Simple Battery Cable Junction Box

[Mark42]

Two series 24 batteries are being re-located to the front of the boat. A length of 4 AWG cable runs to the back to connect to the outboard motor starter cable. I couldn't find a junction box to connect the outboard motor cable to the battery feed cables (at least not for under $100 or so). So I made this junction box:

The box is a exterior electrical 2x4" square PVC box. A couple of 304 stainless (aka 18/8) carriage bolts, washers, hex nuts, wing nuts, and washers are all the hardware that's needed. And about 4 ounces of epoxy.

Two 5/16x2" carriage bolts were used. The sides of the head were ground to make it square so it wouldn't break loose and spin in the epoxy if over tightened. About 3/8" were cut off the end to clear the box cover. Then 4 ounces of epoxy was mixed and poured in. After cure, the carriage bolts were labeled + and - to avoid any problems. A 3/4" x 2.5" slot is cut in the bottom to allow the 4 AWG cables with lug ends to come in and connect.

And the cover is attached. The screws that came with the box will be replaced with stainless screws.

Now its ready to be screwed to the inside of the transom. It will keep the battery cable connections dry and prevent anything from making contact or shorting out the posts. All for under $20.

I know, its not high tech, and I didn't make nice water proof labels, but it serves the purpose, took less than an hour to make, and fit the budget.

 

[ajgraz]

Re: Simple Battery Cable Junction Box

Very nice. You should make and sell those on EBAY.

As long as you mount that with the slot facing downward so the box can't fill with water, looks like that should work out.

My only critique is you should use 5/16" hardware for the positive, but 1/4" for the negative (standard sizes on battery cable lugs). Another layer of safety against reversed hookup.

 

[Mark42]

Re: Simple Battery Cable Junction Box

Very nice. You should make and sell those on EBAY.

As long as you mount that with the slot facing downward so the box can't fill with water, looks like that should work out.

My only critique is you should use 5/16" hardware for the positive, but 1/4" for the negative (standard sizes on battery cable lugs). Another layer of safety against reversed hookup.

Yes, the side with the wire opening will face down to prevent water dripping in.

I noticed that the battery posts are 5/16 pos and 1/4 negative, but all the cables are 5/16" lugs regardless of polarity. Next time I'll take your suggestion!

So how much do you think these will fetch on ebay?

 

[fish_on_the_deck]

Re: Simple Battery Cable Junction Box

My only critique is you should use 5/16" hardware for the positive, but 1/4" for the negative (standard sizes on battery cable lugs). Another layer of safety against reversed hookup.

I was thinking the same thing, except I thought it was 3/8" for pos and 5/16" for negative. Thats what my batteries are as well as Blue Sea's electrical products.

Overall though... pretty cool. one problem with enclosing studs like that though is you cant see them as they start to corrode... I'd lather some dialectric grease on there before closing them up.

nice little project!

 

[ajgraz]

Re: Simple Battery Cable Junction Box

So how much do you think these will fetch on ebay?

Slap a sticker on them that says "Bleu Sea Systemz" and you'll be able to sell them for $40 or $50 apiece

IIRC my battery posts are 5/16" and 1/4", I guess they could be 3/8" and 5/16", all I know for sure while sitting here at work is that they are different from one another.

Agreed with the guy above that the box is not strictly necessary, just so long as the posts are covered...I once made some lug hook-ups with some s.s. hex bolts, a bit of 3/4" polyethylene sheet, some counter-sinking, and some red and black rubber terminal boots.

 

[Mark42]

Re: Simple Battery Cable Junction Box

I thought a design that was not in a box, but realized that where this is going is a storage area. Worried about things like an anchor shorting out the terminals. The PVC box is pretty tough and should give good protection.

Ordered custom cables from gregsmarinewiresupply.com and didn't think to order them with different size lugs. So all the ends (12 of them) are 5/16" w/shrink wrap. The cables are red and black pairs, so it should be easy to keep track of which is which.

 

[nofuss]

Re: Simple Battery Cable Junction Box

Good idea I have a terminal post that is exposed and i was thinking of a way to cover it up and i like the box. did not think of that. and I also plan to add a connection point for my inverter, and although its inside its cheap enough to make it worth the extra effort to get a good box. Im coward though, so i would also include a plastic barrier between the pos and neg and i will make them diferent sizes. standard marine. would save me some money

also standard marine terminals are 3/8 positive and 5/16 negative.

