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Author Topic:   Extending battery cables
modenacart posted 02-02-2009 07:52 PM ET (US)   Profile for modenacart   Send Email to modenacart  
I want to run my battery cables under the console. What is the best way to extend the cables. Water likes to stand right at the drain but not very much.
HAPPYJIM posted 02-02-2009 08:04 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Go to an electrical supply store and buy an underground high voltage repair kit. It will have all you need to splice and seal the conductors for a water tight repair.

Others may have ideas to add.

modenacart posted 02-02-2009 08:09 PM ET (US)     Profile for modenacart  Send Email to modenacart     
That is a great idea. What gauge wire do I need to use?
Chuck Tribolet posted 02-02-2009 08:23 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
How much TOTAL cable required? What motor? Both of those
will influence the size of the required cable.


Bella con23 posted 02-02-2009 08:31 PM ET (US)     Profile for Bella con23  Send Email to Bella con23     
I have used the underground repair kits at my employment an have no doubt it would do the job.
My question is why not replace the entire length rather then splicing onto the short cable?
modenacart posted 02-02-2009 08:41 PM ET (US)     Profile for modenacart  Send Email to modenacart     
Motor is an Evinrude 88, 1995. I think the cable lengths will be about 10 feet or so, I haven't measured yet.

I didn't really think about just replacing at the engine, I suppose so. Which would be easier/cheaper?

jimh posted 02-02-2009 10:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Let's go over this one more time.

Extending Battery Cables

Don't Make Splices, Especially in the Tunnel
If you want to move the battery to the console from the transom, do not splice the cables so the splice is in the rigging tunnel and subject to chronic immersion in water. A splice in the rigging tunnel is the worse possible place to make a splice. You can't see it. You can't easily repair it. It is buried in a tunnel.

You Must Increase Conductor Size
If you want to extend a high-current circuit like the engine starting circuit, you have to increase the size of the conductors so that the total voltage drop is not excessive. Typically the original cables were just large enough to work for the original length. They will be too small for the longer length. You cannot extend them using the same gauge of cable.

The Size of the New Cables
If you want to extend the cables, you have two choices. You can add to the original cables with cable that is very much larger than necessary so that there is almost no voltage drop in the new cable segment. Or you can discard the original cables and replace them with a new length of the appropriate size, which will be larger than the old cables but not as large as if you only replaced a portion of the cables.

Let me give an example. Let's say the starter motor can tolerate a voltage drop in the cables of 2-volts maximum. The original cables were probably sized so that they provided no more than 1-volt drop. In the new installation we want to maintain that same margin.

If we keep the original cables and extend them, the total voltage drop in the system will be too high. Even if we use monster cable to extend, there will be some drop in the new cable. There will be drop in the splice. The original drop of 1-volt was all we were willing to tolerate. So any addition adds more voltage drop.

If we discard the original cables and replace with with cables of one or two size larger, we can double the length and keep the voltage drop the same. We also get the huge advantage of no splices in the rigging tunnel.

People have extended their cables, they have put splices in the rigging tunnel, and they have used really large cable, much bigger than necessary, but I don't think that is the best way to go.

I am not familiar with this device called an underground splice. I am sure it works well for underground cables. But the splice in the rigging tunnel will be an underwater splice. Also, long underground cables were already of the correct cable size. If they break they are spliced back together. It is not really practical to pull out a mile of wire from underground--not an option. So they splice it.

On your boat you have the option to not make a splice in a bad place. Exercise the option.

Chuck Tribolet posted 02-02-2009 10:27 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Dunno what boat. Take a tape measure and follow the whole
route from stud on the motor to stud on the battery.

I just took a tape measure to my 16'7" Montauk. It looks like
7' of cable just to get from the motor to the tunnel. About
16' overall.

The manual for my '97 Evinrude 90 says :

1-10' 4 ga.
11-15' 3 ga.
16-20' 1 ga.

The factory (I think, or dealer) battery cable is 2 ga.

In conductors, there's no substitute for cross-section. If I
ever have to rewire that, 1 ga.

West Marine has a crimper in the store. Use good marine
grade cable.


Chuck Tribolet posted 02-02-2009 10:28 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     


modenacart posted 02-03-2009 11:49 AM ET (US)     Profile for modenacart  Send Email to modenacart     
All good suggestions. I will splice close to the engine and that will be one of the points I anchor to the wall. I will go with either 2 or one gage cable.
Tohsgib posted 02-03-2009 12:56 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
My mechanic rigged my 15 CC and about 6 months later it started turning over slower...and slower....and slower. I replaced the starter to no avail. It was then that I found out he had spliced my cables in the tunnel. Nice job with liquid electrical tape, tape, etc but no match for salt water and electricity, so do NOT splice in he tunnel...again.

