"Dick Locke" wrote in message
...
I am thinking about installing dual electric primary winches, which
are 1500 watt 12 v motors (still waiting on the electric specs to see
breaker size which will define wiring size. I believe that's startup
wattage.)

The breaker should be sized appropriately to protect the wiring, not the
load. For most motor applications you can ignore the startup draw if you
use a slow blow fuse or a thermal breaker. This is because the startup
current only last for a second or two and a thermal breaker won't trip that
fast. A winch, however, is a different story since it is likely that you
could encounter stall situations during use. A heavy load on the winch will
draw a lot of current, which will cause a voltage drop, which reduces the
torque of the motor which further leads to stall, which makes it want to
draw even more current.

I would recommend using wire of sufficient size to handle the maximum
current with a minimum of voltage drop. Hopefully the manufacturer of the
winch can tell you what the minimum voltage to the motor should be
(hopefully it will be something like 10 volts). Establish what the voltage
of the batteries is likely to be when you are using the winches (11 volts
would not be an unreasonable number). The difference between these two (1
volt in this case) is the maximum drop you can tolerate. Leave a little for
the connections and you can tolerate a 10% drop in voltage.


The boat has two sets of house batteries, one set on starboard about 6
feet forward of the starboard winch, one on port almost directly under
the port winch.

Your 1500 watts at 10 volts will draw 150 amps. I would expect that 6 foot
run to require 20 feet of wire (10 for the positive and another 10 for the
return).

Choose whose table you want to believe. For reasons I never understood this
seems to be a big variable. The manufacturer of the wire you intend to use
should be a good source. Here is one such source:

http://www.ancorproducts.com/

Go to the their "technical informatio", "Wire Size", enter the parameters
(20 feet, 150 amps, 12 volts, 10%) and it indicates that you need a minimum
of 4 awg wire. If it was me, I would hedge my bets and install 2 awg wire
just because I hate voltage drops.

Also look at the maximum current for the wi 4awg has a maximum current
of 160 amps, 2 awg can handle 210 amps. The circuit breaker you install
should not be larger than these respective currents.





Is there any reason why I need to wire the port winch all the way
across the boat to the distribution panel? I'm inclined to hook it up
just after the disconnect switch (or with its own disconnect switch)
directly to the port batteries. It would have a circuit breaker, of
course.


Sounds like a good idea to me, as long as you can count on having
reasonable state of charge in both batteries. I can imagine sailing home
from a weekend and not being able to use the port winch because that battery
is dead!

Rod