Wire gauge to feed a trolling motor

[Lilly001]

In my continuing saga of setting up my boat I just mounted a 55 lbd (50 amp breaker) trolling motor to the bow.
As it’s a stick steer (and I’m a healthy boy) I plan to put the battery in the rear.
My question is it’s a 16’ boat so I figure about 15’ run. Is 8 gauge large enough? Or do I need 6, or even 4 gauge?

 

[Liquid nails]

#8 is good for 40amps

#6 is good for 60amps

I ran #4 on my 24v ulterra.

 

[Lilly001]

#8 is good for 40amps

#6 is good for 60amps

I ran #4 on my 24v ulterra.

Does the run (15’)) make a difference?
Or is it to short to matter?

 

[The Original Rooster]

Does the run (15’)) make a difference?
Or is it to short to matter?

I'm about to remodel my boat too. I found this that might help.https://baymarinesupply.com/calculator
This chart makes better sense to me.
https://www.bluesea.com/resources/1437
So a run of 15 feet is really 30 feet because the chart says there and back.

 

[Liquid nails]

Does the run (15’)) make a difference?
Or is it to short to matter?

15’ isn’t too far I wouldn’t think. That’s about the length of mine from my console to the bow. I’d just make it as short as possible. Also, I had a quick disconnect rated for 60 amps and smoked that sucker one day when the fans were on and I was running at speed 7-10 constantly. Eliminated that out of the equation.

 

[Lilly001]

I'm about to remodel my boat too. I found this that might help.https://baymarinesupply.com/calculator
This chart makes better sense to me.
https://www.bluesea.com/resources/1437
So a run of 15 feet is really 30 feet because the chart says there and back.

O
There is a lot of information to digest in those charts.
But, I’m looking at a 60 amp load @ 25’ and I want minimal loss so I’m reading minimum 4 and better 2 gauge?
Now where can I find the wire? They say tinned multi strand copper w/ 105* insulation. And where can I find the connectors?
It doesn’t look like a normal trolling motor connector will work.
Or am I reading this all wrong?

 

[The Original Rooster]

O
There is a lot of information to digest in those charts.
But, I’m looking at a 60 amp load @ 25’ and I want minimal loss so I’m reading minimum 4 and better 2 gauge?
Now where can I find the wire? They say tinned multi strand copper w/ 105* insulation. And where can I find the connectors?
It doesn’t look like a normal trolling motor connector will work.
Or am I reading this all wrong?

There's a bunch of places online where you can order tinned marine wire and some places that you can order it already with the connectors on them. Amazon even has it. The only part I don't fully understand is the voltage drop part of 3 vs 10% and when that applies. So long as the trolling motor connector can handle the amperage, I would think it would work.

 

[Lilly001]

There's a bunch of places online where you can order tinned marine wire and some places that you can order it already with the connectors on them. Amazon even has it. The only part I don't fully understand is the voltage drop part of 3 vs 10% and when that applies.

I read that as critical vs no critical circuits.
Less that 3% vs 10%.
I want as little loss as possible (does that really matter?) to the trolling motor.

 

[The Original Rooster]

I read that as critical vs no critical circuits.
Less that 3% vs 10%.
I want as little loss as possible (does that really matter?) to the trolling motor.

That's a good point. I don't know. I'm following this thread because I'm soon to be faced with some of the same questions with my boat. A lot of what I've read has said I shouldn't have to go any larger than 6 gauge but I'm like you, I don't want to lose voltage if I don't have to. For what it's worth, I looked up my Motorguide trolling motor and it said this:

Install a manual reset circuit breaker in line with the trolling motor positive leads within 1.8 m (6 ft) of the batteries. These can be purchased from your local MotorGuide retailer or from www.motorguide.com.
Do not extend the included 10‐gauge battery cables more than 1.8 m (6 ft) for a total of 3 m (10 ft). If longer battery cables are required, MotorGuide offers accessory 8 mm2 (8‐gauge) battery cables.

 

[BoosterC]

You should be good with 6ga. If you can afford 4ga and don't have any sharp bends, go for it. Making sure you have solid connections and any solder joints are done properly are probably more important than the difference between running 4ga and 6 ga.

 

[Chris 195 7/8 B&C]

What will drive you nuts is looking at what the manufacture wire size is from the plug to the motor.
I installing 55 lb but mine is foot control.
Battery Tender makes a jam-up receptacle / plug that will accept the above mentioned wire sizes.

 

[Lilly001]

What will drive you nuts is looking at what the manufacture wire size is from the plug to the motor.
I installing 55 lb but mine is foot control.
Battery Tender makes a jam-up receptacle / plug that will accept the above mentioned wire sizes.

Yes on the original equipment. Mine looks like 8 gauge. But it’s running close to 15’ by the time you count the corners.
Im trying to get as much out of the trolling motor as possible because I didn’t want to go to a 24 volt system. I just can’t see dealing with the weight of 2 batteries.
I have considered lithium but I can’t justify paying 8-10 times as much for the batteries.
My boat is a 16’ tracker panfisher so I think 55 lbs will be enough even against the current in the river.

 

[Lilly001]

Sorry. I reread your post and from the plug to the motor looks to be 10 gauge.
Maybe all of my obsession with a bigger wire size isn’t that important?
But at least I’ll do everything I can.

 

[ghadarits]

I’m fairly sure my boat has 6 ga from the factory to run a 24v motor. Go with 6ga. Then you’ll be set for a 12v or 24v trolling motor.

