Battery Wire size for under-console batteries

[ktisdall]

I have a 200ccp with 1986 175 johnson, recently changed out for a 2002 175 evinrude ficht ram.  Last year i ran on the older engine.  I had relocated the battery from near the transom to under the console and added a second battery and proper battery switch.

But i must have under-sized the cables leading aft to the block on the transom where the engine battery cables connected.  I used 4awg cables 15ft long each.  The engine spun too slowly to start on one battery so i always had to use both batteries when starting.

I'd like to correct that but i don't want to buy cables that are too large either since they get expensive fast.  I'm shopping custom cables over on geuinedealz dot com and looking at 1/0 cables.   From their calculator, the voltage drop is reduced from over 6% to less than 3% compared to the old 4awg cables.  I'm using a sample load of 100amps to calculate.

Can anyone give me some direction on this?

--Kevin

[seabob4]

Kevin...are you sure you didn't mean 4 GA...not 4/0?  

2GA will give you plenty of cranking power for a 175 of any type, console to the motor.  Trust me, and the hell with those stupid charts!!

[Circle Hooked]

I agree on the 2ga, that should solve your problems

[Capt. Bob]

From their calculator, the voltage drop is reduced from over 6% to less than 3% compared to the old 4awg cables.  I'm using a sample load of 100amps to calculate.

Where did you come up with the 100 amp load?
Did you measure the draw while cranking?

Why 3%?
Some magic number?

I ask this because it has never been answered by any one on this Forum, yet everything I have ever read leads me to believe that electrical devices such as starter motors work most efficiently with a 3% or less voltage drop from their power supply. I'm guessing that comes from actual electrical engineers that design motors of that type but that's only a guess.

As far as your amp draw, it's not an easily found number. Not in service manuals that I've seen but.... you can measure it and you may also find it by calling the manufacturer. They may provide it (Yamaha in Atlanta will). As an example, I measured a 170 amp cranking draw on my 1991 200 Yamaha. Atlanta confirmed a factory spec of 160-180 amp draw for this year motor. Like everything (and everyone) electrical devices tend to draw higher as they age. :cry:

Armed with the correct amperage draw while cranking and the total amount of wire length in the circuit, you can calculate accurately, the voltage drop. No one can argue that math, period.

Now you're faced with the choice to do what the design engineer recommends or what you read on a Forum. It boils down to what you and your wallet feels most comfortable with because as you stated, that wire gets very costly, very quickly.

Good luck.

[RickK]

I researched and agree with Capt Bob.  I went with 2/0 on my rebuild and 2AWG for my trolling motor feeds to the terminal block in the front of the boat - it'll be like the batteries are in the rear right next to the engine even though they are 15 ft of wire away.  Hard to argue with the engineers, the calcs and the logic.

[seabob4]

While voltage drop tables, amperage draws, calculations based on proven mathematical formulas, and engineers specs are all well and good, I find it interesting that new Yamahas and Suzukis, straight out of the crate, come with approx. 12' battery cable leads that are metric in GA size, midway between 4 and 2 GA.  You can actually fit a 4 GA lug on the ends if you twist the strands really tight, the cable end sort of "swims in a 2 GA lug, I have to crimp down the 2 GA lug quite a bit more than if I was just using standard SAE 2 GA.

So are Yam (and maybe Zuke) telling us one thing and practicing another?  OMC/BRP used to ship their cables loose in the crate, they were basically the same thing.  Merc, of course, gave you nothing.  Merc's like that...

[Capt. Bob]

Well, we agree on the mathematics of voltage drop so again I pose the question of the 3%  allowable voltage drop.

I have been searching for some time for a real reason as to why this % is quoted in so many publications. I have even ran across the 2% or less allowable for starter motor so.......  

Could it be that new marine starters draw so much less amperage?
Yet again, you have been using 2AWG for years so that can't be it.

Maybe a call is needed to an engine manufacturer and see where that gets me.

Using your 12' of 3AWG supplied by the manufacturer would result in a 6.9% drop, more than double the 3%.
Could it be that the manufacturer feels that the voltage drop, which would result in a slightly slower cranking speed and the additional heat generated, are within their allowable tolerances for the motor and any adverse effects caused would not take place within an acceptable time frame to the factory warranty.

That would leave 3% to the engineers, and allowable time to failure under warranty to the bean counters.  

In the end, it all comes down to money.

[seabob4]

Bob, I'm not sure at all of any thing here regarding what the manufacturers say as opposed to what they "authorize".  When I was at Proline, I worked very closely with all the manufacturer's field engineers...John Litjens with Mercury, Jon Ponedel with Suzuki, Dennis Avery with Honda, and Kim Cagle with BRP.  The ONLY motors we hung that required a step up in cable size were Verados, and even then, it was only to 1GA...not 1/0.  And even with Vrods, it was not about the starter, it was about the engine's onboard electronics...Vrods want super voltage in the 12VDC range, as well as the DTS system and the Smartcraft system.  They DO NOT tolerate lower voltages without doing funny, undesirable things.  BRP and Honda are the most low-voltage tolerant, Zuke needs REALLY good voltage when using their SMIS NMEA 2K system when you first initialize the parameters (engine interfaces mainly).  After the initialization phase, they are less affected by lower voltages.

