Dual alternator/batteries/inverter to run A/C in camper?

[Tuesdak]

Fuel consumption for the Cummins Onan RV gensets is on the spec sheets. Pick a genset and open the spec sheet. No load vs. full load consumption just doubles the fuel use. IMO it takes a lot of fuel to run these gensets with no load. Thus the two propane bottles appear to net about 23 hours of genset time.

http://power.cummins.com/rv/generators

The unanswered question is airflow for the generator cooling while doing 65 MPH. Does the suction reverse or fight this airflow? Lance has the cooling intake on the rear and exhaust is on the bottom. This is a question for the Camper manufacturer.

 

[AH64ID]

So I have been thinking about this a little more and here is how I would do it.... caveat is I haven't priced everything out

I am also assuming that each 220A alternator goes to a separate battery.

I would run 0ga wire from each battery to the bed, and each one would go thru a 200A HD CD solenoid and a 150A link fuse. The solenoids would be triggered by a 6 psi oil pressure switch installed in the oil filter housing. This prevents the camper from draining the house batteries.

I would then add a 0ga ground from each battery to the frame, and an additional ground from the block to the frame (the alternators ground to the block).

At the bed I would bring a 0ga neg wire up from the frame and joint it with each of the pos wires in their respective fwd corners of the bed and the would be mounted to the bedside with a quick disconnect.

On the camper I would have the respective leads on each side for the pair of cables from the engine bay, this brings 2 150A pairs of cable into the camper. Each set of 0ga cables would meet at the battery bank.


I would ditch the OEM converter and install a Xantrex Freedom SW 2012 inverter/charger. This will provide 2000W of continuous inverted A/C power (at 104°) as well as be a batter 12V battery charger. The 2012 will probably need 2/0 from the battery bank to the inverter, assuming they are in close proximity.

Now you have plenty of power while traveling supplied by the alternators and an inverter for 120VAC power when dry camping and you don't want to start the generator to turn on the TV or use the phone charger, etc... I am amazed at how much we use our inverter while camping and none of it is for the TV Crockpots, battery chargers, etc.

There you go. I am willing to guess that's a $2200-2500 option without any labor or different batteries.

 

[w6pea]

You can run AC off of an inverter. First you need a large inverter(3k is good 4k is better) Then a battery bank. 4 6volt GC wired in series and then parallel. 8 would be better. You have the duel alt, so 440a at 12v equals 5280 watts. At 70% that is a whisker under 3700 watts. With good cables and what not, this should work. Please keep us updated, your not the first to do this, I say go for it. Also only the small AC run off a 2k genet, like the polar cub. A 13.5 btu will take around 3k watts to run well. They are all a little diff and hard start kits are a good thing to have. But it is doable.

I have a 2500 watt prosine xantrex in my RV. It will not run the A/C you will need too many battery's and at least a 5k inverter. You would be better of with an Onan Generator or a Gentrac Generator.

 

[Bill Stockard]

I have a 2500 watt prosine xantrex in my RV. It will not run the A/C you will need too many battery's and at least a 5k inverter. You would be better of with an Onan Generator or a Gentrac Generator.

I agree. If you check the "Locked Rotor" amp requirement specification on your A/C unit, it shows approximately how much the starting current is required to start the compressor motor. It will be well above 2500 watts!

Bill

 

[Mingoglia]

I think many are missing that my goal is to only run the A/C off the inverter when the truck is running and the alternators are supplying power to the batteries. In this scenario, there will be 4 batteries, and two alternators which will be compensating for the voltage drop the inverter sees. As for the inverter, it will likely be a pure sine wave model with 3,000 watts continuous, 6,000 watts surge. My intent is to run a genset when needed when stopped and camped.

 

[AH64ID]

I have a 2500 watt prosine xantrex in my RV. It will not run the A/C you will need too many battery's and at least a 5k inverter. You would be better of with an Onan Generator or a Gentrac Generator.

2500W is more than enough inverter to run a 13.5K BTU A/C, as long as the 2500W is the continuous rating.

I don't see a 2500W ProSine model, is yours older? There is a 1800/2900 model that would struggle to run an A/C on a hot day even with the proper battery setup.

Your issue, with 2500W of continuous, is likely the battery bank size and/or cable size. Like I pictured above my 1500W inverter drops the output voltage to 11.65 on fully charged batteries because the battery bank, even at 300AH, is too small.

This will not effect the OP as he will have 3-4 batteries to help startup loads as well as the dual 220A alternators providing power.

