Dumb Dual Battery Question: "Start-Only Battery" Wiring (1 Viewer)

[gummycarbs]

I've read a bunch of threads on dual battery installations and I've seen many people talk about having a "start-only" battery. I'm just wondering whether people wire it so that it's truly only used for starting, with the fusible links rerouted to the secondary battery, or if they mean "start and run".

If it's the former, how do people go about rerouting the fusible links to the second battery? Just clip the fusible link endpoints off the OEM harness and route extension wires to the second battery?

Here's a picture of a custom FJ40 dash, because who doesn't like pictures?

 

[greentruck]

Can't speak for anyone else, but start only can mean several things. Most frequently, the context suggests it used to refer to a battery that is dedicated to starting only.

It would need a good fat cable down to the starter.

I use one of the Hellroaring units, but not the one that supports that. Rather, with mine you flick a switch to let the charge build in your primary battery, then start after it's had time to move the charge and use the original starter wiring from the primary battery. The connecting wiring is maybe #10? (it's been a long time since I installed); it's recommended not to crank on it, but so long as you don't keep cranking and get it hot by starting right away I've found this isn't an issue, just something to be cautious about if it's extra cold, having starting problems, etc. My AUX battery permits that, but I would not call it start only, although it's close. Rather, besides the trickle charge function, I plumb the AUX to a single connector on the tranny tunnel that I plug my CPAP into when sleeping in the truck.

I could see if you wanted to run the truck on an entirely separate charge system that the fusible links would be an issue. But unless you're running a second alternator, I don't think they're necessary or at least wouldn't need to be switched. They're protective and the wiring going to them goes to the same ground that the AUX battery connects to, so I suspect they would still protect things even if not directly connected to the start only battery.

 

[Technician1985]

There are many ways to go about adding a second battery, but as a starting point I would remove the factory fusible link and make a new fuse block to accommodate the second battery and associated wiring. One fusible link per battery / charging system IMO.

 

[george_tlc]

Fusible links are there to protect the wiring. Leave the stock wiring alone and connected to the main battery and leave the fusible links ALONE unless you understand exactly what you are doing (i.e. understand what the fusible links are really for and how much current it takes to blow each of them - versus blowing your harness...).

No need to re-invent what has worked extremely well for many people:

One option:

- Main battery is used to power all the stock vehicle wiring.
- Aux battery is used to power fridge, aux lighting etc while camped/stationary.
- Connect both in parallel to jump start if necessary.

Second option:
- Main battery is used to power everything (stock and fridge and aux lighting etc)
- Aux battery is never used.
- Connect both in parallel to jump start if necessary.

Third option:

- Main & Aux always in parallel with lots of capacity to run everything.
- Li-ion/poly jump start pack to jump start if needed.

Fourth option:
- something else

I use option 1 along with a solar panel setup to keep the aux charged while camping.

cheers,
george.

 

[gummycarbs]

Thanks for the replies.

To be clear, I'm not talking about eliminating the fusible links. I'm talking about moving them to the second battery, which seems like it would require me to cut the ends of the wires on the other side of the junction box and add a length of wire for each fusible link (AM1, AM2, and main). I like to minimize modifications to OEM wiring, but I also can see the advantage of being able to power the headlights or stereo for an extended period without impacting the ability to start the engine later.

 

[greentruck]

If you're just starting on the second battery as a reserve in emergency, then why move the fusible links to the second battery? Just leave them on the primary, where they were carefully designed to work and where all the wiring terminates properly already.

Or are you thinking that the starting only concept has to do with making one battery serve no other purpose and it will take over all starting? Because that's not what's going on AFAIK. You still start on the primary battery, it's just that the starter only battery serves exclusively as a backup dedicated to starting only -- or perhaps one other vital or life safety purpose as I do with my CPAP.

I think George summed it up well. The fusible links have to be designed into a circuit. They're not interchangeable in the sense that the common fuse is.

 

[Formulaonehd]

F

Fusible links are there to protect the wiring. Leave the stock wiring alone and connected to the main battery and leave the fusible links ALONE unless you understand exactly what you are doing (i.e. understand what the fusible links are really for and how much current it takes to blow each of them - versus blowing your harness...).

No need to re-invent what has worked extremely well for many people:

One option:

- Main battery is used to power all the stock vehicle wiring.
- Aux battery is used to power fridge, aux lighting etc while camped/stationary.
- Connect both in parallel to jump start if necessary.

