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Old 05-28-2016, 01:51 PM   #15
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Originally Posted by vsheetz View Post
High draw items that operate for some extended period of time will quickly (minutes) deplete your battery bank. Laundry, air conditioning, etc. Microwave or coffee maker usage of a couple few minutes is doable. Low power items such as television, computer, etc. are no problem.
That's one of the things I don't know about the loads - how much they will actually draw over time.

For example the washing machine, I'm guessing it's pretty minimal draw through much of the cycle but high draw while it's on spin, and the AC is max 16A but they're heat-pump units and I don't know if that is what they draw while cooling or if that only happens when they're heating or some combination of things.

I'm guessing that in general their average load is going to be roughly half or maybe 2/3 of their maximum rating. Even with a resistive load like the dryer, they aren't going to be running the heating element continuously.

I think a fairly conservative estimate would have the panels generating 40A on a sunny day (probably 50-60A at noon) so it's not like the batteries would have to provide much of the juice.

Still, it is a lot of current. I was hoping the laws of physics wouldn't catch me trying to circumvent them a la Wile E. Coyote.

Thanks for the input!
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Old 05-28-2016, 02:00 PM   #16
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IF you want a better understanding do a power budget in watt hours/day of usage. Figure that against your storage capacity and solar capacity allowing for losses. For instance 8 hours of A/C will take 2200 watt hours x number of A/C's running so maybe 35,200 watt hours. Divide that by 1200 watts of solar = 29.3 hours of solar at 100% efficiency that you will not get. That should put the problem in perspective.

You probably can get better or worse habits that will help like using the generator for the A/C and doing a load of laundry and maybe dinner at the same time. A significant amount of the generator engine fuel goes to just get the generator going so adding load is incrementally less fuel than starting and running just to do something.

FWIW the last thing I would want for boon docking is an all electric unit. YMMV.
Sorry, I should have specified I was just hoping to run one AC unit, not all three. Hopefully they wouldn't draw their max rated current continuously. I honestly don't know what they actually draw, though I plan on figuring it out via Killawatt or whatever the 12V equivalent of one of those is.

I did figure that when I had to run the generator, I would run all the big loads all at once. No big deal to cook 2 or 3 extra big meals and bag the extras and throw them into the freezer. If the generators already running it's no big deal if the fridge compressor runs a while to get the freezer back down to temp.

If only I could figure out to cook while taking a hot shower...hmm...counter top induction burner perched on the bathroom counter and stirring the food while I take a hot shower, what could possibly go wrong with that combo?
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Old 05-28-2016, 02:12 PM   #17
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Hi dphaynes. For background, I'm a fulltimer and also a full time employed software engineer.



Those values are at 110-120 volts. Covert to 12.5 volts DC and they become 104 amps, 104 amps, & 176 amps (approx). Any of those are a pretty heavy load for a 600 amp-hour battery bank.



Your limit will likely be roof space. I am lucky and have a lot of available space, some rigs don't allow that without an elevated platform.



This is correct. However, your battery bank will only run the inverter for a few minutes at that kind of load.



No, certainly not. We all want 4 kW of solar panels and a 10 kW-h battery bank. The sad reality is that neither is practical (cost, weight, space). Some people are running AC from battery but they have a large LiPo battery bank (costing $10k+).

One solution to the air conditioning is to follow the weather (and use altitude to your advantage). I am in the west so this is easy - my AC's are rarely used. If in the east, not so easy.

I agree with others, an all electric rig is not ideal for boondocking. At least not until we all have a personal nuclear reactor the size of a D cell battery that we just plug into the rig.
Thanks for the feedback!

As I said elsewhere in the thread, I'm assuming the actual load will only be ~1/2 to 2/3 of the max rated loads, though I have no hard data to base that on. Also I think 40A output in sunlight would be pretty conservative for the PV array, so the batteries would only be needed if the array wasn't putting out enough. I have no clue whether the charge controllers and batteries can work in tandem like that, may be a naive assumption on my part.

