How much battery do I really need, if I've got a 3kW generator?

[Grand Tour]

We're sketching out an electrical system for full-time living in a self-done conversion in a Sprinter cargo van. We want to be capable of using 50A or 30A hook-ups, but we don't plan to rely on them.

Our sole "large" electrical load will be our air-conditioner. We're looking at the Coleman Mach 8 15,000 BTU unit. To power it, we're looking at the Honda EU3000is generator.

We don't have any other large electrical loads planned- no microwave or hair dryer. The hot water heater and range will be propane.

We would like to freely use our laptops to watch movies, surf the internet, and communicate with others.

We're planning LED interior lighting, and an AC/DC refrigerator shouldn't draw that much. And we've always got the generator and/or the engine's alternator to bring the batteries back up, depending on whether we're staying in one place for days on end, or driving for hours every day.

We're not planning any solar at this point.

Since AGM batteries do not require venting, can accept a charge faster than flooded-cell batteries, and do not require periodic maintenance, we're considering going with AGM batteries. Probably a pair of 6-volt batteries in series.

I'm not locked into any particular brand, but in looking at Trojan's web site to get some comparative information, I'm seeing their Reliant AGM Deep Cycle batteries come in three sizes- the T105-AGM, the J305-AGM, and the L16-AGM. I think I can fit any of those three sizes, and I have the payload capacity to do so, but I have to ask how much battery capacity do I really need, when the only major electrical draw is the AC, which is powered by the same generator that I can use to recharge my house batteries with anyway?

I'm not averse to spending the money for bigger batteries, but would it really be justified in this situation?

[BFlinn181]

Are you going to have an LP furnace for heat? Your AC/DC refrigerator might use more DC power than you think unless you always plan to be in a place you can use shore power. The more storage capacity in the batteries, the better, I believe.

[fagnaml]

Honda has a good "wattage" calculator to use to select a generator size --> https://powerequipment.honda.com/gen...age-calculator As you stated, an RV air conditioner is the single largest power user and requires 120 volts to operate as will your laptop computers, refrigerator, etc. "House Batteries" with an inverter could power a laptop computer and perhaps a refrigerator for a small amount of time. You must have a generator to power an air conditioner!

House batteries are intended to power 12 volt items (lights, bathroom vent fan, furnace fan, etc. for a long period of time) and are only intended to power 120 volt items for a very small period of time.

Per the Honda wattage calculator, a 3000 watt generator very likely would be too small to provide the "starting power" required for a 15,000 BTU air conditioner. For the travel trailer I once owned, I had two Honda 2000 generators with the parallel kit to provide a total of 4,000 watts of power which was enough to power my 13,500 BTU air conditioner while also operating two televisions and a couple of oscillating fans (the A/C would get turned off to power the Keuring or the wife's curling iron). Two Honda 2000 generators are easier to handle than a Honda 3000 (or larger) generator.

Hope this info helps!

[Grand Tour]

I would think that the additional fuel capacity of something like the EU3000is (3.4 gallons) would give us a longer run time, and it has electric start.

The EU2200i's .95 gallon fuel capacity gives it a rated run time of only about three hours at it's rated output. That would be pretty tough to work around.

Yamaha's EF3000iSEB (also 3.4 gallons) has the ability to do 3,500 watts long enough to start an air conditioner, maybe that would work for us.

A lot of people build these vehicles with NO air conditioner, but we absolutely intend to go places that are hot, and we're not willing to build the vehicle and then find out that we couldn't live without it. We do intend to insulate the heck out of it, use tight-fitting Reflectix type panels for the windows when parked, and make use of shade when it's available, even if it's just shade from our own awning.