I agree. If you check the "Locked Rotor" amp requirement specification on your A/C unit, it shows approximately how much the starting current is required to start the compressor motor. It will be well above 2500 watts!

Bill

Locked Rotor amps is not the starting requirement, locked rotor amps are just that a locked rotor... i.e. a frozen motor. The locked rotor amperage on my A/C unit is 50.5A and it starts just fine with a 30A plug... Many slide-in campers come equipped with a 2500W onboard gen set and those run the 13.5K BTU A/C units, even some TT's come with that size generator.

They typical amp draw at startup is double the running amps and much of that is absorbed by the hard start capacitor.

 

[AH64ID]

I think many are missing that my goal is to only run the A/C off the inverter when the truck is running and the alternators are supplying power to the batteries. In this scenario, there will be 4 batteries, and two alternators which will be compensating for the voltage drop the inverter sees. As for the inverter, it will likely be a pure sine wave model with 3,000 watts continuous, 6,000 watts surge. My intent is to run a genset when needed when stopped and camped.

If your only planned load is the A/C then a 2000W inverter with a 3500-4000W surge capability is going to work just fine. If you really want a 3000W continuous inverter plan on running even bigger cables to ensure enough current can flow.

Just looking at the inverter model I listed above the 2000/4000W model needs 275A of good clean power and the 3000/6000W model needs 350A. That's a decent jump in power when you are looking at the long run you will have from the generators.

I honestly don't think you need that much inverted power, but it is doable.

 

[Mingoglia]

If your only planned load is the A/C then a 2000W inverter with a 3500-4000W surge capability is going to work just fine. If you really want a 3000W continuous inverter plan on running even bigger cables to ensure enough current can flow.

Just looking at the inverter model I listed above the 2000/4000W model needs 275A of good clean power and the 3000/6000W model needs 350A. That's a decent jump in power when you are looking at the long run you will have from the generators.

I honestly don't think you need that much inverted power, but it is doable.

Good to know. I was just browsing around and was going to make a final determination on the inverter once I had hard numbers on what I'm powering. However, most people I know with slideins are using 2000 watt Hondas (or the internal 2500 Onans), so I figured as long as I got something along those lines it would work. Figured 3,000 would be "better", as I assumed it wouldn't pull the additional amps DC if I was running a smaller load than they were capable of running.

 

[Tuesdak]

Unlike generators that will suck more unloaded fuel just by being bigger (aka too big) an inverter that's too big with big enough cables won't hurt anything but your pocketbook. In this use case bigger is better as it gives you some room for high temperatures both from the inverter running in the hot environment with it's output suffering as temperature rises, demand going up and remaining high from high AC current due to extreme head pressure in the extreme heat. Larger also means it will run cooler and cooler running = longer electronics life.

As far as the actual size the 3000 watt inverter is bigger than the standard issue Lance Camper generator 2500-2800 watt rating and that's including a unclear what it is 600w base load other than the AC.

Careful on assuming 4 batteries just being available unless there is heavy 0ga wire between the positive and negative terminals of all 4. Specifically the camper batteries will have to be joined to the truck's batteries with the 0ga wire. It's been suggested above with a quick disconnect, but, it's important enough to explain in detail again. Otherwise the standard camper plug and even the upgraded camper plug Lance requires to run the 12v fridge will NOT carry enough current to be relevant for the high amp inverter. I suggest even a frame ground is too small as this was a weak link (just enough voltage drop with high current to trip the inverter off) for me in the past.

Assuming the inverter is truck mounted and the camper batteries are not tied in with 0ga wire: My concern is although the standard camper plug limits current between the batteries would it get too hot with this big of a load causing voltage drops on the truck system all the time? Every time the AC starts the surge current could cause current to flow from the camper to the truck due to the inverter dropping the truck systems voltage and current would be heating up the camper connector and small wires. Again this is not a standard use case - only starting the engine gives you a load like this and my understanding is the battery disconnect would have the camper batteries isolated till charging voltage is available from the truck. So maybe the AC starting and truck voltage drop would trip the battery isolator preventing the reverse current flow and camper wire heating?

 

[AH64ID]

I too thought about the startup voltage effecting the isolator which is why my last post talked about a simpler setup using a pair of HD CD solenoids tied to an oil pressure switch.

Yes a bigger inverter would be better but at some point you have to mix practicality in there too. That's a lot of big cable to do properly.

 

[Mingoglia]

I too thought about the startup voltage effecting the isolator which is why my last post talked about a simpler setup using a pair of HD CD solenoids tied to an oil pressure switch.

