Starting Amps Required for a 1998 115 hp Evinrude

[kraw2]

Hello,

I am tying to size my battery cable on a boat I am restoring. The engine is a 1998 115 hp Evinrude. What are the needed amps for starting this motor?

Thank you

[slvrlng]

Is the motor a Ficht? They require more amps than the carbed. My 94 175 book says it only requires 500 so I would think your motor wouldn't need more than that (unless its a Ficht).

[kraw2]

It's a carbed motor so I believe 500 amps is plenty.

Thank you

[Capt. Bob]

I'm not an electrician but love masquerading as one so......

The amp draw to break the inertia of the motor when starting is indeed high ( I believe I measured 290 amps) but it's a momentary (think < second +/-). The continuous amp draw on my 200 Yamaha measured at 170 amps. This is the draw as the motor is spinning away just before it fires. I've sized my battery cables based on this (170) and the length of the circuit. I could never find this continuous draw figure anywhere so I actually measured mine with a Fluke amp meter.

I'm sure you are familiar with the voltage drop calculators found on-line. I used this one.
http://genuinedealz.com/voltage-drop.html

With the cost of wire as high as it is, knowing what you actually need is important (unless you're always flush).
The older JohnnyRudes (mid 90s) and it appears my model Yammy need to be spinning at a good clip (300 + rpm) to start quickly (stator /magnets/energize the power packs/ make the good spark, etc) so a fully charged battery with a minimum of voltage drop is a must. I used 3% loss as a guide. I also believe that with the higher voltage, the windings in the starter do not heat as quickly (all based on time of use) and thus last longer.

Told you I like being a closet electrician.

[kraw2]

I'm not an electrician but love masquerading as one so......

The amp draw to break the inertia of the motor when starting is indeed high ( I believe I measured 290 amps) but it's a momentary (think < second +/-). The continuous amp draw on my 200 Yamaha measured at 170 amps. This is the draw as the motor is spinning away just before it fires. I've sized my battery cables based on this (170) and the length of the circuit. I could never find this continuous draw figure anywhere so I actually measured mine with a Fluke amp meter.

I'm sure you are familiar with the voltage drop calculators found on-line. I used this one.
http://genuinedealz.com/voltage-drop.html

With the cost of wire as high as it is, knowing what you actually need is important (unless you're always flush).
The older JohnnyRudes (mid 90s) and it appears my model Yammy need to be spinning at a good clip (300 + rpm) to start quickly (stator /magnets/energize the power packs/ make the good spark, etc) so a fully charged battery with a minimum of voltage drop is a must. I used 3% loss as a guide. I also believe that with the higher voltage, the windings in the starter do not heat as quickly (all based on time of use) and thus last longer.

Told you I like being a closet electrician.

Good Job Mr. Bob,

I am a 58 year old retired plumber, electrician, builder, welder.....You know how it is the older you get.

You are totally correct in sizing the battery cables. Buying a battery is a no brainer.

The boat is a 1976 170 w/115 Evinrude that will be all "new' in a couple of months. Knowing the actual cranking amps needed tells me the gauge of the battery cable needed after calculating the other factors.

Thanks again,

Keith

[kraw2]

Speaking of Yamaha the boat I bought for my son is a 1994 Key West 1720 Sportsman with a 2001 F80 Yamaha. The original battery cables were 8 gauge and the run was about 7 feet total. The battery was located in a small compertment in the stern with a fuel/water seperator. That's a no no. That's mighty small wire. I moved the battery up to the console and used 1/0 only b/c a friend had some left over.

[Capt. Bob]

Mine are sized at 2/0 (4/0 would have gave me some wiggle room) but I shortened up cable runs wherever possible (like battery to switch). I wouldn't want to think about snaking 4/0 through the old Yammy. 2/0 was tight enough. It's amazing how much wire costs nowadays. Should have left the batteries in the back. :x

I was clueless on the voltage draw till I actually measured it with the old 4 gauge wires I used to fire up the motor. I'm glad I did.
Now I'm just over 3% on the drop but the old beast fires off much better.

Good luck.

[seabob4]

4GA if the batt's at the stern, 2GA if the batt is in the console...

4/0?  C'mon Bob, what are you starting, a V24 Cat diesel?

[Capt. Bob]

Well as I stated, I'm no electrician so...

I read up on everything I could find on voltage drop for marine starters. Everywhere I turned, I kept coming back to the 3% voltage drop as the industry standard. Using that, the length of all the existing cables I had first hooked up to the Yamaha and the measured amp draw, I first calculated by hand and then by using the online one from genuinedealz.com. I kept coming up with the same thing.

