Engine wiring question

[NLaudy]

I am running a 2003 25hp Mercury 2stroke on my boat. I am in the process of moving the batteries to the front of the boat.

1- Currently there is no fuse or breaker on the line going from engine to battery. Is there supposed to be one? I figured there would be but I believe this is how it came from factory. If so, what size is needed.

2- The current engine wires are 8ga. Is it safe to extend these wires from 5ft which they are now... To 16ft?

Thanks in advance for any help.

 

[NLaudy]

No one knows?

 

[Whitaker201]

I would like to hear what people say about this too. I am moving my batteries to the front also but my motor is a 92 60hp Evinrude. I already bought 6ga wire for the job but no breaker.

 

[RivRunR]

First of all, I know nothing about running wire to an outboard specifically, but just generally speaking you would want circuit protection for wire running the length of the boat, so that would be a circuit breaker close to the battery.

The gauge of wire needed is determined by total length of the circuit (pos & neg) and the max amp draw of the device, in this case the motor. I have no idea how you would find out the amp draw when starting up an outboard, which I would think would be the point of max amp draw.

So somehow you'd have to find out that amp draw to know both the circuit breaker and the wire size. For example, 6AWG is recommended for a 3% voltage drop for a run of 30 feet at 25 amps. Here's a Wire Selection Chart

Sorry I couldn't be of more help, just don't have any experience with that.

 

[JMichael]

I'm no expert with boat motor wiring either but I've never seen or heard of a breaker installed on the wires that go from a battery to a starter on any kind of motor whether it be automotive, ATV, boat, etc. I'm not saying you shouldn't install one but I would think it's going to have to be a pretty hefty size breaker because I suspect the initial spike amp draw of a starter when it's trying to get a motor spinning has to be pretty large. The big spike in amp draw when the starter first starts to spin the motor might be the reason they don't try to install breakers.

 

[FerrisBueller]

I'd would have to agree with JMichael that I have also never seen a breaker between the battery and motor. I know that on my 25hp outboard there is a fuse installed internally but that is after the starter wires

 

[typed by ben]

NLaudy » 24 Jun 2013, 11:52[/url]"]I am running a 2003 25hp Mercury 2stroke on my boat. I am in the process of moving the batteries to the front of the boat.

1- Currently there is no fuse or breaker on the line going from engine to battery. Is there supposed to be one? I figured there would be but I believe this is how it came from factory. If so, what size is needed.

2- The current engine wires are 8ga. Is it safe to extend these wires from 5ft which they are now... To 16ft?

Thanks in advance for any help.

1. like others said you would need one hell of a breaker to protect a starter wire- in this case 140 amps plus. could you protect it? yes but it is not conventional and not required.

to that point, draw on one of these starters is in the 120 amp range. the chart posted above is a nice guideline but tough to use for this application as its resolution is in 20' increments. you might be better off using this:

https://www.supercircuits.com/resources/tools/voltage-drop-calculator

2. if we plug your givens and the assumed draw of 120 amps we see that your 5' starter leads are in an acceptable range (5%) for voltage drop. lengthen them to 16' however and we lose close to 20% of our voltage at the device. that will be noticeable and while not necessarily dangerous, it will affect starter and battery performance and potentially shorten the life of each, not to mention the life of the solenoid, flywheel, and spur gear

 

[BigTerp]

This is a question that I'm curious to the answer to as well. The manual for my 1994 50/35 Johnson Jet is very specific when it comes to wiring the motor. It details alot of stuff. For example:

Model - 40-50
Voltage - 12-12.4
Amps (maximum) - 32

It also details what gauge wire should be used based on run length of that wire. Which is a much heavier gauge than what I get with the charts posted above. The manual even explains in what order to mount accessories to the threaded battery post with the starter wire. But no where does it mention anything about a circuit breaker or fuses. Based on 32 amps maximum I was planning on installing a 35 amp circuit breaker. But now I'm thinking it's not needed??

 

[chevyrulz]

it doesn't need one because it's wired to the starter solenoid, I extended mine about 8' using 4ga wire & some 4-8ga butt butt connectors from west marine, liquid electrical tape applied liberally.

a solenoid is a switch basically, & it only operates with sufficient current. so it's effectively in the "off" position, until it get's enough juice to click to the "on" position. meaning it's like a tripped breaker that resets itself when you turn the key

if you're adding 16', you definitely want to use the biggest wire you can find, and some very good butt connectors for the junction. the longer the wire, the more resistance, so if the wires are too long, they could over heat & burn up your starter, or worse yet cause a fire.

8ga should be fine, just hook everything up before you hide the wires & make sure it works ok. it's not a ridiculous amount of current, but if you have a poor junction between your existing wire from the engine & your new wire extension to the battery, it could melt

 

[BigTerp]

Thanks Chevy!! Based on my manual, IIRC, it has minnimum recommendations of 8ga for < 6', 6ga for 6'-12' and 4ga for > than 12' (something to that effect). It also says under no circumstance should you run more than 16' of wire. I'm guessing due to the resistance you were talking about.

 

[RivRunR]

chevyrulz » Today, 09:57[/url]"]

...the longer the wire, the more resistance, so if the wires are too long, they could over heat & burn up your starter, or worse yet cause a fire.

...but if you have a poor junction between your existing wire from the engine & your new wire extension to the battery, it could melt

uhm...these are arguments for NOT having a breaker? :?

