Where to get in-line circuit fuses / breakers for aux battery install

K

kevin604

Observer
Hi gang,

After a ton of reading, I have gone out and bought a marine group 27 and a Blue Sea Si-ACR and a ST Blade Fuse Block with Negative bus.

I plan on putting the Aux battery in the pickup bed, which means about 12 feet of wire. I was going to pick 4 gauge. According to the Blue Sea Chart, 4 gauge can handle 80 charging amps and a 110 Amp fuse is required.

I've read a couple of folks here recommending a fuse next to the positive lead on each battery. So 2 X 110 (or 100?) fuses.

The Question:

I haven't seen much in the way of fuses above 80amp. Am I reading something wrong by assuming I need 110 or 100 amp fuse? Ideally this would be a circuit breaker in case in trips in the bush.

Is the idea to use a Fuse block and then add a 100 Amp fuse like this Blue Sea?

Thanks in advance,
 
pugslyyy

pugslyyy

Expedition Vehicle Engineer Guy
I'm with DiploStrat on those big-a** Blue Sea jobs. I use the Class T fuses, but the whole idea is the same - have a fail-safe fuse that can pass any current except for a dead short, but that will blow before your rig melts or catches fire.

What we're talking about here isn't the fuses that protect individual circuits or devices (you still need those), but what stops your rig from burning to the ground.
 
K

kevin604

Observer
pugslyyy said:
I'm with DiploStrat on those big-a** Blue Sea jobs. I use the Class T fuses, but the whole idea is the same - have a fail-safe fuse that can pass any current except for a dead short, but that will blow before your rig melts or catches fire.

What we're talking about here isn't the fuses that protect individual circuits or devices (you still need those), but what stops your rig from burning to the ground.
Click to expand...

Thanks. I think the confusion for me as a newb, is that these fuses are used to trip before the wire shorts/ burns to the ground. So since the Blue Sea supports 120 Amp continuous and 210 Intermittent, then tossing a 200 amp fuse close to either end of the batteries is just pure safety.

A bit more reading has me finding out that the Sub-woofer gang is all about power and protection. Lots of cheap audio options. Like this one:

Thanks for the responses. Ordered! Now just to figure out optimal fuseblock location for accessories :)
 
Jsweezy

Jsweezy

Explorer
So with this BlueSea ACR setup your running a 200 amp close to the battery before wiring the positive of each battery to the ACR? I just wanted to make sure cause I am going to be setting up a similar configuration.

Thanks!
 
K

kevin604

Observer
Jsweezy said:
So with this BlueSea ACR setup your running a 200 amp close to the battery before wiring the positive of each battery to the ACR? I just wanted to make sure cause I am going to be setting up a similar configuration.

Thanks!
Click to expand...

That is the best way to do it from what I understand. 200 amp at 12" from each battery. So I bought a 2X 12" premade 12" ring terminal wires and I'll connect the two circuit breakers together by a 10 foot cable.

Now just because, my access to 0 gauge is delayed and I had to get 4 gauge. So I will be using 80 amp circuit breakers on that. It will also make the wiring easier as the wire is smaller and more flexible. I know the BlueSea can handle 120 amps, but I have a big 100AH battery and my needs are limited to a very efficient fridge and some LED lights. So I don't think I'm in danger of running the battery down anytime soon. So for my upcoming trip I'll wire it all up temporarily and report back.
 
rayra

rayra

Expedition Leader
You always want to fuse at a rating lower than the wire will bear, regardless of the rated capacity of the device or power source connection. You want the fuse to blow before your wire catches on fire.
Maybe stating the obvious, but the OP is talking about 4AWG / 80 Amp wire and using 100 Amp fuses. Seems like he's looking at it from 180deg the wrong direction. Upping the fuse rating to exceed the wire capacity, so the fuse wont blow. Which is the complete opposite of what you want. The entire point of a fuse is to cut power before the other elements of your circuit fail / blow / catch fire.
Maybe I'm misunderstanding the OP, been a long day.
 
A

AndrewP

Explorer
rayra said:
You always want to fuse at a rating lower than the wire will bear, regardless of the rated capacity of the device or power source connection. You want the fuse to blow before your wire catches on fire.
Maybe stating the obvious, but the OP is talking about 4AWG / 80 Amp wire and using 100 Amp fuses. Seems like he's looking at it from 180deg the wrong direction. Upping the fuse rating to exceed the wire capacity, so the fuse wont blow. Which is the complete opposite of what you want. The entire point of a fuse is to cut power before the other elements of your circuit fail / blow / catch fire.
Maybe I'm misunderstanding the OP, been a long day.
Click to expand...

I was thinking that too. Only the wire size matters to determine the fuse size. 4ga wire in an engine compartment = 136 amp capacity. I'd use a 100-125 amp fuse.
 
rayra

rayra

Expedition Leader
Verkstad said:
To split hairs,
Fuses should not exceed ampacity of devices either. Not sure what "power source connection" means...
Click to expand...

Well let's just trump that and say 'the fuse should always be rated LESS than anything connected to it, device OR wire.' ;p


/getting a bit like 'Maslow's heirarchy of needs', innit?
 
B

bunce1260

Observer
I just recently installed my aux. battery using the $50 aux battery thread on here. I have an 80amp isolating relay, a 110 AH battery with about 20ft of #4 guage wire, I used this website http://www.wirebarn.com/Wire-Calculator-_ep_41.html with a 5% voltage drop to calculate safety tolerances.

Out of interest I'm now running 30 amp fuses next to each battery just to see if it will blow. It's been a few weeks and they're still doing good. Although I haven't discharged the battery a great deal yet.
 
A

AndrewP

Explorer
The voltage drop thing isn't about "safety tolerances" and the ampacity of your wire is much higher than 30amps. The too small fuses are inducing voltage drop in your system just by being too small. This will give you the gist of it:
http://www.pbase.com/mainecruising/fuse_voltage_drop

Voltage drop is often mis-interpreted too. Any drop you get is determined by resistance losses, which is determined by wire size AND current. So once your batteries are nearly full, and current flow drops to very low levels, your voltage loss will be essentially zero. It will take your battery marginally longer to charge, but in the end, it will come up to full system voltage.

Put some 80 amp fuses in your system and use it to it's full potential.
 
B

bunce1260

Observer
Sorry, regarding safety tolerances I meant with regard to the length of wire and amps and what's a safe guage to use.
 
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