[Harrysait]

One flooded 6 volt golf cart bat will give you about 200 ah to use, I assume an AGMis about the same. You need to add up your estimated amp usage by hours to determine how many batteries you will need. Also you don’t want to run them below 50% state of charge so you really get only about 100 ah per battery.
Very hard to get enough ah out of batteries to run an ac, so don’t even think about it. Run from generator or shore power only.
Your ac/dc refer wil take more battery power than you think, unless it is very small. Check it’s consumption before you decide on batteries. Our 10.7 cf RR uses about 100 ah per day.
No point in wiring your coach for 50 amp service, you won’t need it or be able to use it all. If only 50 is available use an adaptor 50 to 30 amp.
What are you doing for fresh water holding tanks?
Which Sprinter model, 2500 or 3500? Big difference in carrying capacities.
You should plan on installing an inverter, will find it very convenient.
You say you won’t rely on hook ups, then you will be running the engine or generator a lot, unless you add solar. Self install solar is not really that expensive but will give you lot more freedom. Enough to run your small rv (except a/c) maybe $600.

[Grand Tour]

Originally Posted by BFlinn181

Are you going to have an LP furnace for heat? Your AC/DC refrigerator might use more DC power than you think unless you always plan to be in a place you can use shore power. The more storage capacity in the batteries, the better, I believe.

Not planning a furnace at this time, but I'm certainly open to discuss it. Now I've got one more thing to research.

We prefer warmer weather than cold, and we would probably choose where to be, based upon that. Even during the times we've been cold (hunting, camping trips, etc.), we just bundle up and bust out our sleeping bags. If it got too cold for us, we'd probably just go somewhere warmer.

And again, we plan to insulate the heck out of this thing.

[Grand Tour]

Originally Posted by Harrysait

One flooded 6 volt golf cart bat will give you about 200 ah to use, I assume an AGMis about the same. You need to agg up your estimated amp usage by hours to determine how many batteries you will need. Also you don’t want to run them below 50% state of charge so you really get only about 100 ah per battery.
Very hard to get enough ah out of batteries to run an ac, so don’t even think about it. Run from generator or shore power only.
Your ac/dc refer wil take more battery power than you think, unless it is very small. Check it’s consumption before you decide on batteries. Our 10.7 cf RR uses about 100 ah per day.
No point in wiring your coach for 50 amp service, you won’t need it or be able to use it all. If only 50 is available use an adaptor 50 to 30 amp.
What are you doing for fresh water holding tanks?
Which Sprinter model, 2500 or 3500? Big difference in carrying capacities.
You should plan on installing an inverter, will find it very convenient.

Hey, I really appreciate the input.

We're not gonna try to run the A/C off the battery.

The Trojan T105-AGM has a 20-hour rating of 217 amp-hours. The Trojan J305-AGM has a 20-hour rating of 310 amp-hours. And the Trojan L16-AGM has a 20-hour rating of 370 amp-hours.

We're looking at much smaller refrigerators. Something like the 3.1 cubic foot Norcold 0788, which draws 3 amps on 12VDC.

We're looking at the 3500 (one-ton) dually, with a GVWR of 9,900 pounds. It's a "de-rated" version of the 11,030 pound GVWR version of the same vehicle, intended to avoid the legal issues of having a GVWR of over 10,000 pounds. The bare vehicle itself weighs roughly 6,000 pounds, giving us a payload capacity of roughly two tons. Our two motorcycles in the back weigh a combined total of only about 600 pounds, wet. There's no way we would try this with a 2500, and there's no way we would be comfortable without having dual rear wheels. We'll probably upgrade the suspension with aftermarket components, to include a 1.5" rear sway bar from Hellwig, Koni shocks, and MCU helper springs front and rear from sprinterupgrades.com out of Oregon.

Been looking at fresh water tanks from Plastic-Mart. It looks like I can fit about as large a water tank as I want, between the right rear wheelhouse and the right rear cargo door, to the right of the motorcycles. That would keep the fresh water inside the insulated vehicle, so in the unlikely even we go somewhere cold, we don't have to worry about it (or any of the fresh water plumbing) freezing. The one I was looking at just now, is 42 gallons. And I would probably err on the larger size- just because we have a big tank, doesn't mean we have to fill it all the way up, all the time. The standard fill/vent/outlet fittings would work for us, but Plastic-Mart can do custom locations that might work just a little bit better if we want to pay a few extra bucks.