 

[GTMODawg]

Does the run (15’)) make a difference?
Or is it to short to matter?

It'll make a difference at 12, 24 or 36 volts. Not so much in a house and 115 volts but the % of voltage drop would be the same and at low voltage VD is far more impactful....DC motors are voltage tolerant but the corresponding electronics are not as much and the longer the conductor the lower the voltage, higher the current and thus less battery duration. There isn't a big difference in cost between #8 and #4 tinned marine wire, XLPE insulation rated at 105 degrees. Its all over priced but the #4 will ensure proper voltage is available at the load, as long as all terminations are done correctly and properly protected against corrosion.

In general terms SAE automotive wire is not appropriate for marine applications but is far better than building wire like THHN or the like. I have used Romex with solid conductors in a boat but it ain't ideal. Marine grade XLPE tinned copper is the only real way to go when wiring a boat. There are some situations where PVC insulated marine grade wire would be acceptable...in a raceway for example, but it is about as expensive as XLPE. In a typical 25 foot or less fishing boat electrical system there isn't enough wire to make much of a cost difference and the trouble caused by bad connections and expecially untinned copper in a boat are many.

 

[GTMODawg]

I'm about to remodel my boat too. I found this that might help.https://baymarinesupply.com/calculator
This chart makes better sense to me.
https://www.bluesea.com/resources/1437
So a run of 15 feet is really 30 feet because the chart says there and back.

All conductors in any electrical circuit which are not intentionally grounded are current carrying conductors. Genrally speaking there is no such intentionally grounded conductor in most boats unless it has sleeping/living quarters. The "ground" or "negative" wire in a DC circuit is the return path to the source and voltage drop due to the resistance in that conductor is part of the overall VD in the circuit based on the total length. All VD calcs are based on the base formula of Vd being equal to current times impedance. In a simple circuit impedance is purely resistance and resistance is relative to the type of conductor being used, the size conductor and the ambient operating temperature as well as the length. In a fancy new trolling motor the electronics and the motor itself would have more or less resistance than the conductors themselves in the form of impedance but for practical purposes and the availability of standard sized conductors the resistance of the conductors themselves and the load is sufficient to calculate VD. If one were designing a buss bar or a non standard conductor size the impedance would be relevant but with standard conductor types and sizes it is sufficient to use straight resistance.

 

[GTMODawg]

O
There is a lot of information to digest in those charts.
But, I’m looking at a 60 amp load @ 25’ and I want minimal loss so I’m reading minimum 4 and better 2 gauge?
Now where can I find the wire? They say tinned multi strand copper w/ 105* insulation. And where can I find the connectors?
It doesn’t look like a normal trolling motor connector will work.
Or am I reading this all wrong?

Best Boat Wire in Jesup. Has anything anyone could ever need to wire anything in a boat and the best prices I have ever found anywhere. I know a couple of custom aluminum boat manufacturers in Washington State who deal exclusively with them and I have bought a pile of stuff from them over the years and they don't care if it is a foot of wire or a mile....they have it and are happy to ship it. I have never set foot in the place because they sell online but if one were in the area I would bet they would be a fantastic source for answering questions and advice.

 

[GTMODawg]

I read that as critical vs no critical circuits.
Less that 3% vs 10%.
I want as little loss as possible (does that really matter?) to the trolling motor.

The less VD your circuit has the better....it absolutely makes a difference in the performance of a low voltage, relatively high current load like a trolling motor. If you were only going to run that load for a few minutes at a time it wouldn't make much difference but if you are like most folks in a small fishing boat the trolling motor never shuts off during the day. Your batteries will perform better day to day, will allow for multiple days of fishing between charges when necessary and will last longer when connected to a circuit with 5% VD versus 10%.

I have a 2072 Jon boat I have recently "renovated" including re-wiring completely. It has 18 circuits in it LOL. Our house is about 3500 square feet and it only has about 30 circuits in it. The boat has a circuit for every 5 square feet of space where the house has one for every 100 or so feet of space. I may have overdone it a bit in the boat but I have 2/0 marine wire from the back of the boat to the front and have another marine fuse block with ground bar at the front and then fed my trolling motor with #4 wire from that block, about 4 feet. The 2/0 wire is about 22 feet long. I ran my trolling motor last Friday for 8 hours and 15 minutes, maintaining speed from .8 to 1.2 MPH with crazy wind and when I hooked up the charger at the house it went into discharge mode because the batteries were completely charged and had to be discharged some to begin recharging. Had I wired that boat with romex, as I have done in the past, it would have worked but the batteries would have been deader than the beer at a fundraising event when I got home and they would not last nearly as long getting worked that way.

 

[GTMODawg]

I’m fairly sure my boat has 6 ga from the factory to run a 24v motor. Go with 6ga. Then you’ll be set for a 12v or 24v trolling motor.

6 AWG is standard in reputable boat manufacturing and when terminated properly is sufficient but 4 AWG is not much more expensive and is better if any of the terminations are dodgy and most will be in a few years. Many boats have #8 trolling motor circuits and they will work but they aren't ideal. 6 is the standard in most applications.

 

[GTMODawg]

Just checked and stock is limited LOL....surprise surprise....but #8 is about .80 a foot, #6 is about $1.25 a foot and #4 is about #1.80 a foot making a 15 foot circuit cost $24, $37.50 and $54 respectively. $16.50 difference between a circuit that is sufficient and one that is over built but will prolong battery life, battery charge and tolerate the inevitable loose terminations in a marine application far better than the lower cost one.