Originally Posted by btrayfors
Starting circuits are important! This is no place to guess or to skimp on wire size. Inrush current typically can exceed 1,000 amps, then drop to several hundred amps.
Typically, starter cables
on boats are way undersized, in my experience. As Maine
says, the difference between AWG2 and AWG1/0 cable is very noticeable.
I would not wire ANY starting circuit with less than AWG1/0. For longer runs (over 15' round trip) I would use AWG2/0.
The proper ANL or MRBF fuse size for a small diesel
is in the 200-300A range. I'd prefer the upper figure and, on my boat with a 4-108, have a 400A ANL in a start circuit with AWG 2/0 cable.
And, I would NEVER solder lugs or crimp connections on a boat. Good crimpers are available (they're a bit pricey but WELL worth it). Be sure you have a crimper which is designed for the type of lug or terminal to be used.
There are numerous threads on crimping and soldering which provide great info and pictures.
I have been meaning to get back to thread but work just keeps getting in the way
It is not often that I disagree with Bill's comments but I have to say I don't share his concern about starter cables being way undersized. Sure larger sized cable is always better (assuming lugs etc will fit on the terminals and such) but mostly we use larger cable to eliminate voltage drop to voltage sensitive devices or to increase efficency of circuits that are mostly turned on.
A starter motor is very tolerant of low terminal voltages due to being series wound. In this instance I referring to the voltage present at the terminals of the motor, not the battery
terminals. It is used for a few seconds at a time so efficency is not an issue.
What it is not tolerant to is low current capacity of the supply source (the battery). Providing the battery
can deliver its rated CCA, some extra resistance in the wiring
will only cause a voltage drop at the motor terminals.
A 12 volt, 1 KW series wound motor will deliver 1KW (almost) when connected to 6 volts (but drawing twice the current and having a lower RPM). Of course there are limits, mainly due to winding restraints and overheating
but even at a full 12 volts, there are limits (mainly overheating).
I am not recommending to go small in wiring
size but likewise I don't believe in going oversize just to keep the motor terminal voltage near to battery terminal voltage and yes, to repeat again, big IS better but not always necessary. This is a case of don't sweat the small stuff - IMO.