Help me design my off grid RV system.....LONG!

Crazy Cooter · July 2011

Hi all! Been reading here on and off for a while and finally decided to join up and post.

I'm expecting a new 5th wheel toy hauler in the next few weeks and need to set it up before we can really use it. This one is 10 feet longer, much more luxurious than the last with many more lights and area to light, therefore expect it to be a "Power Hog".

My current trailer which is sold and to be delivered next week has 4) T-105's, Xantrex 458 2K inverter, Xantrex Link 1000, 3) 120W PV's, and an Old school Mark 22 controller. It served us pretty well during the sunny season, but winter we needed more power.......Always seemed like we were 60-90Ah down per day of cloudy weather

Since I hate listening to generators while camping, I ordered this new ride without the $5,700 generator option. I did take my little Yamaha 2800 inverter with me for backup on the 11 day winter trips since the solar could not keep up. I'd like to get to a point where I only take the generator when we need A/C.

This time, I'm thinking of 600-1000 watts PV, either 4) T-105's or 2) L16's depending on the compartment size, 2KW pure sine inverter, some kind of battery monitor, and of course an MPPT charger controller. May even buy more PV if I can swing it.

My Dad is in the RV biz and has seen too many issues with the Xantrex stuff of late and likes Magnum now. I have been looking at Outback as well. Both look to have good hardware, but Outback looks like it takes the cake with integration in mind. Magnum have a cleaner sine wave output?

I hated the appliances humming while operating and assume this was the dirty waveform of the 458. I want to avoid this if possible. The new ride has flat panel LCD TV's so I assume they will appreciate a cleaner AC signal. My coffee pot didn't work as well mobile as it did in the house either....nothing an extra scoop didn't fix, but the higher RMS voltage of a pure sine inverter surely would help.:cool:

I'm not a rich man, but made a few mistakes on the last build and want to do it right this time....or at least as good as I can afford.

Do I go Outback everything and integrate the whole mess?

Or Magnum for most of it and match up a charge controller?

Is there something better in my budget?

Tony

Cariboocoot · July 2011

Re: Help me design my off grid RV system.....LONG!

Welcome to the forum, Tony.

Since this is essentially an off-grid system the same rules apply. Rule #1 is reduce your loads, not expand them!

Electric coffee maker? ERK!
Rule #2 is you design the system around the loads. Don't guess at how many batteries you need; calculate a reasonable expectation of use, knowing that is all else fails you have a generator. The size of the battery bank normally dictates the size of the PV array, but with an RV there's a limit to the amount of "roof real estate" available, even on a big one. Some people make up "stowable" arrays to negate this problem.

As far as the "cleanliness" of the output waveform, the Outback and the Magnum aren't significantly different. Magnum does have a power factor corrected charger, which is "easier" on small generators. Outback's integration is good, but is that likely to be an issue here? You probably won't have multiple charge controllers, much less multiple inverters; that's where the integration shines.

So let's go back to Rule #1 and call it "Step #1" and figure out some numbers for maximum Watts and total daily Watt hours.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

Thanks for the reply.:D

I don't have anything that would tell me what my exact daily total demands are on the system. I only know what I am short at the end of a cloudy day. I could likely get away with a 225ah battery bank if I had more PV and a more efficient charge controller.

Most of our loads are 12V lights, fan, and Ham radios. The coffee pot only runs for 7-10 mins. Microwave for 2-10 mins.

I just got a 12v/120v refer/freezer that draws 4.2A on 12v....50% duty cycle a real figure? This one is new to me and not in the original specs of the old trailer.

What we had before did the job OK, just in the winter was very marginal. The biggest helper was the catalytic heater to reduce furnace run time.

Since most of these loads occur during the day, maybe increase PV and reduce battery size? If we just did weekend trips, none of this would be an issue.

Cariboocoot · July 2011

Re: Help me design my off grid RV system.....LONG!

PV and battery size are integral. If you can have enough PV to charge the batteries you'll find they're in "Float" for some good portion of the day, meaning there's "extra" Watts not being harvested that cn allow you to turn on big power users.

So, to go about it "sideways":

If you can fit four T105's and get 450 Amp hours @ 12 Volts that would give you up to about 2700 Watt hours at 50% discharge. That's a pretty fair amount of power: about what runs my whole cabin.

That much battery is going to want something along the lines of 865 Watts of array to keep it properly charged. Can you fit that much up top? The higher Wattage panels are also physically larger, and not necessarily a good choice for RV mounting due to flexing issues. A "small" panel is about 2.5 feet by 5 feet, and you'd probably need 4-6 of them.

