Small System for Pop UP RV

Kamala · April 2009

I recently purchased a small hard side A-Frame pop up camping trailer and wish to add PV panels to charge an AGM battery bank. The battery bank will power all 12VDC appliances and an add on inverter which will, in turn, power the 120VAC receptacles. I have been reading this forum and have found it to be very helpful. I think I have done my homework so will spare you all the details of all the loads involved and get right to the parameters that I have calculated.

The camper will remain parked *almost* permanently in an open area in west central Wisconsin, 60 miles WNW of St. Paul MN. I will use the camper *mostly* only on weekends. Friday evening to Sunday afternoon, or about 48 hours per week. During that 2 day period, I will use about 800 WHr/Day. I figure about 3.5 hr usable sun per day. I think this is slightly above the annual average for my area but low for the summer months. Initially, the PV panels will not be mounted on the camper. The batteries *must* be AGM since they will eventually be stored under the bed in the camper (no out gassing.)

At 800 WHr/Day a 450AH battery bank would be 30% discharged. 400 W of PV would recover some of this for the next day (Sunday.) Five more days should have the batteries fully charged by the next Friday.

I plan to use:
Batteries- 4 6V 224AH (Fullriver DC224-6) 2 parallel banks in series
PV Panels- 2 12V 205W (Kyocera 205GX-LP) controller may determine connection
Controller- Morningstar MPPT w/temp sensor
Inverter- Samlex PST-200S-12 (TSW 2000W 12V)

Concerns:
PV connections should probably be in series since the controller is rated a 15 amps and parallel panels would deliver about twice that. While voltage in series (~54) would be adequately less than the controller's 70V limit.

AGM batteries are rather sensitive to the 3 stage charging cycle. The battery specs mention only 2 stages, "cycle" @ 7.25V~7.45V and float @ 6.8V~6.9V. Or, for the bank wired as described above 14.5V~14.9V and 13.6V~13.8V. If the 14.5 to 14.9 figure refers to bulk charge, that would make sense. The Morningstar goes to absorption at 14.3V and then floats at 13.7V after 3 hours. The controller specs do not give the bulk charge voltage but, as I understand it, the bulk stage is a current dump and voltage is not very meaningful. As long as it is under 15 volts.

I would connect the 12V circuits of the camper to the load output of the controller and the inverter directly to the battery

There are some parasitic loads in the camper such as gas detectors and LP igniters but these should be well under 1A.

At sometime in the future I may take the camper on the road. It has a 12V 65AH flooded deep cycle mounted on the trailer tongue that I will have removed. Is it safe to allow the tow vehicle alternator (heavy duty) to charge the AGM battery bank? Should the controller be disconnected while towing?

BTW I did some testing with a 750W modified sine inverter and a 100AH AGM and found that the on board converter drew 8A with no load. Since the converter is just a battery charger/replacer when connected to shore power I have triped it's breaker off and will only use it if actually plugged in to a campground's 120VAC service. And if "plugged in" should the Morningstar be disconnected?

Questions? Comments? Thanks.
Kamala

Solar Guppy · April 2009

Re: Small System for Pop UP RV

SunSaver is 15A ... so you would need two for 12V battery operation

Kamala · April 2009

Re: Small System for Pop UP RV

Kyocera 205GX-LP panels are rated 26.6 volts @ 7.71 amps. Two connected in series would be rated at 53.2 volts @ 7.71 amps. My max DC draw will be about 8 amps (through the SunSaver.) Current drawn by the inverter will not go through the SunSaver. I do not understand why I would need two controllers.

icarus · April 2009

Re: Small System for Pop UP RV

Kamala,

Welcome to this site,, and to the world of PV.

I commend you for doing your homework! Too few people spend the time to figure out where to begin.

I have one question,,,How did you come up with 800 wh being 30% of 450 ah of battery?

By my calcs,, (likely to be wrong as anybodies!) 450ah of battery would translate to~ 5000 wh. (100% dod) So that ~30% would be ~135 ah or ~1600wh.

So that your loading would be ~15% not 30%.

On another note, remember that you wouldn't be able to charge at 100% efficiency, but more like 60-80% given controller and battery charging efficiencies.

Also, while I don't think that your fridge nor your detectors will really draw 1 amp continuously, a 1 amp draw over the course of 24 hours is ~ ~300 wh/day,,, the rough equivalent of about 1/2 my daily load!

I'm not sure I would both having the vehicle charge the house batteries,,,you would have to consider peak alternator voltage and the fact that agms don't like excess charging voltage (as I understand). If you were to use the vehicle,, I wouldn't worry about disconnecting the controller either.

I am not clear as to what you are asking in the final paragraph. Are you suggesting that a MSW draws 8 amps with no load? Wow!

Finally, I wouldn't have any problem drawing down my battery ~20-30% and give it a full week to recover. If I found that it doesn't recover in that week I would make the changes needed to get it to charge.