 

[RivRunR]

FWIW, this is quoted from another boating site...looks like fuses/breakers aren't used (but probably should be) and that a battery disconnect switch is an alternative.

There are two approaches to extending the battery cables of the outboard motor: splice in a new extension and re-use the old cables, or discard the old cables and get a new, one-piece, splice-free cable. We explore each solution.

SPLICED BATTERY CABLES

If you wish to extend the battery cables by splicing in a new conductor, the new conductor will need to have very low voltage drop. The existing battery cables were probably sized to be about the smallest conductors which would provide proper voltage drop for their length, so the extension cables need to be very large size conductors in order that they have almost no voltage drop. Because a spliced cable will have extra connections, these connections are also potential sources of additional voltage drop, and one must be very careful that the splice and its connections are very well made so as not to introduce any additional voltage drop into the circuit. The location of the splice must also be considered. If it is below deck and in an area where water can pool and stand, the splice must be absolutely waterproof.

NON-SPLICED BATTERY CABLES

Discarding the original battery cables and replacing them with new cables of the proper conductor size for the total length of the circuit eliminates all of the splice and connector problems. If the conductor is run in a tunnel there will not be any spliced connections which may be in standing water. Generally this results in a smaller size conductor being used than if you splice an extension onto the original cable. Although you will have to purchase more cable, the cost will be about the same because the price of the smaller cable will be less per foot. The smaller cable will be more flexible, which is a benefit for use with an outboard motor.

FUSING

If the extended conductor runs through a tunnel or conduit, consideration ought to be given to using a fuse to protect it. In most cases engine starting circuits are not fused because the peak current is very high and fuses which can tolerate such a current are very expensive, bulky, and difficult to find. Inserting a fuse also adds more connections to the circuit, and these are also sources of potential voltage drop. Most installation do not use a fuse. Locating a primary battery disconnect switch near the battery is a reasonable alternative. This means you will also have to relocate the primary battery distribution switch to be closer to the battery.

 

[chevyrulz]

RivRunR » 28 Jun 2013, 16:07[/url]"]

chevyrulz » Today, 09:57[/url]"]

...the longer the wire, the more resistance, so if the wires are too long, they could over heat & burn up your starter, or worse yet cause a fire.

...but if you have a poor junction between your existing wire from the engine & your new wire extension to the battery, it could melt

uhm...these are arguments for NOT having a breaker? :?

haha nah, having additional insurance is never a bad thing. It wasn't my intention to argue against having a breaker or fuse on your power wire from the battery to the starter. I've just never seen one on a starter circuit so I assume, perhaps dangerously, that they're not necessary.

 

[BigTerp]

Now I'm back to being confused again #-o

 

[RivRunR]

BigTerp » Yesterday, 15:55[/url]"]Now I'm back to being confused again #-o

Sorry...didn't mean to confuse matters.

And again, I don't have any hands-on experience, but it just seems to me that circuit protection would be a good idea if you're running wire the entire length of the boat with what may be a large (but brief) amp load.
The first step would be to do some research to try and find out how much amp load there is at ignition. If you can't find out on the www, then maybe you could find someone local that would let you use their ammeter. Then you'd have to decide if the right-sized breaker is practical and affordable. If it's not, then I guess your next best option is to leave the wiring exposed as much as possible (so you can quickly see if there's a problem) and install a battery disconnect switch.

Either way, you're going to need some pretty heavy wire to avoid both melting/fire and to avoid major voltage drop.

On the other hand, if you're moving your starter battery to the bow just for weight distribution, maybe an easier answer is just to add weight to the bow and leave the starter battery in the stern.

 

[BigTerp]

No worries, I just want to make sure I'm doing things correctly/safely, especially when it comes to electrical work. You've already been a HUGE help!!

Now, based on what my manual says for my 1994 50/35 Johnson jet if I'm going to install a breaker I would want something like a 35amp breaker, correct? Or am I way off base here?

From my manual:

Model - 40-50
Voltage - 12-12.4
Amps (maximum) - 32

 

[typed by ben]

id like to know more about specifically what that amp rating means... as i have a hard time believing thats all the starter will draw

to size that breaker you will want to multiply your full load by 125%- in your case the breaker would need to be 43.75 amps. round that up to an even 50 amps since nobody makes a 43.75 amp breaker

but again i sincerely doubt thats all your starter draws. it may take 35 to spin it but who knows what it will take to get it spinning initially. maybe they arent counting the spike; who knows

 

[JMichael]

typed by ben » Yesterday, 19:05[/url]"]id like to know more about specifically what that amp rating means... as i have a hard time believing thats all the starter will draw

to size that breaker you will want to multiply your full load by 125%- in your case the breaker would need to be 43.75 amps. round that up to an even 50 amps since nobody makes a 43.75 amp breaker

but again i sincerely doubt thats all your starter draws. it may take 35 to spin it but who knows what it will take to get it spinning initially. maybe they arent counting the spike; who knows

I'm with you, but I've already stated that so I'm content to sit back and watch this now and see what happens. There's a reason that motor mfg's don't install breakers on the motors starter wires but a lot of people seem to be ignoring that.

 

[typed by ben]

yeah its kind of an odd problem. i think they dont bother because the load is only momentary.

 

[NLaudy]

Thanks for all the information everyone. Since I had already bought the 8ga wire I went ahead and connected it with the butt connectors. The motor starts up fine as it did before. I reckon I will keep an eye on it and time will tell.