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  1. #1
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    Will this inverter setup work?

    Tried searching previous posts and saw some conflicting info so just wanted to confirm what I did today will work. I ran 10 gauge wire (3 wire with protective sheath only using 2 wires) from the dc side of the fuse box (20 amp fuse) to behind the tv. Total length of cable was 35 feet (although I could cut some off if really needed). My plan is to get a 300 watt inverter for powering the tv or charging a laptop (not at same time) and place it near the tv entertainment center. I figure I should usually be running less than 100 watts (the tv is 65). Will this setup work? I’ve seen where people just tapped into the 14 ga stereo wire and had no problems. I was hoping 10 gauge would be plenty sufficient but second guessing myself.
    Last edited by Justa5th; 03-18-2019 at 09:55 PM. Reason: Clarification
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    Long Hauler howson's Avatar
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    Quote Originally Posted by Justa5th View Post
    Tried searching previous posts and saw some conflicting info so just wanted to confirm what I did today will work. I ran 10 gauge wire (3 wire with protective sheath only using 2 wires) from the dc side of the fuse box (20 amp fuse) to behind the tv. Total length of cable was 35 feet (although I could cut some off if really needed). My plan is to get a 300 watt inverter for powering the tv or charging a laptop (not at same time) and place it near the tv entertainment center. I figure I should usually be running less than 100 watts (the tv is 65). Will this setup work? I’ve seen where people just tapped into the 14 ga stereo wire and had no problems. I was hoping 10 gauge would be plenty sufficient but second guessing myself.
    I'm not an electrical engineer and my conclusions could be wrong, but below is my analysis of your setup.

    A 300W inverter will pull (maximum) 30 amps of 12VDC. If the max (based on stated fuse size) will be 20A, why not get a smaller inverter?

    When calculating wire runs you have to double the length (circuit is out and back). That's 70' for your circuit. Designing for a max of 20A that's 8ga wire.

    10ga wire will work for 100W (10A) @ 70', but I suggest replacing the 20A fuse with a 10A fuse so the component capabilities match.

    Below are my notes and references.

    Click image for larger version. 

Name:	Wire Response.jpg 
Views:	17 
Size:	99.5 KB 
ID:	18468

    Hope this helps.

    -Howard
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    @Justa5th - A better way to do this, that you might want to consider, is to place the inverter close to the batteries and make the longer run to the entertainment centre on the 120V side. The current at 120V will be 10% of the current at 12V, so you can use much smaller gauge wire. A 300 watt inverter will typically have a surge capacity above that. You might want to have wires and fuse on the 12V input side capable of 400W (just a guess) = 35A. 400/12=33 amps.

    Rob
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    Quote Originally Posted by howson View Post
    I'm not an electrical engineer and my conclusions could be wrong, but below is my analysis of your setup.

    A 300W inverter will pull (maximum) 30 amps of 12VDC. If the max (based on stated fuse size) will be 20A, why not get a smaller inverter?

    When calculating wire runs you have to double the length (circuit is out and back). That's 70' for your circuit. Designing for a max of 20A that's 8ga wire.

    10ga wire will work for 100W (10A) @ 70', but I suggest replacing the 20A fuse with a 10A fuse so the component capabilities match.

    Below are my notes and references.

    Click image for larger version. 

Name:	Wire Response.jpg 
Views:	17 
Size:	99.5 KB 
ID:	18468

    Hope this helps.

    -Howard
    Great info. I didn’t realize I had to calculate in both directions. My only thought with getting a 300 watt inverter vs smaller is so the inverter won’t work as hard. Hoping to keep the fan from running on the inverter a lot or pushing it to the limits.
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  5. #5
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    Quote Originally Posted by Cate&Rob View Post
    @Justa5th - A better way to do this, that you might want to consider, is to place the inverter close to the batteries and make the longer run to the entertainment centre on the 120V side. The current at 120V will be 10% of the current at 12V, so you can use much smaller gauge wire. A 300 watt inverter will typically have a surge capacity above that. You might want to have wires and fuse on the 12V input side capable of 400W (just a guess) = 35A. 400/12=33 amps.

