Fuse size battery to starter?

[orangeTANG]

I have a 1985 Mercury 18XD and I'd like to put a fuse inline between the battery and motor to protect it from a reoccurance of an issue I had last week when the solenoid stuck open and caused melting and smoke of the wire between solenoid and starter.


the local boat shop has fuses that attach to the battery post then you connect the existing wire to it. only thing I need to know is what size fuse I need.

anyone know either the size or what I need to do to find out?

 

[gm280]

Re: Fuse size battery to starter?

That would be hard to say not being able to test the current draw on your setup. But I do know it is going to be a high number for such a fuse. If you had a current meter to install in series with the battery positive red wire, you could determine the true size. Another way could be to measure the ohmage (resistance) of your starter and use ohm's law to calculate it... But that too may be hard to do because it could be in the milliohm range and most DVM's, VOM's or analog meters usually don't read that small a resistance valve... And as resistance goes down current goes up!

 

[Scott Danforth]

Re: Fuse size battery to starter?

the problem with a fuse in a high current draw system is that to get a fuse large enough to prevent smoke, it wont prevent the wire from getting hot.

starters draw a lot of current for the initial moving of the load, then the current drops off as the load starts moving.

 

[orangeTANG]

Re: Fuse size battery to starter?

can I base it off the size of the wiring either the thinner one between solenoid and starter or battery and motor? what other options do I have for a quick disconnect method? right now the battery is in a battery box and the wire is attached using wing nuts. when this happened it was a real scramble to get to the battery and get the wing but off with pliers.

 

[Scott Danforth]

Re: Fuse size battery to starter?

you would be looking at about a 150 to 200 amp fuse. generally for starter wiring, the wire is sized off the average current draw, and not the inrush current.

you would be better to have a $5 battery switch vs a $50 fuse and holder

 

[schematic]

Re: Fuse size battery to starter?

ditto Scott

Battery disconnect is a good idea at any time. Do not install a cheap "post mounted knob disconnect" if you plan on open-circuiting a cranking engine. The open arc produced will ignite the gassing battery and rip your face off.....