Raw Starting Current 101

[BobG]

I got the brilliant idea to relocate my batteries from the transom, into the console. On a 24 foot pontoon, how much wire should that take, right?

Well as it turned out, it took 20 feet (with maybe a foot or two of slack). I ran 6 gauge Marine grade cable, to extend the cables for the motor up to the starting battery. 6 gauge is pretty easy to work with, so I figured why not?

I went to start my motor for the first time of the season this week. It cranked really slow, and wouldn't start. Oh crap! I'm praying that it's just not heavy enough wire. As it turns out, the cables on the motor are 4 gauge - but I had to discover that by cutting the lugs off the end - I couldn't find any documentation on it.

So, I go back to West marine (I was in a hurry and knew this was gonna hurt), and 2 gauge is 5 bucks a foot - and they don't have butt splices, lugs etc. for 2 ga. Not to worry! Did you know that if you run two wires of any gauge in parallel, that it's the same as running 3 gauges smaller? So running another run of 6 gauge, gave me the same as 3 gauge cables. Of course, I had to mount some heavy-current terminal blocks in the transom to do the one-wire to two-wires connection, but that now gives me a handy place to connect jumper cables, if I ever have to. Did West Marine have two binder blocks, or even (God forbid) a TWO POST binder block with a heavy barrier between them like they show on their web site? Oh heck no. So I bought two different terminal blocks (one with a big red boot).

[OK Toon]

Bob, you are pretty dang handy when it comes to marine electrical. I wish I had those skills. I have a battery switch but I haven't built up the courage to try and install it yet. I've seen all sorts of diagrams and pictures but I think I just need to have someone who knows what they are doing watch over my shoulder so I don't damage the motor or blow myself up.

[Hawk_308]

I did the same thing with my trollling motor batteries yesterday . I thought I had enough 4 ga wire to do the job around the house , which should have been a little over kill. Of course I forgot using half of my 4 ga on another project so I had half as much as needed so as a temp fix I ran 2 10ga for the shorter run and used the 4 gauge on the longer run . Ill pick up some more 4 ga by the weekend and do it like it should be but I was hoping to try the trolling motor today .

[BobG]

Oh - by the way - doubling up the wires made all the difference in the world! She fired right up!

Amazingly, the cables on my Merc 115 were NOT MARINE GRADE WIRE!!!
I was baffled, when I cut the lugs off, and stripped the wire, and saw that it was just plain copper - not tinned.

[BobG]

Bob, you are pretty dang handy when it comes to marine electrical. I wish I had those skills. I have a battery switch but I haven't built up the courage to try and install it yet. I've seen all sorts of diagrams and pictures but I think I just need to have someone who knows what they are doing watch over my shoulder so I don't damage the motor or blow myself up.

Hah - it all started when I was 12 years old (1969). My dad was in the USAF, and taking a correspondence course in electronics from RCA. As soon as he finished a book, I would snap it up, and do it myself. By the time I was 18, and went into the USAF myself, my electronics fundamentals course was a snoozer, and because I had also had a nuclear physics class in high school, I was able to correct the instructor on how transistors actually work. Boy was he PISSED!

I could work on a tutorial on doing a battery switch installation. Maybe there are a lot of things like that I could do. A huge part of my job today, is producing documentation for the people that have to follow behind me, for support. I'm actually pretty good at it.

Also, I feel that there are others on here who know a lot more about marine electrical than me. A lot of things change when you put this stuff in a marine environment. I'm still learning those differences. Just like when you build a piece of equipment to go into space (I have - part of the Hubble Space Telescope) everything changes. Teflon coated wire, etc., etc., etc.

[Drago]

Just like when you build a piece of equipment to go into space (I have - part of the Hubble Space Telescope) everything changes. Teflon coated wire, etc., etc., etc.

bob,
God forbid, hope it wasn't the mirror! That was a real fiasco!

[BobG]

bob,
God forbid, hope it wasn't the mirror! That was a real fiasco!

Nah, Faint Object Spectrograph. http://en.wikipedia.org/wiki/Faint_Object_Spectrograph

[mike]

At least you got it going... why did you move the batteries?

[BoatCop]

One note on the Marine Grade cables, or lack thereof.

Marine grade electrical wire/cable is only required (by the USCG, NMMA & ABYC) when run in or through a closed space where fuel vapors might be present.

We all know that when you label anything with the word "marine", it doubles or triples in price. As everyone wants to reduce manufacturing costs and maximize profits, they will use the "cheaper" non-marine cable. The main difference, and what makes it "marine", is that the insulation has better resistance to hydrocarbon (oil/fuel) exposure.

As there are essentially no closed fuel or engine compartments on an outboard rigged pontoon, there's no requirement to use marine cables. (There are exceptions for a few manufacturers who place a fuel tank inside the center toon on a tri-toon, like our Crest)

[tuned]

Hey Bob. I hate to be a negative Nancy here, but I'm not totally convinced that going from 4 gauge on a short run to 3 gauge on a substantially longer run is quite enough. I couldn't tell if you meant 20 feet round trip or single run (motor to helm). Remember that you need to double your pull distance to calculate how much your wire will carry. I'm guessing that you need to use 40 feet (ish) when looking it up.

I have kinda lived with my nose buried in the West Marine ampacity charts for the last twenty years or so. Here they are: http://www.westmarine.com/WestAdvisor/M ... d-Ampacity
Looking at the 10% drop chart (for intermittent and non-critical loads). I took a rough guess at your starting current (150 amps) and original cables (8' X2=16'). These numbers show 4 gauge as acceptable.
Now if you take that amperage up to 40' and it looks to come in at 2 gauge or larger.

If your motor is running great and starts instantly, you probably will get by. If, however, you need to grind for a few seconds at any time, your wire could heat a bit. I'd hate to see you burn up a nice bow thruster. Recommend at least monitoring your wire temp for a while. Hopefully it stays cool and your summer ROCKS.

If I have made bad assumptions on numbers or miscalculated in any way, then I humbly apologize and you can chop me up into little bits and use me as mulch in one of those CO pot gardens

[r&s20]

i did pretty much the same thing as bob, without the nifty bow thruster. i relocated my batteries to my console for better weight distribution.my cables were not marine grade, so i bought a set of 4 gauge jumper cables and made new battery cables from those.i saved about 50 bucks versus buying regular battery cable wiring

[Rascal]

Cheap.... http://www.bestboatwire.com/

Rascal

[Cowracer]

When I mess with electricity, stuff like this usually happens...



Tim

[Bamaman]

Bob: You're a brave man to take on such projects.

I'm an electrician--well an amateur electrician. White to white, Black to black and green to green. And I've always got my little A/C light tester to keep myself from getting fried.

In your case with 12 volt DC, if it works you've done good.

Without any high power sucking sound system or trolling motor, I just stick with my single battery for simplicity's sake. And it's nice that if I ever have boat problems, I can call a neighbor to come tow me in--15 miles is as far as I can get away from home on our lake.

[BobG]

Hey Bob. I hate to be a negative Nancy here, but I'm not totally convinced that going from 4 gauge on a short run to 3 gauge on a substantially longer run is quite enough.

Reasonable points.
She fires right up.