You are definitely in "MPPT charge controller territory" here; the array will be big enough to make it worthwhile.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

I found my current controller floating buy noon in sunny conditions with -60-90ah showing on the Link 1000. The distance between the controller and the battery bank was too long with too small of conductor. We'll be fixing that this time with the controller being mounted within 1-3 feet of the bank with much larger wire. I wasn't anticipating that kind of growth with the last system since it was my first and didn't know what to expect.

Should be able to fit all that no problem. I have 3) 2x4 panels on the current unit with 210 sq ft of roof with room to double that. The new one will have around 320 sq ft of flat space.

This rig has 50A service, but only has one A/C, so I assume it will only use one leg since the other is usually used for a second A/C. Do I need an inverter with two inputs/outputs? Like the Magnum MS2012-20B? Or is the MS2000 or MS2012 what I would need?

Some of my buddies swear by their MX60's. Should I get the FM60, FM80, or maybe a Morning Star Tri Star MPPT 60. Looking like 800w+ will require FM80 anyway......

This is looking like a $5K project. A lot better than listening to a genny run all day!:roll:

Cariboocoot · July 2011

Re: Help me design my off grid RV system.....LONG!

I have an Outback MX60 charge controller. It is the quintessential MPPT controller. Out-of-date it may be, but it is flexible and dependable. The few faults it has aren't worth the words to mention. No reason why you can't use an FM60 with a Magnum inverter. In fact they're a pretty good value compared to some of the other choices, vis: the Morningstar that has you buying "extras" to get the same display features or the Midnight Classic which has functions you won't use.

The Magnum MS2012 is probably a good inverter choice. But be sure to check how the 120 VAC wiring of the unit is set up: you don't want to feed two hots off one inverter and then run in to trouble if you connect to "shore power" or fire up a 240 VAC gen. Nor do you want half the outlets to be dead when on inverter power because there's no feed! I can't advise more precisely on this because it's a "look at the wiring diagram" matter. So look at the wiring diagram. Make sure you know what goes where. And check the A/C load to make sure a 2 kW inverter will handle it; I'd have my doubts, but there's so many variations in A/C these days you can't say it won't or it will. :roll: It's a shame you're limited to the 12 Volt system, as 24 Volts opens up more inverter options. If you do need 240 VAC supply you could run an autotransformer or stack a pair of Outbacks.

The little inverter gens are nicely quiet and fuel efficient. No problem feeding the Magnum off one of those, providing you don't turn too many loads on.

niel · July 2011

Re: Help me design my off grid RV system.....LONG!

i'll attack this in a general sense. some particulars i can't comment on as i don't know if the rv takes 240vac or only 120vac for example and how that might effect your choices as that can get involved in speculation too involved without more info.

obviously, you'll have a bit more loads than before just because the rv is bigger. conservation and an inverter generator can make up for any ups or downs. from my viewpoint you may have had too little pv before to keep the batteries fully charged and the battery bank may be the right size with the 4 t-104s. i'm guessing you just lacked some stored backup power because the pvs weren't able to keep up with the demand. if it turns out i'm wrong then before you buy the batteries you can revisit this with better info on the battery needs. giving extra battery capacity a proper charge may also need to be visited, but the inverter generator would still be there to provide power if need be. the idea is to lessen that need of the generator and i believe more power in pvs and an mppt controller may do well to lessen that need to run the generator. you won't totally get around the need for the generator of course and you do want to watch your batteries more closely to be sure you won't drain them beyond about 50% and to log the requirements better on your batteries. a good hydrometer and a battery monitor may help you achieve this better and do write things down to be able to look back at it just in case. if you go to expand on the battery bank later be sure you address the higher charge needed and do so before the batteries get abused or maybe a year old to keep the new batteries from being dragged down by the old batteries.

some might say to verify your loads first before opting with a battery bank that same size again, but i see it as a bit of autonomy for those extended times or even in an emergency. the only thing is, you do need much more in pvs to charge it properly as we often recommend a charge rate between 5% and 13% and coot will quickly point out that trojan likes their rate at least about 10%. with that being a possible problem it does open the realm of possibility for maybe agm style batteries with their higher efficiencies and no gassing when properly being charged making them a tad safer in an enclosed area. the drawback is they cost more.

you have a quite a bit on your plate to consider and doing it up right, as you put it, can be very costly, but sometimes well worth it. i can't say that some compromises won't present themselves that are viable to save $, but is more your call than ours. we can still give you an opinion on those compromises too as the final decision is yours to weigh.

mike95490 · July 2011

Re: Help me design my off grid RV system.....LONG!

