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Old 02-14-2014, 03:21 PM   #81
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If we believe this chart and Escape used a 55A converter, round trip cable length could be up to 96" on 8ga cable. Myron's 50A max draw inverter would also fall in this range. I could certainly be wrong but if the total distance of Myrons round trip cable run from the inverter, to the converter lugs, then out to the battery and back are under the 96" limit would he not be good to go?
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Old 02-14-2014, 03:31 PM   #82
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Originally Posted by MyronL View Post
My 4AWG wire runs from the inverter to that machine screw where the red wires converge in my picture. No farther. If that is a bad idea I will change it and continue the inverter line out to the battery. I really do not want to do that. Dbailey, might an option be to reduce its inline fuse (AGU fuse holder) to say, 30 amps?
Myron,

Even on my little 300W inverter with a 30A fuse, proper installatin required it be connected directly to the battery, with the fuse at or as close to the battery as practical.

I'm afraid the bottom line is that, in your case, proper installation would mean running the 4AWG to the battery with the recommended fuse at the battery if you can.

If you run the 4 AWG to the battery, problem solved.


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Old 02-14-2014, 03:46 PM   #83
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Bob,

The wording in the chart suggests that "calculations" are concerned only with voltage drop due to resistance of the wire. It may not take in to consideration the insulation temperature rating, or the ability of the environment to shed heat. At a given current, 12 inches or wire will get just as hot as 12 feet.

The NEC ratings do that. The proper chart to use is the one I have attached above, that considers both the type of insulation, and the location of the wires (a raceway as opposed to free space).

I would not feel comfortable with the current levels in the chart you have provided.


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Old 02-14-2014, 05:43 PM   #84
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If you are going to install a permanent inverter, it is best to use the recommended wire size from the battery to the inverter. If you have a pair of 6V batteries, don't forger the jumper between them.

While you may not feel you will ever use it for more than a fraction of its rating, needs change (as do owners). Xantrex recommends a minimum of #0 for all its permanent inverters. That is overkill for a 600 watt inverter, however there are good reasons. If the wire size is too small, the voltage drop due to battery & wire resistance may cause the voltage at the inverter to drop below the cutoff level well before the battery is actually too low.

While you can do what ever you want, a safe & practical installation would replace the battery cables with full sized wire to the inverter, then run the original smaller wiring from the inverter terminals to the converter. Proper sized fuses (or circuit breakers) should be installed at the head of each section of wiring.
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Old 02-14-2014, 05:45 PM   #85
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Doug
I may be missing it but I don't see where the distance of the run is used on either of the 2 charts you mention.
It isn't... Safety concerns determine the maximum load on the wire, in that a particular amperage across a particular gauge wire generate a certain amount of heat in the wire.

Yes, a longer wire will dissipate more power and therefore generate more heat, but both the heat generation and the heat dissipation are proportional to the length of the wire, so the temperature attained is independent of the length. Note that this assumes that the heat can dissipate evenly along the wire... I'm sure there's a joke about spherical cows here.

Where the length of the wire comes in to play is in voltage drop. Voltage drop will be proportional to the resistance of the wire and the length of the wire. Wire twice as long, twice the voltage drop.

But generally voltage drop isn't a safety issue. So I'm guessing the charts show the safe amperage capacity of the wire. I looked to a different chart (not mentioned in my earlier post, but here's one: Voltage drop tables | Sunelco Solar, Wind, Hydro Electric Power -- it gives maximum length allowing a 5% voltage drop. You can also find calculators that tell you the voltage drop given length, gauge and amperage, such as this one: Voltage Drop Calculator).

This is why I broke my original response up into 1) is it safe, and 2) will it work with the inverter.
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Old 02-14-2014, 05:47 PM   #86
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Good point Jon!

I've always replace my jumper with a huge wire as a mater of course, but originally it was only an 8 or 10 gauge.

It needs to handle the total maximum current of all connected loads.

Canadian Tire sells some proper battery cables, short with lugs on each end.


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Old 02-14-2014, 05:53 PM   #87
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A slight aside; Canadian Tire also sells jumper cables that don't work because they don't carry enough current. I threw them away and got proper heavy duty jumper cables.
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Old 02-14-2014, 06:49 PM   #88
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"...So when the inverter is drawing its maximum current (50A as limited by the fuse) the power distribution panel may draw up to say 40A (as limited by the circuit breaker). The 8 gauge wire will supply 90 amps. The wire will get hot, because the total protection (fuse and CB) are too high to prevent the wire from getting hot."

Thank you John. That makes sense to me.