With an 88hp you don't need anything crazy 3 gauge will be fine.

L H G posted 02-03-2009 01:58 PM ET (US)     Profile for L H G    
The proper way to do it is to use a pair of HD terminal studs with red and black rubber/plastic covers, readily available at West marine and others. The original engine batt cables go on these, just as if you were connecting to a battery. Then you use heavier gauge cables, also with crimped on ring connectors, to bring the console installed battery's voltage to these studs. For most situations, you need a 5/16" stud and a 3/8" stud, and they should be mounted on the boat where they are out of the way. If they get wet once in a while it's not a problem. This is a permanent solution. When you change engines, just connect the new engine's cables to these studs.

Boston Whaler used this approved detail on the later classic Montauks when they moved the battery into the console.

modenacart posted 02-03-2009 05:25 PM ET (US)     Profile for modenacart  Send Email to modenacart     
Ok, it looks like I will be ok with 10 feet of 4 awg. How does this wire look?

[Posted an absurdly long URI that pointed to some auction taking place on an on-line auction website which ruined the line wrap]

or would this be better?

[Posted an absurdly long URI that pointed to some auction taking place on an on-line auction website which ruined the line wrap]

Basically tinned or not tinned it looks like. [Changed the topic of discussion to a new topic. Please begin a new thread to discuss a different topic. Thanks--jimh]

jimh posted 02-03-2009 09:38 PM ET (US)     Profile for jimh  Send Email to jimh     
Use appropriate wire to extend your battery cables. Most wire used in a boat must be "marine grade" wire which generally means the insulation material can tolerate water and oil. Compare with Underwriter's Laboratory (UL) standard 1426. Marine grade wire is usually pre-tinned and made of many strands of relatively small conductors. Battery cables are generally made with a rubber insulation and are very flexible.

If you want to give absurdly long uniform resource indicators, please form them into hyperlinks using the UBB TAGS for URL.

HAPPYJIM posted 02-03-2009 10:13 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Underground splice kits are used for repairing OR splicing conductors for waterproof use. I have used them in making splices for everything from irrigation system electrical control valves, low voltage(12VAC) lighting systems and 220VAC submersible water pump installations. They are salt water proof and work pretty good. I have systems that are still in use in salt water environment for over 20 years.

I use the 3M kits. Everything is in the kit to do 2 conductors.

jimh posted 02-03-2009 11:36 PM ET (US)     Profile for jimh  Send Email to jimh     
How much is a splice kit suitable for use with 2-AWG wire?
HAPPYJIM posted 02-04-2009 01:00 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Would need to check with my supplier but I have a bunch that are for 12/10 wire that are 2.99 retail.
modenacart posted 02-04-2009 04:27 PM ET (US)     Profile for modenacart  Send Email to modenacart     
Where do you get the kits? I still wouldn't' do the splice in the hull.
L H G posted 02-04-2009 05:42 PM ET (US)     Profile for L H G    
Would any Montauk 170 owners be willing to tell us how Boston Whaler configures the engine battery cable extensions to the console mounted battery?
Chuck Tribolet posted 02-04-2009 06:37 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Dunno about the 170s, but my classic Montauk has a single
cable from motor to battery. No splices. As it should be.


L H G posted 02-04-2009 07:39 PM ET (US)     Profile for L H G    
Chuck - since you have an Evinrude, I assume your dealer changed that installation, and changed out the original battery cables on the engine. The only complication I can see in doing it that way, is when repowering, and how those heavier cables would connect into a different engine. I am hoping to get information on how the factory is doing it on the factory rigged Mercurys. Several years ago, I saw a new classic Montauk at a dealer, rigged with a 2-stroke Merc 90, and it was done as I described above. I'm wondering if the factory is still using the same terminal stud system today.

jimh posted 02-04-2009 10:38 PM ET (US)     Profile for jimh  Send Email to jimh     
I think installing the terminal studs to join the original engine cables to some new extension cables is the wrong way to go. We are talking about a small boat. New battery cables for the engine of the proper size would cost less than all the terminal posts, ring connectors, and monster wire you'd need to go the other way. Then you have these terminal studs in an open transom. Where do you put them? If you put them on the outer bulwarks, you just add four feet of cable to the run. If you put them in the center, they are out in the open. Get the right length of cable for the motor and run it to the battery in the console. It will be cleaner, cheaper, and more reliable. Those terminal posts are $35 each!
jimh posted 02-05-2009 09:08 AM ET (US)     Profile for jimh  Send Email to jimh     
I checked the price of terminal posts--they're less expensive than I thought for a particular item designed just for this purpose with two terminals:

Retail price is about $21.

OEM battery cables of longer length will probably be priced like gold--well actually like copper.