 

[dude11]

Re: Simple Battery Cable Junction Box

Hey-Great idea!! Looks good-and should work very well too.Plus you'll have an easy access to some "juice" in the rear if needed.

 

[fish_on_the_deck]

Re: Simple Battery Cable Junction Box

Ordered custom cables from gregsmarinewiresupply.com and didn't think to order them with different size lugs...

I had some custom cables made by New Wire Marine:

Custom 2AWG cables

Its really simple to select terminal sizes, color, etc you want from only one product, instead of having to look through and put each lug, heat shrink, labor etc into your cart. Plus you can add custom printed labels on each end... really a top notch product... I'd like to see how the prices compare.

Yeah I agree that its a good idea for covered lugs in a cargo area.

@nofuss: I thought it was 3/8 and 5/16...

 

[guzziprov]

Re: Simple Battery Cable Junction Box

Here is a great pre made item that will work as well.

Have made my own version before but liked the ease of just buying one this time, have always gotten good quality from this company.

http://bluesea.com/category/9/38/productline/overview/400

 

[Mark42]

Re: Simple Battery Cable Junction Box

I had some custom cables made by New Wire Marine:

Custom 2AWG cables

Its really simple to select terminal sizes, color, etc you want from only one product, instead of having to look through and put each lug, heat shrink, labor etc into your cart. Plus you can add custom printed labels on each end... really a top notch product... I'd like to see how the prices compare.

Yeah I agree that its a good idea for covered lugs in a cargo area.

@nofuss: I thought it was 3/8 and 5/16...

Here is the comparison of 3 pair of red/black 4 AWG cables, (2ft, 5ft, 13 ft), tinned marine grade wire with 5/16" lugs and shrink. It is what I ordered from Greg's.

New Wire Marine............. $104.50 + ship $16.68 = $121.18
Greg's Marine Wire Supply.... $76.96 + ship $ 9.95 = $86.91

Greg's is lower than New Wire by $ 27.54 on the product, and about $5 shipping. Although Greg's doesn't offer the label at each end of the cable. That is a nice touch.

Here is a great pre made item that will work as well.

Have made my own version before but liked the ease of just buying one this time, have always gotten good quality from this company.

http://bluesea.com/category/9/38/productline/overview/400

Doh! That is what I was looking for. But I expect its a little on the expensive side. Looks to be quality product.

 

[arks]

Re: Simple Battery Cable Junction Box

Mark- Your setup looks great, but I used these when extending my battery cables:
http://www.iboats.com/Dualbus-Plus-...02288452--**********.982009204--view_id.38627
I like the fact that the cover protects the lugs but is easily removable without tools. Good product.

 

[fish_on_the_deck]

Re: Simple Battery Cable Junction Box

Greg's is lower than New Wire by $ 27.54 on the product, and about $5 shipping. Although Greg's doesn't offer the label at each end of the cable. That is a nice touch.

oh well... looks like depending on the cable types and lengths (I used 2AWG and less cable) it may be more or less of a delta, and the labels are a neat plus... guess you always gotta shop around for each item to save the most $$.

I was getting one of their custom switch panels anyway, and just threw the couple cables I needed in the cart too... I was very happy with all thier products.

@arks... thats a nice looking bus bar too... I've used the lugs that guzz posted too.

 

[Mark42]

Re: Simple Battery Cable Junction Box

oh well... looks like depending on the cable types and lengths (I used 2AWG and less cable) it may be more or less of a delta, and the labels are a neat plus... guess you always gotta shop around for each item to save the most $$.

I was getting one of their custom switch panels anyway, and just threw the couple cables I needed in the cart too... I was very happy with all thier products.

@arks... thats a nice looking bus bar too... I've used the lugs that guzz posted too.

As long as you got a high quality product, that is all that matters. The price you paid is less than most wire retailers, so you did get a good discount price.

BTW, I have been looking for a spec on how many amps a starter motor pulls. I know it will vary with model of motor. I need a reference to plug into one of those online calculators to see what the current drop will be over the length of the cables I chose.