    Rob

    I considered doing it this way but I was trying to stay away from doing more basement/battery connections cable runs etc. I had the underbelly off (doing the same stuff you did) and ran some cable while I was there. I think we will probably end up installing a full inverter setup in the future but would like to use the rig for a year or so first. Honestly seemed like an easy way to watch tv for the few times we do it while boondocking but maybe created some problems.
    Last edited by Justa5th; 03-19-2019 at 08:59 AM.
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  6. #6
    Long Hauler howson's Avatar
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    Quote Originally Posted by Justa5th View Post
    Great info. I didn’t realize I had to calculate in both directions. My only thought with getting a 300 watt inverter vs smaller is so the inverter won’t work as hard. Hoping to keep the fan from running on the inverter a lot or pushing it to the limits.
    Rob's approach makes a lot of sense (see his earlier post). I'm actually doing exactly what he suggested with my setup as my 3000W inverter is next to my batteries so the 4/0 and 2/0 DC wire runs are very short. The long AC wire runs will be 6/3 wire from the inverter to the fuse panel (and back). Of course you'll need a separate outlet for the inverter AC connection behind the TV, or if you wanted to get fancy you could tie in a small automatic transfer switch into the existing outlet so it is powered by the inverter or shore power automatically. (Or make it simple with a manual transfer switch.)
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  7. #7
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    Quote Originally Posted by howson View Post
    Rob's approach makes a lot of sense (see his earlier post). I'm actually doing exactly what he suggested with my setup as my 3000W inverter is next to my batteries so the 4/0 and 2/0 DC wire runs are very short. The long AC wire runs will be 6/3 wire from the inverter to the fuse panel (and back). Of course you'll need a separate outlet for the inverter AC connection behind the TV, or if you wanted to get fancy you could tie in a small automatic transfer switch into the existing outlet so it is powered by the inverter or shore power automatically. (Or make it simple with a manual transfer switch.)
    I agree. I believe when (if) I do a large inverter I will definitely wire towards battery etc. I guess I just need to figure out if the way I did it now is acceptable and “safe”. I will change out the fuse to 10 amp. I may also go back and remove some more wire. I’m thinking I could probably remove 5’.
    Last edited by Justa5th; 03-19-2019 at 09:11 AM. Reason: Grammar
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  8. #8
    Site Sponsor Cate&Rob's Avatar
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    Quote Originally Posted by howson View Post
    Of course you'll need a separate outlet for the inverter AC connection behind the TV, or if you wanted to get fancy you could tie in a small automatic transfer switch into the existing outlet so it is powered by the inverter or shore power automatically. (Or make it simple with a manual transfer switch.)
    If you want to leave the TV plugged in and be able to switch that single circuit from shore power to inverter, you will need a 120V DPDT (double pole double throw) switch. You have to switch both the power and neutral wires. These are not cheap . . . but, are available. https://www.amazon.com/Pass-Seymour-.../dp/B00R8MMALK

    Rob
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  9. #9
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    Switched the fuse for a 15 amp (lowest I had). Had an old 400 inverter laying around so hooked it up. 4 hours runtime on tv and no issues/heating of wires etc. I think I feel pretty confident this will work for our needs. I hope by the end of the year bump up to a full rig inverter.
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  10. #10
    Long Hauler howson's Avatar
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    Quote Originally Posted by Justa5th View Post
    Switched the fuse for a 15 amp (lowest I had). Had an old 400 inverter laying around so hooked it up. 4 hours runtime on tv and no issues/heating of wires etc. I think I feel pretty confident this will work for our needs. I hope by the end of the year bump up to a full rig inverter.
    Is that 400W you found a pure or modified sine wave inverter? You might want to read this article if you're not sure: https://invertersrus.com/pure-sine-vs-modified-sine/

    Loads of info online about the difference between the two types. If you didn't get a lot of noise from the TV you may be fine--the only intent of this post is to inform.
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