Can using the wrong wire gauge decrease the performance of the trolling motor?

[shingo]

I bought a used boat and it has a plug to connect my trolling motor.

My trolling motor is a minn kota power drive V2 which use 8 gauge wire, but I saw that the wire connecting the battery to the socket is only 12 gauge. I know this can cause overheat but can it also decrease the performance of the engine?

I'm asking because my top speed is 2 mph with my 16 feet aluminium boat, which I find a bit slow.

Thank you

 

[Scott Danforth]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

I would be more concerned about a fire than I would be about performance.

attempting to pull the 40-50 amps thru 12 gauge wire will turn it into a toaster element.

 

[Grandad]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

An undersized wire will definitely create poor performance. As mentioned by Scott, your first concern is safety since an undersized wire gets hot. It gets hot because the wire is actually using up your battery's energy. That energy is not being delivered to your motor, so it will underperform due to the lower voltage it actually receives. - Grandad

 

[shingo]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

An undersized wire will definitely create poor performance. As mentioned by Scott, your first concern is safety since an undersized wire gets hot. It gets hot because the wire is actually using up your battery's energy. That energy is not being delivered to your motor, so it will underperform due to the lower voltage it actually receives. - Grandad

I bought the boat used, it has been used with this cable for 15 years without issue. I'm going to buy a replacement cable today. I guess 8 gauge wire will be good for a 55 trolling motor? should I go with a 6 gauge? any downside?

The wire is 8 feet long.

 

[gm280]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

All of the above comments are absolutely true and safety IS the main concern.

With that stated, One can use 12 gauge wire even in a 55 amp draw condition. BUT it has to be short enough NOT to cause heat. A piece of 12 gauge wire of a really small length can work at 55 amps, but when you get into long runs it will glow red hot and certainly cause fire and other things too. Think about fuses. Those fusible elements are very small gauge wires (for simplicity in this case) but then they are only about 1/4" long or even shorter.

Bottom line is, you have to size the wire not only for the amperage draw, but also factor in the length of the wire run too... The longer the run, the bigger the gauge wire for the same amperage capability...

 

[Grandad]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

I agree with gm280 that the longer the run, the greater the problem with performance, but not temperature. The increased length adds proportional resistance, increasing the total voltage drop throughout the length and ultimately reducing the current flow. As the current flow is restricted, the amount of heat generated per unit length is reduced, though the effect on performance is magnified. Heat energy dissipated in a wire measured in electrical units is Watts = Amps x Amps x Resistance. Doubling the length doubles the resistance which by Ohm's Law cuts the current in half. Since current has a squaring relationship in the formula, dividing the current by 2 divides the dissipated wattage by 4.

When you replace the wiring, make sure that you replace both the positive and any undersized negative wires, since both contribute to the circuit's total resistance. - Grandad

 

[shingo]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

I agree with gm280 that the longer the run, the greater the problem with performance, but not temperature. The increased length adds proportional resistance, increasing the total voltage drop throughout the length and ultimately reducing the current flow. As the current flow is restricted, the amount of heat generated per unit length is reduced, though the effect on performance is magnified. Heat energy dissipated in a wire measured in electrical units is Watts = Amps x Amps x Resistance. Doubling the length doubles the resistance which by Ohm's Law cuts the current in half. Since current has a squaring relationship in the formula, dividing the current by 2 divides the dissipated wattage by 4.

When you replace the wiring, make sure that you replace both the positive and any undersized negative wires, since both contribute to the circuit's total resistance. - Grandad

IT's a simple boat with a very simple circuit : a 12 gauge double wire goes from the both pole of the battery and then go to a socket, the trolling motor is plugged in the socket.

I will replace both the positive and negative.

 

[shingo]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

So, would you use 6 or 8 gauge?

 

[Auger01]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

I woukd use six to keep the voltage drop resonable.

 

[Grandad]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

So, would you use 6 or 8 gauge?