Yes a bigger inverter would be better but at some point you have to mix practicality in there too. That's a lot of big cable to do properly.

Based on your first post, I was thinking the following. Do you feel another way may be better now?

1) Upgrade truck with some AGM Odysseys or similar.
2) Marine 500 amp isolator in the engine compartment as close as possible to the batteries.
3) Appropriate gauge wire run in a suitable wire loom to the bed of the truck.
4) Appropriately sized quick disconnect plug in the bed of truck and camper.
5) 2 Trojans or similar Golf Cart batteries wired in series.
6) ~2500-3000 continuous pure sine inverter mounted as close to coach batteries.
7) Camper shore power plugged directly into inverter (or into a receptacle wired into inverter).

The Trojans, which will have ~14 volts as they'll be receiving power from the truck batteries, which will be getting a charge from the dual alternators *should* (I think) be able to handle the dip of what I assume will be up to a 11k BTU A/C (I've narrowed the camper down to an Arctic Fox with the 11k, and a Norther Lite with a 9.2k). The inverter I was looking at cuts off at 11.4 volts if I remember correctly.

 

[AH64ID]

See my post from yesterday afternoon. Very similar but slightly different.

For the reason JDoremire brought up I would use a Heavy Duty Continuous Duty solenoid that is closed with an oil pressure switch over the isolator. A voltage drop at A/C cycling shouldn't be enought to open the isolator but may as well eliminate the possibility.

Upgrading the camper batteries is a great idea. Upgrading the truck batteries to a dual-purpose is also good, but I would put it last on the list of need to do.

Look into an inverter/charger vs a traditional inverter. They will be easier to wire inline and are generally a little better at what they do, especially since you want pure sine wave.

I think that having two sets of cables from truck to camper will also decrease the voltage drop during the cycling of the A/C.

Which inverter are you looking at?

 

[zb39]

It's also easy to add 2 more golf cart batts to the camper. This would give you 4 in the camper to hook the inverter to. I have added batts to every coach and camper I have ever had.

 

[Mingoglia]

This is pretty sexy. You can hook up to it with a laptop and configure it to do things such as bring the genset automatically on/off based on power needs or even if say the temp gets to a certain level while you're gone and you want the A/C on. It can also aggregate multiple power sources and use them each individually or consecutively based on a priority you set. I've also read of people for instance running a 15k BTU A/C with only a 2k genset. So when the A/C kicks on, it will pull as much power as you set (say 1,500 watts) from the genset, and supplement that with the inverter/batteries. When the compressor kicks off, it can run straight from the genset....then boom, compressor kicks on and it pulls from both sources again. Pretty cool. Ain't cheap, but the chicks dig dudes with the cool toys:

http://www.amazon.com/Victron-Energ...?srs=9586809011&ie=UTF8&qid=1456665195&sr=8-7

For those not wanting to click the link, here's the description:

Product Description
The Multiplus is a powerful true sine wave inverter, and includes a sophisticated battery charger with adaptive charge technology and a high-speed AC transfer switch in a single compact enclosure. CONFIGURABLE with DIP switches for most parameters, so you don't need a dedicated remote panel to program or operate the inverter. Can also be configured with a PC and optional serial cable, and connects to various Victron remotes including the Digital Multi Control and Color Control GX. DUAL LEG CHARGER keeps your start battery charged separately from the house bank without the need for relays or splitters. POWER ASSIST (sometimes called hybrid technology) allows the inverter to supplement shore power or generator when loads exceed a set amount. The charger output can also be moderated when incoming AC is limited. STACKABLE for increased output, or create a split or 3-phase system. VERY LOW POWER CONSUMPTION - just 15W in normal mode, 4W in search mode. BUILT-IN TRANSFER SWITCH with less than 20 millisecond response. All Victron products (except batteries) are backed by an industry-leading 5-YEAR WARRANTY through their worldwide service network.

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[AH64ID]

Very nice!

 

[2014 Ram Longhorn]

Another idea to help would be to look at www.modmyrv.com. It is a simple website with input from campers like you and I. Look at the inverter, batteries and A/C sections. All have good idea and knowledge. Also, look at youtube. There is a couple called, gone with the wynns. They have an article about running their a/c off batteries and solar panels. And it worked. But, make sure you get a good inverter. Pure sinus wave is the best. Nature Power Sine Wave Inverters are darn good, but not cheap. They sell them at Camping World and online. I have one in my 5th wheel and a bank of batteries. It runs my whole camper except the a/c. Good luck hunting.