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Discussion Starter #1
I will have 3 parallel 100Ah Battleborn batteries in my Transit. I’m working on the wiring design and noticed the Battleborn documentation says 3 batteries can provide 600A for 30s, and “wires and fuses should be sized accordingly.” What does this mean exactly, and where does it apply? Which wires and fuses need to be sized for 600A?

My elec. system is designed for longevity and not high power output. My max load is <30A, and my average load will be closer to 10A. If I am not intentionally drawing 600A, under what conditions would 600A run through my wiring & fuses?


  1. How much amperage should the battery parallel connections be sized for?

  2. Does the wire between the batteries and ground need to be sized for 600A, or can it be protected with a T-Fuse located near the battery?

  3. If I place a 100A T-Fuse on the positive wire between the batteries and the positive bus, will this protect upstream wiring and components?
I appreciate your help!
 

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it depends on how you want to look at it, in a car accident it might get scary, or you can leave car accidents out of the equation like most people do here. (most but not all.)
4/0 cables (or even 2/0 since your loads are small) should be fine as long as they are short and can not rub on anything.
 

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I think you just need two fuses and no breakers. I would change the wiring to look like this:

Positive battery terminal to 100A fuse to Positive bus
Positive bus to Sterling to Disconnect switch to 70A fuse to CCPs
Positive bus to Disconnect switch to Distribution panel

Negative battery terminal and Distribution panel and Sterling to Negative bus
Negative bus to Chassis ground

I would use 4 gauge wire throughout.

I think the negative bus for small loads is built into the distribution panel.

The size of each fuse is to protect the wire from overheating. The fuse on the positive terminal should have a large Ampere Interrupt Capacity (a terminal fuse block or a class T fuse).
 

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Discussion Starter #5
Thank you for your advice.

I'm reading all I can find, but feel like I am still misunderstanding some fundamentals. In the past I have used AGM batteries, but never had a parallel configuration. And when I decided to use the Battleborn batteries, I was focused on how long I could run given my loads, and not the high amperage that could flow through my system.

So to clarify, the 600A surge would happen only if there was a short between the battery bank and the distribution panel?

But if my loads (fridge, fan, lights, etc,) only draw 30A max, wouldn't a 150A T-Fuse on the positive wire of the battery bank only blow if there was a short? Why do I need a higher amperage fuse there?

Should my distribution panel be rated for more than 100A?

I always thought if I needed more capacity I could add a 4th battery, but that would require even larger wires / cables / fuses capable of handling 800A!
 

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They are telling you to protect your system with proper fusing and the capability is 600a. You obviously don't want to fuse it that high because with a short you will have issues with fire.

Just make sure that each wire you use to power something is fused appropriately for its wire size. The main bus fuse should be the max you'll be pulling to protect the system as a whole.

I've seen 20 GA wires turn glowing hot in 2 seconds and there's nothing you can do unless you have tools immediately available to cut the connection. They'll melt the insulation instantly and fill the cabin with smoke before you even know what's happening. Fuses will keep you from having fires.
 

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In the past week or so I pondered this same question. The 2 each 100Ah batteries in parallel I chose are rated to provide 700 Amps for up to 5 minutes. But, that is a lot more than I'll ever need.

What I did to select a value for the main battery fuse was calculate the max expected load for my system. This will be mostly from the inverter, rated at 2000 Watts with the ability to spike for up to 20 seconds to 6000 Watts. 2000W/12V gave me 167 Amps. I doubled that number to allow for any other possible 12V loads, spikes, and general wiggle room. This made the number to plan with 334 Amps. I bought a 400 Amp fuse to put on the main battery line. A little over half of the bank's potential max current.

This 400 Amp fuse rating is still well below the potential 700 Amps the batteries can deliver, while also being well above the expected less than 200 Amp load. The fuse is there as a worse case scenario protection. The way I see things, it is best to avoid sizing the main fuse too closely to the actual loads you will be running.
 

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The size of the battery bank only affects the Ampere Interrupt Capacity (AIC) needed for the battery terminal fuse. You can correctly run wee little wires from a huge battery bank.
That's correct. As mentioned, you want to fuse the system for your max expected use, period. And size the wire accordingly. In fact most of the wire sizing is based on voltage drop, not heat, so with the Battleborns, you can get away with smaller wire since they are already at a healthy system voltage and have very little sag. Number four wire should be fine.
 

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I will try to make some suggestions and answer you questions on the circuit diagram.

Your circuit shown is acceptable, but some suggested changes. I would put the 100 amp fuse as close to the battery as possible. All wires beyond the 100 amp fuse should be sized to handle 100 amps up to the distribution panel. I would not put in the 40 amp fuse, just run the larger wire to the distribution panel. No need for the 150 amp fuse on the negative.

The 100 amp fuse will protect everything up to the distribution panel from seeing more than 100 amps, after the distribution panel the fuses in the panel protect the items from current more than the fuse you use there. The only way to draw 600 amps is to have a very large load or a short in the system. The short or load would have to occur before the 100 amp fuse (If you ever put jumper cables on to start a vehicle that would be a high load that bypasses the 100 amp fuse). The wires between the batteries should be large enough to handle the 100 amp load. 4 gauge should be large enough for your application. Large enough to blow the 100 amp fuse if shorted, and you will only have about a 0.3 volt drop if you draw 30 amps total and have 10 feet of wire from the batteries to the distribution panel and 10 feet of 4 gauge on your ground wire. If you have less than 10 feet then the 4 gauge is even more appropriate.

Your wire from the CCP panel to the charger and from the charger to the battery should be large enough to handle the 60 amp charge current. So if it is short i would use 4 gauge, but if longer than 10 feet i would use 2 gauge just to minimize the lost power (voltage drop). Make sure the ground wire from the battery pack and the charger hook to a really good connection, or you can have lost power there.

To give you an example in a car you have a battery capable of over 600 amps of current, but only a smaller gauge wire to the fuse distribution panel. The only large wire is to the starter, to your fuse box is more likely between a 6 and 2 gauge wire with a 100 to 200 amp fuse on it. Since you have a fuse you don't need to worry about the 600 amp rating of the battery.

Hope this helps and not confuses.
 
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