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Old 05-08-2014, 10:07 AM   #1
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Fuse sizing for inverter

I installed a cheap 1200 watt continuous/ 2000 watt surge Chinese inverter primarily to watch TV on the hook. Paid 90 bucks for it, so yea it's cheap. Bought at harbor freight.

The battery cables are #2 AWG 15 feet long. If my calculations are correct, for the 2000 watt surge I would need a 166 amp fuse installed as close to the battery as possible.

If amps = watts/volts then amps = 2000 watts/ 12 volts which yields 166 amps. Correct? or
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Old 05-08-2014, 11:42 AM   #2
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Using NFPA 302 Table 9.12.5(b) Allowable Amperage of Conductors for Under 50 volts You are about right. The table of amperage's is based on temperature rating of conductor Insulation and inside or outside engine spaces.
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Old 05-08-2014, 03:12 PM   #3
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As obthomas said, you are about right, probably a bit more current due to the battery voltage dropping below 12V and 5% inverter losses, but close enough.

But just running a TV and assuming it is a medium size LCD, not a CRT or a plasma, you will see less than 100 watts from the inverter, maybe 10 amps DC max. With the proper size fuse to protect it, 18 gauge wire will work.

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Old 05-08-2014, 04:42 PM   #4
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With the proper size fuse to protect it, 18 gauge wire will work.

David
I ordered a fuse block that attaches directly to the battery with a 125 amp fuse. Like this: Blue Sea Systems Terminal Fuse Block
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Old 05-08-2014, 05:16 PM   #5
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I'm really surprised that the installation instructions didn't mention the fuse size and cable size for installation. The instructions for my Xantrex are very specific.

15 feet is a very long run for that much current and it's really 30 feet if you didn't include the negative return. You may have enough voltage drop in the cables to shut down the inverter if you put a serious load on the inverter.

It's best practice to make the DC cables as short as possible to minimize voltage drop. There is very little voltage drop in the 120 volt AC wiring. It's just like in your home.
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Old 05-08-2014, 09:07 PM   #6
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Guys, like David said, based on what the load is here we're building a mountain. It's a TV . fuse it as you are and let's move on.

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Old 05-08-2014, 09:33 PM   #7
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Guys, like David said, based on what the load is here we're building a mountain. It's a TV . fuse it as you are and let's move on.

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It's not a TV, it's a 2,000 watt peak inverter. Who knows what might be plugged into it.

If you're going to do something you might as well do it correctly. That means follow the instructions and ABYC standards. Use the correct sized cable and correct circuit protection.
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Old 05-08-2014, 09:56 PM   #8
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My point is the op asked a simple question and we're turning this into a !another long drawn out issue. Just for the record I also agree that all projects should be done correctly.

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Old 05-08-2014, 11:17 PM   #9
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I ordered a fuse block that attaches directly to the battery with a 125 amp fuse. Like this: Blue Sea Systems Terminal Fuse Block
Sounds like you're well protected, Tim. The 125A fuse will blow before causing wiring damage...that's the key. Your 1200W continuous power is 100A at 12V. If you hit the peak of 2000W for a sustained period, you will blow the fuse. No problem...that's the intent, right?

If you add additional loads to the circuit besides the TV and notice the inverter humming from low voltage, consider upgrading your cable size. Until then, sounds like you're good.
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Old 05-09-2014, 06:49 AM   #10
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To interrupt BIG juice the class T fuse and fuse holder has the best chance.
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Old 05-09-2014, 06:55 AM   #11
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If a #2 wire is rated at lets say 115 amps over 30', size the fuse as to not allow the wire to become the fuse, so possibly 100 amp fuse.

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Old 05-09-2014, 02:05 PM   #12
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I have a generator and don't need no stinking inverter.
I have Chinese LEDs and love them.
I have guns onboard.
Diesel rules.
I despise gel cell batteries
Teak decks suck
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Old 05-10-2014, 10:11 AM   #13
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I'm with Ron size the fuse for the inverter not the TV. You might as well run the TV directly off the DC buss and have -0- inverter losses or have a chance of the inverter bypassing the correct source ABYC standards for a marine inverter.
Most TV LED TFT units smaller than 26" use a wall transformer power supply that feeds the TV 12-14VDC. The TV has built in voltage regulation and most have a Zener diode which protects from over-voltage, spikes or transients from the DC buss in the vessel. Properly size the DC fuse to the TV and it's internal protection will at worst cause the DC fuse to blow feeding the TV power.
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Old 05-16-2014, 08:13 PM   #14
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Why not something like this that gives you a disconnect too? 187-Series Circuit Breaker - Surface Mount 150A - Blue Sea Systems

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I ordered a fuse block that attaches directly to the battery with a 125 amp fuse. Like this: Blue Sea Systems Terminal Fuse Block
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Old 05-17-2014, 06:38 AM   #15
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Motors starting are usually the cause of a high current requirement.

Check the fuse size with the batt partially discharged and run your blender or vacuum.

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Old 05-17-2014, 06:49 AM   #16
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Please speak plainly I (don't know about others) am not a mind reader

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I have a generator and don't need no stinking inverter.
I have Chinese LEDs and love them.
I have guns onboard.
Diesel rules.
I despise gel cell batteries
Teak decks suck
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Old 05-17-2014, 07:19 AM   #17
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Will the battery monitor register the inverter DC use.

Thanks guys for all your input. I got a 125 amp fuse and will finish the install early next week. I don't think we will use the inverter for anything else but the TV. I did try our 1200 watt pop corn popper and it worked. That maxed out the inverter, but again it worked. The TV probably pulls max 300 watts.

I do have a question concerning the battery monitor and the inverter. I haven't had a chance to check it out yet, but will the battery monitor register the inverter use (DC side) with the hook up I've got. The inverter is connected to the positive terminal of one of the house batteries and the negative is connected to the negative side of the same battery. My house bank consists of 4 AGM batteries connected in parallel. The shunt of the battery monitor is connected to the negative side of one of the house bank batteries but not the same one as the inverter.

Below is a schematic.
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Old 05-17-2014, 07:59 AM   #18
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Why not something like this that gives you a disconnect too? 187-Series Circuit Breaker - Surface Mount 150A - Blue Sea Systems
That's not a breaker/ fuse I would use it won't handle high inrush currents.
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Old 05-17-2014, 11:51 AM   #19
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Motors starting are usually the cause of a high current requirement.

Check the fuse size with the batt partially discharged and run your blender or vacuum.

.
That makes no sense. The fuse should be sized for the capacity of the DC cables unless the inverter manufacturer specifies something less.

It doesn't matter if the battery is partially discharged or the blender or vacuum is running. There is no need to do anything other than reading the instructions or looking up the capacity of the cables.
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Old 05-17-2014, 12:35 PM   #20
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I have a generator and don't need no stinking inverter.
I have Chinese LEDs and love them.
I have guns onboard.
Diesel rules.
I despise gel cell batteries
Teak decks suck
Dang. . . A man after my own heart .. .. .. .. obthomas for president !! LOL
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