Battery Cable Sizes
I am getting ready to install a new house bank consisting of six 6-volt golf
cart batteries. 1/0 cables will carry the maximum load I need. My question
is what size do the series and parallel interconnecting cables need to be
between the batteries?
Tom Manning
Tom,
The 6 golf cart batteries will be wired in 3 parallel pairs, each pair in
series to produce 12v. The short jumper making up each 12v pair caries 1/3
of the current, so needs to be 1/3 the ampacity as the main supply cables
(to and from the battery bank). An increase of 3 numbers (#0 to #3) means
half as much copper. So use #4 for the series interconnects.
Depending how you wire them, the parallel connections might carry 2/3 and
1/3 of the current. Just look at your wiring diagram and imagine what
portion of the full current load must flow through each wire. For wires
carrying 2/3 of the current, you could use #2 or #1 wire. These are
normally short connecting cables, so voltage drop is seldom much of an
issue.
As for your #0 (also known as #1/0) main cables, have you considered voltage
drop, or looked only at ampacity (the safe current carrying capacity due to
heating and fire safety)? Cables carrying power to the main DC panel should
be sized for maximum 3% voltage drop, since it's in series with all the
branch circuit voltage drops on all your 12v equipment. I find the voltage
drop tables in the West Marine catalog to be the simplest to use.
As for availability, #3 is very rare. #1 and #0 are not so hard to find,
though not at West Marine or other marine stores. I get a lot of wire at
Skycraft surplus in Winter Park, FL, near Orlando. Much of it is NASA
surplus and very high-grade stuff.
Mark Richter, m/v Winnie the Pooh, Ortona, FL
Mark's Mobile Marine, Electrical system design, installation, repair.
I am getting ready to install a new house bank consisting of six 6-volt
golf
cart batteries. 1/0 cables will carry the maximum load I need. My question
is what size do the series and parallel interconnecting cables need to be
between the batteries?
the advice i got when i installed my inverter and 8 GC batt bank was to use
the same cable gauge for the entire system, including the interconnects..
because of the inverter size and the 6' distance bet bank and inverter, i
used the 4/0 cables recommended in the install manual. i really dont' see
why you would use smaller cables for your 3 interconnects... they are so
short, we're talking a few pennies... well maybe not pennies but quarters..
:-)
pascal
miami, fl
70 hatteras 53my
----- Original Message -----
From: "Mark Richter" richter-pooh@rocketmail.com
To: trawlers-and-trawlering@lists.samurai.com
Sent: Tuesday, January 16, 2007 9:42 AM
Subject: Re: T&T: Battery Cable Sizes
Tom,
The 6 golf cart batteries will be wired in 3 parallel pairs, each pair in
series to produce 12v. The short jumper making up each 12v pair caries
1/3
of the current, so needs to be 1/3 the ampacity as the main supply cables
(to and from the battery bank). An increase of 3 numbers (#0 to #3) means
half as much copper. So use #4 for the series interconnects.
<<i really dont' see why you would use smaller cables for your 3
interconnects.
For a bank made up of (6) golf cart batteries, I count 7 interconnect
cables. Besides the extra and unnecessary cost, larger diameter cables are
difficult to bend, and take up too much space at the top of the batteries,
making it difficult to access the water fill caps. Ease of maintenance is
an important feature, and should not be sacrificed without cause.
I try to size every wire on the boat correctly, rather than using the theory
that bigger is always better. For many house battery systems on 40'
trawlers, this comes out to #2/0 cable for the main battery bank feeds, and
#2 for the interconnects, but every case needs to be looked at and figured
for its requirements. Long leads will need to be larger than short leads.
3000 watt inverters need larger leads than 1000w inverters.
And don't forget to get a properly sized fuse into every hot wire that
doesn't crank the engine, per ABYC suggestions. I was called to a boat near
here last week to investigate the cause of a fire. The owner had just
installed a wind generator on the aft deck, and left to go to town. A
neighboring boat owner saw smoke, went aboard and pulled main panel wires
out until the smoke stopped, saving the boat and maybe the boatyard. The
owner had connected the wind generator with polarity reversed, and that
circuit (along with 5 others) had no fuse protection. The #10/2 cable was
melted and fused together in several places, and the 25 amp regulator melted
and burned. The needed fuse and holder would have cost about $5.
Mark Richter, m/v Winnie the Pooh, Ortona, FL
Mark's Mobile Marine, Electrical system design, installation & service.