I did look at the LiPO setups (like Lithium Batteries — AM Solar) About $5,500 is all I can afford for the whole solar setup so yeah, those $ amounts tend to make the head spin like Linda Blair at 45rpm. The fact that they're now down to "only" $8K to $10K is encouraging though, not that long ago those would have been an easy $20K. I'm hoping by the time my batteries need to be replaced the lithium ones will be relatively affordable. I budgeted for $4,500 and 5 years estimate life for the original batteries (assuming I get off my butt and do proper maintenance on them, which the many-worlds interpretation of quantum mechanics says *will* happen in some universe...though the odds of it happening in this particular one seem fairly slim...)
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Old 05-28-2016, 02:14 PM   #18
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For the up front investment to do the amount of Solar, Inverter upgrade, Battery upgrade you need to satisfy your wish list ( $ 5-10 grand depending on how much DIY effort you contribute ) you can buy a lot of Diesel.

Consider enough solar to do everything except AC units , washer / dryer, and cooking items like microwave / convection oven. Can always run gen an hour or two when need to do a load of wash and or cook with electricity.

If you are serious about solar then the cells in panels are series wired and even partial shade on a panel really reduces output, so you may want to consider placement on roof carefully. The super serious people have solar panel tilt capability and park so their panels are tilted facing south. Others raise their panels many inches above the roof but leave them flat to about the height of top of the AC units so that they can't be shaded by other items on the roof of the RV.

With multiple panels, they can be run in series or parallel, the advantage of series is it's more efficient (less power lost in cabling to controller) the advantage of parallel is less output lost if the solar panel array is in partial shade.

One thing is get a good MPPT technology What is Maximum Power Point Tracking (MPPT) solar charge controller for the same # of solar panels on the roof you will get much more power transferred into your battery bank ( up to 15-20 % more )
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Old 05-28-2016, 02:50 PM   #19
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For the up front investment to do the amount of Solar, Inverter upgrade, Battery upgrade you need to satisfy your wish list ( $ 5-10 grand depending on how much DIY effort you contribute ) you can buy a lot of Diesel.

Consider enough solar to do everything except AC units , washer / dryer, and cooking items like microwave / convection oven. Can always run gen an hour or two when need to do a load of wash and or cook with electricity.

If you are serious about solar then the cells in panels are series wired and even partial shade on a panel really reduces output, so you may want to consider placement on roof carefully. The super serious people have solar panel tilt capability and park so their panels are tilted facing south. Others raise their panels many inches above the roof but leave them flat to about the height of top of the AC units so that they can't be shaded by other items on the roof of the RV.

With multiple panels, they can be run in series or parallel, the advantage of series is it's more efficient (less power lost in cabling to controller) the advantage of parallel is less output lost if the solar panel array is in partial shade.

One thing is get a good MPPT technology What is Maximum Power Point Tracking (MPPT) solar charge controller for the same # of solar panels on the roof you will get much more power transferred into your battery bank ( up to 15-20 % more )
It's a long-term cost issue (I'm assuming minimum of 10 years in this one) as well as the wish to avoid fossil fuel if I'm not actually driving. I realize they get **** for mileage but I only plan on at most ~4,000 to 5,000 miles per year so relatively speaking the generator use could account for a significant percentage of the actual fuel consumed.

The dealer uses an Outback FM80 controller which is MPTT Outback Power Inc. - Charge Controllers FLEXmax 60/80

I can't do the tilting panel thing. My knees are already screaming "Replace Me!" and ladders in particular are excruciating. The service manager suggested that it's easier to add extra panels (hence my interest in 1200W vs. their usual 900W system) rather than the complexity/hassles of a tilt system.

Given that we can build space shuttles and drive rovers around on Mars, you'd think someone could come up with a sunlight tracking system with an inflating bladder that lifts one edge of the panels up as needed. Like the big airbags the rescue squads use to lift vehicle after an accident.

Hmm...come to think of it they use those to lift big semi trucks and sometimes even trains. I bet I could get those cheap so all I'd need is gimbal mounted floors and just tilt the whole RV towards the sun...

I might have to replace the induction range with one of the gimbal mounted ones like they put in sailboats, but other than that, what could possibly go wrong?
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Old 05-28-2016, 03:04 PM   #20
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The value of the silence that solar provides cannot be calculated. For me, it is worth a lot.

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I can't do the tilting panel thing. My knees are already screaming "Replace Me!" and ladders in particular are excruciating. The service manager suggested that it's easier to add extra panels (hence my interest in 1200W vs. their usual 900W system) rather than the complexity/hassles of a tilt system.
Some more real world experience. With flat mounted panels, I get about 80% rated output in the summer months (most everywhere in the west). During the winter months, I get close to 60% rated output in Arizona. Solar Power Winter Update - JdFinley.com
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Old 05-28-2016, 03:07 PM   #21
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The dealer uses an Outback FM80 controller which is MPTT
That controller appears to have a maximum input voltage of 60 volts. Keep that in mind (too low for me).
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Old 05-28-2016, 03:11 PM   #22
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You should be thinking in terms of running from battery power and that battery amps are more than 10x what the 120vac amperage is. Your solar is basically a battery charger rather than a direct power source - it only produces significant power during peak sun periods, which often does not coincide the peak load periods. A hot but cloudy afternoon is one obvious example.