Crazy Cooter wrote: »

...
What we had before did the job OK, just in the winter was very marginal. The biggest helper was the catalytic heater to reduce furnace run time.. .

FURNACE ?? Coffee Pot ??

Get 2 catalytic heaters and a campstove.

Crazy to run this off an inverter off 12VDC. I'm not even designing a furnace in my off grid house, and reluctant to use radiant heat to save the 100W the circulation pump draws.

AIR CONDITIONING ?? Are you insulated ? Will doors be open, like in a barn while the AC runs ?

mike95490 · July 2011

Re: Help me design my off grid RV system.....LONG!

Cariboocoot wrote: »

..... It's a shame you're limited to the 12 Volt system, as 24 Volts opens up more inverter options. If you do need 240 VAC supply you could run an autotransformer or stack a pair of Outbacks.....

Or if you step up to 24V , the Xantrex XW24xx would give 240 out for you, has intergral charger, AC1, AC2 inputs, and transfer switch... $$

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

I know a lot of you guys think I'm crazy, but I'm limited to 12V/120v as that's what RV's are wired with and nearly everything is runs on 12V. I'm not going to throw out $1,000's in new appliances and rewire the whole rig to make it energy efficient. It needs to be universal and mobile.

Coffee pot is only like 16ah pr day. I can have that power back in less than an hour. Furnace is just used to top off and circulate air and only had a run time of half hour a night even when real cold.....6ah. This new ride is a 4 season RV and I ordered with dual pane windows.

Don't have room for a catalytic in the bedroom unless I want to chance a fire.

It's cheaper and easier to just slap on some more PV and have a happy life. I conserve at home so I can live in luxury while on vacation....8)

If this were a cabin I was building from ground up, things would be different.

6-185w panels on the way....got a smokin' deal since two of my buddies are doing both of their houses and got them on the same order. The rest can wait till it gets here.

The whole issue is lack of sun due to clouds or shade from trees. When I spring camp in the desert, I have plenty of clear days and no trees, but its not always like that. Having more than I need will fix er up.....

niel · July 2011

Re: Help me design my off grid RV system.....LONG!

we have had discussions on these areas i am about to bring up and it can be good food for thought for you.

you can have an awning type arrangement with a few pvs that may give you a better angle to the sun if it is located on the correct side of the rv to take advantage of it.

another option is remote-able pvs so that you can put a few pvs into better view of the sun when the rv is shaded.

now if you do either of those things, both of these need to have theft in mind as you don't want to leave a few pvs laying around while you aren't there or able to see them. they need to be put away into the rv when theft is a possibility so keep that in mind in mountings for these types of arrangements.

icarus · July 2011

Re: Help me design my off grid RV system.....LONG!

16 ah is about ~ 200 wh! ~ 30% of my daily total.

It seems like you have a pretty good grasp of the basics but here is my rule of thumb for off grid, (and it has born itself out fairly well over the years in the real world).

Take the name plate rating of the PV, divide that number by 2 to represent all cumulative system loses, then multiply that number by 4 to represent the average number of hours of good sun one can reasonably expect on a daily basis averaged over a year. You can adjust that number up or down,, but you do so at your peril. If for example you live in the desert SW where you get 300+ days of sun you might adjust it a bit, but the 4 hour rule works pretty well for cloudy days, rainy days, sunny days all averaged in.

So for example, a 1000 watt system might look like this: 1000/2=500*4=2000 wh/day.

The reality however is the equation is even worse for an Rv, as the PV is seldom if ever ideally suited. I would probably derate another 25%, leaving ~1.5 kwh/day,, or less.

So, as with all reasonable solar equations, they all start with the loading, and then they work backwards. Start with your expected loads, figure out how to reduce them to an absolute minimum, and then design a system to fit.

Just as an FYI, we live off grid with ~400 watts of PV. We routinely use 5-800 wh/day, and on average we recharge daily. With 450 ah of battery, we can go three days with no sun before we need to charge from some source. On an ideal cay, we can generate ~ 2 kwh.

Welcome to the forum, and keep in touch,

Tony

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

niel wrote: »

we have had discussions on these areas i am about to bring up and it can be good food for thought for you.

you can have an awning type arrangement with a few pvs that may give you a better angle to the sun if it is located on the correct side of the rv to take advantage of it.

another option is remote-able pvs so that you can put a few pvs into better view of the sun when the rv is shaded.

now if you do either of those things, both of these need to have theft in mind as you don't want to leave a few pvs laying around while you aren't there or able to see them. they need to be put away into the rv when theft is a possibility so keep that in mind in mountings for these types of arrangements.

