Fuse at battery?

[Zach_F]

Foreword: I am an electrical dunce. Go easy...

I'm about to install a group 31 battery with terminals too far away for the stock cables to reach. I've seen some use short jumper cables and power poles to extend, and others copper bus bars. I'm wondering if something like mega fuses could be used instead to provide the necessary reach. I'd be attaching one end to the battery terminals and the other end to the stock pos and neg wires.

I plan to install a Blue Sea fuse block with an in-line breaker to run my accessories. Not sure if having a fuse at the terminal becomes an issue or a failsafe. If it would work, what amp rating?

Thanks in advance.

 

[Bumbo]

You SHOULD fuse off the battery, but sometimes people don't. Best practices says yes... It's a personal decision that should be made based on your own preferences and layout.

For example... fuse block literally inches away from the battery vs the fuse panel with a mains line going across the engine bay... two very different layouts that accomplish the same thing. The latter having a greater chance for disaster if there was a compromised line that was not fused.

Its impossible to answer your technical and sizing questions without information.

If you plan on using a large MEGA fuse before the panel then you would size that fuse to protect the mains cable... and that would be based on whatever size (AWG) and length you decide to use. There are online circuit sizing calculators out there to help your determine all that good stuff.

Circuit Wizard - Blue Sea Systems

Fusing the fuse block is not redundant as the fuses on the fuse panel are at each individual circuit level. Having fuses in line like that would not present any challenges or issues.

 

[Zach_F]

Its impossible to answer your technical and sizing questions without information.

If you plan on using a large MEGA fuse before the panel then you would size that fuse to protect the mains cable... and that would be based on whatever size (AWG) and length you decide to use. There are online circuit sizing calculators out there to help your determine all that good stuff.

This is where I fall flat on my face, even with the calculator - mainly because I don't know enough about the stock current demands. Here's how I see the connection flows in my mind (scary place):
Pos battery terminal -> short bus bar -> mega fuse of unknown amperage -> positive connections: stock (alternator, starter, primary fuse box) + 4 AWG 18"-24" -> 100a breaker -> Blue Sea fuse block -> accessories

Neg battery terminal -> short bus bar -> mega fuse ?Amp -> stock negative connections + 4AWG ground from Blue Sea block

I hope that makes sense and can help determine fuse amp rating. Thanks!

 

[Bumbo]

1st off you don't NEED to fuse anything on the negative side... I am not saying there are not protection benefits in certain situations, but generally speaking, not needed.

Why are you even trying to re-wire the OEM stuff in the first place? Just leave it alone.

I presume you are hooking up a fuse panel for AUX accessories?

If so... "stock current demands" should have nothing to do with what it is you are trying to accomplish.

Just add a branch off the main battery and fuse it...

Battery > Mega Fuse > Breaker(Optional) > Fuse Panel > Accessories
4 AWG Wire main <10 foot run? 100-125A fuse and ur good to go.

 

[Zach_F]

Thanks, Bumbo. See my responses in bold. This is all based on the need to extend my battery cables and trying to do it in a way that is safe and maybe even increases the safety margin over a buss bar or jumper cable.

1st off you don't NEED to fuse anything on the negative side... I am not saying there are not protection benefits in certain situations, but generally speaking, not needed.

Why are you even trying to re-wire the OEM stuff in the first place? Just leave it alone. Because the existing cables won't reach the new battery's terminals. My thought was to use a mega fuse as an extension of sorts rather than a buss bar or jumper cable to extend the cables and make them reach.

I presume you are hooking up a fuse panel for AUX accessories? Yessir

If so... "stock current demands" should have nothing to do with what it is you are trying to accomplish. This was based on the idea of having a fuse between the battery and the existing cables.

Just add a branch off the main battery and fuse it...

Battery > Mega Fuse > Breaker(Optional) > Fuse Panel > Accessories
4 AWG Wire main <10 foot run? 100-125A fuse and ur good to go.

 

[riceandpho]

you can but you dont need too, i would use a 150amp circuit breaker unless you carry lots of spare anl fuses.

 

[Bumbo]

you can but you dont need too, i would use a 150amp circuit breaker unless you carry lots of spare anl fuses.

This isn't directed towards you, but your comments made me want to reinforce when its appropriate to use a fuse, and when its appropriate to use a breaker...

Breakers are NOT replacements for fuses... A breaker can fail where a fuse would not.

A dead short on a breaker can generate enough heat to weld it open, causing a catastrophic failure where a fuse would have just ended up blowing.

A fuse should be used to protect the cable...

A breaker should be used to manage the load...

Here is a design example:

For example... if you only had 4 AWG cable, and two powerful loads (say a air compressor and a winch) Lets just say each one can use 100 amps each.

Both can function, but not at the same time...

In this scenario I would have a 150 amp fuse on the line to protect the line, and a 125 amp breaker to manage the load. If there was a scenario where both were accidentally turned on at the same time, you would trip a breaker to cut the load, but leaves the fuse intact.

If you were to have a malfunction in wiring which includes the breaker, the fuse would then protect the system.

 

[Bumbo]

Thanks, Bumbo. See my responses in bold. This is all based on the need to extend my battery cables and trying to do it in a way that is safe and maybe even increases the safety margin over a buss bar or jumper cable.

Why not just get (build or buy) a new length of cable and just re-do that leg of the connection?

If you are going to extend it using the method you are talking about, I would oversize the wire and fuse or at least match the stock... Just measure it... Stock might be 2 AWG.

By biggest concern with fusing the entire car would be introducing points of high resistance and voltage drop... Things like jump starting, cold starts, or other high current situations might leave you stranded or with blown fuses.

