Battery Fuse Size

Yosemitebob · 06-05-2015, 08:31 AM

OK, I have not found this info. What would be the size of the fuse if I was to install one in the main battery cable. I have two 6v batteries in series for 12v at 232 AH rating.

cb1000rider · 06-05-2015, 11:05 AM

Quote:

Originally Posted by Yosemitebob

OK, I have not found this info. What would be the size of the fuse if I was to install one in the main battery cable. I have two 6v batteries in series for 12v at 232 AH rating.

You haven't found it because there isn't one in the main cable. I assume you're talking about adding one. I'd think that the max amps you'd be pulling would be starting the genset and running the inverter at the same time (for just a second) assuming you have an inverter. If it were me, I'd be looking into typical stereo equipment wiring - as they handle typical battery gauge wires and also have large fuses. Pulling a number out, I'd say 100 amps.

**chuckster57** · 06-05-2015, 11:14 AM

I wouldn't use a fuse, an automatic circuit breaker would be my choice. 100 amps seems high to me, factory uses 30A.

Yosemitebob · 06-05-2015, 12:06 PM

Thanks guys wide space there 30 to 100. Ok, so here is my theory. All my electronics is up front with the battery. Solar which is only a 30a and it is fused, the remote electronics, which is fused, batteries (not), and a 600w linear which is fused, I want to use a fuse as for the simple reason it will melt (ANL type of fuse) if there was a fire up front disconnecting the battery by doing so. Leaving everything disconnected, perhaps I'm really over thinking this. I was not going to use the fuse as a link for electric as so much I was going to use it as a fuseable fire link, but didn't want it to break before that point.
You think I being over cautious.

Chuck, that is why I can't use a breaker type.

cb1000rider · 06-05-2015, 12:45 PM

Quote:

Originally Posted by chuckster57

I wouldn't use a fuse, an automatic circuit breaker would be my choice. 100 amps seems high to me, factory uses 30A.

You Sure? If he's got a 600 Watt inverter that's 600 watts / 12 volts = 50 amps. If he had a generator, I'd expect that thing to pull at least 30A when turning the starter. I haven't measured slide motors, but I'd expect them to be in the 10-15 amp range running...

All of this adds up, it's all got to flow through that "main" fuse... That being said, it really depends on the electronics in his trailer.

If it's low draw, you could put a simple analog amp meter on it and see what it draws peak.

Fuses should be configured so that they're not lower than 120% of the peak *expected* draw. Just remember that it's sum of everything "in use" at once.

Yosemitebob · 06-05-2015, 03:53 PM

OK, so given the assorted electronics I have, that do run off the battery i.e., 600 walt linear, shortwave transmitter, a 1,000 w inverter arriving soon, generator, although it has it's own battery start, three slide motors, three vent motors, three separate landing motors, one in front and two in rear, MPPT20 solar charger, given all of them I could be at or over 100, but also given that I would never be able to start them all at one time anyway, I am going with a 60 or 80 amp fuse, which is the ANL type that can melt away if for some unfortunate reason I had a build up of heat in the front compartment.

**JRTJH** · 06-05-2015, 04:58 PM

Bib,

Maybe this isn't the "current technology" thinking, but a in line fuse on a main power line isn't necessarily intended to protect any specific component, rather it is intended to protect the distribution wire (cable) so it doesn't become overloaded and "melt down" creating a fire hazard. Think of it as the "main circuit breaker" in a house wiring system. Usually they are 200 amps or 225 amps, and then "after that breaker" the wiring divides and each circuit is further protected by additional breakers or fuses.

I'd think that if you're considering a fuse "at the battery cable" you'd want to determine the gage of that specific cable, protect the wire and then let the individual circuit fuses protect components further "downstream".

According to what I learned years ago, this is the "amperage capacity" for each DC wiring size based on a 15' run of wire:

4 ga 70 Amps
6 ga 50 Amps
8 ga 30 Amps

Keep in mind that these are "maximum recommended amperage" so you'd want to "step down" one fuse rating to protect the wire.

As an example. If the positive cable from the battery is 4 ga, consider a 60 amp fuse, if it's 6 ga, consider a 40 amp fuse and if it's 8 ga, consider a 25 amp fuse. That way the fuse will "blow" before the wire gets hot enough to cause any damage to the insulation. Also remember that this is for a 15' wiring run. A shorter run will handle greater amperage a longer run would handle less.

You aren't attempting to protect the "downstream components, any component supplied by that positive cable (on a branch line) should have its own "in line" fuse protection. Your "goal" in fusing the main cable is to protect that cable, so fuse appropriately based on the amperage that cable can carry for the total length of that cable run.

I hope this makes some sense rather than confusing the issue even further.

Yosemitebob · 06-05-2015, 05:05 PM

That makes perfect sense to me at least, as that is what I've been basing it on. My cable is 4/0, the fuse is 18" from the battery 6 additional feet to the breaker box. Downstream, each individual item has it's rated inline fuse. So, with all the info so far, I believe I'm headed in the correct direction.
Thanks all

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