House Bank Fuses

[Uncle Bob]

Hi, after reading many posts regarding fuses on battery banks, I have decided that I really should fuse mine.
The question is, with a house bank consisting of three pairs of 235 ah 6 volt fla batteries do I install one 250 amp anl fuse at the battery buss or fuse each pair individually close to the battery.?
Also what size fuse would you install in this instance ?
Thanks .

[travellerw]

Great question.. I had the exact same question recently..

To add a little.. ANL or MEGA fuses?

[paulajayne]

The absolute safest way would be to fuse between all batteries as well as an inline fuse based on your max current draw on the house batteries as well as trips on each circuit.

Fusing between pairs is a good option but base the fuse sizes on max house current draw as you will not be pulling motor starting current through them.

HTH

[exMaggieDrum]

If the batteries are close to each other I would recommend only fusing the last positive cable that goes out to the boat systems (panel, et al). You can use different types of fuses but what you are really fusing is the wire not the batteries. So you need to follow the fuse/wire guidelines. You are protecting the wire from melting so you don't want too big a fuse. If you go too small for the amp draw you will be blowing fuses unnecessarily.

All the basic boat/marine electrical books discuss this. I like the Blue Sea products and they have a pretty good set of how to's online and in their catalog. West Marine also has some tutorials. Since you are starting out I would recommend getting a couple of the basic electrical books, or one of the all systems books, like Nigel Calder's.

You need to have a big enough fuse to handle the largest amp draw you would ever see but no larger than 150% of the recommended fuse for the main wire coming off the batteries. Any wire coming off the batteries must be fused, e.g. for bilge pumps, electronics, main panel, etc. And each one must be fused separately. And every wire that is smaller than the big wire downstream must be fused for that wire regardless if the bigger wire is fused farther upstream.

[ColdEH]

I even fused the wire going to my starters on the main engine and generator . I only use a 250 amp class T fuse , even though the start motors draw much more it is only for a few seconds. No problems . Always protect the wire .

Maine sails site sums it up pretty good .
Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com

Regards

[barnakiel]

Always size for the wire. You do not want the wire insulation to melt ...

I understand what you say about fuses between the cells but I have not seen any in real life on many boats.

I would also NOT place any fuse into the starter wire. Unless there is an override, not fused circuit, in line.

b.

[ColdEH]

Originally Posted by barnakiel

Always size for the wire. You do not want the wire insulation to melt ...

I understand what you say about fuses between the cells but I have not seen any in real life on many boats.

I would also NOT place any fuse into the starter wire. Unless there is an override, not fused circuit, in line.

b.

I understand the point .

When I bought my boat and really started to crawl around it I found one one the starter wires touching a pulley and worn through . After that I rewired and fused that wire . If I do blow the fuse i have one right at hand or I can jump the holder if necessary. I like the piece of mind to know I am protected .

This is an excerpt from Maine Sails site.

""
Question: How does a 250A fuse deal with an average starting current of 286A and not trip?
The secret is in the duration. This engine starts, from a loaded starter to unloaded, in just 0.75 seconds, as evidenced by the; "TIME 765mS".

If you look back at the trip delay curves for an ANL you'll see why this 250A ANL fuse has never blown despite over 1000+ starts on this engine since the installation.""

Regards

[exMaggieDrum]

Originally Posted by typhoon

I even fused the wire going to my starters on the main engine and generator . I only use a 250 amp class T fuse , even though the start motors draw much more it is only for a few seconds. No problems . Always protect the wire .

Maine sails site sums it up pretty good .
Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com

Regards

Maine Sail has been a great contributor to this site and others. I had not read the above referenced pages but just did. They are an excellent reference for this subject.

[Frankly]

Sounds like we have similar set ups. I have two sets of 6V GCB midships and a third set of 6V GCB in the fwd bilge. Normally all are connected in parallel but each set has a battery switch for isolation. The two midships sets feed a one/ two/ both switch and the battery switch common feeds a home made high amp fuse distribution block. In this common feed is a 250 Amp Class T fuse right at the battery switch. All the individual feed fuses for various systems are type ANL.

4- 6V GCBs are pushing the interrupt rating of the ANL fuses so the Class T in series solves (hopefully) the high current interrupt situation. The fwd bank is connected to the high amp fuse block with ANL fuses on each end. The fwd bank feeds a couple of small house loads along with windlass and 3 HP bow thruster. All fwd circuits are protected by breakers or ANL fuses.

The aft high amp fuse block feeds SSB, Inverter/ Charger, Alt, IP Panel, Eng Starter, Fwd Bank. Some small fused loads are also tapped from the bus bar.

This set up has worked well for us for 10 years and I sleep pretty well knowing that I have covered most reasonable scenarios. Blue Sea Systems has some information about applying ANL fuses that you might find useful. They have a lot of delay in the trip curves.

Blue Sea also makes a Fuse (type BT if I remember) that connects directly to the battery screw terminals. I have always preferred to connect to the lead post so I passed on including them.

Tried to attach a pic of the high amp fuse block. Not sure if it will work out.

[smac999]

if the batteries are in the same location there is no need to fuse jumpers. make them correct lengh and direction and non of them will touch and have any chance of shorting.


if you have batteries spread out around the boat (like 10' apart (not a good way of doing it) then I'll fuse jumpers on both sides. the problem here is that if a jumper fuse blows likely nobody would notice as things would still work. but you'd have less capacity. so when your battery monitor says -50% your battery might really be at -75% because the other half is sitting full with a blown fuse. and people might not catch this.


fuse the main line leaving the whole bank. the size of fuse depends on the size of wire and what is running from the house bank. and if the engine can parallel off the house bank to start it.


the one I did last week was 300a MRBF but it was 2/0 to house switch and could parallel to engine.


and a 300a on the engine battery.


MRBF fuses are really handy here.

[Uncle Bob]

Originally Posted by smac999

if the batteries are in the same location there is no need to fuse jumpers. make them correct lengh and direction and non of them will touch and have any chance of shorting.


if you have batteries spread out around the boat (like 10' apart (not a good way of doing it) then I'll fuse jumpers on both sides. the problem here is that if a jumper fuse blows likely nobody would notice as things would still work. but you'd have less capacity. so when your battery monitor says -50% your battery might really be at -75% because the other half is sitting full with a blown fuse. and people might not catch this.


fuse the main line leaving the whole bank. the size of fuse depends on the size of wire and what is running from the house bank. and if the engine can parallel off the house bank to start it.


the one I did last week was 300a MRBF but it was 2/0 to house switch and could parallel to engine.


and a 300a on the engine battery.


MRBF fuses are really handy here.

Yes the batteries are spread, not ideal I know, however that is the space that I have to work with and maintain trim.

Your comments regarding the monitor are what have kept me from fusing them to date, and still I procrastinate.

At this point I am leaning towards ANL fuses on each battery pair, knowing that a greater level of vigilance will be required.

Thanks one and all for the input, all further comments most welcome.
Cheers.

[smac999]

check out bluesea MRBF fuses. so much easier on batteries. especially jumpers.