Circuit breaker protection for Trolling Motor

[BlindHog]

Someone told me the other day that the reason I have burnt up two trolling motors in 5 yrs is I need a circuit breaker between it and the battery. ?:eusa_wall

Can anybody explain this to me?

Sounds logical I guess, but.....

[whistlingwings]

Thermal breaker maybe...if you have a lengthy run in between the motor and the battery

[David B]

Look at the size (ga. ) of the wire you are running between the two and then the distance. Is this something you installed or is it factory?
It seems that most of the smaller boats come with a wire ga. that is merely insufficent.
You need to know what the trolling motor is rated at amperage wise as well before you buy a breaker.

[whistlingwings]

I=V/R

I being current in amps
V being voltage
R being resistance

Most MFG's will use a #10 wire for runs for trolling motors. #10 copper has a maximum of 15 amp power transmission rating per 1000ft according to NEC
The longer the run the more resistance the wire will create lowering the efficiency of the wire to carry current.

Resistance in a circuit is dealt with by Heat and voltage drop.

1: heat, resistance increases, voltage drops and creates heat to dissipate the voltage.

2: Loaded circuit..such as trolling motor running, voltage drop causes heat in the motors switch causing the switch to fail 90% of the time. The armature can also degrade. The lamination of the winidings can fail leading to a shorted circuit which in turn creates more heat and eventually leading to an open (burned windings).

Theorhetical Circuit.

12VDC power supply
Trolling motor pulling 25 amps at the source
10' length of run #10WG

Will have a 1.027 Voltage drop at the load
Voltage load at the end of circuit will be 10.973Vdc
8.56 percent voltage drop.

A Circuit breaker will truly not provide much protection unless you upgrade the wiring to #8AWG or better to keep your current load down and your supply voltage as close to 12vdc as possible. A circuit breaker only protects against an over current situation, such as a short

[David B]

Winston,

I was hoping someone would come on and explain it in details. I surely would have butchered it up had I tried.
This is one of those times when bigger is always better.
I actually moved my battery in my boat when running a T motor.

Thanks for the e - class.

David

[BlindHog]

Thanks, guys, but you are talking to someone who runs a VERY low tech boat (and doesnt understand basic electricity 101).

I should clarify, I have a johnboat, with the battery connected to the basic Minn Kota transom mount motor. Nothing else runs off battery. The motor's cord is what comes from factory, I guess 10 ga. and about 3' long. No variables, or customization, just basic stuff.

WW - are you saying installing 8 ga wire on my motor could help me?

When you say "keep your current load down and your supply voltage as close to 12vdc as possible" What can I do to accomplish these?

The only technical info I recall from my discussion with this fellow (who rebuilds trolling motors) was that when the voltage is low, that is when I can burn it out.

Someone on a fishing forum told me to use a fusebox with 50 amp fuse. (Make any sense?)

[whistlingwings]

If its a Minn Kota with the twist grip speed selector, the selector switch is the weak point. Not much you can about it. With your short run of cable the factory cable is sufficent to carry the load but the switch eventually overheats and fails.

[Kevin Hall]

For what it's worth ...

I've always used #4 wire for a trolling motor. It's better to have "too much" wire (capacity) than not enough.

[BlindHog]

Winston - That rings a bell, he said something about making the motor into a singlespeed (the highest one of course) is a solution I think after one burns out and is fixable. I only use fastest speed anyway. I wonder if you would come out ahead doing that modification before a problem arises.

[whistlingwings]

Been there...

Can be made 3 speed via toggle switches, low, med, high. With the addition of 3 diodes you can have 3 speeds in reverse as well.