A/C and boondocking

[rothskeller]

How important is air conditioning in a Class B when boondocking? I'm new to this, researching my first van. I know if it was a car, I would consider it essential; cars can get deathly hot even on a mild day. If it was a house, I wouldn't worry much about it. But an RV? I'm not sure.

It matters because I'm trying to decide what type of batteries I need (AGM vs. lithium) and how many of them. If I don't need A/C, my newbie math says I can cover most of my energy needs with solar, plus some minor engine time, and I could probably get by with AGMs. If I do need A/C, however, I'll have to go lithium (which I'd prefer not to do), and then I have to figure how much of it I need (at about 150A draw). So I'd love to hear from folks whether A/C while boondocking is a necessity, a waste, or somewhere in between...

[The rest of this post is detail of my newbie math, not essential to read unless you're interested. All feedback welcome.]
I'm working through Sportsmobile for a custom rig on a shorty Sprinter platform. They estimate 50Ah/day for the refrigerator. I figure 20Ah/night for the CPAP. They're recommending an Espar system for heat; its electrical consumption is 3A, so figure 12Ah/day. Another 10-15Ah should easily cover miscellaneous stuff: lights, stereo, short usage of microwave, water pump, etc. So 100Ah/day is a reasonable maximum, not counting A/C. Sportsmobile estimates the solar brings in 80Ah on a good day, so not much other charging is needed, and most of that is probably covered if I drive somewhere during the day. And 220AH AGMs seem like they should be sufficient for that, yes?

And by the way, the reason I'd prefer to avoid lithium is that Sportsmobile puts AGM batteries under the van, but puts lithium batteries inside it. That would cost me a bunch of precious storage space, and a shorty Sprinter doesn't have much of that.

[SteveJ]

Whether you need boon dock A/C or not depends on where/when you go and your tolerance for heat. A Fantastic roof fan will help a bunch and they are quite frugal with the current draw. Less than two amps on high.

If you want A/C for more than a very few hours on a hot day you will have to use a generator or in dash A/C.

Even if you could get by running the A/C on a not quite so hot day, you would still have to get the batteries replenished. That would be quite a bit of run time on a genny, whether it is under hood or conventional unless you will be relocating daily or doing a Shamrock tour.

Solar ain't a gonna cut it for A/C. It sounds like you are already running a deficit on that.

HTH.

[booster]

I think that one place you have a weak spot in your calculations is the solar. You don't mention how many watts of panel but at 80ah per good day I assume in the 250 watt range. You really can't count on getting good solar days all the time, and most of us don't count on it more than one in 3 days unless you are in the desert. Lots of campsites are shaded, also. 220 ah of AGM gives about 176ah of usable at 80% discharge, so you have less than 2 days of power if sitting and bad solar conditions. If you move around a lot, you can get by that way, as you will charge from the engine some, depending on if you have an extra alternator for how much you will charge. The Sprinters are allegedly limited to something like 40 amps with stock changing systems, IIRC. 220ah of AGM will accept about 90 amps without overheating them during charging.

For a couple of years, we did fine with 260ah of wet cells, 300 watts of solar, compressor frig, but were only using about 50-60ah and had a larger alternator that charged at over 100 amps (but got the batteries hot).

I would say you are close if you drive quite a bit and always have a sunny campsite, but AC is out of the question. We have 440ah of AGM now and don't consider it for running AC. As was mentioned, you always have to replace what you use, so battery capacity isn't everything, and AGMs take a long time, up to 10 hours on charge, to get full. For short shots of AC to cool down a hot van, I would just run the engine and dash air.

[Bud]

"I think that one place you have a weak spot in your calculations is the solar."

Agree, and solar means SUN which means HOT and more ac.

Hi rothskeller,

There have been discussions here that if you're not going to have a conventional generator (LOUD onan, honda, yamaha,........) for ac, instead an advanced rv like system there may not be any need for solar.

If you need ac one day a year, it is a conventional generator or shore power. Me, I'll choose the shore power and delete the generator. Then go boondocking when the ac day is over. But then after a hurricane I have used the LOUD onan for days. And I've used it when the forecast was just wrong.

Bud

[rothskeller]

Originally Posted by booster

You don't mention how many watts of panel but at 80ah per good day I assume in the 250 watt range.

I got my data from Sportsmobile's web site. They're quoting 5A per 100W panel, 2 panels, 8 hours of sun, 80Ah.

Originally Posted by booster

You really can't count on getting good solar days all the time, and most of us don't count on it more than one in 3 days unless you are in the desert. Lots of campsites are shaded, also.

That's helpful to know, thanks!

Originally Posted by booster

220 ah of AGM gives about 176ah of usable at 80% discharge.