If you have some enclosed space at the transom to install a terminal post, it might be a workable solution. On an open boat with a big splash well and wide notched transom, you'd have to put this terminal post high under the gunwale on the starboard side.

HAPPYJIM posted 02-05-2009 09:55 AM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Any good electrical supply store will carry the kits. 3M is a brand name well known in the electrical industry.
Chuck Tribolet posted 02-05-2009 06:47 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
My wiring was likely a factory pre-rig (on a different Montauk
hull, but that's another story).

1-AWG is $7.99/foot at West Marine.

This not something to do as cheaply as possible, it's something
to do RIGHT.


jimh posted 02-05-2009 09:10 PM ET (US)     Profile for jimh  Send Email to jimh     
You should realize that when you decide to move the battery from the stern of the boat to the console that you are degrading the electrical circuit. It makes no sense electrically to move the battery farther away from the motor it is going to start. It also makes no sense mechanically to move the battery forward. The stern often is the smoothest riding part of the boat, so locating the battery there gives the least shock and physical impact to the battery. (Maybe "shock" wasn't the right word to use.)

With the increase in engine weight that comes with some of these modern motors, it has become more common to see the weight of the battery, and particularly the weight of two batteries as is often the case now with these big motors, moved to a more central position in the boat for the purpose of helping to balance the fore-and-aft trim. But it makes little sense electrically.

To maintain the battery starting circuit with the same minimal voltage drop you will have to make a substantial increase in the size of the conductors used to connect the motor to the battery. With the price of such cable at $8-per-foot, you can see this is not going to be an inexpensive project.

modenacart posted 02-05-2009 09:38 PM ET (US)     Profile for modenacart  Send Email to modenacart     
2 awg marine tinned cable is about $2.30 a foot shipped on eBay that has passed UL Standard 1426. If you doing go to the marina, you don't pay an arm and a leg.
swist posted 02-06-2009 12:04 PM ET (US)     Profile for swist  Send Email to swist     
I must be missing something here. Why would you not just run new cables? As far as I can see, some sort of splicing arrangement is:
1) More complicated
2) Harder to do right
3) Not even viable if you have to increase the cable size
4) If not more expensive, then close
5) Not recommended by at least some sources

So the reason you would splice is....?

modenacart posted 02-06-2009 12:38 PM ET (US)     Profile for modenacart  Send Email to modenacart     
Because its going to be a lot harder to run the larger cable under the engine cowling.
bluewaterpirate posted 02-06-2009 01:22 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
This is a similar item to the one Jim mentioned in his post. The picture is of the upper bilge area on my Ventura. Image-4892322-31023570-2-Web_0_70a1f7ee6b12beddfeeb0a93e5242770_1

As others have said this is something you don't want to do as cheap as possible.


jimh posted 02-06-2009 06:00 PM ET (US)     Profile for jimh  Send Email to jimh     
That terminal block and cover look nice. What brand or manufacturer makes that model?
L H G posted 02-06-2009 06:45 PM ET (US)     Profile for L H G    
Bluewater - Are you telling us that BW is using these Terminal Posts when the boat's batteries are not within the reach of the Mercury factory installed engine [battery] cables?

Or are they removing the engine's original cables, and installing new, full length, heaver wire size, cables?

Jefecinco posted 02-06-2009 06:53 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Winter must be solidly upon us. Thirty one posts on this subject.

We all know the correct answer is that if the OP chooses to move the battery on his boat and requires longer cables to do so the optimum solution is to use new one piece cables of the proper specifications and gage.

We'll be out on the water next week and hopefully catching a cooler full of speckeled sea trout with a red drum or two thrown in. :=)


bluewaterpirate posted 02-06-2009 07:39 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
That is original factory rigging from 2002.


L H G posted 02-06-2009 07:46 PM ET (US)     Profile for L H G    
If Jef is correct, then, someone ought to clue in Boston Whaler.
HAPPYJIM posted 02-06-2009 09:16 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
A properly done splice is electrically the same as a straight run of wire. You will not have any resistance in a splice if done the right way. Splices are done every day in the electrical field. Everything from high voltage transmission lines that come directly from power plants to micro voltage signal wire is spliced in the industry. I see nothing wrong with a properly done splice or a terminal block arrangement. A terminal block would make it easier to trouble shoot an electrical problem. I would avoid a splice that could not visually be inspected.

I've worked as a shipboard electrician on a Coast Guard Cutter and later as an aircraft electrician on C-130's. I was a Quality Assurance inspector and inspected countless splices on C-130's. When done properly, they are inspected once and never inspected again. The only place , that I can remember, that splices were prohibited was in the fuel quantity system where signal voltages, in fuel tanks, could cause an explosion under the right conditions.

Go one gauge up from what is existing from console to existing battery location. Then use a splice or terminal block and use existing wire to go from there to engine.