I have thought about the tilting brackets for the roof, but in the desert we can get 70mph gusts of wind without notice and those things would be pretty large sails. The portable setup is out as well. I don't want to load and unload any more than I have to. Breaking camp needs to be a 30-45 min job at most or it's just too much work......which is the reason I'm camping in the first place....to get away from it. Theft would be a factor as well since we camp in remote areas and are away from the RV for hours at a time.

Outta site is outta mind?

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

icarus wrote: »

16 ah is about ~ 200 wh! ~ 30% of my daily total.

It seems like you have a pretty good grasp of the basics but here is my rule of thumb for off grid, (and it has born itself out fairly well over the years in the real world).

Take the name plate rating of the PV, divide that number by 2 to represent all cumulative system loses, then multiply that number by 4 to represent the average number of hours of good sun one can reasonably expect on a daily basis averaged over a year. You can adjust that number up or down,, but you do so at your peril. If for example you live in the desert SW where you get 300+ days of sun you might adjust it a bit, but the 4 hour rule works pretty well for cloudy days, rainy days, sunny days all averaged in.

So for example, a 1000 watt system might look like this: 1000/2=500*4=2000 wh/day.

The reality however is the equation is even worse for an Rv, as the PV is seldom if ever ideally suited. I would probably derate another 25%, leaving ~1.5 kwh/day,, or less.

So, as with all reasonable solar equations, they all start with the loading, and then they work backwards. Start with your expected loads, figure out how to reduce them to an absolute minimum, and then design a system to fit.

Just as an FYI, we live off grid with ~400 watts of PV. We routinely use 5-800 wh/day, and on average we recharge daily. With 450 ah of battery, we can go three days with no sun before we need to charge from some source. On an ideal cay, we can generate ~ 2 kwh.

Welcome to the forum, and keep in touch,

Tony

I am aware of some of the losses and inefficiency to be expected. I just took what almost worked perfect in my other trailer, added the extra planned loads that I know about, then estimated the rest. Might be a little overkill in the sunny season, but in the winter, it means no generator needed......one less thing I have to pack and lock up.

My goal is to be self sufficient under all conditions without worry. Wake up in the morning, and flip the switch for coffee. My radios will likely draw 30-40Ah per day too....so more is security.

If I have extra power, I could always sell it off to my buddies!;)

Cariboocoot · July 2011

Re: Help me design my off grid RV system.....LONG!

The closer you are to the Equator the less of an issue the panel angle is. If you were to try Winter camping up here you'd be disappointed, because the panels would be nearly perpendicular to the sun.

Frankly, if you've got room for six 185 Watt panels on the roof you're probably going to be happy. Even with a loss of 33% you'd have enough to keep that battery bank up, and with judicious load usage there should be plenty of power all-round. Unless it rains through your vacation, of course.

techntrek · July 2011

Re: Help me design my off grid RV system.....LONG!

I plan on switching out the stock A/C in my camper with a mini-split. They have been discussed many times here, a quick search will bring up those threads. Bottom line, they are so efficient you could run one of them for 2 nights on low from 5-6 batteries (taking into account the Peukert effect). About 260 watt-hr on low. That is for a 9000 btu unit so you probably would want to mount 2 of them, one in your bedroom, which would be the only one running from the battery bank. Leave the other one for when you have hookups or a genset running.

A downside is they are 2 piece units intended for residences, so you would have to mount the condensor(s) on the roof and secure them well, plus mount a new vent window where your current A/C is. But its something to think about.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

techntrek wrote: »

I plan on switching out the stock A/C in my camper with a mini-split. They have been discussed many times here, a quick search will bring up those threads. Bottom line, they are so efficient you could run one of them for 2 nights on low from 5-6 batteries (taking into account the Peukert effect). About 260 watt-hr on low. That is for a 9000 btu unit so you probably would want to mount 2 of them, one in your bedroom, which would be the only one running from the battery bank. Leave the other one for when you have hookups or a genset running.

A downside is they are 2 piece units intended for residences, so you would have to mount the condensor(s) on the roof and secure them well, plus mount a new vent window where your current A/C is. But its something to think about.

Are you using the mini split for heat as well as cooling?

I have almost no need for A/C in my trailer as we camp from Labor Day till Memorial Day. We let the mobs do their camping in the peak season. I have used it more in my back yard while loading than anywhere else.8)

solar_dave · July 2011

Re: Help me design my off grid RV system.....LONG!

Crazy Cooter wrote: »

Are you using the mini split for heat as well as cooling?

I have almost no need for A/C in my trailer as we camp from Labor Day till Memorial Day. We let the mobs do their camping in the peak season. I have used it more in my back yard while loading than anywhere else.8)

Some do act as heat pumps and are very effective.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

Cariboocoot wrote: »

The closer you are to the Equator the less of an issue the panel angle is. If you were to try Winter camping up here you'd be disappointed, because the panels would be nearly perpendicular to the sun.