From there, an electric pump (brand and model to be determined) could use PEX pipe to push the water straight forward to the kitchen sink on the right side up by the sliding side door, with a "T" at the front of the garage to take it to the left side to plumb into the ventless tankless propane water heater (looking at Excel #10016) located on the rear wall of the shower stall, right in front of the bed/garage. Not planning on having hot water in the kitchen sink, nor are we planning to have a bathroom sink at all.

We would hang a dowel in the shower stall so that the shower could double as a closet, and store the porta-potty in there too. Just lift out the closet dowel with everything on it, lay it on the bed, pull the porta-potty out, and use the shower, then put the porta-potty and closet dowel back in.

We do plan to have an inverter, but since the generator would be powering the A/C directly off the 120V breaker box, I'm thinking we probably don't need a massive inverter. I'm certainly open to input.

I didn't realize that there were adapters to connect 50A power supply to 30A vehicles. I just assumed that 50A was more common, and I could carry a 30A to 50A adapter if only 30A service was available. But again, I'm all ears.

And we haven't ruled out solar. But after installing two Fantastic Fans or Maxxair fans and a Coleman Mach 8 air conditioner on the roof, we'd have to be careful of allowing those items to even partially shade our solar panels, as that would pretty much reduce our solar power generation to zip.

[Soppy]

The Honda EU3000 should be able to run the A/C unit. You mentioned the fridge is AC/DC . Does it have a propane option ? If not it will use quit a bit of power and you will need a large battery bank. You will have to run the generator any time you need the A/C on.
A couple of hundred amp hrs of battery power should be enough for the DC stuff. You could also consider a small sine wave inverter for charging laptops.
Your best bet would be to rent a generator for a day and see what you can actually do with it.

[twinboat]

A eu2000 Honda has a fuel pump. It can be adapted to larger boat type gas tanks and run all day, but like you said, you will need 2 of them.

A eu2000 is a 1600 watt, 13.2 amp generator.

The eu3000 is 2800 watts, 23.2 amps.

Honda now offers a eu2200. 1800 watts, 15 amps. A pair will get you up to standard 30 amp shore power service.

[Grand Tour]

Originally Posted by Soppy

The Honda EU3000 should be able to run the A/C unit. You mentioned the fridge is AC/DC . Does it have a propane option ? If not it will use quit a bit of power and you will need a large battery bank. You will have to run the generator any time you need the A/C on.
A couple of hundred amp hrs of battery power should be enough for the DC stuff. You could also consider a small sine wave inverter for charging laptops.
Your best bet would be to rent a generator for a day and see what you can actually do with it.

The batteries I was looking at were The Trojan T105-AGM has a 20-hour rating of 217 amp-hours. The Trojan J305-AGM has a 20-hour rating of 310 amp-hours. And the Trojan L16-AGM has a 20-hour rating of 370 amp-hours.

I'm not opposed to running something like four of the T105-AGM batteries in series-parallel for a 12-volt output with a 20-hour rating of 434 amp-hours. But I could also run two L16-AGMs in series, with a 20-hour rating of 370 amp-hours. The dollars per amp-hour appear to be pretty close to the same price, and I can package either one.

Either way, I'm planning on having to run the generator for hours every day, because of the A/C unit. It's not like I'm trying to boondock for a week without starting the generator. There's going to be extra electrons available for the refrigerator, every single day.

I am interested in the thoughts of others with experience in this area, as to what battery bank would be most appropriate for something like this. There's a big difference between 200 amp-hours or so (100 or so of which would be usable down to 50%) and 400 amp-hours or so (200 or so of which would be usable down to 50%).

