guide too..
http://www.the12volt.com/wiring/recwirsz.asp

Good info...

Thanks Capn!

Here are two references:

http://www.uscgboating.org/safety/boatbuilder/electrical_landing.htm

http://www.geocities.com/wetdog205/Dual_Battery_Install.html

I think the boatbuilders handbook sez that each battery negative must go to the engine block (not from battery to battery). But you can look at the handbook to find out for sure.

WetDoggg, you didn't say what how you were going to connect the 2nd battery and if you were going to use a switch or not.

I have my 2nd battery GROUND cable connected using the same 2 gauge stuff as the original (now starting) battery. You can ground it at the ground post of the other battery, just put them on the same post together.

I use an 8 gauge cable for the red/hot/charging cable, as nothing else on the boat except the starter requires anything close to a #2. If you use a switch and might start the boat with battery #2, you will have to have the heavy 2 or 4 gauge cable from battery-to-switch. You only need 8 or 10 gauge from battery or switch to the house panel.

I don't use a switch, I do use a Yandina combiner (about $60 onlihne from Yandina.com) connected to the starting and house (deep cycle) battery. It has worked great the last two years, and on the boat I had before that.

Example installs from Yandina

troop...yes I will be using a switch. Sounds like 2 gauge is the way to go. Anybody have a good online source for this stuff?

Forgive me troop, but I have to disagree a bit.

Using a battery-to-battery ground is not best practice in my opinion, especially if you are going to potentially start the engine with either battery via 1-both-2 switch.

To meet federal law and ABYC recommendations, the grounding circuit to the engine must handle the entire load, which means, in this case - both batteries.

If this were a twin engine installation, seperate grounds for each battery would be mandatory as federal law.

Doggg, I don't want to get into parts selection for you, but consider Blue Sea's "Add a battery kit"

http://bluesea.com/category/1/productline/overview/329

It includes a switch and a combiner - Blue Sea's "version" of the Yandina combiner.

Whichever hardware you go with, assuming you want both batteries for starting, I would recommend the use of both a switch and a combiner.

There are some high-current combiners on the market so you can forgoe the switch, but I like the ability to select the "mode of operation" with a switch.

I buy all my wire from here: www.genuinedealz.com

Its all marine grade. They can make custom length battery cables for you with the ends already attached. Just give them the length you need. They charge you a buck an end for labor to install the connectors.

I do carry the Blue Sea Add-A-Battery Al mentioned. I did originally have it in my first post, but it didn't answer your question, so I pulled it.

Last time I checked, West Marine's price on it was $149.99.

Al, you are right when it comes to dual engines. I made the assumption it was for one engine, in which case you can combine the ground cables.



For dual engine

Troop - although not mandatory by regulation, I would do the same for a single engine as well.

In your situation, I can see that if you are not using the second battery for engine starting you can get by with a battery-to-battery connection, but if I were to do an installation and intended to start with both batteries, I'd run a ground from each battery to the engine.

And I'll never admit to ever over-designing anything...

That is basically what the above diagram does...I'd be willing to bet that if you got a single-engine, dual battery set up from the factory with a brand new boat, they would set it up as diagram #1 above.

Can't see the diagram.

But nevertheless:

ABYC standard E-11 (AC and DC Electrical Systems on Boats).

11.5.2.7 DC System Negative Connections

11.5.2.7.2 The negative terminal of the battery, and the negative side of the DC system, shall be connected to the negative engine terminal...

11.5.2.7.4 If the negative side of the DC system is connected to ground, the connection shall be made ONLY from the engine negative terminal...

While not federal law, the ABYC is considered best practice by many in the marine industry.

This is the link to the page...
http://continuouswave.com/whaler/reference/dualBattery.html

Also, for the dual engine, that drawing is incorrect. The engines themselves must be tied together, at the engines, not the batteries.

Here is a drawing right out of the USCG regulation (which is federal law):



Notice the disclaimer, jumper cables at the battery may not serve as jumper connectors for this purpose.

Another excerpt from the USCG regulation covering this instance:

If there are two or more starting battery installations and the negative terminals are connected by a common conductor, that common conductor does not satisfy this grounding requirement. Additional conductor(s) are necessary.



Remember, the internet is full of truth and false statements.

Al, can you see it now? I think we are saying the same thing as the ground cable is still connected to the engine ground, just does not make redundant cable runs.

Except that both batteries are sharing the same ground.

Since its my contention that any disagreement should be within the course of reasoning rather than being simply argumentative, please realize that I respect your opinion, and want to make this conversation simply a statement of what others say. I'll offer the reasoning the USCG publishes as to why the grounding should be done in this manner:


The purpose of this requirement is to prevent accidental passage of the battery supply current through fuel systems and smaller electrical conductors that may be common to engines. If one of the grounded cranking motor circuits accidentally opens (breaks) due to corrosion, vibration, etc., the accidental passage of starter motor current could melt fuel lines or burn up smaller conductors such as instrument wiring. Both of these hazards could lead to fire and explosion accidents. The common conductor circuit referred to in the regulation is a circuit made up of jumper conductors and may include a common bus bar.



While again this discusses dual engines, the same situation might occur in a single engine with two batteries, if both batteries can potentially be used for starting, and there is only one ground wire from both batteries to the engine.



That might very well be true for some manufacturers, however, I am talking best practice here, and ofen in a retrofit, especially if the batteries are not located adjacent to each other, its no more costly to run a ground to each engine - so why would it not be the prudent thing to do.

So should there be a ground wire connecting both batteries and ground wires to the engine block? Or simply a ground from each battery to the engine???

I went through some of my old photos, and here is a photo of my Vista268 factory installed dual battery system (single engine). You can clearly see a negative cable from each battery going to the left of the photo as shown by the arrows (presumably to the engine ground), and there is no interconnect cable between them.



However, I have an owner's manual for an older Vista 258, and the wiring diagram does show both batteries with a common ground.

So here is a manufacturer that did it both ways. I have no idea when the ABYC recommendations and the USCG regulations were put in place, so either it was a before-after regulation kind of thing, or the boat builder learned the right way to do it in later years.