40 amp fuse for 36 amp draw. Is it enough?

[harrisg]

I have installed a Minn Kota EM42 engine mount trolling motor that I will use for an emergency motor on the Columbia River. It's on a 16ft 1983 Invader. I need something to get me out of the shipping channel in case something happens to my Volvo Penta AQ125A main engine. <br /><br />Since I have fried the controller box, I've hooked it up to a 50A on off switch which will give me full power on forward only. My question is, since the draw for the EM42 is 36 amps, will a 40 amp fuse be enough or should I use a 50 amp?

 

[Silvertip]

Re: 40 amp fuse for 36 amp draw. Is it enough?

You will probably pop the 40A fuse immediately when the motor is switched on as current draw is at its highest with the motor stalled or at motor start. You can try it, but I'd bet a 50A will be needed.

 

[jlinder]

Re: 40 amp fuse for 36 amp draw. Is it enough?

Upinsmoke is right. Large motors many times have the specification showing amperage draw while stalled. You would be suprised at how high it is.<br /><br />I would even think that a 60 amp circuit would be better, if all the components in the circuit will support it.<br /><br />Also, there will be a pretty big surge on the 50A switch, and that is what burns switches. You might want to look at a relay to take the load.

 

[swist]

Re: 40 amp fuse for 36 amp draw. Is it enough?

You need to watch out for the types of switches you use for large inductive loads, like motors. Not only do you have to worry about the start-up current spike, but there is also an issue when you turn off the motor - a collapsing magnetic field can induce a reverse voltage of a couple of hundred volts for a brief instant and give you a big spark which can take out a plain old switch after not-too many on-off cycles. That's why a lot of motors are switched though contactors (relays) that provide protection against some of this stuff, not to mention avoiding running #8 wire (40 amps) back to some megaswitch.

 

[Richard Petersen]

Re: 40 amp fuse for 36 amp draw. Is it enough?

A car starter motor Starting Relay is what you need. Use your 50 amp switch to energize the relay. Put the 60 or 70 or 80amp fuse in the trolling motor lead somewhere. Do you know how to wire in a starting relay? If not, I can draw a diagram and scan it to you in a E Mail.

 

[harrisg]

Re: 40 amp fuse for 36 amp draw. Is it enough?

Cyclop2, I would really appreciate a diagram on how to put a relay in line because electricity is not my strong suite . My email is traderzelick@yahoo.com. The black 10 guage from the motor goes right to ground side of battery. The positive from the motor is 10 gauge then connected to 6 gauge then through an on/off switch then to an inline 50 amp fuse just before connecting to the positive side of the battery.

 

[Richard Petersen]

Re: 40 amp fuse for 36 amp draw. Is it enough?

I sent the E MAIL on Friday at 7:40 pm.

 

[jlinder]

Re: 40 amp fuse for 36 amp draw. Is it enough?

Sounds like you are fusing a ciruit at 50 amps that is in part only 10 guage wire. 30 guage wire is only rated for 30 amps.<br /><br />If you are going to fuse at 50 amps you really want it to be 6 guage all the way.