Trolling motor blows fuses

[jasone]

Hey all, looking for a little help here.

I have a 40 lb Minn-kota trolling motor on my 17' bass boat.  I have been using it on setting number 5 and have had no trouble out of it.  

The other day I was trolling along and it suddenly gave out.  I checked the in-line fuse on the lead wire next to the battery and it was blown so badly that the heat had melted the fuse.  After I removed the fuse (30 amp) and debris, I replaced it with a 20 amp fuse and after about 10 minutes it blew as well.  

After that I got fed up and put the setting on the motor to 4.  I never had another problem.

What could possibly be causing this?  The only thing I did different was to use my bow fishfinder.  

Thanks in advance for any help.

J

[Way2slow]

First off, do away with the fuses and install a 40 amp circuit breaker if that's a 12 volt motor

Next pull the prop off and make sure it's not wrapped with line or something.

Thirty amps is right on the hairy edge of what that motor will draw on high and you really need to go to 40 amps, and no way a 20 amp is going to make it.

[jasone]

That sounds like a plan.  You don't think the 40 amp breaker would allow my wires to melt do you?

I will give it a try.  Test it at home.

J

[Way2slow]

What size cable to you have and how long are they? #8 fine strand cable can handle 35 - 40 amps, anything smaller than that and you should look at upgrading. Even if it's #10, it's not going to melt your cable but the voltage drop caused by the internal resistance of the wiring will reduce the performance of the trolling motor when on high speed. A cheap upgrade would be to go to Home Depot and get you some stranded #6 house wire. They have it in single conductor on the bulk roles. This only has eight - 10 strands of copper and while not as good as the fine strand battery/marine cable, it's a lot cheaper and will more than fit your needs.

Electrons flow over the surface area of a conductor, so the smaller the conductors, the more conductors there are inside the same guage wire, and the more surface area it has, therefore a greater load carrying capacity for the same guage wire. Thats why you'll see #6 battery/marine cable rated for approx 55 amps and #6 stranded house wire rated at approx 45 amps even though both are #6 guage cable.

Meant to mention, unless you have a large tank to run it in to load the motor and keep it cool, you can't test it at home. Motor is not going to draw anywhere near the amps out of the water as in the water, plus the motor depends on the water to keep it cool.

I got to thinking about it and checked wire size ratings and need to make a couple of corrections here, #8 AWG is rated for a max of 55 amps, #6 AWG 75 amps, but these ratings are based on the absolute max ampacity before the insulation starts melting.  My numbers are what it should handle without the internal resistance causing a reduction in performance or any heating of the cable when running on max.

[jasone]

Thanks for the tips.  That's my next option is to just rewire the dang thing.  I think it's got either #8 or #10.  I am not sure which.  They are about 16' long.

J

[George Welcome]

If the trolling motor came with a 30 amp inline fuse than you need to use a 30 amp fuse, whether you stay with the inline or go to a circuit breaker. None of the trolling motors are designed to run on high speed for a sustained period of time.

I would suggest you have the motor looked at to have the draw checked. A fire on a boat is a very nasty occurence.