Wire sizing for inverter in small camper

LVLAaron

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I DIY'd a 400AH 12v LifePo4 to go into "Stubby Bob". I'll keep the battery in the rear, and need to run cables to the front where the main wiring hookups are.


The unit has a 1000 watt inverter onboard. All of the factory battery wiring is 2GA to the inverter. I don't plan on ever running something that needs 1000 watts.. Maybe a fan or a laptop charger. Anything bigger I'd run the generator.

I'd like to save a few hundred bucks and use some wire that I have on hand, which is 4ga welding wire. So two questions


  1. Would I be OK running 4x 4GA wires? 2 pos 2 neg from my pack up to the front of the trailer? It's 15 feet.
  2. Do I need to put a breaker in at the battery? It's a JBD 150A BMS.
 

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boondox

Chief Engineer, RedNeckTech Industries
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Breaker or fuse, yep. Size it 20% over your max load or charge. If you go breaker, don't buy cheap amazon crap. Actually, don't buy cheap fuses either.
 

boondox

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4 AWG will be fine, heck I use 6 AWG in a similar setting.

Well, this is why a calculator can be handy. Assume the 15 feet posited by the OP. He said 1000 watts maximum but I would add 20% to cover any loads aside from the inverter and some surge. The OP doesn't state it but we will guess that it is a 12V system. So that means we are going to provide for 100 amps of load. Using a 6 AWG wire that comes out to a 12.27% loss. Way too much. Even 4 gauge comes in at 7.7% loss, too much for me. Two runs of 4 gauge comes out to 3.85% loss, acceptable.

Even if we go for exactly 1000 watts with no overhead that comes to 83 amps. With a single run of 4 awg that is 6.53% loss. 6 gauge would be 10.3%.
 

corn18

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According to that calculator, I need 1 AWG wire for my 2,000 watt inverter. 200A, 12V, 2ft.

But I used this ampacity chart, and it says I need 3/0 for 200A.

That's a huge difference. I ended up using 2/0 because that's the biggest that would fit in the inverter input. That's also what Xantrex recommended.

Wonder what the right answer is?
 

time2roll

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I would be at the single #4 and a 100 amp fuse near the battery or bus. Done.
 

boondox

Chief Engineer, RedNeckTech Industries
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Ampacity refers to the continuous load a wire can handle without exceeding its temperature rating. So it depends on the wire type and temperature rating. And on if it is in conduit and what type of conduit and so on. You should be fine with 2/0 in your application.
I would be at the single #4 and a 100 amp fuse near the battery or bus. Done.

Agree with the 100 amp fuse. The usual loss that is considered acceptable I think is 5%. You could get away with 7.7%.
 

LVLAaron

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12V system. I'm going with 2GA. Found a 25 foot roll in the shop. As some have assumed, It'll never be a 100 amp load.. Laptop charger, Fridge, some 12v fans. What's that, 20 amps?
 

boondox

Chief Engineer, RedNeckTech Industries
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2 gauge will be fine, 5% or so loss. For me, if you have a 1000 watts inverter I would wire as if you may use it some day, you never know. Or down the line you sell it and the new owner sees a 1000 watt inverter and tries to put it to work. Having all the components in a system sized correctly is just good practice.
 

rmaddy

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For me, if you have a 1000 watts inverter I would wire as if you may use it some day, you never know. Or down the line you sell it and the new owner sees a 1000 watt inverter and tries to put it to work. Having all the components in a system sized correctly is just good practice.
This is good advice. Don't wire a 1000W inverter like it's a 500W inverter.

2 gauge will be fine, 5% or so loss.
5% is a lot for an inverter. Some devices won't like getting such low voltage. For something critical like an inverter I would try to get less than 3%.
 

12VoltInstalls

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This is good advice. Don't wire a 1000W inverter like it's a 500W inverter.
I like your thinking.
Plus if there’s a ‘situation’ and insurance or liability is involved it needs to be right.

A good 1000W inverter is -80A or ~160A surge. Even though we know that surge will only be a few seconds at best with inexpensive inverters before shutdown, the cost difference to oversize batteries-to-inverter cable is usually sorta small in real-world terms. Then if you ever want to use a vacuum…
 

Zil

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But I used this ampacity chart, and it says I need 3/0 for 200A.

Wonder what the right answer is?
The Blue Sea chart is calculated for marine grade, stranded wire. The insulating covering is rated to a much higher temperature. 105 degree C. in dry locations. Outside engine rooms. Not in conduit. So the right answer is what wire do you have. Your chart is also for 120V/240V household and industrial applications. Probably HomeDepot wire.

I usually use 1% voltage drop to select my cables. Using 1% allows some head room for the loss in crimps, connections, fuses, and especially circuit breakers.
 
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corn18

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The Blue Sea chart is calculated for marine grade, stranded wire. The insulating covering is rated to a much higher temperature. 105 degree C. in dry locations. Outside engine rooms. Not in conduit.
But I selected my 80 deg C insulation as a degrader in the Blue Sea calculator (that is what I am using). It did up the wire size by one size when I used 80 deg vs 105 deg insulation. I prefer the Blue Sea calculator, not because it gives a smaller answer, but because it is designed for our application. No clue what application that amapacity chart is made for.
 

12VoltInstalls

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Blue Sea chart is calculated for marine grade, stranded wire. The insulating covering is rated to a much higher temperature. 105 degree C. in dry locations. Outside engine rooms. Not in conduit.
There is an assumption that we would naturally use the right quality and rated wire for the stupid high 200A or 300A 12V loads.
Good point to bring up.

In servicing equipment utility trailers with winches and/or 12V-driven hydraulic motors one of the biggest takeaways I got was how poorly people understand the loads. I argued with the boss once; other employees at his direction were installing a 10Klbs winch on a tilt trailer. They opted to run cables down the trailer to the pivot and back to the deck front due to the dangle from tongue to deck when the deck was lowered. Using 2ga! I calculated the load and loss to require 2/0, 1/0 not quite minimum. They ran the winch (no load) and said it was fine.
I had to walk away or my mouth would have got me fired. I was appalled.

Is there a decent chart or calculator tool online for low voltage dc high amp cables in conduit? I’m not aware of one myself. Then again I’ve not yet experienced that application.
 
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