I have jumped the motor using 15' 8AWG cable, and you would think the battery is just on a 3 foot cable, because it spins so fast. I went with the 4 AWG because the online calculators show that for the length of cable needed, there will be a much smaller drop in voltage using the 4 AWG over 6 AWG, and not enough of a voltage savings to justify the expense 2AWG cable.

I suspect from a practical application, the 4 AWG will perform very well. Will find out this weekend when the cables are delivered.

 

[Greg Mrozinski]

Re: Simple Battery Cable Junction Box

Mark,

For my resto project I am going to relocate the batteries forward to the bow area. Total run to and from the motor is about 34'. I have a 1983 Johnson 115 Hp. I didn't get a definite on the amp draw from the electric forum but estimated on the high side to be around 100-150 amps. I also used Greg's for my wire (great cutomer service and very helpful). We figured 2 AWG would probably work for my application. I safe sided it and went with 1 AWG cables. One area to look at is how big the opening is in the engine for the wire to run through and if the larger AWG size will fit.

Let us know how you made out.

 

[Mark42]

Re: Simple Battery Cable Junction Box

Mark,

For my resto project I am going to relocate the batteries forward to the bow area. Total run to and from the motor is about 34'. I have a 1983 Johnson 115 Hp. I didn't get a definite on the amp draw from the electric forum but estimated on the high side to be around 100-150 amps. I also used Greg's for my wire (great cutomer service and very helpful). We figured 2 AWG would probably work for my application. I safe sided it and went with 1 AWG cables. One area to look at is how big the opening is in the engine for the wire to run through and if the larger AWG size will fit.

Let us know how you made out.

Thanks for that info!

My setup will be a 13' run of 4 AWG to a junction box, where the outboard starter cable will connect.

If your 115hp draws 100-150 amps conservatively, then my 90 V4 will pull the same. With less than half the length of the run of your boat, I think the 4 AWG should be OK.

I used this calculator to decide on the wire gauge (scroll to the bottom to plug in your values): http://www.powerstream.com/Wire_Size.htm

Using that calculator, for the length of 4 AWG that is being used, the voltage drop is only 0.7 volts at 120 amps. That is the point where the outboard starter cables will connect. The starter cables are a full 10 feet long (much longer than my application needs) which means that a few feet can be cut off and new lugs applied to reduce resistance and therefore voltage drop. I just hate to cut a well sealed wire!!!

 

[Mark42]

Re: Simple Battery Cable Junction Box

You folks were right about the posts being 3/8 on the positive side. I ordered all the ends in 5/16" cripped lug ends. So I went to drill the lugs from 5/16 out to 3/8", but changed my mind at the last minute. Drilling out the lug is reducing the material, making a thinner lug. So instead, I took a tapered 3/8" punch and drove it through the lug end. Being that the lug is copper, it easily stretched out to 3/8" without breaking or cracking.

Probably could have just drilled them out, but using the punch retained material on the lug. Probably not a real issue for my application, but just nice to know it can be done.

 

[Yacht Dr.]

Re: Simple Battery Cable Junction Box

Im trying to be polite here Mark..

Why not just replace the lugs with correct size ?

Its just flux,solder,fittings and shrink tubbing..

Takes only 30 mins or less per fitting..

IMHO streaching without breaking the lug is not really a metallic characteristic of metal..its not bubble gum could you lose properties in the copper by expansion ?

YD.

 

[Mark42]

Re: Simple Battery Cable Junction Box

Im trying to be polite here Mark..

Why not just replace the lugs with correct size ?

Its just flux,solder,fittings and shrink tubbing..

Takes only 30 mins or less per fitting..

IMHO streaching without breaking the lug is not really a metallic characteristic of metal..its not bubble gum could you lose properties in the copper by expansion ?

YD.

If they were soldered on, I might consider it. But marine cables are not allowed to be soldered, they must be crimped. And these crimps are done with special equipment I don't have.

Also note that the copper used in lugs is very soft compared to what you are used to, so yes, it does stretch out easy.

Think of it this way: Do the lugs loose conductivity or other properties when stretched and/or compressed when being crimped?