wiring trolling motors

[cray]

I bought a 50lb powerdrive bow mount. Installed trolling motor plug that came w/ 10 ga wire. Ran 10 ga from the battery at the rear to the trolling motor.

Did I go to light w/ the wire?

[Kevin Turner]

Most likely yes.

[carlcmc]

what does heavier gauge get you? i ran 8 gauge for my new 70 lb minkota

[Moose-Hunter]

The heavier gauge wire, the less resistance between your battery(s) and your motor. The lower the resistance, the lower the power drop. Especially if the cable runs are greater than 10 feet...

I just completed a 74lb., 24 volt install. One battery is in the forward storage compartment, the other back near the stern. I used 6 gauge for my power/ground runs to connect the batts and also up to the motor plug.

In this case, bigger IS better...

[Genofish]

i have a on-board charger that i need to extend the starting battery leads. the charger is in front and the battery in the back. what size wire is needed??

[carlcmc]

how can you gauge how much power drop you are getting and whether it would be wise to install heavier gauge?

[TSCTSC]

Yeah....where can I get marine cables for my wiring. I know I can get 14 gauge wires in red and black from Walmart etc, but cables are (Contact US Regarding This Word) hard to find. Also, I used 14 gauge to connect my charger from the back to the front battery. I hope that is correct as the wires on the charger itself were also 14 gauge.

[wayner]

10 guage is way to light of wire! Your trolling motor most likely has 8 guage leads on it. In my opinion the trolling motor plugs with the 10 guage are insufficient. I took mine back to cabelas when I realized it was only 10 guage. If you are powering you bow mount with your battery in the rear you should run 6 guage for that kind of distance. If you battery is in the bow you can use 8 guage. Also don't forget to fuse the positive lead as close to the battery as possible. Marine dealers sell nice circuit breakers that work also. 40 amp should work. 50 would work also. I have purchased 6 guage cable by the foot at Napa before. Wayne

[Valv]

I think unless you have high thrust motors, 10gauge is plenty enough for your 50lbs. Most of boat mfg installs 10 gauges for 12v and 24v motors, if they do it it's enough, they study this and don't want to get sued for undersized wires.

Yes larger is better but I think too large is an overkill.

[carlcmc]

i installed a 70lb thrus at front of my 20' pontoon boat and ran 8 gauge to the batteries in the back. Do you think that is sufficient? Is it worthwhile tearing it out to replace with 6 gauge? What exactly would one gain with the increase in gauge?

[TSCTSC]

Wow...you guys are running huge gauges. But is it the same for battery charging? THe marine battery charger comes standard with 14 AWG wires. I use these to run to my batteries.

[Giant_Jackpot]

14 should be fine for charging. Not quite as many amps going through with a charger compared to the motor itself.

[fish-n-geek]

A typical "acceptable" power drop is 3% for a load circuit. So you need to combine the amp draw of the motor, the voltage, and distance to determine the proper wire diameter.

A 50lb powerdrive has a max amp draw of 42 amps. If you have a 16' boat, we'll say 32 feet of wire, for a guess. I get a whopping 4 gauge wire for pushing this much power over that much cable. If you had the battery in front and only had a 10' round trip, you would be fine with 8 gauge.

A 16' (one-way) run of 10AWG wire carrying 42 Amps at 12V will have a voltage drop of around 1.6V or 13%. This works out to about 10.4V at the motor instead of 12V.

The same run of 6AWG (my boat) has a voltage drop of .6V or 5%, resulting in 11.4V at the motor, versus 12V.

For the 20' pontoon with a 74lb and 8AWG: I'm going to still assume 42amp max draw, since that's what the 70lb minnkotas are rated at. You get a drop of 1.3V or 10.8% with 10.7V at the motor. Going to 6AWG would get you to a .8V drop or 6.7% with 11.2 at the motor.

These are based on assumptions about the wire resitance, etc. The only way to *really* know what your drop is for a given brand/gauge of wire is to put a load on it and measure the load and the voltage drop.

How much makes a difference? Well, I'm going to walk really far out on a thin branch and see if my math holds me up.

A motor with a max draw of 42amps at 12V uses 504 watts. Assuming 100% efficiency for sake of discussion, this puts the motor at 2/3HP. (.6756). When the voltage drops to 11.5V, we get 463 watts, or .6206 HP. Further to 11V, we are at 423 watts, ro .567 HP.

Extrapolating beyond where I'm sure my math will hold me, a 1V drop (8%) reduces the effective horsepower of the motor by 16%. Kind of like getting 42HP out of a 50HP outboard.

Clear as mud??

-rus-

[cray]

so what happens if you run 14 ft of 8ga to a 10 ga plug and then back to 8ga motor leads?

[fish-n-geek]

14 feet of 8AWG has a .9V drop, six inches of 10AWG has another .1V and say six foot 8AWG leads to the motor is another .4V. Hence a 1.4V drop, assuming that that is even remotely valid, which I think it is. Its all about how much power you are losing to heat from resistance. There is probably also a little bit of loss at each of the 8 to 10 connections, which will have higher resistance than clear wire.

You're burning off 4 watts in the six inches of 10AWG, so whatever amount of heat that works out to....

[carlcmc]

whoa. i'm impressed with your analysis. That might be enough for me to run 6 or even 4 gauge?

[kato811]

gees i think we all should hook our trolling motors directly to the batterys LOL. i think i need to upgrade my wiring after reading this post thanks

[fish-n-geek]

All the numbers are hypothetical, as each brand/type of wiring has slightly varying resistance characteristics. I'll probably measure the voltage drop on my motor to see how close it is to the calculated values, and I'll let you all know.

-r-

[dnoz]

I just did this on my boat went from 12 volt to 24 volt system. You can get the wire at Home Depot. 8 or 6 guage wire was .25 per foot.

[fish-n-geek]

By calculation, the voltage drop on my 6AWG should be .257V

I measured a voltage drop of .25V, so I'd say the calculations are pretty close. I also only measured a 9amp draw on my motor, but that was dry. I'm curious what it will draw when I am heading into the wind, etc.