The correct gauge to use always depends upon the actual current needs of the specific motor plus a consideration for the length of your wire. In your case, I'd suggest that you look up what gauge the motor manufacturer recommends. The length in your case is not excessive, so I wouldn't be too concerned about that aspect. Using a larger than necessary cable can cause problems sometimes with terminal fittings and there is a diminishing return in the benefit of larger wire. Typically circuits carrying up to 40 amps would use a #8 AWG wire. A #6 AWG wire would be rated at about 60 amps, depending upon the insulation temperature rating. To get a feel for your current situation consider that the resistance of a #12 AWG wire is about 2.5 times the resistance of a #8 AWG. Since losses occur on the square of the currents, the losses in the #12 are about 6 times the loss in the #8. - Grandad

 

[shingo]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

This is the recommendation from minn kota :

My wire goes 8 feet from the positive of the battery to the electric engine and another 8 feet back, so the circuit is 16 feet total.

Minn kota recommend 8 gauge for a 10 feet circuit and 6 gauge for a 20 feet circuit. I guess 6 gauge won't be overkill.

 

[shingo]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

Just finish replacing the 12 gauge by 6 gauge, man that cable was old, oxidized and very very small.

I don't know if it will increase my top speed, but I should have less loss in the system and more safety.

 

[Grandad]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

Hi shingo. Glad to hear she's ready to go. Please report back and let us know if there is an improvement. - Grandad

 

[gm280]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

shingo, very good choice of gauge. Like Grandad said, please report back with your results because others will also learn from this thread and that IS what this forum is all about... :thumb:

 

[Barnacle_Bill]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

Make sure you installed a 50 amp circuit breaker at the battery

 

[shingo]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

I installed a 60 amp circuit breaker, not a 50 amp. Minn kota recommend a 60 amp breaker for a 55amp electric motor.

I tried yesterday with my boat and it's not a huge difference but is is there, my top speed is now 3.3mph, the condition were around the same as last time, so I'm pretty sure the wire gauge made a difference.

 

[Scott Danforth]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

that is about a 55% increase

 

[Grandad]

Re: Can using the wrong wire gauge decrease the performance of the trolling motor?

I tried yesterday with my boat and it's not a huge difference but is is there, my top speed is now 3.3mph, the condition were around the same as last time, so I'm pretty sure the wire gauge made a difference.

An increase from 2 MPH to 3.3 MPH is a substantial percentage increase. One thing that you may also notice is that you'll likely have a greater range on a battery charge. More of the battery's energy will be spent on propulsion, rather than wasted as heat in your wiring harness. - Grandad

 

[tommytx]

Couple of ways to check the loss.
1. wrap your hand around the wire while at full speed.. anything more than the slight warm is wasting power big time....just slightly warm after a while is ok...but when you have no loss due to resistance its not losing anything.. if more than slightly warm down to the next number... like 12 to 10 to 8 to 6... the smaller the number the bigger the wire..
2. If you have a dc volt meter and can access the ends of the wire at the motor.. put black meter lead on the ground of the battery and the red lead on the end of the wire going to the motor as close as possible to the motor as possible.. more than half a volt... 0.5 volt is too much loss go to a lower number of wire. As you accelerate the motor you should see the voltmeter climb slightly... greater than 1/2 a volt is too much loss.

 

[UncleWillie]

To put some example numbers to this ...

Assume the battery is at 12.00 volts and the wire run is 12.5 ft out and back 25ft round trip.
Assume the motor draws 50 amps at 12 volts. 600 Watts (.24 ohms)
25 ft of 12ga has 0.04ohms resistance.
.24Ohms + .04 = .28ohms ... 12v / .28 = 43amps ... 43A * .24 = 10.3v ... 10.3v x 43A = 434watts ... 434w / 600w = 74% power.

You are running the motor on 10.3 volts. The equivalent of a dead battery.
You are loosing 26% of your power to the 12 gage wiring.
This is definitely a case where Bigger IS Better, and overdoing it doesn't hurt a thing.

Disclaimer: The electrically inclined, will realize that I ignored all the motor impedance factors,
but this simplified example makes the point.