Wiring Question. Adding an Inverter - Page 2 - Escape Trailer Owners Community

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Old 05-04-2015, 06:45 AM   #11
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I'll be there, stop in and say Hello....look for "BlackJack" on the front of my trailer.
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Old 05-04-2015, 09:27 AM   #12
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Don't forget to increase the jumper wire size between the batteries. The install instructions that came with my 1K inverter suggested #0 wire...
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Old 05-04-2015, 11:15 AM   #13
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Thanks Jon. I was surprised when my wiring kit arrived and it was #4 wire. Seems pretty heavy for 12v. Jumper cables aren't that heavy and carry the same current.

My wiring plan is for the + to go to + on battery 2 and - to - on battery 1. Is that how your inverter is connected?

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Old 05-04-2015, 02:20 PM   #14
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Greg, a #0 gauge wire is heavier than a #4 and will allow for a much higher current draw.



Quote:
Originally Posted by Greggo View Post
Thanks Jon. I was surprised when my wiring kit arrived and it was #4 wire. Seems pretty heavy for 12v. Jumper cables aren't that heavy and carry the same current.

My wiring plan is for the + to go to + on battery 2 and - to - on battery 1. Is that how your inverter is connected?

Greg
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Old 05-04-2015, 05:16 PM   #15
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#4 AWG Cu 75 deg C = 85 amps when in a raceway or cable
#4 AWG Cu 75 deg C = 125 amps in free air (Air temp= 30 Deg C)
#1 AWG Cu 75 deg C = 130 amps when in a raceway or cable
#1 AWG Cu 75 deg C = 195 amps in free air ( Air temp = 30 Deg C)
Notes
Ampacity is based on using terminations rated for 75 Deg C (NEC standard)
Free air ampacity assumes an air temp of 30 Deg C
Table 310-16 & 310-17 NEC Allowabld Ampacities of insulated Copper Conductors
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Old 05-04-2015, 07:30 PM   #16
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Quote:
Originally Posted by Greggo View Post
I was surprised when my wiring kit arrived and it was #4 wire. Seems pretty heavy for 12v. Jumper cables aren't that heavy and carry the same current.
As Steve listed, the required gauge of wire is determined by how much current it needs to carry, not the voltage, so the fact that it's 12 volts doesn't matter. An inverter putting out 1000 watts will need to take in a bit more than 1000 watts, and at 12 volts that means over 80 amps... so it needs #4 according to Steve's table.

Booster cables are as heavy as #4... just not cheap ones. A couple of reasons that the inverter will need relatively heavy gauge:
  1. Booster cables are used only briefly, while the inverter may be used for long periods, so heat can build up.
  2. Power loss is important, so even if a cable is thick enough to safely carry the required current, it may not be thick enough (have low enough resistance) to efficiently carry it.
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Old 05-04-2015, 07:42 PM   #17
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Quote:
Originally Posted by Greggo View Post
My wiring plan is for the + to go to + on battery 2 and - to - on battery 1. Is that how your inverter is connected?
I must be missing something... there are no numbers on the batteries in the original photo of your trailer, or in the linked diagram of batteries in series, so I don't know what you mean by "battery 1" and "battery 2".

One cable connects the two batteries of your set directly to each other. That's the jumper Jon mentioned. Think of that cable and the terminals it's attached to as internal parts of one big battery, so you don't connect any devices (such as the inverter) to them, just as you wouldn't pry open the case of one battery and clip a connection onto the parts in the middle of it. After declaring those terminals off-limits, there is only one other positive terminal and only one other negative terminal left, so there's no choice about where to connect the inverter's positive and negative wires.

An inverter by itself can easily use more current than a trailer would normally use for everything else combined, which is why it usually gets its own connection to the batteries. That jumper wire directly connecting your batteries is the one you must upgrade to make the combined big battery able to safely and efficiently handle the higher current.
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Old 05-04-2015, 08:01 PM   #18
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My battery has tags on each connection that labels and numbers them. Done by the factory, figured they all shipped that way. Smart!

Thanks for the help. Got 'er figured out.

Greg
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Old 05-04-2015, 08:13 PM   #19
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While the wire table is fine under normal circumstances, I'd follow the manufacturer's wire size specifications, particularly when feeding the inverter from a pair of 6V batteries.

Yes, #0 is oversized, at least on paper, but the problem with inverters is that they shut down if the voltage at the inverter is too low. A pair of 6V batteries will have more internal resistance than a pair of 12V batteries with the equivalent amp hour capacity (sources in series increases internal resistance, sources in parallel lower it). Add the source resistance, the jumper between batteries & what ever wire length you have to get between the batteries & the inverter, fuses, switches, etc. This is the total resistance, which determines the voltage at the inverter.

If the total resistance is such that the input of the inverter sees less than the cut off voltage, even though you have well charged batteries, it may shut down under load. If your batteries are down a bit, the situation is even worse. This is the reason inverter manufacturer's often suggest larger wire than a standard wire table indicates. From Xantrex's Install Manual: "Note: Xantrex recommends a size 0 cable with a maximum cable length of 6 feet (1.8 m)."

If you are never going to use the full capacity of your inverter, and have very short runs between it & the batteries, you may get away with going by a wire table, however it is a lot easier to install the proper size wire once rather than having to change it in the future.
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Old 05-04-2015, 09:01 PM   #20
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The general rule for sizing conductors that are supplying loads that are continuous ( The Code defines continuous as 3 or more hours) is to take the amp draw of the load and multiply by 1.25 . IE: 100 amp load X 1.25 = 125 amps ,so you would use a conductor rated for at least 125 amps. In reverse an over current device such as a circuit breaker should not be continuously loaded above 80% of its current rating IE: A 20 amp breaker should not be continuously loaded beyond 16 amps. Running electrical equipment at 100% is a poor practice and leads to problems
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