[C320-list] Charger/battery fuses

[Jon Vez]

Hi Bruce,

The short answer is yes, your upgrade is probably the culprit. To answer
your questions, the fuse is there to protect the wire, not the device and
per ABYC any wire attached directly to the battery should be fused within 7"
of the battery's positive terminal. I had a '99 as well and Catalina did not
do a very good job of properly fusing our boats. They get around the 7" rule
by putting the wire in conduits--different discussion.

So you need a fuse that will protect your wire based on size and large
enough to meet the current requirements of the device it is attached to. If
your '99 was wired as mine was, it is probably a 6 gauge wire rated for 105
degrees. If this is the case, then you could install a fuse as large as 120A
and as small as 40A (the size of the load of your charger). Since the load
on this wire will never carry anything but your charger's max amperage, 40
would be fine. An elegant way to accomplish this is with a Blue Seas MRBF
fuse holder/fuse. These simply attach to the positive terminal on your
battery. If your main battery positive cables are also not protected by a
fuse (mine was not). You can purchase a dual MRBF and take care of both.
Having said this, make sure the fuse is not blowing due to a cut or chafe in
the wire which would cause a dead short and potentially a fire--this is
exactly what the fuse is designed to protect against...
The Blue Seas website has some excellent information on this topic. Also
google 'Marine Ampacity Tables' for fuse sizing. WM and Calder also have
this information...

Regards,

Jon Vez (formerly 99 #582)

-----Original Message-----
From: c320-list-bounces at lists.catalina320.com
[mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of B. Stumpp
Sent: Tuesday, September 10, 2013 11:10 AM
To: c320-list at lists.catalina320.com
Subject: [C320-list] Charger/battery fuses

A couple of years ago I discovered there are 20-amp cartridge-type fuses
in-line between the charger and the batteries on our 320.   Found these the
hard way when a battery wasn't charging and I thought we had a bad
battery.found a blown fuse using a continuity test.  They are in-line in the
red cables and are basically stuffed out-of-sight up under the starboard
settee.  A couple of questions related to these fuses: 

1. What is the purpose of these fuses?  Apparently not all 320's have them.


2. In the past couple of weeks I've blown two of the fuses on battery #2.
The boat originally had a 20-amp charger.  This past winter I replaced the
charger with a 40-amp Xantrex charger.  We haven't been out sailing much
this year and, since the engine charges the batteries, we did not notice
when the first fuse blew - could have happened early on but not sure.  Could
the fuse be blowing because of the charger upgrade?  If so, would it be
okay/safe/correct to change to a 30- or 40-amp fuse?               

3. What is the correct fuse designation?  I previously had FNM-20, then
could only find FLM-20 at the electronics store and a friend's 310 used a
TRM-20.    

4. Has anyone else had experiences with these?  Anyone upgraded their
charger and changed these fuses?  

Bruce Stumpp

#647, 1999 Catalina 320, Adventure

Frog Mortar Creek, Maryland