It helps to actually measure what types of currents are flowing though that cable in normal operating conditions, you might be throwing money at a problem, or even creating new ones. It helps to have a DC clamp meter to measure/capture peak current during testing since you have now introduced accessory loads into a OEM circuit.

My recommendation is to just get a crimper, wire, lugs, and new battery posts are just re-do those factory connections and maintain an OE level of design and reliability. Its pretty much what I did, then I added my AUX panel on top of that, as a separate system. Its pretty much an excuse to do "the big 3" upgrade... (google it)

 

[Zach_F]

Why not just get (build or buy) a new length of cable and just re-do that leg of the connection?

I'd have to redo all the cables since none of them will reach the posts as-is.

I'm not quite ready to dive into Big 3 at this time, and from what I've seen it is a bear on the 5th gen. I can see how the fuse is a liability in the idea I had, which was already my concern. I was hoping I was wrong.

For now, I think I'm going to use copper bus bar between the terminals and battery posts like the image below (another member with same battery I have), but placed on amg fuse holders for shielding and support so they aren't just cantilevered out to the cable. I'll run the Aux fuse block off the threaded post with a 150A at-battery post fuse. That will run along 4AWG to a 100A breaker and then to the fuse block.

http://s328.photobucket.com/user/titanpat57/media/20160131_143144_zpshxuiwmwb.jpg.html

 

[Bumbo]

You probably should have started with that picture because it makes a lot more sense as to what your actual problem is...

There is nothing wrong with a copper bus bar like shown in that picture... just make sure its well insulated in hopes to prevent the chance of shorting it out.

Something like this might work out well for you too... its a bit more insulated, hardened, and shrouded around the hardware and base areas... easy and nothing to fabricate...
https://www.bluesea.com/products/category/18/5/BusBars/PowerBar
https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs


Just curious but why are you adding a breaker for the AUX in addition to the fuse? Do you really need load management? If you just want it for a service disconnect, but you can always just start pulling fuses too... cost effective and less complexity.

Depending on the types of accessories you plan on running... you might want to consider this route...

Battery > Fuse > LVD > AUX Fuse Block

https://www.bluesea.com/products/7635/m-LVD_Low_Voltage_Disconnect
https://www.bluesea.com/products/7615/ATD_Automatic_Timer_Disconnect
https://www.bluesea.com/products/7611/BatteryLink_Automatic_Charging_Relay_-_12V_24V_DC_120A

The last item can be used as a LVD too from what I read... you can always double check with blue sea.

Its just a thought, but at least that way you can run loads unattended and never have to worry about killing your starter battery...

 

[Zach_F]

You probably should have started with that picture because it makes a lot more sense as to what your actual problem is...

Yeah, in hindsight. Sorry you had to try to make sense of all that crap.

Just curious but why are you adding a breaker for the AUX in addition to the fuse? Do you really need load management? If you just want it for a service disconnect, but you can always just start pulling fuses too... cost effective and less complexity.

All the other info I had gathered up to this point said that a breaker was the right move, rather than a fuse alone. Most Blue Sea block arrangements I've seen have incorporated a breaker. I had originally planned to go breaker-only but I continued to read that a fuse as close to the battery as possible was a good idea for additional safety.

The original idea was the mega fuse as a "bus bar with safety" but since scratching that I figured I could go with one of these for the aux line only in addition to the breaker (since I already bought the breaker).

 

[Bumbo]

That's cool, nothing wrong with a breaker, and the fuse you selected is a good one.

I just see a lot of people buying breakers when there really isn't a need for one. Just because many arrangements have it, doesn't mean its required.

Many people buy them because they want a way to "turn off" the aux panel and use it as a switch, when really what they wanted was a LVD but just didn't know about it.

So what type of loads are you going to run to the AUX panel? Anything persistent?

 

[Zach_F]

So what type of loads are you going to run to the AUX panel? Anything persistent?

Persistent load will be an ARB fridge. Since it essentially has a LVD I don't think I'm going to set one up yet. Eventually I'll have 2x aux light circuits, winch, cb/ham, maybe on-board air and additional hot outlets.

 

[Bumbo]

Persistent load will be an ARB fridge. Since it essentially has a LVD I don't think I'm going to set one up yet. Eventually I'll have 2x aux light circuits, winch, cb/ham, maybe on-board air and additional hot outlets.

I presume this is a single battery setup so a high cut-off is very much needed otherwise you risk not being able to start the truck.

But you are right... the ARB does have a built in LVD so you should be good there with the high setting which has a 11.8v cut-off. Anything lower and you risk not being able to start the truck.

Low 10.1v
Med 11.4v
High 11.8v

Its good to note that AGMs have massive power reserves but it comes at the cost of being able to delivery higher starer currents. Its just the trade-offs when it comes to application. I would at least drain down to 11.8 and 11.4 and allow it to cut-off, then make sure you can start the truck before trying it for the first time on a big trip or something.

As long as you don't forget to shut off loads like the ham radio or anything you might have plugged into a hot outlet like chargers / inverters then you should be fine.

Just from experience I have found in the chaos of a trip sometimes its easy to forget about items that might put you in that situation... I really like a fool proof system and allow the truck to manage itself.

Personally I am a big proponents of whole system LVD... it only takes 1 mistake or lapse in time to kill the starter battery, which also ends up being harder on the battery degrading overall service life.

LVD for what you want is pretty affordable... but if you feel like you need it, its simple to add down to road at any given time as well.

Good luck with the rest of the project.

 

[Zach_F]

Thanks, Bumbo. You're the man.