Second option:
- Main battery is used to power everything (stock and fridge and aux lighting etc)
- Aux battery is never used.
- Connect both in parallel to jump start if necessary.

Third option:

- Main & Aux always in parallel with lots of capacity to run everything.
- Li-ion/poly jump start pack to jump start if needed.

Fourth option:
- something else

I use option 1 along with a solar panel setup to keep the aux charged while camping.

cheers,
george.

First option you mentioned (the likely option i will be going with) is the aux battery connected to the alternator directly with a relay ?

 

[george_tlc]

F

First option you mentioned (the likely option i will be going with) is the aux battery connected to the alternator directly with a relay ?

My sig will take you to my website. My aux battery writeup can be found there and will answer your question

cheers,
george.

 

[rc51kid]

you are over thinking it. George hit it on the head. You are describing his first option where the factory battery does the factory job of starting the truck. All other crap like a fridge or winch is wired to second batt. This is a valid way of doing it.

I have the Hell roaring system and set it up his second way. Just because that is how they recommend it. Works great. My second batt should always be ready to start the truck no matter what. But his first way of doing it is fine also.

 

[890man]

I also have the hellroaring configured as option 2. I have the largest capacity battery I could fit there and a decent "backup only" secondary batt. I prefer this setup but most choose option 1.

If you did want your fuseable links on the secondary battery, I wouldn't cut the factory wiring. I would run a larger gauge, fused cable to a terminal block to the back of the primary batt box and connect the links there. I just can't see why you would want to though.

 

[SmokingRocks]

God I got flamed hard recently on mud for suggesting what you guys are saying. Don’t get me wrong it’s how mine is set up, but people laid into me and said that the aux battery needs to be for starting purpose only and the main battery powers all the lights n stereo n stuff.

I have three batteries. Main, Aux and Rear. The aux is my ‘savior’ battery / jump battery. The main powers all the factory items, stereo and starter, and the rear handles my fridges water pump and comfort accessories, it also is charged by my solar panel when the engine is off. Once the rear batt floats up to 13.4 v it links to the main battery and floats it to 13.2 then it links to the aux batt.

It’s clunky but it works.

 

[890man]

What thread was that?

 

[Desert Dino]

Fusible links are there to protect the wiring. Leave the stock wiring alone and connected to the main battery and leave the fusible links ALONE unless you understand exactly what you are doing (i.e. understand what the fusible links are really for and how much current it takes to blow each of them - versus blowing your harness...).

No need to re-invent what has worked extremely well for many people:

One option:

- Main battery is used to power all the stock vehicle wiring.
- Aux battery is used to power fridge, aux lighting etc while camped/stationary.
- Connect both in parallel to jump start if necessary.

Second option:
- Main battery is used to power everything (stock and fridge and aux lighting etc)
- Aux battery is never used.
- Connect both in parallel to jump start if necessary.

Third option:

- Main & Aux always in parallel with lots of capacity to run everything.
- Li-ion/poly jump start pack to jump start if needed.

Fourth option:
- something else

I use option 1 along with a solar panel setup to keep the aux charged while camping.

cheers,
george.

My setup is Option One

 

[SmokingRocks]

@890man Flaming starts here.

I'll be the first to admit that several of my comments were erroneous, as I stated, however come to find out I was less wrong than they suggested but whatever. Regardless Mud should be a place where we can actually share ideas not s*** on other peoples work and give them the while doing it. There are many ways to skin the cat, do what works for you.

 

[SmokingRocks]

I've used option #2.

Reason was that the stock wiring includes things like dome lights and stereo which sometimes I like to run. If I am running two fridges and other aux items of the aux battery and the stereo and some lights off the main battery I may end up with two flat batteries. Option 2 allows me to have a reserve jump battery.

I've modified option 2 a bit by adding a third 'rear' battery to handle the fridges so that I lessen the number and severity of cycles the main battery undergoes (the fridges run 24/7)

I am in the process of drawing up my next revision of my set up to be more in line with a 'dedicated start' battery. My plan is to move the entire start circuit (solenoid and starter supply) to the Aux battery.

 

[FJP971]

Not to hijack the thread but I plan on going with Option #1 soon and I'm trying to figure out which Bluesea controller/isolator to use. I was thinking about using this setup: https://www.amazon.com/dp/B000RZNP5K/_encoding=UTF8?coliid=I2L20PXLMBK1R3&colid=3LO43FPD7CHK1&psc=1

Is that my best option that is still somewhat affordable? Thanks in advance.