Frankly, if you've got room for six 185 Watt panels on the roof you're probably going to be happy. Even with a loss of 33% you'd have enough to keep that battery bank up, and with judicious load usage there should be plenty of power all-round. Unless it rains through your vacation, of course.

Starting out with much better equipment this time, so I hope the results will reflect that.

Kinda funny you should mention rain on the vacation.....It rained and snowed 80% of my last vacation. That is what prompted the RV upgrade this time.......

techntrek · July 2011

Re: Help me design my off grid RV system.....LONG!

If you don't need A/C you won't want to use a mini-split off-grid for heat. Using your propane supply would be more effective, leaving your electric supply for other loads. Now, if you already had the mini-splits installed and were only going to be away from hookups for a day or two, yeah, maybe it would make sense, but not long term.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

techntrek wrote: »

If you don't need A/C you won't want to use a mini-split off-grid for heat. Using your propane supply would be more effective, leaving your electric supply for other loads. Now, if you already had the mini-splits installed and were only going to be away from hookups for a day or two, yeah, maybe it would make sense, but not long term.

Yep, no real need for A/C while camping yet.

We have camped with hookups 4 nights in 7 years. This is why the solar is so important to me. Catalytic heater was the best energy conserving money ever spent!

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

Six of these is what I picked up tohttp://www.platt.com/CutSheets/Suntech/SuntechSTP185S_24Adb+.pdfday:

Now if I can just get the rig delivered, I can start on the build.:grr

mike95490 · July 2011

Re: Help me design my off grid RV system.....LONG!

What was the price (if you can say)

36V / 5 amp. So you are using MPPT style controller with them right ? That's 80A at full power (@14V). But since that 80A will only be a full noon, parked on the equator, maybe one off the 60A controllers would work, and if it did surge, they self limit to rated amps.

feedhorn · July 2011

Re: Help me design my off grid RV system.....LONG!

Tiltable panels are a great help and my mounting has held up to the 70 mph gusts. It seems the body of the rig breaks up the gusts so that panels don't get full blast.

See my four-way mounting system:

http://www.youtube.com/watch?v=xNK_ZQQGM0U

Its a hassle to climb on the roof to tilt panels but I've always found the extra power to be rewarding.

FH

Cariboocoot · July 2011

Re: Help me design my off grid RV system.....LONG!

MPPT controller is a must here, as the panel Vmp is so much higher than the system Voltage.
Flat on the roof of an RV the angle will be less than ideal. Factor in the usual panel derating and you probably won't see 60 Amps very often, much less 80. Good charge controllers can be programmed to limit the Amps so you don't exceed recommended maximums for the battery bank. If you go with the four T105's that's a limit of 45 Amps. You should have power to spare from those panels.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

mike90045 wrote: »

What was the price (if you can say)

36V / 5 amp. So you are using MPPT style controller with them right ? That's 80A at full power (@14V). But since that 80A will only be a full noon, parked on the equator, maybe one off the 60A controllers would work, and if it did surge, they self limit to rated amps.

$1.65w At that price, figured I could afford to over build by 30%.

Was planning on using the FM80 for this build. Figured 80 over the 60 for insurance. Where I camp in the desert, I have see well over what my system was rated for in short periods of 20deg temps and full sun bursts. Then I could add more later i needed.

Were looking into incorporating a grid tie into this now possibly......

The tilting may be an option here too. I just really don't want to have to go up on the roof and do it. I'll know more when the rig gets here middle of the month.

Crazy Cooter · July 2011

Re: Help me design my off grid RV system.....LONG!

Here is one solution to tilting.......http://www.youtube.com/watch?v=hV9Icty47Q8&feature=related

Wonder how long before that breaks......

Crazy Cooter · August 2011

Re: Help me design my off grid RV system.....LONG!

Figured I would update this with a few pics. Some of the pics didn't come out though...

The trailer finally showed up, but had some issues that are getting fixed before we can use it. May as well make good use of the down time.

I ended up the the Magnum MS2012, ARC50 remote, BMK kit, 6-185W 45V panels, FM80 controller, and 2 Deka 8D AGM batteries. We painted the roof with rubber ceramic paint for better thermal efficiency and an extra layer of protection for the EPDM roof.

Tucked under the floor

Some of the low voltage wiring

We'll take some more pics tomorrow as we wrap this project up. The batteries didn't make it in the week, so that will be the holdup.

Help me design my off grid RV system.....LONG!

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