Or replace entire run with one size larger conductor. Save old conductors just in case you want to go back to original set-up.

Jefecinco posted 02-07-2009 09:48 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     

Like you I've used 3M termination and splice kits. The applications were usually for 4160 volt direct burial applications at forward bases for military power uses. Also used for 13,800 volt applications in overhead distribution systems. The direct burial cable and aluminum clad overhead cable is waaaaay too expensive to avoid splices so we use them and they work well.

In small craft applications with untrained owners doing the work I feel the optimun solution for extending battery cables is to replace them with a properly sized cable. That's just me. As an electrical power systems kind of guy I like to wear a belt with my suspenders. When you have to ship home one of your guys in a box because of failure to follow safety procedures you get paranoid about leaving anything to chance. One person in 35+ years of working medium and high yoltage is one too many but the job goes on.

A least with spliced battery cables the probable worst case failure is fire. That's usually surviveable in warm inshore water even without a working radio with DCS.


modenacart posted 02-07-2009 04:05 PM ET (US)     Profile for modenacart  Send Email to modenacart     
Guys, this is just a spliced wire to the battery. The splice will be out of the water and out of the path under the hull. It will be perfectly fine. Using 2 awg cable will be more then sufficient.
bluewaterpirate posted 02-07-2009 04:39 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
The terminal block used by Whaler on my Ventura is made by BlueSea. Yes, on my Whaler used the battery cables that came with my 225 Opti and connected them to the primary starting cables via a BlueSea terminal block. I've seen this method used by a number of other manufacturer's. I've never had issue with this install and it's the orignal cabling that came stock on the Ventura.

Here's a picture of the block. 4892322_2160096_60426627_WebSmall_3/ Image-4892322-60426627-2-WebSmall_0_d3df8eaac4bc14a3b77bb76e0c2b75d1_1


L H G posted 02-07-2009 08:13 PM ET (US)     Profile for L H G    
Thank you for that information, Tom. I have seen that detail on many of the newer Whalers, and with all of the armchair experts around here, I was beginning to think I was either losing my mind, or Boston Whaler's factory rigging work was incompetent, cheaply done or a safety hazard.
jimh posted 02-07-2009 10:56 PM ET (US)     Profile for jimh  Send Email to jimh     
On a small open boat you should expect the deck to be flooded at some time. When there is a foot of water in the boat is precisely the moment when you want the electrical system to not fail. Placing any electrical terminals or equipment near the deck level is a poor practice, and the fact that it is done by a boat builder doesn't mean it's the best solution. It probably means it's the most expedient for manufacturing.
Casco Bay Outrage posted 02-08-2009 08:57 AM ET (US)     Profile for Casco Bay Outrage  Send Email to Casco Bay Outrage     
Modenacart -

Take my lesson to heart.

On my 1987 Montauk (3rd owner) I suffered two seasons with starting issues. I was left stuck at the ramp on one occasion and stuck on an island on another. (see as an example. Sal, Jim H and others on this board tried to help troubleshoot the problem.

A year or two later, just prior to selling the boat, I ran new battery cables from the console back to the engine. Lo and behold, there was a splice about 2' from the motor I never saw. It was well done, electrical tape, heat shrink, metal crimp etc. When I pried open the crimp, corrosion. Man, was I pissed at myself for not finding it 2 years earlier.

Running the battery cable through the engine grommet to the studs is easy.

Choice is yours.

bluewaterpirate posted 02-08-2009 06:01 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
I agree ... I would never splice in the the tunnel.

On the current Whalers there are areas for cable runs that lead to locations in the bilge that are accessible and out of the bilge itself. On my Ventura the terminal block location is surrounded by an area designed to move water away from it and into the bilge for removal. The terminal block is easy to get to and can be inspected with ease. After each underway period it's one of the many areas I look at just to safe. Here are some pictures of the terminal block and surrounding area. The battery wires run from the helm to the terminal block by way of the area under the starboard gunwale. 4892322_2160096_60525969_WebSmall_3/ Image-4892322-60525969-2-WebSmall_0_debe85034720eba0fb2f12356810e829_1 4892322_2160096_60525964_WebSmall_3/ Image-4892322-60525964-2-WebSmall_0_2c5dd46af7c8ccfe02bc55e675b6f4dd_1 4892322_2160096_60525998_WebSmall_3/ Image-4892322-60525998-2-WebSmall_0_a8f455e0eac11e05d31f71e1d610a1a4_1 4892322_2160096_60525967_WebSmall_3/ Image-4892322-60525967-2-WebSmall_0_7cf736e3e3069ee2c4417dede5d3617f_1

My Ventura has been used extensively in saltwater over the last seven years and I've yet to see even a trace of corrision on the battery connector wires or the terminal block. They were well sealed by Whaler at the factory.


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