[snowman1]

A Honda EU3000i is a heavy generator, 160 lbs or so. And that's without the wheels. Like others have said, two 2000 or 2200 watt genny's weigh about 50 lbs each and are much easier to handle. Also, you sure you have the room for L-16's or even the 305's? L-16's are 18" high and weigh 150+ lbs. You'll need two of the L-16's to make a 12 volt bank. I've got a 40' pusher and I don't have room in my battery bay for even the 305's. If you have the room Lifeline 8D AGM's 300amp/hr 12 volt deep cycle battery would be a great battery at 1/2 the height of L-16's. The industry standard for AGM batteries. Two of them would give you 300 amp/hr useable.

You'll never be able to run an air conditioner off your batteries so forget about it. People with 1200 amp/hr banks and stacked 3000 watt inverters only get a few hours w/o solar. And speaking of solar, you really need to look at getting some panels up on that roof. Without a decent solar array up there, you're going to be running a genny quite a bit. Even with solar the genny will be full time if you need to run the air conditioner. You just don't have the battery bank and the massive inverter setup. Those are the facts of boondocking in one of these rigs.

If you can get over the upfront cost, I'd look seriously at LifePo4 batteries in a rig your size. Just got back from AM Solar and there were several rigs in there like your Sprinter getting lithium battery upgrades done. Lithium has numerous advantages when it comes to charging and discharging characteristics that flooded wet cell and AGM's can't even begin to touch. And when it comes to charging cycles, the cost begins to come down closer to AGM's though it is still more money.

Finally, you said something about two motorcycles out back weighing about 600 lbs. You're not planning on carrying them are you? The hitch required to haul two 300 pound bikes on the back of that Sprinter would weigh a couple hundred pounds putting you close to 1000 pounds hanging back there. No reputable shop would ever install a system like that on a Sprinter chassis nor does anyone make one. I've only seen a couple of motorcycle lifts on motorhomes and they were all on 45' DP's with tag axles. You simply do not have the chassis to handle that kind of weight hanging off the back of your motorhome. My coach has a 13K lb rated front axle and a 20K lb rated rear axle and I wouldn't even entertain the thought of carrying that kind of weight back there. You're going to need a trailer which you'll probably need anyway. Good luck in your research.

[Grand Tour]

No, I did not say that I was going to try to run my air conditioner off the batteries. I said that I was going to run it off the generator.

And no, I did not say that I was going to hang 600 pounds of motorcycles off the trailer hitch. I said that I was going to put them inside the van.

[BFlinn181]

Originally Posted by snowman1

Finally, you said something about two motorcycles out back weighing about 600 lbs. You're not planning on carrying them are you? The hitch required to haul two 300 pound bikes on the back of that Sprinter would weigh a couple hundred pounds putting you close to 1000 pounds hanging back there. No reputable shop would ever install a system like that on a Sprinter chassis nor does anyone make one. I've only seen a couple of motorcycle lifts on motorhomes and they were all on 45' DP's with tag axles. You simply do not have the chassis to handle that kind of weight hanging off the back of your motorhome. My coach has a 13K lb rated front axle and a 20K lb rated rear axle and I wouldn't even entertain the thought of carrying that kind of weight back there. You're going to need a trailer which you'll probably need anyway. Good luck in your research.

What a difference a preposition can make! The OP said "Our two motorcycles in the back weigh a combined total of only about 600 pounds, wet."

No hitch or lift, I'm guessing a ramp to roll the bikes up and parking them inside. He referred to it as a 'garage' so it'll be a mini 'toy hauler.'

[Grand Tour]

Originally Posted by BFlinn181

No hitch or lift, I'm guessing a ramp to roll the bikes up and parking them inside. He referred to it as a 'garage' so it'll be a mini 'toy hauler.'

Bingo!

One of our biggest challenges, is going to be to preserve as much headroom as we can in our loft bed over the garage. I have some ideas...