As far as Yamahas, I worked very closely with Vito Pauluzzio both at WC/AS and quite a bit at Stamas.  Never a problem with Yam supplied cables.  On some boat models, particularly the 290 and 310 Express, because of the locations of the batts, we had to "extend" the cables.  We did this using Power Posts and adding in the appropriate lengths of 2 GA.

I'm not saying who's right and who's not, I'm just giving my experiences working directly with the guys from the factories...

[Capt. Bob]

Understood Bob.

I spoke with Yamaha USA in Georgia a few minutes ago and they supplied a couple of interesting facts gleaned from some source they have.

Using a 2014 HPDI 2 stroker 175 hp motor they stated that the continuous amperage draw was a whopping 195 amps.

They also stated that acceptable voltage drop should measure 0.7 v or less. They also stated that there was an (*) next to that and the (*) read "0.4 v or less (new date)". My understanding is this is an updated acceptable range.
These must be manuals for technicians or possibly engineers. Who knows?

If we use the logic of a .7 v drop or less, we can back into wire size and/or distance from source. Interestingly, using a 3AWG and the .7 v drop, you could locate the battery 9' from the motor or in other words have a total circuit length of 18'. That stated, using 2AWG with the .7V drop, you circuit run is increased to 11.5'. That would leave a half a foot to scratch your back with.

In either case, the % voltage drop is closer to 7% which is more than double the 3% I've seen just about everywhere and once again leads back to my original question from so long ago. It would appear that Yamaha is concentrating on actual voltage supplied to the starter (still calculated via voltage drop) but allowing the % to fall where it may. Still.......

Running the same calcs using the .4v drop results in a shorter total circuit (about 11 feet) with the 3AWG and about 14' with the 2AWG. As would be expected, the % drop decreases and is just above 3%.

There you have it. Knowing your amperage draw and total circuit length is needed to properly size the wire but it appears that older allowable voltage drops will double the 3% often quoted.

In the end I opted to use the 3% drop in relocating my batteries forward of the fuel tank. I couldn't quite hit it but the .5v drop I have appears to fall in the range of the .7v- .4v I learned about today so I'm content. 8)
This equates to a 4% drop overall and the motor spins very well.

Getting back to the original post, I feel Kevin's estimated amp draw is too low. I'm unclear on the length of the circuit (how much total cable you will have in the circuit) but feel that using a .7v drop might still be feasible with the 2AWG. Using 150 amp draw would give you about a 30' total circuit.
Would that work where you now have the batteries?

Interesting ideas and the first time I found any real math leaning away from the 3% figure. As I stated in another thread, the best search engine is the telephone.

Good luck

[flounderpounder225]

I use number #2 AWG on my battery install under the console works good

[ktisdall]

Wow - this is a hotter topic than I thought it would be.

The existing wire is 4awg not 4/0.   I corrected that typo in the original post.  Sorry for any confusion.

I took 3% voltage drop because the charts I have seen offer that as an usable option to 1%.   I thought that would be reasonable vs the cost of larger cable and getting to 1%.

I took 100 amps as a good-rough-guess at what the load might be.  Sounds like 150 is a closer estimate and it may be impossible to know without test equipment.

The idea of 'calling up BRP' sounds like an exercise in frustration.  What's the number of the engineering dept?

The engine-attached cables seem to be about 4awg or possibly less, and I expect that will affect the voltage drop 'seen' by the starter, even though those are only long enough to tie into the power posts inside the transom.    My effort is to try as much as possible within financial limits to make the motor think the battery is still located in the stern.

Sounds like many folks use 2awg cables for the type of extension I'm doing.  I'm ok with the cost to go to 1/0 cables.    The one-way cable length is 15' from battery to transom (I measured the ones I took out).  So total circuit length is 30' to the power posts.

So I'll go with 1/0 cables and it should be much better than what I had, but still under $200 for the cables all made up properly.

Thanks all.

--Kevin

[ktisdall]

Kevin...are you sure you didn't mean 4 GA...not 4/0?  

2GA will give you plenty of cranking power for a 175 of any type, console to the motor.  Trust me, and the hell with those stupid charts!!

Thanks!  I like your style....

--Kevin

[flounderpounder225]

I use number #2 AWG on my battery install under the console works good

Correction, mine is #1 AWG from Genuine Dealz...

[seabob4]

I used to do quite a few bow thrusters, both at Stamas and PL.  Stamas, we used Vetus thrusters.  Stern located batt, the most we ran was 1/0.  At PL, since they hadn't done them before and I had, I was put in charge of that "program".  First tried Volvo QL (the rep was a good friend of my boss... ).  Nothing but 4/0 cable...you guys ever work with that chit?  About the size of a quarter in dia., had to go out and buy one of those linesman crimpers (real long handles, about $500...) to crimp on the lugs!  Told the rep, "Your motor isn't very efficient, is it?"  He didn't really comment.

Next was Lewmar.  Same rated thrust motor, same tunnel diameter and prop size...yet only required 1 GA from stern to thruster.  VERY efficient motor, just a few more $$ than Volvo.  So what it takes for a piece of equipment to operate well given a certain voltage and said pieces of equipment's efficiency (read that amp draw under load) has a lot to do with cable size.

We finally went with Florida Bow Thrusters to do our install, as the head honcho didn't like the time it took to detail in the tunnel.  They used Vetus thrusters, and, once again, 1/0...

[jdupree]

When I re-wired my boat and moved my batteries under the console I went with #2 AWG.  Perfectly fine as the others stated.  My motor turns over very quickly and I don't see any kind of voltage drop either.