Good luck,

T

Solar Guppy · April 2009

Re: Small System for Pop UP RV

Your 53V @ 7.7 amps gets converted to 12V @ 31 amps .. thats what Mppt charge controllers do.

Your Battery is charged by the controllers and the inverter runs off the battery @ 12V

Kamala · April 2009

Re: Small System for Pop UP RV

Thanks SG & T,

RE controller: I think I will go with parallel panels and a 12V 30A controller. Blue Sky?

I did my WH calcs for a week based on 2 periods of 2 and 5 days each to account for loads present while not actually at the site. These are negligible, more like less than 100mA. But ya gotta over design, ya know. As for the 800 WH... I did not make this part very clear. If I use the system for 48 hours on an overcast weekend, I'll use 1600 with no PV. And, Icarus, since I used much of your methodology in my calculations, it is not surprising you came up with 1/2 of what I did for DoDc.

Charging from the tow vehicle is a long way off, so that's off the table for now.

The on board converter is made by Elixir. In that test I just plugged the campers power cord into the MSW inverter. With all camper breakers off the battery drain was 160mA. That's the inverter stand by. Camper breakers on, all appliances off, the drain shot up to 12A and slowly came to rest around 8.5A. I think the battery charger in the converter requires TSW. This configuration also screws up my AM radio reception. So the converter breaker stays off. Not much point in using an inverter to run a battery charger anyway.

Well, I'm gonna head out soon, grab my DVM, pick up a Kill-A-Watt and take some more measurements.

Thanks again
K

icarus · April 2009

Re: Small System for Pop UP RV

Got it,, in regards to the calcs.

I am still not sure what your onboard "converter" is. Is it an inverter/charger? If it is,, and you are powering it from the batteries,,, and it is trying to charge the batteries at the same time you would be attempting to perfect perpetual motion.

Tony

Kamala · April 2009

Re: Small System for Pop UP RV

The "converter" is a charger for the tongue mounted flooded battery (also charged by the tow vehicle.) At this time it is my only source of 12VDC. Which I have tried to charge with two 15W amorphous (yuck) panels. The MSW inverter was run off a separate battery.

Quabillion · April 2009

Re: Small System for Pop UP RV

I think that you are on the right track here.

All looks good on the math, and Solar guppy got you straight on the charge controller.

One thing I might consider is an even LARGER charge controller. This way if you ever wanted to add more panels, your controller will not need to be replaced, as it will be rated for this additional feed. Also run any extra wires for these future panels at the same time you install the system to save headache in the future.

Be careful, solar, and the freedom of movement it gives is VERY addictive to us RV'ers. Or you might just end up like me, with a whole roof full of panels.
Welcome to the club/forum

Solar Guppy · April 2009

Re: Small System for Pop UP RV

For the cost of a Blue Sky, consider the Xantrex XW-Mppt , its 499.00 and a 60 amp unit and MUCH better controller ... If you can get an Outback MX-60 ( the old units ) those are good as well , I'd stay clear of the FM series, they still have a number of bugs to work out and the firmware is not field upgradeable

icarus · April 2009

Re: Small System for Pop UP RV

SG,

What is your concern with BlueSky controllers?

I realize that the MX 60 had (has) a great more capability,,, but the BS 2512 seems to work pretty well for a small array IMHO. I like the fact that it doesn't run with a fan. I am also sorry that you can't run 24 or 48 vdc arrays with it,, but that is a small sacrifice. I respect your experience and opinion.

Tony

Solar Guppy · April 2009

Re: Small System for Pop UP RV

As part of the Sunsaver testing, I tested BlueSky and our favorite the BZ, both now collect dust and get used 100% as bookends in my Office

The BlueSky, while much better than the BZ, It is still a very dated design, pretty low efficiency compared to the Sunsaver, VERY RF noisy , the tracking is so-so and with large inverter loads its stops tracking all together, can't handle the 120hz ripple on the battery, swamps the Mppt ability to P&O and just flat stalls.

The Inverter test was a 300 watt SureSine with a 200 aH WetCell Battery .. hardly some huge load

On the Larger controllers, The XW is convection cooled and needs no fiddling to have optimum performance, its only 150 more than most BlueSky models

Windsun · April 2009

Re: Small System for Pop UP RV

Solar Guppy wrote: »

The BlueSky, while much better than the BZ, It is still a very dated design, pretty low efficiency compared to the Sunsaver, VERY RF noisy , the tracking is so-so and with large inverter loads its stops tracking all together, can't handle the 120hz ripple on the battery, swamps the Mppt ability to P&O and just flat stalls.

On the Larger controllers, The XW is convection cooled and needs no fiddling to have optimum performance, its only 150 more than most BlueSky models

The XW-SCC is the only larger controller around that I know of that has FCC certification. We stopped carrying some of the Blue Sky models, partly because they make so much RF noise we were spending too much time on those complaints.

