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Old 02-17-2014, 03:43 PM   #15
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Originally Posted by Protagonist View Post
Current in equals current out. Same wire gauge throughout, unless you really want the smaller wires to get hot due to increased resistance.

Thanks for helping. Since the Airstream came with 4 awg on the battery side of things and the Samlex manual suggests 150 amp fuse for 4 awg, perhaps I should just put in a 150 amp fuse and if it blows, reduce my ac needs. In other words, even though I have a 2000 watt inverter, don't use more than 1000 watts. I am trying to convince myself that I can avoid rewiring the Airstream by just ensuring that the wiring is still protected. Jim
PS "current in equals current out" another dah moment for me. Thanks for reminding me to remember something that I once new but had obviously forgotten? No shaking your head, Lewster.
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Old 02-17-2014, 05:17 PM   #16
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PS "current in equals current out" another dah moment for me. Thanks for reminding me to remember something that I once new but had obviously forgotten? No shaking your head, Lewster.
Well, it is a gross simplification, and doesn't account for voltage drop over distance or other losses. Entropy does still apply, after all, so current in equals current out isn't exactly true. But when laying out circuits, best to assume that it is true and use the same wire gauge throughout the circuit.
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Old 02-17-2014, 07:02 PM   #17
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One of the beauties of DIY is that you can get away with things like under sizing wire, making loads of resistance generating connections, and using the wrong size fuses. If I did stiff like that, or even hinted at it……. my a$$ would be gra$$

IMHO, spending a few bucks more for the proper gauge wiring makes a lot of sense, especially when your peace of mind and physical well-being may be at stake.
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Old 02-17-2014, 07:41 PM   #18
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Most manufactures of inverters recommend not loading the inverter to more than 80% of the rated capacity. Especially if that load is constant.
Even if the #4 wire is THWN-2 it is only rated at 95 amps which equates to 1140 watts at 12 volts.
Not much point in using a 2,000 watt inverter.
Whereas THWN 2/0 wire is rated at 175 amps. That's 2,100 watt capacity.
How much trouble is it to pull in new wire?
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Old 02-17-2014, 08:33 PM   #19
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OK. Now I'm frightened. The Samlex manual says to use 2x#2 awg wire along with a 300 Amp DC-FA-300 fuse. I know what the fuse is but I don't understand the wire requirement. Are they saying to use THHN 2/0 gauge? If they are, I will do that. Jim
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Old 02-17-2014, 08:50 PM   #20
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OK. Now I'm frightened. The Samlex manual says to use 2x#2 awg wire along with a 300 Amp DC-FA-300 fuse. I know what the fuse is but I don't understand the wire requirement. Are they saying to use THHN 2/0 gauge? If they are, I will do that. Jim
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Old 02-17-2014, 08:58 PM   #21
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Thanks for your input Lewster. I appreciate it a lot. Jim
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Old 02-18-2014, 05:37 AM   #22
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Most manufactures of inverters recommend not loading the inverter to more than 80% of the rated capacity. Especially if that load is constant.
Even if the #4 wire is THWN-2 it is only rated at 95 amps which equates to 1140 watts at 12 volts.
Not much point in using a 2,000 watt inverter.
Whereas THWN 2/0 wire is rated at 175 amps. That's 2,100 watt capacity.
How much trouble is it to pull in new wire?

Thanks. I now understand why Airstream is limiting their factory inverter to 1000 watts. My biggest draw comes from the coffee pot for 10 minutes in the morning and it is 980 watts. Jim
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Old 02-18-2014, 08:47 AM   #23
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Lewster is a pro and must do what is technically and legally correct. His advice is always good as gold. But, his customers pay for the very best installations.
I have found during years of boat ownership and now an Airstream that some requirements are excessive and the effort for a DIY'er is too much to undertake.
As an example, I needed to put a shunt in the battery box and run some new wire into the trailer. The pro would have cleaned all of the sealant out of the penetration, run some different DC cables, put the shunt in the trailer...all in an area where access is difficult. The labor cost for a pro would have been steep. I fought my way through it and made minimal changes to what was already there, albeit not up to a pro's standards. My install works just fine and is just as safe as the original trailer. So, I suggest that a guy can do modifications safely without having to gold plate the installation.
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Old 02-18-2014, 07:52 PM   #24
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Thanks for the input Larry. I think I may be at a " don't sacrifice the good for the sake of the perfect" moment. Seems to me that fuses were invented to protect wires from excess current so as long as the fuse is appropriate for the wire gauge, I should be a happy DIY camper. The size of the inverter is actually irrelevant and given the cost of the fuse, one would be inclined to be prudent in his use of electricity, just like at home. I can sleep comfortably with that. Jim
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Old 02-18-2014, 09:37 PM   #25
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With a 2,000 watt inverter. You will take the fuses out pretty easily. Unless they are rated for the inverter load. Which you will not be able to accomplish with smaller wire.
If you install fuses rated at 95 amps. You will blow them when the inverter reaches about half of it's rated load.
Without an ammeter to monitor the load and even with one. You won't know when you reach that threshold until it is too late.
Like you said, the fuses are not cheap.
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Old 02-20-2014, 01:46 PM   #26
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Smile Not as bad as I thought

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Rich, there is a very substantial in-line fuse that you've blown. (They cost around $40, BTW). It is located behind a black plastic shield that's located in the box that you can't get to. The heavy positive battery wire goes from your battery to one side of the fuse. Then you have the fuse. On the other side you'll find the red wire that goes to the positive side of your inverter. How do I know this? Well, I replaced my 700 W inverter with a 2000 W model and inadvertently touched the positive to ground. (Accidents happen?) I traced the circuit and found the fuse. NOT easy to get to, and not cheap to replace. Barry
Well, Barry, I got the storage box out without too much trouble at all. I removed the 4 screws from the top, then found 3 more under the L-Lounge. I took those out and the whole box just lifted out, exposing the entire front.

I opened the black cover and found the A3T110 fuse and removed it, checked it, and it is blown. I found a replacement on eBay for about $23 including shipping. It should arrive by 2/25.

I had contacted Airstream and they told me it was an auto-reset breaker in this model. Either it's been replaced with a fuse or it has always been a fuse. I know the PO had never replaced it. Airstream also told me I'd have to remove the entire lounge to get to it and that proved not to be correct either. PO had the couch recovered in leather but I'm pretty sure the support boxes are original.

All in all, I think I was lucky and I've learned a lot about at least the front of my AS.

Rich
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Old 03-02-2014, 03:02 PM   #27
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Mine is also all fixed now. It seems that when I was installing the new inverter, I touched something, created a short and blue a fuse. The fuse is located in the positive line between the inverter, the inside battery bank and the inside battery bank's connection point to the outside batteries at the battery side of the solenoid switch. This means that since the solar panels are connected to the controller and then to the inside battery bank, and there is a disconnect to the outside batteries (blown fuse), the outside batteries were receiving no input from the solar panels while the inside batteries were receiving a charge. Since the Airstream is in storage and only being maintained by solar, and the solenoid switch is in "use", the outside batteries eventually died. The controller is only getting information from the inside bank so all appears ok. Clearly, I need battery a monitor that reports on each bank independently. Too cold to do this now so I will fiddle with it in the summer. It will also be interesting to see if I was able to rescue the the two AGM batteries that have been on a smart charger for several weeks after being deader than a door nail for a week. Jim
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