Thinking now... if off the grid with the furnace on, a couple LED ceiling lights on, the converter is doing its thing, drawing X number of amps, and I plug in a laptop and a camera charger the inverter now kicks in it's draw of amps .......now, my 8 AWG battery wires will begin to heat up if that total amperage load between them exceeds.... "X". And that's when the trouble will (may) begin.

Oops got to go.... M
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Old 02-14-2014, 06:52 PM   #89
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Quote:
Originally Posted by dbailey View Post
The sources (I've seen it repeated in many places) that indicate the maximum capaity of 8AWG wire as 24A all note that it's a very conservative number. The same charts show the maximum capacity for 14AWG wire as 6A. I know house wiring allows 15A on 14 gauge wire.
Okay, but that only means that residential wiring practice allows 2.5 times the current of the conservative rating... but 100 amps through an 8 AWG wire is four times that same conservative rating.

Quote:
Originally Posted by dbailey View Post
Is AC vs DC relevant for amperage rating? I don't think so...
I don't think so either (assuming that the AC currents are RMS rather than peak).

Quote:
Originally Posted by MyronL View Post
My 4AWG wire runs from the inverter to that machine screw where the red wires converge in my picture. No farther. If that is a bad idea I will change it and continue the inverter line out to the battery.
I think that - or replacing the original 8 AWG wire with 4 AWG or better, or using another method to limit the inverter's current draw - would be a good idea.

Quote:
Originally Posted by MyronL View Post
Dbailey, might an option be to reduce its inline fuse (AGU fuse holder) to say, 30 amps?
Sure, as long as you accept that if you ever draw over 300 watts from the inverter, the fuse will blow. It would be a way to be safe, at the expense of functionality.

Quote:
Originally Posted by MyronL View Post
On Page 2 of my users manual, "Comprehensive Protection" states the inverter automatically shuts down if the battery voltage drops below 10.5 V. or if the input voltage rises to more than 15.5 V. , or, if AC output overloads attached to the inverter exceeds its operating limits. Converter installed fuses max out to 50 and my in-line inverter fuse is a 50. How could I not conclude no wiring changes are needed?
Sorry, but I don't see any relationship between those protective voltage-based shutdowns and the fuse sizes. The output overload shutdown won't have a chance to work because a 50 amp fuse will blow first.

As for the comparison of the converter fuses and the inverter fuse, remember that they are not duplicating the same level of protection, since the 8 AWG wire is taking both the current to the DC distribution panel and the current to the inverter, not just one or the other. If the wiring is appropriate for 50 amps, it seems likely to be inadequate for 100 amps, right?

I think part of the problem is the dual use of this 8 AWG wire in the design of any converter-equipped RV: when on shore power, the converter is making current flow to the battery; when on battery power, the DC circuits are drawing current from the battery instead on the same wire, and 50 amps is adequate for both purposes. The inverter is not used when on shore power, so the relevant situation is when on battery power... and both the factory-installed DC circuits (for lighting etc) and the inverter are pulling current through this wire in that situation. In that battery power situation the converter itself is irrelevant.

Quote:
Originally Posted by MyronL View Post
It is the AGU 4ga input fuseholder and yes I deliberately chose the 50 over the 60 amp fuse. I cannot imagine using the inverter simultaneously for anything fuller than my laptop and a camera battery charger and (this is a real stretch)my 19 inch tv.
I understand this approach, which is why I commented that the 50A limit to the inverter would not be an issue if you never use more than about 500 watts.

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Corrales Dave loves his Cappuccino machine but me, I'll be sticking to my propane-fired Melita.
You can even have cappuccino on a propane stove - get an Italian-style espresso maker, or do it all (espresso and milk frothing) in one device with the Bialetti Mukka or equivalent. Just in case anyone is balancing electrical capacity with fancy coffee addiction...
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Old 02-14-2014, 07:53 PM   #90
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Originally Posted by Vermilye View Post
If you are going to install a permanent inverter, it is best to use the recommended wire size from the battery to the inverter. If you have a pair of 6V batteries, don't forger the jumper between them.

While you can do what ever you want, a safe & practical installation would replace the battery cables with full sized wire to the inverter, then run the original smaller wiring from the inverter terminals to the converter. Proper sized fuses (or circuit breakers) should be installed at the head of each section of wiring.
I knew if I waited long enough someone would say exactly what I'd say.

I've done that in my boats, previous trailer and will do it as one of the first things I do when I get my 19 in April.

The only thing I do in addition to this is take the opportunity to add in a marine battery switch so that one battery is always isolated from the other unless you select "both".
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