Really? I had understood from my reading that you can only discharge AGM batteries down to about 50% before the voltage drops too low to run things. And you can only charge it rapidly back up to 80%. So that would imply a usable capacity of about 30%, or 66Ah. Is that not correct?

Originally Posted by booster

220ah of AGM will accept about 90 amps without overheating them during charging.

So, recharging from 50% back up to 80% would take roughly 45 minutes at that rate. Does that sound believable?

[skagitstan]

We've built our own van conversion, so some of this may not apply to what you can get with Sportsmobile.
First, we don't have house air conditioning in our van. We never found it necessary in any RV we've had before Annie the Van.

At least around where we would willingly go, cars need A/C for two reasons:
1. Cars are parked with 0 to minimal ventilation, for security reasons. That's a major reason they get so hot.
If you are at your campsite, you will have as much ventilation as your windows, awning, and fans allow. We find we can get the inside pretty close to ambient, even in direct sun. And if ambient is too hot to be outside, we'd just as soon not go camping there. Why go camping to just sit in your camper?
2. Any vehicle will have A/C for driving, which is when you want the windows closed. Which is what the car A/C is used for.

We do have a fair amount of solar (~540W) up on a roof rack. It provides some insulation against direct solar on the roof.

We do have AGMs inside (about 400AH), because they fit with our space needs...we have a fixed bed, with electrics, water systems and storage space beneath. We've built Annie to be mildly 4 season capable.

All our heating needs are propane fired. That tank is underneath.

Our main draw for the electrics (batteries/ solar) is to power our 7CF compressor fridge. We don't have a microwave. The fridge is far and away our largest electric load...draws about 5-6A when on, and runs at about 50% duty, so it is about 72AH/day.
We've found that even under the deepest shade cover, we can run at least 3 days without getting down to 50% SOC.

We do have a Maxxair fan, and an inside air circulating fan for the very hottest days.
But our experience (at least here in the PNW), is that with a bit of care in selecting your boondocking site and orientation, an A/C just isn't necessary.

[booster]

Those are very optimistic numbers for solar gain in most cases. The normal rule of thumb would be about 30ah per day per 100 watts, which is probably pretty good. Sun right over head a bit better, sun at low angle worse.

The AGM "rules" are all over the map. Some claim you will destroy your batteries if you go below 50%, some claim the life will be cut in half going to 80% down to from 50% down (it cuts the cycles in half, but the actual recovered energy closer to 20%), and some of us think that using using the full 80% capacity is worth a slight loss of life to not have to double the amount of expensive heavy batteries and haul them around.

The losing voltage reasoning does apply, but only if you are going to be using big loads on the batteries. If you are in the normal 10-20 amp loads, you should be able to go to 80% down without voltage going too low. We tested ours with 1/2 the bank, or 220ah of capacity, and it would run the 100+ amps to the microwave to about 60% down well. This was with relatively new batteries.

For the recharging, what we have found with our Lifelines is that they will take up to about .4C in amps (176 amps for us with 440ah) continuously without getting too hot. Ours are underneath the van, behind the axle, so it is a pretty hot area, so if in a cooler spot they might take more. At 220ah, you would be 88 amps. Often the hardest part is limiting the current so they don't take too much, as they will take enough to overheat themselves in most cases. Your time estimate should be pretty close at 45 minutes from 50-80% as long as you have the 14.4v or so charging voltage and the right current.

Without knowing exactly how your camping style will be, as you likely don't either as none of us had a clue before we actually did it for a while (usually finding out our guesses were quite inaccurate), it is hard to predict how it would all work out for you. The biggest thing is how long you stay in one spot without shore power, and if you drive at all and how much while doing it. Solar would be next in the most important, I think.

We like to plant ourselves for some longer times, so we needed to size our batteries for 5+ days even without sun or driving. Our emergency fallback to recover all that use after the 5 days would be our dual alternator system that will charge at up 300 amps if we need it (for about 15 minutes our batteries will accept that much and not get too hot). We would normally be driving and charging at about 180 amps until near full, and then we would shut of the alternator charging and let the solar finish charge.

The big downside of AGMs is that the final 20% of charge takes a long time, in the range of 6-8 hours in most cases, to get to the true full of them accepting .5%C amps. They also need to get that full every 7-10 cycles for maximum life. Most smart chargers on shore power don't do this very well, so it is also a bit tough to do for all the other sources, too. You can get shore chargers and solar chargers the accurately measure the amps to charge accurately to full, but they aren't exactly inexpensive. Engine charging has no controls on it at all, either current limiting or accurate charge ending (you can get smart chargers and regulators, but none accurately measure amperage and control of it).

