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Old 21-01-2015, 10:16   #1
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Batt To Inverter Cable Length Question

This old boat has a couple of rusty old inverters in one of the engine rooms, installed about 8 inches over the top of the battery bank. These were Harbor Freight inverters by Previous Owner, bless his heart. One failed last year, the 2KW is still going but it's a rusty hunk and getting uglier.

I bought two new inverters, a 650 watt for day to day computer/phone recharging/ low wattage use, and a 2000 watt for full house load applications. I got remote switches for both. I also have a great location in a hanging locker inside the cabin to install them, but it's probably about 8 or 9 ft. from the battery bank location. The manual says six ft. maximum. What will I lose if I stretch that to 9 ft?
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Old 21-01-2015, 10:20   #2
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Re: Batt To Inverter Cable Length Question

6 more ft of cable. LOL


Just go up one size on the cable and you should be ok. It's not like you're going to draw max. power for 3 days straight, are you?
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Old 21-01-2015, 10:24   #3
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Re: Batt To Inverter Cable Length Question

Not really so simple, max.

The little one should not be an issue, size the cabling for the load.

The big one will be an issue, not because it's beyond the six feet, but because you'll be starting to deal with BIG cabling.

For example, our 1500W uses 2/0 cables and is six feet away, total 12 feet.

2000W for eighteen feet (9 each way) is a larger load for a longer distance requiring larger cables.

Determine the load, size the cables based on the length accordingly.
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Old 21-01-2015, 11:21   #4
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Re: Batt To Inverter Cable Length Question

2000 W gives 2000 W / 12 V = 137 A
Distance between the battery and inverter 9 ' = 1.8 m
Cross sections for maximum 3% voltage drop 137 * 1.8 / 10 = 30 mm²
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Old 21-01-2015, 11:57   #5
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Re: Batt To Inverter Cable Length Question

Sorry Lars, you need to take into consideration the total return distance which is 5.5 m. I don't know where you got 1.8 m for 9 ft. Its actually 2.72 m for 9 ft.
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Old 21-01-2015, 12:33   #6
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Re: Batt To Inverter Cable Length Question

Is not 0.3 * 9 = 1.8?
Sorry, but you are right it is 2.7
In this simplified counting model you count the distance only one-way.
Current 167 A
Distance 2.7 m
Wire Size for 3% voltage drop 167 * 2.7 / 10 = 45 mm²
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Old 21-01-2015, 22:46   #7
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Re: Batt To Inverter Cable Length Question

4/0 cable for 2000w 10' away.


it's way more then 160a. as they are not 100% efficient. and they can probably surge 2500-3000w




the magnum manual fuses the 2000w at 300a. and requires 2/0 for 5' and 4/0 for 10'.


check the manual for yours.
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Old 22-01-2015, 10:58   #8
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Re: Batt To Inverter Cable Length Question

If mounting inverter in multi-purpose area/ locker, just make sure you don't restrict air flow through it with anything like fowl weather gear. The inverter can quickly over heat and may result in non- recoverable failure.


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Old 22-01-2015, 10:59   #9
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Re: Batt To Inverter Cable Length Question

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Originally Posted by socaldmax View Post
6 more ft of cable. LOL


Just go up one size on the cable and you should be ok. It's not like you're going to draw max. power for 3 days straight, are you?
Ditto, just up the wire size. They probably specified on the safe side.
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Old 22-01-2015, 11:06   #10
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Re: Batt To Inverter Cable Length Question

Household inverters are NOT the same as marine inverters. It is OK to use a household (or car) inverter so long as you take the AC directly off of the inverter plug. You should NEVER hard wire a non-marine inverter into your boat's AC circuits. Not sure you are doing that but FYI. S It has to do with safety - read up on it if you want to know the details. Safety as in not killing someone. Also has to do with isolating the AC grounding circuit from shore power which can cause AC leakage. Too complicated to discuss here.

Also inverters should not be installed over battery banks, especially wet cells. They will corrode very quickly. It is done but not recommended. Find a better spot.
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Old 22-01-2015, 11:17   #11
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Re: Batt To Inverter Cable Length Question

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Originally Posted by smac999 View Post
....requires 2/0 for 5' and 4/0 for 10'.
That part doesn't add up. A smaller wire for a longer distance? I think you have it backwards...
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Old 22-01-2015, 11:20   #12
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Re: Batt To Inverter Cable Length Question

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Originally Posted by AfterHoursNLCT View Post
That part doesn't add up. A smaller wire for a longer distance? I think you have it backwards...

Smaller gauge number , the bigger the wires!


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Old 22-01-2015, 11:58   #13
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Re: Batt To Inverter Cable Length Question

If you can install inverter the shortest distance to batteries you can run a/c power longer runs w/o affecting power. We have 3000 watt 3' from battery and ran a/c power cords tucked away with outlets through out our boat. Your biggest lost of power is battery to inverter. good luck...P.S. get rid of harbor freight inverters i bought couple for our big truck and shorted out and almost burnt our truck down
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Old 22-01-2015, 12:01   #14
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Re: Batt To Inverter Cable Length Question

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Originally Posted by AfterHoursNLCT View Post
That part doesn't add up. A smaller wire for a longer distance? I think you have it backwards...
I believe we where talking dia. not AWG..
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Old 22-01-2015, 12:43   #15
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Re: Batt To Inverter Cable Length Question

smac999 had it exactly right. AWG 4/0 cable is larger than AWG 2/0, and is the proper size for a 2000-watt inverter installed about 10 feet from the batteries (one way).

Be advised also to install a proper fuse. Only three types are acceptable, in order of preference:

1. Class-T
2. ANL
3. MRBF (terminal fuse).

These should be installed as close to the batteries as possible. ABYC calls for "within 7 inches".

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