[C320-list] Battery Cable Size

[Jeff Hare]

Hi Dave,

Just my thoughts, but even assuming ~35-40' length (round trip) at 40A (Charger max output is divided up across each of the outputs and shouldn't exceed 40A):

1 AWG is more than sufficient.  1/0 is probably just wasting money and creating problems for you when you go to add connectors that'll fit your charger.

Side Note:

When you're talking about an externally regulated high output alternator (125A+ wired to AGM batteries, 2/0 cables are more likely what you're after for this run.)

Remember 350-400 Ah batteries yield ~200 Ah or less of usable power max.  Assume you drew down those to the 50% level, To restore 200Ah to batteries takes a 40a charger a good 5-8 hours at nearly full power to accomplish that.  For those with internally regulated stock alternators, recharging the same amount will take close to 10 hours to restore the capacity because the alternator will heat up almost immediately and drop its current output ~proportionally.

-Jeff Hare
2001 #809 Woodbine II

-----Original Message-----
From: C320-list <c320-list-bounces at lists.catalina320.com> On Behalf Of Dave Hupe
Sent: Tuesday, June 12, 2018 3:04 PM
To: C320-List at Catalina320.com
Subject: [C320-list] Battery Cable Size

 I have just upgraded my boat's original battery charger (NewMar 50 amp) to a Promariner Pronautic 1240P (40 amp) with a remote panel.  It seems to be running great (and not running hot like the original charger, which bothered me a lot although it didn't cook my batteries).
In the process of doing all this, I have investigated my compartments more and discovered that a previous owner replaced the original 2 positive battery cables and the negative cable with much heavier ones.  The original cables were cut off and left in the wiring channels,  and replaced by 1/0 AWG cables.  However, instead of running straight positive cables from the starboard batteries to the port side battery switch, the new cables were joined/bolted together (at lugs on the ends of each cable) under the flooring (in the widest bilge area) and taped over.  Moreover, the positive cables started appropriately as red cables at the batteries, but were both joined to black cables that ended at the control switch. I don't understand why the previous owner did this, except possibly he used preassembled cables that already had wire lugs on them. Obviously, the bolted together cables are not a good idea (especially in the bilge area). So, I intend to replace these positive cables with straight runs from each battery to the #1 and #2 switch terminals. Each run is almost 17 feet long. My question...….is 1/0 AWG battery cable a good/proper size?
Dave Hupe
1994 Cat 320 (#32)
Holland, MI