Both show I need a cable with a cross section on 70mm (squared) and that's a 2/0 cable. Trust me, I measured the voltage drop and amp draw with 4AWG cable. My cranking voltage dropped to 10.4 volts (on a fully charged battery) which equated to a 13% drop.
Is not 3% drop the industry standard? The calculator shows an 8+% drop with the 2AWG.

[seabob4]

My opinion...

Let's look at new outboards, straight out of the box (crate).  Yamahas and Suzukis both come with the batt cables already attached, both are basically 4GA (I think it's actually a metric equivalent).  Etecs I believe (didn't hang many) are attached as well, those cables are more like 2GA.  OMCs used to ship with the cables loose, but still 2GA.  Mercurys do not get cables as part of the rigging kit, but Optis require 2GA, Verados 1GA.

So let's ask a question.  We all know that starters have to work harder when lower voltages are present, thus the life span of a starter would be shortened do to the resistance and associated heat buildup that are the result of a low voltage situation.  So why would manufacturers supply their motors with undersized cables?  Yes, I realize spare parts is part of doing business, but I can't think that a manufacturer would deliberately undersize their battery cables in hopes of selling a bazillion starters down the road.  So, IMO, the cables provided with the motors, either 4 or 2, are more than adequate to handle the starting loads of the motors they are attached to.  BTW, even the 225/250 models of Yam and Zuke come with the 4GA type cables.  Now, these cables are only long enough to assume the start batt is going to be located in the stern area.  Naturally, if the owner is going to relocate the batt to the console (VERY popular these days), then one should step up the cable size to 2GA.  But 2/0 or 4/0?  Just not necessary.  Nothing wrong with it, but gets awful damn pricey real quick...

I've re-rigged many a 10, 12, even 15 year old boat where, unless the bilge areas were just NEVER taken care of, the original batt cables were still in fine shape.  And no complaints from the owners in regards to difficulty getting the motors to turn over.  

So use your head and common sense.  Batts mounted aft, 4GA will be fine.  Move the batts forward?  Step up to 2GA...

[kraw2]

Using the calculator #2 is what I come up with.

[wingtime]

I have a 78 Jeep with a built up inline 258 six.  It has high compression so it was always hard to crank..  man unless the battery was fully charged and even then it would barely turn over...  the positive batt cable and the solenoid would get crazy hot.  I was thinking of buying an high torque performance starter for it...  the jeep has been sitting and I was trying to start it the other day..  same deal would barely crank...  then I was looking at the positive batt cable..  4 ga...  Now I know I didn't build it with that size cable...  hmmm  so I went and picked up a 2GA cable... keep in mind this is a 20" long cable...  Tried to start it and the thing spun over nice and easy and started right up!  So an undersized cable will cause problems...  but 4/0!?!?!   Holy cow!

[Capt. Bob]

Using the calculator #2 is what I come up with.

I love discussion on things like this so....

First, since SB has wired hundreds (maybe 1000+) boats over his career he is a viable source in this and as such, let's use his example of the manufacturer supplying the 4AWG cable. With the battery mounted in the stern, using 170 amps as the current draw (until someone can show a lower value) and a distance of 5' (60") one way, plug in those values into the calculator. I think you will find that the voltage drop is 3.6%. This sounds like the parameters I have found in searching for what % drop is desired (though it was always stated not to exceed 3%) close enough for Government work.

Now use 2AWG and move the battery so that the one way run increases to 10'. Calculator shows a 4.6% drop.
Move the battery to 15' and you get 6.8% drop.

I originally had 18' run one way so use that distance and you get 8.2% (with 2AWG).

Therefore the question is this: Is 3% voltage drop industry standard or can one use, say 10%? This has been my dilemma. Which to use. Using 2/0 and shortening the run a couple three feet helps the problem by getting you close to the 3%.

Interestingly enough, motor manufacturers literature on cable size/lengths usually don't exceed 20' or 2AWG.
Do newer motors use a lower amperage draw? Is 3% unrealistic? I can't find any information stating no. Is 10% the real number? What is everyone else using? How many even know their % drop?
Who cares?

What length, amperage did you (Kraw2) use in the calculator?

[kraw2]

I used the Blue Sea Calculator with 120 amps @ 20 ft. run. It recommends 1 gauge cable for the allowable 3% voltage drop.

At Genuinedealz it shows a huge cable. Way too big for my application.

SeaBob recommends 2 gauge.

The 120 amps is a "guestimate" of the actual cranking amps needed. I still don't know what amperage is actually required or needed for the '98 115 OMC engine. I'm sure I'm close enough but before I purchase the cable I will find out. I hate to buy #1 when #2 is acceptable. It usually takes less than a second to start the motor or any motor.

[Blue Agave]

2GA will do the job. I have a 16' run of 2GA on my boat and it fires up my 200 ponies no problem. All the boats we rig at the shop are rigged with a 20' run of 2GA and we have not experienced any problems.