Battery Wire size for under-console batteries

[GoneFission]

OK - here we go with the (somewhat) engineering side...   :rabbit:   Almost all of the above COULD be correct!  Wire size is dependent on many factors - not just current.  The type of wire can make a big difference - each wire insulation has a temperature rating - as temp rating goes up, so does current capacity.  Look carefully at the wire type and temperature rating on the jacket!  A 1/0 wire with a 105 degree temp rating has about the same rated capacity as a AWG 2 with a 185 degree rating...  

Also, you have to consider duration of use - instant/periodic current is different from continuous - most Code ratings are for continuous current.  

The number of strands (typically 17 versus 31) does not really make any difference for capacity, but does make a big difference in flexibility and bend radius.  

Length of run makes a big difference when you are nearing the capacity of the conductor, but makes little difference at lower currents out to about 50 feet at 12 volts.  24 volts has less line loss than 12 volts and reduces current by about half - so make sure that bow-mount trolling motor is a 24 (or 36!) volt motor if you want to run reasonable size wire from stern to bow.  

Terminal type also can come into play - most ring terminals are rated for the full current of the conductors that fit into the terminal if the are PROPERLY crimped/terminated.  But some terminals require special crimpers - manufacturers (Panduit, T&B, etc.) only warranty their terminals when their crimpers are used with the terminals as a system...  Also the terminal must be compatible with the conductor and connecting terminal/block - no aluminum to copper, etc.  Blade-type terminals should not be used in marine or other applications subject to vibration.  Screws on terminal blocks all have a required torque value based on type/material/size, but you rarely see torque screwdrivers being used...  

So could a AWG 2 wire work from the battery to the starter motor?  Yes, depending on several factors.  Would a AWG 2/0 work also?  Yes, again depending on the same several factors.  Would 2/0 be "better" than 2?  Not necessarily, depending on wire type, terminal types, and bend radius required...  

It's not quite as easy or simple as it sounds sometimes.  I recommend going with what the manufacturer used/recommends or use some solid experience that includes the various parameter described above.  

Good luck!

[Capt. Bob]

Good stuff.

Again I ask, do you feel the 3% voltage drop is an industry standard or more of a guideline?

It appears that Yamaha, at one time felt that a .7 v drop was acceptable but have revised it to .4 v. To me that means (assuming a properly sized and fully charged power source) that it really doesn't matter where you place the battery or size the wire as long as you fall within their recommended voltage drop.

I guess the real question boils down to "what is the minimum allowable operating voltage of the outboard's starter"?
That would take into account the necessary speed needed to produce the voltage to fire the engine yet not cause permanent damage to the starter itself.
9v? 10v? 11v? 12v?

[GoneFission]

Bob - the industry standard in wiring codes is actually 2%, not 3%.  But remember that's a continuous rating.  10 volts to the starter would be about a 20% voltage drop - that's a lot!  But the capacity of AWG 1 wire should be enough:

XHWW type wire = 195 amps
THWW type wire = 220 amps

Even plain old TW type wire comes in at 165 amps.  So AWG 1 should be fine as long as you keep your runs as short as possible and make sure the terminals are properly done.

[Capt. Bob]

Thank you John.

As stated before, I've asked repeatedly about the 2-3% voltage drop. Answers have ranged from looking at a cow's ass to a list of who's who in the boating industry but never a hard, mathematically sound, engineered based, not "cause that's the way we always do it" answer. It's hard for me to understand coming from a environment of creating contacts that require work to fall within given specifications and then holding contractors to those specs but hell, this is an internet Forum, not the real world.
Too bad I couldn't run a 36v starter and charging system on my old Yamaha. Think of the reduction in wire size that would make.

As I've stated, my concerns have always been based on the distance (in my case 25', one way) between the battery and the starter motor and the actual voltage drop (measured) at the starter.
I do know this. My old Yamaha starts easier with the larger gauge wire but also seems to deliver a more efficient (measured) charge back to the battery. At the same time it appears that I'm (in speaking with the company that built the motor) within the allowable voltage drop for that motor. Guess that makes me an expert, just ask me.

At the end of the day it's a boat, not your health, your home or (for many of us) a livelihood. One must spend their coin where they see best.

