Auxiliary batteries. Same question different situation?

[husker77c]

I am about to finish up a 12 valve cummins swap into my 94 F350 and I have two questions.

1)
The intercooler I used interferes with the factory battery trays so I moved my factory batteries to my tool box with a run of 1/0 welding lead. I installed a junction block and 150 amp ANL fuse under the hood on the cable running to my batteries in the back.

I ran my starter wire, also 1/0 from the junction block to the starter. Now when I crank the truck I almost instantly blow the 150 amp fuse. I know I'm pulling more than 150 amps when starting so I don't know how to have enough amperage to start while still using a fuse to protect the run of wire back to the batteries in the tool box.

2)
I was also considering running two optimas under the hood in the factory locations because with their small size I can fab up some trays for them. But if I go that way id like to use the tool box set up as an auxiliary battery bank. My current batteries, which are group 65 Diehard AGMs and aren't that old and I'm not sure I could still use them because I think both batteries need to be the same in that situation. Trying to use the tool box batteries and also two new optimas under the hood if possible.

Any suggestions ?

 

[4x4junkie]

Yeah, 150 amp fuse is completely insufficient...
I'm just guessing on this, but I think you'd need something closer to 800 amps (or stacking two 400A fuses together) if you're looking to have it fused and want to crank over a big diesel without it blowing. I'd also suggest heavier wire too (3/0, or maybe even 4/0 if your run is lengthy because it's a crew cab). Finally, the fuse needs to be at the batteries if it's to protect the wire, not under the hood.

As for mixing batteries, if they are on an isolator of some sort, there's no issue there. You can even mix flooded & AGM batteries if you want as long as they are isolated. Any batteries wired hard-parallel of course do have to be the exact same type & brand, and of similar age w/similar use history (new is best).

 

[quarkster]

Battery-to-starter wiring is never fused.

Because of the extra cable length needed to reach your remotely-located batteries, you have a lot more cable that's potentially exposed to insulation damage, short-circuiting, and a potential electrical fire.

I'd triple-insulate the cables, using high-temperature silicone-over-fiberglass aircraft insulating sleeving, with high-temperature corrugated wiring loom tubing over that. Also use aircraft-style insulated clamps to secure the wiring to the chassis/bodywork every foot or so it can't move and chafe.

I used a similar insulation scheme when I ran wiring through a frame rail from engine bay back to my cargo-bay mounted air compressor and fridge, but that was only pairs of paralleled #12 AWG, and it was breaker-protected.

 

[IdaSHO]

Battery-to-starter wiring is never fused.

Correct.

Reason being, is that fuses are sized to protect wiring.

The wiring for the starter battery is sized from the MFG to far exceed the potential load, so it needs no protection.




I run 3/0 wire for my cables on my Powerstroke, knowing that the starter can pull upwards of 400 AMPs
Not sure what your 12V starter draws. May be substantially less.


Either way, Id suggest you find out, and verify that you are within the capacity of the cable you are using using an ampacity chart