There are lots of discussions that have been on this forum about AGM charging and controls, so you should be able to find enough reading material to make you head spin Of particular interest might be a hybrid AGM and lithium system currently being put together by a member. It uses a single, smaller, lithium battery to fast charge as the AGMs get to 80% and then the lithium finish charges the AGMs after the charging is shut off to drastically reduce the needed time on the charging source. If it all works out, it will be really slick.

Gut feel is, that if you actually wind up using 100ah per day, you probably would need a bit more battery and solar, but until you do it, you won't really know or not.

[gk&hc]

A/C needs will depend on where you go. We spent 7 weeks in the Northeast US and Canadian Maritimes last summer in a class B, and used the A/C once, but needed the heat more often. We have also been in Florida in June with the RV, and ran the A/C every night (we weren't boon docking). As other posters have noted, a powered vent fan is a big help in warm weather.

[hbn7hj]

If you need A/C without shore power you need a generator. The number of times that happens per year is low but it does happen-traveling cross country we stop at a noisy truck stop to run the A/C all night to sleep, attending the Oshkosh fly in, where it is cool at night, it provides a place of refuge on a hot afternoon. For me the A/C-generator combo is a necessity. This past year it was used a half dozen or so important times. We use the wheels to take us to places A/C is not required.

Having it adds to flexibility of use. The RV is available in any weather at any time of the year and any place.

[BBQ]

Originally Posted by hbn7hj

If you need A/C without shore power you need a generator. The number of times that happens per year is low but it does happen-traveling cross country we stop at a noisy truck stop to run the A/C all night to sleep, attending the Oshkosh fly in, where it is cool at night, it provides a place of refuge on a hot afternoon. For me the A/C-generator combo is a necessity. This past year it was used a half dozen or so important times. We use the wheels to take us to places A/C is not required.

Having it adds to flexibility of use. The RV is available in any weather at any time of the year and any place.

I would use the other RV to go to Oshkosh... the RV-8

[hbn7hj]

I used a Long-EZ to get to Oshkosh but the Roadtrek was much more comfortable while there.

Amazing that the RV brand airplanes are still increasing in number. I would do it with one stop but I think it could do it non-stop from Phoenix. It was a not a destination for an empty tank arrival.

[InterBlog]

Originally Posted by hbn7hj

If you need A/C without shore power you need a generator. ....

If the A/C is to be run for long durations, yes. But not if it is used as a stop-gap measure.

I live in the deep south, and I've driven cross-continent solo. If I do this in the summer, it can take me up to 3 days to escape 90+ degree heat, depending on the prevailing weather. My typical pattern is be on the road by about 7 a.m., drive until noon, have lunch, take a nap, and then get back on the road until near nightfall. During the "take a nap" part, I run our roof A/C off our lithium battery bank. It can only power the roof A/C for about 2 hours (300 AH battery) but that much is a lifesaver (by way of comparison, FitRV has a larger lithium battery and can run their A/C for 3 hours 19 minutes).

I could not do that kind of travel without that capacity. I can't use a generator in the public places where I pull over for a nap (usually restaurants so that I can get lunch) - it's far too loud and I would be asked to leave.

What the other poster said is true - the design decisions have to be based on how the OP intends to use the rig. In the sweltering south, I have very specific needs.

[avanti]

Originally Posted by InterBlog

If the A/C is to be run for long durations, yes. But not if it is used as a stop-gap measure.

I live in the deep south, and I've driven cross-continent solo. If I do this in the summer, it can take me up to 3 days to escape 90+ degree heat, depending on the prevailing weather. My typical pattern is be on the road by about 7 a.m., drive until noon, have lunch, take a nap, and then get back on the road until near nightfall. During the "take a nap" part, I run our roof A/C off our lithium battery bank. It can only power the roof A/C for about 2 hours (300 AH battery) but that much is a lifesaver (by way of comparison, FitRV has a larger lithium battery and can run their A/C for 3 hours 19 minutes).

I could not do that kind of travel without that capacity. I can't use a generator in the public places where I pull over for a nap (usually restaurants so that I can get lunch) - it's far too loud and I would be asked to leave.

What the other poster said is true - the design decisions have to be based on how the OP intends to use the rig. In the sweltering south, I have very specific needs.

Yes. This hits the nail on the head. The reality is this:
--If you have a medium-sized (200+Ah) AGM battery and a large inverter, you can run your A/C for around an hour.
--If you have a large (400+Ah) AGM or lithium battery and a large inverter, you can run your A/C for around two hours.
--If you want to run all night, you need either (a) a ridiculously large lithium battery, or a genset and a campsite that lets you use it.

All three scenarios are useful depending on your travel habits, but they come at very different costs.