IMO you would be better off with more batteries and fewer solar panels. You can charge (at least somewhat) for many hours each day, but the panels only produce high amps for a few hours. If even that.

You need to work out a daily power budget, estimating demand (120v and 12v) vs the size of the battery bank and the ability to re-charge. A couple of a/c units on a hot day can easily consume your entire stored power supply in just an hour or so. Six batteries will give you about 600 amp-hours @ 12v, or about 7200 watts for one hour. But wait, you can only use about half that without damaging the batteries, so now its 3600 watts for one hour. Your two (or 3?) roof a/c units will pretty well chew that up. If the sun is direct overhead, the 1200 watts of solar replaces about 90A during that same time. Then what?
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Old 05-28-2016, 03:17 PM   #23
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Might be a stupid question, are you planning on parking at places without utilities a lot?
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Old 05-28-2016, 06:05 PM   #24
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This is good advice. I pull into a campground once every 2-3 weeks to dump/fill, do laundry (onboard), and take a REALLY long, hot shower.

Making your own window shades is not very hard (RV Windshield Sun Shade - JdFinley.com) and you can get pretty crazy with the shade material that is available. I purchased a big roll (6' x 100') 80% UV Resistant Fabric and have been toying with it - it definitely helps to keep the temps down.

I was thinking about sun sails - keep the sun off the coach.

http://www.amazon.com/Windscreen4les...words=sun+sail
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Old 05-28-2016, 06:41 PM   #25
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Might be a stupid question, are you planning on parking at places without utilities a lot?
I don't, I plan to stay at lavish resorts where the cabana boys plug in the power for me and and shapely young women wear bikinis while they empty the poop tank for me. Unfortunately my monthly budget plans to stay in places without utilities as much as practical...
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Old 05-28-2016, 07:32 PM   #26
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I've got 1400 watts of solar which will sustain us (almost) indefinitely with good sun conditions in lower latitudes with a residential frig and moderate use of TV, LED lights, water pump and small electrical items - plus unknown phantom draw. A/C and extended M/W use requires generator runs.

Recommend you consider the following if you're pressing ahead:
- Previous responders have provided solid advice
- Talk with AM Solar staff (search postings on IRV2 and web)
- Think about lithium battery bank versus AGMs (more useable capacity - expensive, but do the math on useable amp hours versus other battery types)
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Old 05-28-2016, 08:34 PM   #27
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I think you've gotten some good advice from the earlier postings, including checking with AM Solar. I have about 1,000 watts of solar on my coach, which keeps me pretty happy occasionally boondocking and keeping the refrigerator running in storage (no electricity). As said earlier, the solar is just to keep the batteries charged. What will determine what you can run, even for a short time, is the peak current requirements for your devices. When you talk about air conditioners and the like, I think you're going to be disappointed. Here's a link from Honda Generators showing the approximate start-up wattage and running wattage for various appliances. Honda Generators wattage estimates. They list RV Air Conditioners, and for a 13,500 BTU/hr unit the start-up wattage is 2,800 watts, compared to 1,800 watts continuous. I have a 2,800 watt inverter, but I don't think it would handle even one of my 15,000 AC units starting by itself. I certainly wouldn't have enough solar to keep the batteries charged for even an hour or so of operation a day.

For myself, I'm lucky to get 500-600 watts peak out of my solar, and you can't count on more than 8-12 hours per day (not all at peak power). When you add it up, I can run the refrigerator all day, and occasionally the lights, computer equipment, and televisions. Microwave and coffee maker added in will ensure I need to run the generator a bit. I wouldn't even dream of the AC and washing machine, let alone dryer.
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Old 05-28-2016, 08:55 PM   #28
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Running the washer/dryer off batteries isn't practical. I've read articles on off-grid houses, where the number of solar panels and weight of the battery bank aren't limited, and they still fire up a generator to do laundry (although they generally use a clothes line instead of a dryer). Generators need regular exercise.
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