Inverter Question and Tire Question (the latter is worrysome)

Hi all

We are heading out on the maiden voyage a week from today. After a summer of much learning, must renovating, updating and SPENDING...we are reaching the home stretch.

First question is the lesser important of the two but still important:

I am installing my 1500w pure sine wave inverter with 200A ANL inline fuse on the positive side to a bank of 3 brand new, group-29 flooded wet cell deep cycles tomorrow. My quandary is: My bats are up under the hood and I don't think the inverter going up there is a good idea so potentially exposed to the elements. I have heard you want these installed as close the bat bank as possible...what is the farthest (in inches or feet) that one could run a cable from the bats to the inverter without causing too much drop? Also - what is the smallest awg you would go on the wire? I have a 54" 4awg on there now but if I am to run it inside a bit out of the weather - could I use the extra 10awg cable I have to do this run a few feet? Or is that too far and too small a cable?

Second question of much more import:

having been sitting in the same spot the last few months while we got her ready - her back drivers side outside tire (we have a 36ft 1984 pace arrow class A MH with 8r 19.5 tires) today seems to have sprung a bulge. A decent sized one. We had an appointment tomorrow afternoon before we noticed this to get all 6 tires replaced before we hit the road - the tire service place is just under 5 miles from us and we could go slow...should I risk driving on this to the tire place, would I be ok at low speeds and being careful of bumps? or should I call good sam, put my membership to the test and have someone come to put the spare on before driving it to the garage? 

thanks as always everyone

I will let someone else answer the wire question, but as far as the tire, I would drive it there. I on the other hand am impatient. If it makes you the least bit nervous, call your roadside and have them worry about it.

Okay, that's definitely too small (the cable).  The 4 awg is too small, and 10 awg shouldn't even be considered.  This is one area you don't want to cut corners.  12 vdc doesn't travel well, and needs low resistance cabling, I.e. large, to avoid excess voltage drop, which makes heat, which burns things down.  With a 200 amp fuse, and a 1500 watt inverter, I would go to at least 0 or 00 awg.  That should be good for 8 to 10 ft.  There are calculators for this, and should be in your inverter manual.  If you know total maximum draw we can do an accurate voltage drop calculation.

P.S.  This is far more serious than the tire issue.  The tire may or may not make it to the shop - you still have one left.  Just drive carefully.  Undersized inverter cables can burn you down and kill you.

Yeah, the 10 ga is way too small - a max or maybe 50A over a very short distance and 30A for any length over a few feet.  The 10 ga wire would melt before that 200A ANL fuse blew.

Your 1500 watt inverter could draw as much as 145 amps, so even the 4 ga is rather small. 1/0 gauge would be recommended and 2/0 better. However, I suspect that your batteries couldn't supply that much amperage for more than 2-3 minutes, so the sustained load won't be that high. At 1000 watts, the amps would be about 90, which isn't too bad.

I would be willing to drive the tire for that short distance. The risk is modest if you keep it below highway speeds.

You should also be careful of mounting the inverter too close to the bank or in the same enclosed area of the bank, this would provide a source of ignition that you don't want near your batteries.>>>Dan

Made it to the tire place safely - the bulge didn't give me any issues I just went nice and slow much to the chagrin of the folks behind me the entire one lane way lol. All new tires were put on (much to the chagrin of my wallet) (I payed more for the new tire set than I did for the darned rig itself haha) and all breaks and under guts checked out and were OK'd by the techs as safe to tool around the country on.

I made a mistake on the cable gauge - I have 2awg batt cables connected to the inverter not 4. Are these safe or do I need to get an even bigger cable??? And with 2awg cables (if they are in fact ok)...did we come to a consensus on the minimum footage run I could go before a big voltage drop? would a 74" cable be ok? I think that size could get the inverter tucked away in the cabin and still reach the bats under the hood.

I find conflicting amp ratings for 2 awg cable, most likely because of differing coverings (insulation) and different assumptions about voltage and temperature. Wire is generally rated much higher for 12vdc than for 120vac, and automotive-grade insulation has a higher rating then typical residential wiring.  Looking at this 12v table from a solar panel distributor, it says 2 awg will deliver 100 amps over 7.2 ft.  100 amps @ 12v is 1200 watts, but your inverter will have about a 10% overhead (power loss) so I would expect that 100 amps to deliver only about 1080 watts. If you tried to pull the max 1500 watts the inverter can deliver, the amp demand would go to (1500/12) x 1.1 = 137.5 amps. 

Given those numbers, I cannot bring myself to say "OK" to using 2 awg. You really need 1/0 for that much current. 1/0 gives 150 amps for 11.5 ft, which gives you a bit of head room on both amps and distance.

If you decide to gamble with the 2 awg, PLEASE use a smaller fuse so that fuse blows before the wire melts. 125A or maybe 150A max. And make sure the connectors on the ends of the cable are high quality and properly attached.

Last night I found the site recommending size for a Xantrex 1500 watt inverter and it was 2/0 for 3-6 feet. Tom was doing maintenance so the post didn't save.

If you're only going six feet, 150 amps, which represents the maximum draw of your inverter, will yield a voltage drop of 0.289, which is 2.41%.  You're fine at that length - under 3% voltage is excellent.

Most inverters have a surge load about double the continuous load rating. If you have any startup loads that is when the cable sizing will be a factor.

Jeff said:

Most inverters have a surge load about double the continuous load rating. If you have any startup loads that is when the cable sizing will be a factor.

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True, but she has a small battery pack,  with limited output,  and the typical inverter can only supply surge current for a few seconds.  Having said that, I always prefer the largest cabling that is practical.

and the typical inverter can only supply surge current for a few seconds.

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Larger inverters are often rated to handle over-capacity for 2-5 minutes. We don't know which make & model she has.

My default is to always just go to 4/0 awg, but she is already using the 4awg. Even with her 200 amp fuse, her max voltage drop is 5.11%; certainly still reasonable, but not optimal.
Edit--- 2awg @ 200 amps = 3.22% voltage drop.

4 awg and 4/0 awg are drastically different sizes.

Which is why I default to 4/0.... 

4/0 is great if needed but at $10/ft and being very stiff when installing I would be inclined to use the aize required. (I had to use 4/0 this spring)

Jeff said:

4/0 is great if needed but at $10/ft and being very stiff when installing I would be inclined to use the aize required. (I had to use 4/0 this spring)

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I use type 3 marine grade which is spun from many small strands, therefore,  extremely flexible.  Also, being fully tinned,  it will last forever in my application.  Price is not cheap,  but I'm unwilling to cut corners on this critical system.

My Inverter/Charger is electrically centered between two battery banks with nine cable-foot runs to each.  I used 3/0 welders cable and can't imagine working with anything heavier.