Battery Charger In Line Fuse

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KevinMc
Posts: 85
Joined: Sun Sep 08, 2013 5:36 am

Battery Charger In Line Fuse

Post by KevinMc »

This past week while sailing the lower Chesapeake I noticed both the house and start batteries were not charging while on shore power or generator but would charge while underway. The charger constantly stayed in standby mode and my first thought was the Xantrex Truecharge2 40A was shot since it's probably original to the boat (2003).

Further testing showed the charger was fine but the 40 amp in-line fuses for both the house and start batteries were blown. (The 40A fuses are about 6 inches from the battery terminals and installed as part of the red charger cable running from the charger to the battery.) I replaced both fuses and the charger immediately kicked in and began charging at 100pct - for about 3 minutes when the 40A fuses blew again.

I replaced the fuses a second time and the charger began working right away but I noticed the in-line fuse holder was getting warm - then hot. I turned off the charger, cleaned the connections and made sure everything was tight. My thought was a bad connection may be showing resistance and that's why the fuse holder (on the charger side) was getting hot. After cleaning the connections it was still hot so I decided it's time to actually read the Xantrex manual where I found the solution.

I have 6 awg cable running between the charger and battery and the manual states the in-line fuse should match the wire size to prevent overheating and possible fire. For 6 awg cable the correct size fuse is 80 amps - not the 40 amps which were installed. My guess is at some point the 40A charger went to 100pct output which overheated and then blew the 40A fuse. I have no idea how long the fuses have been blown since most summer sailing we do are day sails. I got rid of the in-line automotive type fuse holder and fuses and upgraded to fuse blocks and ANL fuses.

As a FWIW I suggest you check your charger manual, see what size fuses should be installed for the size charging cable you are using and check t make sure you are not undersized.
Kevin
#59
NavSta Norfolk Marina
yodagwb
Posts: 117
Joined: Fri Jan 27, 2006 8:34 am

Re: Battery Charger In Line Fuse

Post by yodagwb »

How old are the batteries? If the fluids are to low and the plates not covered(maintenance issue) or the batteries have shed enough where they are starting to short at the bottom(age issue), the charger will through all it can at them trying to charge the batteries which it is seeing as being discharged. There in lies the reason for the in line fuses. The problem could very easily be the batteries and not the charger or the wiring. Try putting a battery that you know is good on the charger in place of the current batteries and see what happens.
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TBOT422
Posts: 424
Joined: Sun Jun 26, 2011 5:36 pm
Location: Clearwater, FL

Re: Battery Charger In Line Fuse

Post by TBOT422 »

I would check your charger manual as well. We have the original 30-amp Charles charger, and it requires a 40-amp fuse as the current does spike at initial start up. If you really have a 40-amp charger, I would suspect that it requires more than a 40-amp fuse before the battery.

Good Luck
Gary & Janet
The Best of Times (Hull #422)
KevinMc
Posts: 85
Joined: Sun Sep 08, 2013 5:36 am

Re: Battery Charger In Line Fuse

Post by KevinMc »

The batteries are two year old and were fine and thanks for the suggestion.

The problem was the previous owner was using 40A fuses between the charger and the batteries and the manual required 80A. Once I replaced the automotive style fuse holder he had installed with the proper holder and fuses (I used ANL fuses) the charger kicked on and keeping the batteries charged to a 94pct SOC. I've installed the Balmar SmartGauge this past spring which seems to work pretty good and has provided accurate SOC for the sailing year so far.

From everything I've read with two year old batteries keeping a 94pct SOC is pretty good so I'm not concerned why I'm not at 100pct and I figure I've got another few god years on these batteries.
Kevin
#59
NavSta Norfolk Marina
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