Dual Battery Fuse

[awheeler]

Adding a 2nd battery to my truck. I will be using a blue sea relay along with a switch for 1-2-both-off.
Everything I've read has said to put a 100 amp fuse on the batteries. I want to use my second battery for emergency jumps. So I can't use a fuse right? I figure the starting process will take a bunch more amps than even a 150 amp fuse could handle.

Thanks

 

[Mike S]

Adding a 2nd battery to my truck. I will be using a blue sea relay along with a switch for 1-2-both-off.
Everything I've read has said to put a 100 amp fuse on the batteries. I want to use my second battery for emergency jumps. So I can't use a fuse right? I figure the starting process will take a bunch more amps than even a 150 amp fuse could handle.

Thanks

Without knowing what the vehicle is it is pretty hard to know what the starter draw will be. A Maxi-fuse may be plenty. You need to do a bit of research.

 

[Dave Bennett]

The National Luna Power Pack states: 85 amp (continuous) , 400 amp (peak)

Sounds like both batteries combined for starting may spike over 100 amps, do your research!!!

 

[Mr. Leary]

I use a 300 amp circuit breaker. My max current draw is around 275 amps while winching.

 

[Antichrist]

If you choose the right fuse setup you can bypass it for jumping.
What I've done in the past is just connect the two batteries together using a normally off 200amp continuous duty relay (it should handle most starter 30 second on cycles), switched from the cab and powered from the aux battery. Saves having to dig out the jumper cables.
Just use the fuse in the circuit that feeds your aux equipment, excluding the winch. Use an battery disconnect, rated at least 400amp continuous, in the winch feed.

 

[awheeler]

Here is my wiring diagram

This is going in a 2010 Tundra. The battery will be located in the back canopy since I have no room up front.

Switch on batt #1 will be the normal operation. Truck will start from #1 and blue sea relay will close and charge #2 when truck is running.

Switch on batt #2 will allow me to start from #2 but more importantly, turn key and run stock accessories like stereo off of #2.

switch to both will of course allow me to start on both.

That's what I have so far. I would like to fuse the batteries but I'm not sure if 150 amp will be enough. I may just go 250 amp and call it good.

Thanks for all the help

 

[Antichrist]

What I will do: Route the cables carefully, secure them periodically, give them abrasion protection where prudent, and move on to the next project.

Same here. I was assuming he wanted a fuse between the battery and fuse block because he had a long run.
I wouldn't fuse between a battery and starter or winch.

 

[Sheep Shagger]

I do not think the stock location battery needs a fuse at all.

I kind-a disagree, on a wire run that length with that potential amps, it should be fused at both ends, just for safety. Let's say the wire run between the batteries rubs off some shielding, the fuse on the 2nd battery will blow and protect that, but then you still have a live wire with "potential" welding amps arking from the starter battery. That's quite dangerous.
I have 3 batteries all on the frame rails, 2 one side are so close it's a direct connection, but to the 3rd on the opposite frame rail is fused at either end of the wire run with 300amp fuses (G0 wire). It's only fused to protect the wire run, no other reasons.

 

[awheeler]

I talked with a couple guys at Napa Auto and they felt that 150 amp would be plenty. When they do starter tests on a gas truck they only take about 60-80 amps. A diesel truck would take significantly more however.

I do want to fuse just to be extra safe. I plan to do a fuse as close to the positive as possible on both bats.

EDIT: I've done some further research and it sounds like the amp draw will be well above 150!!!! I'm having a hell of a time finding the amp draw. I'll try the dealership next.

 

[keezer37]

I talked with a couple guys at Napa Auto and they felt that 150 amp would be plenty. When they do starter tests on a gas truck they only take about 60-80 amps. A diesel truck would take significantly more however.

I do want to fuse just to be extra safe. I plan to do a fuse as close to the positive as possible on both bats.

EDIT: I've done some further research and it sounds like the amp draw will be well above 150!!!! I'm having a hell of a time finding the amp draw. I'll try the dealership next.

Your NAPA guy is correct. On average, no more than 90 amps are drawn by a gas engine starter, less as the cylinders wear and it's easier to crank.
I use 150 amp due to a long run and tested it out of necessity, even ran the truck for a week without a primary battery.
Go to http://www.hellroaring.com/ for even more head scratchin' info and drawings.

 

[lexwoody]

If you have two batteries in parallel, than there is no reason for a fuse between the two batts. Just fuse aux devices! My setup is two yellow tops in parallel with a 200 continue duty solenoid connects when key is in on position. A main hot wire (2gauge) ran from the primary batt to a rear fuse panel. 150 amp water proof breaker also under the hood for protection to the panel. 2nd batt is just for starting and every thing is hook to the main when key is off and both when key is on.

 

[refried]

with no load a basic gear reduction starter will draw about 75 amps, cranking an engine it will draw 125 - 250 amps depending on conditions (Diesels draw 450 - 700 amps). puttting a fuse on a starter wire is not a good idea.

 

[sargeek]

I think the fuse on both ends of the Positive Cable would be prudent way to prevent a vehicle fire. A short on the cable would be provided power from both batteries.

Does present some problems for high current applications.

 

[awheeler]

Okay here is what i'm doing....

Since the Blue Sea relay and switch will be just inches from the primary battery I will not fuse that primary circuit. This will give me unfused primary battery starting. The likelihood of the switch failing is very small.

The second battery I do want fused because it has 12 feet of large gauge wire going to it. I will fuse the second battery at 250 amps and hope that works towards jumping the primary if need be. I can always pull the battery and manually jump it if need be.

Thanks again everyone,

 

[Backroad Explorer]

awheeler, It was nice to meet a fellow ExPo member today at NAPA. If I can help in any way let me know. Stop by when your done with your project I'd like to see how it comes out.

Brian