Thanks again for the time John and a straight answer.

[seabob4]

Bob, you and I (and quite a few others) know that when it comes to wire or cable, bigger is ALWAYS better.  Necessary?  Maybe not.  But better?  Yes.

One thing that we really need to consider, which some here and elsewhere don't seem to, is cost.  Most of us, even though it has often been put as, "Spring for the extra $$ and get the...", don't HAVE the extra $$ to go ahead and "spring".  $50 here, $50 there, may not seem much, if anything, to some people, but, to others, it means a lot.  So those of us that don't have the luxury to "spring" for the extra $$, we have to make do.  Not to diminish the quality, but to get the right part at the least cost.

Perhaps a study should be conducted on the longevity of starter motors and the charge rates and longevity of batteries when using 1 GA cable as opposed to 2 GA cable, to actually see if using the lesser GA cable has an effect on both, and if that effect warrants the use of the larger cable based on reduced life span of the starter and battery.  The old "cost-benefit analysis".  

So in the meantime, I will continue to support the use of 2 GA, as, in the real world, I have yet to see the negatives of its usage.  I have re-rigged many boats moving the batts to the console, on boats with 20 year old motors...and starter motors close to that age, if NOT that age.  They turn over like champs.

I'll leave it at that...

[GoneFission]

Seabob - AWG 2 would probably be fine as well - again depending on wire type, length of runs, and type of termination.  Here are the same numbers for AWG 2:

TW type wire - 140 amps
XHHW type wire - 170 amps
THHW type wire - 190 amps

The only one that would concern me here would be the TW - I think some starters pull 150 or so amps.  AWG 2 picks up .184 ohms per foot, so you can run out the length of run to keep it within 2% (or 3% or whatever).  Again - AWG 2 should be fine if you keep the runs short, use the right wire type, and proper terminals.  

Also remember that most 4-stokes are high compression engines that require higher current for starting than low compression 2-strokes.  Also, magneto or stator systems need more turning speed to generate spark than fully electronic systems.  The worst-case scenario would be a modern 4-stroke engine with a magneto ignition system - we could be looking at 200 amps+    - but thankfully, I don't know of one like that!  

[Capt. Bob]

In speaking with Yamaha, they mentioned that their V-8 F350 drew 260 amps at start up.  

My interest piqued in this subject after reading an SB post about 2 years ago. He suggested to a member to use 2AWG wire in response to a battery relocation in the console.  I had been having OK starting with the Yamaha but she wasn't spinning (my perception) all that fast. Also, by the end of the day, it seemed like the battery wasn't getting a good charge. Anyway, I measured the cable size on my long run (battery to starter) and it was bigger than a 4AWG but smaller than a 2AWG (carried over from my old CCP). My concern was that at the end of the day, I didn't want to end up buying cable too small and being dissatisfied with the results. As stated, these cables are not cheap. Also, I had fried a starter armature in my 96 Rude using these cables but it never occurred to me that the size may have contributed to the failure.
Live and learn.

[seabob4]

Size MAY have contributed Bob, but what about corrosion?  How did the cables look when you removed them?

[Capt. Bob]

When I installed them on the CCP (1996) they were new (and expensive then). The starter failed (without warning) 3 years later. I just assumed it was a bad starter from the git go. That would have made them 14 years old by the time they hit the WAC.  That starter quit just before I moved to Tallahassee and I rebuilt it up here about 8 months after it failed. It worked fine after that, right up to the time I sold the motor. I believe it's still working fine so... I just didn't put the voltage drop idea in my head until I read the cable size post. Anyway...

I did redo the connections when I used the cables on the WAC but hey, 14 years could have been a contributor to the slow spinning.  As I stated, I wanted a "warm and fuzzy" feeling that buying new cables only a size or two bigger would solve the problem. I erred on the mantra the alcoholic test woman lives by..."bigger IS ALWAYS better"

This is all good stuff Bob and I trust some members will use it in the future (the alcoholic test I mean ).

I would have though you'd be watching the Hawks.

[seabob4]

I am Bob.  I have 2 displays out in the shop.  Live streaming on one, forum du jour on the other...



Plus it's warm enough outside tonight...