Boat Builder Central - Builder Forums

Hi all,

I plan to relocate the battery from the aft locker to under a seat in a cabin.

Can I junction the stock outboard cables to a new short run (4AWG) of cable with proper terminals to the battery ? I dont want to disconnect the current ones on outboard and re-wire.

I used 12 AWG for the main electrical cables in the current layout. I hope the extra length required will still be ok on the existing circuit. I am adding about 8' of new cable but will check my schematics for loads, length and ampacity.

The main switch and fuse are also relocated.,I cant stand where they are now in the aft locker with the lounger platform on.

Maybe, but not my favorite idea. You'd need a commercial quality crimper. I have one, but you can also just use a hammer impact tool which is cheap enough.

It depends, really on the engine and starter.

But also, connections subject to moisture and eye terminals would not be good.

So, the only way to connect the wires would be butt connector for 4 gauge.

And those are subject to one caveat.

You are adding 16 feet, not 8. Current calculations always include both the hot and the ground.

Assuming you have 4 gauge and a 90-100 amp starter which is the maximum allowable ampacity for 4 gauge, the maximum allowable length is only 10 feet total for 3% drop, which is only enough for your current case.

If you have an 80 amp draw, 15 feet total @3%. Still too much for the addition.

So, som assumptions, best case.

80 amp draw, current case is 10 feet, adding 16 puts you at 2 gauge in almost every case.

It can be done, But, unfortunately, you are going to be drawing down hard and I recommend you switch to 2 gauge or correct my assumptions.

Also, 100amp is one gauge.

However, I have one question in my next reply.

Are you moving the battery for weight change? Or to get a different locker? Or because you are moving the helm?

Hi fallguy1000,

Yes mainly for weight change and i just do not like where it is (same with main switch and fuse)
located now)

Not the end of the world and can live with the current layout but...

I can always relocate the battery and main switch under the lounger platform and out of the aft locker. i.e. use the outboard cables stretched out.
Right now the excess cable is coiled next to the battery. That also moves a fair bit of weight somewhat nearer to the middle.

Fyi If doable I was going to use pre crimped cables on Amazon. I also saw butt connectors for heavy cables being available.

Maybe this is a waste of effort and should leave as is. I guess it bothers me too much

What size outboard do you have, what is the starting amps required, and what is the alternator output? This will determine the size wiring you need.

cape man wrote: ↑Thu Aug 11, 2022 10:42 am What size outboard do you have, what is the starting amps required, and what is the alternator output? This will determine the size wiring you need.

Alt output is something that is easily found because the manufacturer wants you to know it and replacement parts are for each size and type motor, flywheels and block sizes are different. But a single starter motor could be applicable to a number of different HP motors and finding what a outboard starter motor draws for a said HP is very hard to find. My starter motor does not have amps on it and my service manual does not have it either, nor does the troubleshooting section of the manual. Service shops will even tell you need heavy gauge wire. Anyway....

May be easier to take the size cable that came with the motor, then the length of the cable and figure what amperage that cable can carry via a marine wire selection chart. Add the extra length needed to reach the new location of the battery and look at a marine wiring chart to figure what gauge wire is needed. Then use a bolt style terminal block to connect factory cable to add on cable. You can get custom made cables; with the ends you want for a little more than the parts needed to do it. Here is a Mom and Pop place, even if their website is fancy or they sold out the last few years.
https://www.customcableusa.com/products ... y-the-foot

For the bolt style terminal block:
https://www.wholesalemarine.com/blue-se ... ower-post/

OQ, Custom Cabke and Wire was used by a lot of guys back in the early days CL and some others used them for their boats. They have everything you basically need from switches to fuses to cables in all sizes. They were always slightly cheaper back then 15 years ago. I don't know now with the price of copper having risen so much. Tom

Hello Marc
I have done just what you're wanting to do. I have junction posts in the starboard aft locker with both the positive and negative cables from the outboard landed there and then continuing to the helm bulkhead with 4 gauge cables. You can add another couple of feet to that as the cables go from a off/on/combine switch to the start battery. My 9.9 spins over very well on the starter but I haven't checked voltage drop. The start battery is an old agm (8 yr at least) that was rated at 100ah when new. I have a couple of crimpers so the wiring went fairly well. What type of battery do you have? If you put a flooded lead acid inside the cabin it is recommended to vent it outside which causes a bunch more work. I went with some salvaged agm's from old solar powered sites and have they have worked out well.
Doug

TomW1 wrote: ↑Thu Aug 11, 2022 1:21 pm OQ, Custom Cabke and Wire was used by a lot of guys back in the early days CL and some others used them for their boats. They have everything you basically need from switches to fuses to cables in all sizes. They were always slightly cheaper back then 15 years ago. I don't know now with the price of copper having risen so much. Tom

Since you posted a link a few years back, I have been ordering most all my wire, terminal ends, terminal blocks and so on from them. The "Mom" and the "Pop" I have talked to over the phone a few times due to not having exactly what I was trying to order, they are like doing business with BBC when it comes to customer service, they are easy to work with and strong need to take care of their customers, new and regulars. Seems he told me at one time or another that they work out of the house or garage, I may be wrong, but their website and name has changed, my saved link is under a different name but still works.

Just saw your post saying you have an agm battery. Should be good to go.

Hey guys thank you for the replies.

Doug N...this is great. I don't suppose you can forward photos of your set-up to "escape1463@gmail.com" or we can discuss ovee phone ? I would like to talk if possible.

Yes it is a Group 21 AGM. I can get all the parts required from a few narine shops around here and AWG pre terminated cables of different lengths as well.

I will go measure the boat this evening and also the Merc cables to see what is required.

Marc

Just to be clear, ABYC has made no accomodation and all battery lockers require venting. An AGM battery, while technically sealed can still outgas hydrogen sulfide?, but if it does, it does not breathe back and so agms get waffled if overcharged and heated up.

It did happen to me because I thought I could draw 12v off a 24v bank. What happens is the bank is constantly overcharging the 'good' one. And I waffled an AGM. So, the experience is real to the textbook reasons.

Any battery locker should be relatively easy to vent outside the living space.

Doug N wrote: ↑Thu Aug 11, 2022 2:38 pm Hello Marc
I have done just what you're wanting to do. I have junction posts in the starboard aft locker with both the positive and negative cables from the outboard landed there and then continuing to the helm bulkhead with 4 gauge cables. You can add another couple of feet to that as the cables go from a off/on/combine switch to the start battery. My 9.9 spins over very well on the starter but I haven't checked voltage drop. The start battery is an old agm (8 yr at least) that was rated at 100ah when new. I have a couple of crimpers so the wiring went fairly well. What type of battery do you have? If you put a flooded lead acid inside the cabin it is recommended to vent it outside which causes a bunch more work. I went with some salvaged agm's from old solar powered sites and have they have worked out well.
Doug

I did the same thing with my HMD. Battery is up front, these boats need all the weight up front that they can get. I have a terminal block under the gunnel with heavy Guage wiring to the battery to extend the outboard cables. Our little 9.9 kickers don't draw much juice. I wouldn't worry too much. I think the factory cables on my EFI Suzy are only 8 gauge.