[booster]

Originally Posted by avanti

Yes. This hits the nail on the head. The reality is this:
--If you have a medium-sized (200+Ah) AGM battery and a large inverter, you can run your A/C for around an hour.
--If you have a large (400+Ah) AGM or lithium battery and a large inverter, you can run your A/C for around two hours.
--If you want to run all night, you need either (a) a ridiculously large lithium battery, or a genset and a campsite that lets you use it.

All three scenarios are useful depending on your travel habits, but they come at very different costs.

Yep, I would repeat things mentioned by others earlier, no matter how you store power, or how much power you store, and then use, especially in a short time like with AC, you have to recover that energy, plus whatever inefficiencies there are in the discharge/recharge process. Big alternator systems can do it for those that drive enough, but even those are only going to net about 165ah per hour of driving if you have a Nations setup. A Delco would get you more, but only ARV uses them. If you need to recover 800ah of battery from running the AC overnight, you are looking at close to 5 hours of driving needed, every day if you are using up the batteries every day with the AC. That is a lot of driving to average every day, and it would take even longer to recover if idling due to lower output at idle. Then put on top of it all that you would need the AC during the day also being likely, and you might never catch up so you could run the AC the whole time you wanted without the engine being run 8 our more hours a day, which is not a good thing. The proverbial "death spiral".

AC on batteries is really just a short term thing, IMO, as the examples that have been shown would indicate. If you are in the heat and need near full time AC, you really only have two reasonable choices, shore power or a generator, I think.

[rothskeller]

Originally Posted by avanti

Yes. This hits the nail on the head. The reality is this:
--If you have a medium-sized (200+Ah) AGM battery and a large inverter, you can run your A/C for around an hour.
--If you have a large (400+Ah) AGM or lithium battery and a large inverter, you can run your A/C for around two hours.
--If you want to run all night, you need either (a) a ridiculously large lithium battery, or a genset and a campsite that lets you use it.

An excellent summary; thank you.

[skiMore]

I don't have an RV yet.

The roof top AC units seem pretty large for a classB. Do you really need that many BTUs? I guess you may if you plan on parking in the middle of parking lot when it is 100 plus out, but what about less extreme conditions?

[InterBlog]

Originally Posted by skiMore

...

The roof top AC units seem pretty large for a classB. Do you really need that many BTUs? I guess you may if you plan on parking in the middle of parking lot when it is 100 plus out, but what about less extreme conditions?

The question may be moot. Someone correct me if I'm wrong, but the smallest unit for sale in our market might be 11,000 BTU, which is what we have on our 11-year-old rig -- and even those have become rare, as most are now in the 13,000 to 15,000 range. Whether or not you NEED a unit that big is irrelevant if smaller ones are not for sale.

Depart from the roof context and additional options may present themselves. Some DIYers have adapted small residential window units, for example.

Whether or not any of it is needed depends on the owner's usage scenarios.

[avanti]

There is also the point that larger A/Cs are not even necessarily DESIRABLE in a B van. If (as is typical in our case) the target is humidity reduction more than temperature reduction, a larger unit is actually BAD. The optimal system will just barely run continuously for purposes of dehumidification. An over-sized unit will cycle on and off constantly, and thus only be removing humidity intermittently.

[Shoalbiz]

I agree that much will depend on how you wish to use your rig, whether you want to travel with one or more dogs, etc. Elsewhere on the forum you can find a little info on a new lithium based, dual alternator, solar power generating/storage system that was just debuted for the new Winnie Travato class B’s. It’s from Volta Power Systems and supposedly, with their “Off Grid Kit,” you can run the roof AC all night just off the battery, with a system that is more compact, lighter weight, faster charging, more integrated and more powerful than anything else out there. I know, grandiose claims but Advanced RV is using the Volta systems in its builds now also. Have no idea of the costs of the different kits or if Sportsmobile is using them. Seems like they would, though, if ARV already is and there is enough customer demand for such capabilities. Also seems like a great fit for the Winnie Revel, which would really bump up the off-grid capabilities of that 4x4 RV.

[skiMore]

Originally Posted by InterBlog

The question may be moot. Someone correct me if I'm wrong, but the smallest unit for sale in our market might be 11,000 BTU, which is what we have on our 11-year-old rig -- and even those have become rare, as most are now in the 13,000 to 15,000 range. Whether or not you NEED a unit that big is irrelevant if smaller ones are not for sale.

Depart from the roof context and additional options may present themselves. Some DIYers have adapted small residential window units, for example.

Whether or not any of it is needed depends on the owner's usage scenarios.

In some ways it may be moot, but... We are talking about building very expensive battery/generator/solar systems to power AC units that may too big for a small class B RV. Wouldn't it be a lot smarter/easier/efficient to come up with the correct size AC and then design the correct (smaller) battery setup to power it?