Electrically challenged

[padlin]

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?

[JohnE3]

Originally Posted by MyronL

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.


Cheers,
John

[JohnE3]

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.


John

[Vermilye]

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.

[dbailey]

Originally Posted by padlin

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.

[JohnE3]

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.


Cheers,
John

[gbaglo]

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.

[MyronL]

"...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

[Brian B-P]

Originally Posted by dbailey

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.

Originally Posted by dbailey

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).

Originally Posted by MyronL

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.

Originally Posted by MyronL

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.

Originally Posted by MyronL

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.

Originally Posted by MyronL

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.

Originally Posted by MyronL

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...

[Ron in BC]

Originally Posted by Vermilye

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".

[JohnE3]

Ron,

The isolation switch won't work with the standard Escape install; they use dual 6V in series.

... unless you mean to put a relay/isolator in, or in line with the tow vehicle so the trailer is disconnected when not charging.

Cheers,
John

[MyronL]

OK, think I get the point. I'm going to replace that 8 gauge factory wire running from the battery to inside terminal, and my inverter, with 0 gauge copper. And, between the two batteries. Why take a chance, right? Guessing 4 feet will do. Hmm... or, ...should it be my old 4 AWG?

See where on EBay a 50 foot spool of "0" gauge goes for eighty buckaroos? No wonder people are stealing it, and other vendors are not saying their product is aluminum.

Here's a pix of Dave's battery. He's got a factory inverter, it is 1000watt. Note the 100w fuse? Neglected to ask him what gauge they used there. Can't tell from this pix.

By the way Doug, nice graphics post#71

[jamman]

We have a factory-installed 1500W inverter and dual 6V batteries. They ran 8 gauge wire between the batteries and the converter/12V panel. They ran dedicated 4 gauge wire from the batteries to the inverter. I replaced the factory 8 gauge wire between the 2 batteries with a shorter 4 gauge wire.

[MyronL]

Originally Posted by jamman

We have a factory-installed 1500W inverter and dual 6V batteries. They ran 8 gauge wire between the batteries and the converter/12V panel. They ran dedicated 4 gauge wire from the batteries to the inverter. I replaced the factory 8 gauge wire between the 2 batteries with a shorter 4 gauge wire.

Sheesh!

[Ron in BC]

Originally Posted by JohnE3

Ron,

The isolation switch won't work with the standard Escape install; they use dual 6V in series.

Cheers,
John

Thanks John, but it will work fine. Two 6V batteries would be considered one bank and not switched independently. Anyway, in my case I'm getting my trailer with one group 27 and I'll add a second to make two banks.

Myron, are wire isn't created equal. Some have very fine individual strands and some are quite coarse. The coarse ones are much harder to install in confined spaces etc.

Ron

[Brian B-P]

Originally Posted by Ron in BC

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".

Originally Posted by JohnE3

The isolation switch won't work with the standard Escape install; they use dual 6V in series

Originally Posted by Ron in BC

Thanks John, but it will work fine. Two 6V batteries would be considered one bank and not switched independently.

I think that was John's point; it was at least what I would have posted if John had not covered it first. The two 6V batteries are indeed a single bank, so a bank-selector switch would have no function.

Of course with Ron's two-bank plan (consisting of two Group 27 12-volt batteries) the selector switch would make sense.

[Brian B-P]

Originally Posted by MyronL

Here's a pix of Dave's battery. He's got a factory inverter, it is 1000watt. Note the 100w fuse?

Although the annotation on the photo says "100 watt fuse", it is of course a 100 amp fuse. It looks like a Bussmann MAX automotive fuse, which I think would be more convenient than the AGU style. The terminal-mounted holder is convenient and ensures that the fuse protects the system from overcurrent due to damage anywhere along the entire length of the attached cable causing a short-circuit; I don't think it's a Bussmann holder.

[Brian B-P]

Originally Posted by jamman

I replaced the factory 8 gauge wire between the 2 batteries with a shorter 4 gauge wire.

I think that's wise, especially if the 8 gauge plus 4 gauge wires are needed to handle the maximum current, since the inter-battery jumper carries the total current flowing in all attached circuits. I suppose if overloading is not an issue and the other wires are that large just to minimize voltage drop, then the jumper is too short to be important to voltage loss.

[padlin]

In Myron's install, removing the factory 8ga and installing 4ga to the inverter and 8 from the inverter lug to the converter gives him 95A capacity, which covers max combined load.
As the correct temp 8ga can handle 55A, would a valid option be to leave in the factory and add a 2nd run of 8ga from the inverter to the batteries or is 1 4ga better then 2 8's?

In either case one would use a 4ga jumper.

For Jamman's install, is the dedicated 4ga sufficient for the 1500w inverter?

[MyronL]

I mis-spoke. Dave's is a 100 Amp fuse. Off to Home Depot-ski today, confident replacing all the 8's with 4's will do me just fine. "0" is so bloody stiff, and expensive, and probably anal. But where do I get a Bussmann max automotive fuse? Ahh-- it uses a Red Spot Fuse holder. Must check with Pep Boys for that.