I just wish that Morningstar would come out with a 30-40 amp version of the SS-MPPT.

Solar Guppy · April 2009

Re: Small System for Pop UP RV

Windsun wrote: »

The XW-SCC is the only larger controller around that I know of that has FCC certification. We stopped carrying some of the Blue Sky models, partly because they make so much RF noise we were spending too much time on those complaints.

I just wish that Morningstar would come out with a 30-40 amp version of the SS-MPPT.

Your wish will happen sooner rather than later ... 45 and 60 amps versions .. The primary reason I just upgraded my test arrays for supper accurate competitive testing

icarus · April 2009

Re: Small System for Pop UP RV

Now I am irked!!

The reality is that the Morningstar MPPT is too small and the Xw is too big,,, so I'm left with what I have. I confess I have mine mostly plug and play,, so that watching the effect with ac load is not something I had either thought about nor monitored.

While we all strive to have "the best" we can, in the real world,, good enough is often good enough. As my neighbour said,, when I suggested that he upgrade his C 35, "Why,, it works fine and I get fully charged by ~noon!"

Tony

Solar Guppy · April 2009

Re: Small System for Pop UP RV

I agree, if it works and your happy I wouldn't change a thing

Keep in mind a few things, This is what I do for a living. I design and test converters and controllers. I also get paid to test all competing models and its my job to test all sorts of configurations to see what works and how well and what doesn't. I understand Mppt as I've implemented it in 4 generations of products, so I know what too look for in testing the controllers.

The investments I have in arrays and test equipment I know of no manufacture that has the abilities I do and its necessary for realtime side-by-side comparison as solar is so variable its the only way to know if its the controller or something else

There are lots of choices for controllers, I'm just making recommendations based on very accurate and detailed testing I get paid to do.

For the Current crop of controllers, Big, Nothing is better than the XW-Mppt, Small, nothing is better that the Morningstar ... I think by the of this year, we will have more things out there and likely a different who is the best.

icarus · April 2009

Re: Small System for Pop UP RV

So,,, in you opinion SG, am I better off with the BlueSky,, or just the simple Morningstar sunsaver that it replaced? When I had only the Sunsaver I had no way to measure the output so I can't really compare now with then. (I also have a couple more panels)

Tony

Solar Guppy · April 2009

Re: Small System for Pop UP RV

With your cold weather Mppt will give good gains pretty much year round, so the BlueSky over a MorningStar PWM controller should be the right choice. Over a MorningStar Sunsaver Mppt, no, but I assume your over the 15 amp maximum and that's why you went with the controller your using

Pretty soon, you will grown again, then it will be time for yet again another controller. This is why for users like you it can make sense to the the 60 amp box even if you have 20 amp loads

icarus · April 2009

Re: Small System for Pop UP RV

Thanks SG,

You are right, the sunsaver MPPT is too small. The only way that my system is going to grow is if I can realistically use the 120 vac element on the LP fridge,, but it is hard to justify another couple of $1000 on a bigger system to save ~$.30 worth of propane/day.

As I have learned,, as PV has gotten cheaper,, and fridges have gotten better,, if I had to start over I would buy a conventional fridge. As it stands now,,, We can't use all the power we generate most of the time,, even as I come up with ways to use it.

Thanks for the help,

T

Kamala · April 2009

Re: Small System for Pop UP RV

Thanks to all for your responses to this post.

I returned from my weekend at camp a few hours ago. Didn't find the Kill-A-Watt at Menard's so I got an Am/Watt instead. Doesn't do kWH or PF. Didn't use it! The fridge went out Friday night refocusing my work. A three amp fuse kept blowing after 3-4 hours of use while on PROPANE! I brought the camper back to the dealer today and they said they'd never seen this before. Thankfully it's under warranty. So I wait. Anyway, I took several amperage measurements on the 12VDC system to update my usage estimates. Not much change. Original estimates seem reasonable.

I am pleased that my OP elicited the responses that it did.

SG: Thanks for the warning about RF generation in the BS CC. I wonder if Tony has any complaints in this regard. Given his location he may not use many RF devices. Still, that type of interference can be picked up by other A/V devices.

This weekend at the site helped me to think more in terms of "usage profiles." That is, what time of year is it (sun angle and energy needs) and what am I doing with the camper. The camper is parked most of the time on a 40 acre plot that straddles a popular western Wisconsin river. I can get there in just under an hour. Primary Usage is as a weekend getaway in summer or winter. Secondary Usage is as a week long getaway in summer only. Tertiary Usage is as a mobile camper away from winter.

In primary use the plan I have put forth is workable. 2 days use, 5 days to recover. In secondary use, where the planned 2 days use is stretched to a possible 9 days, the original may become inadequate. I will need more storage or more recharge ability. In the tertiary mode, the furnace fan, almost 4 amps, changes everything.

To SG: The Xantrex seems too large. Physically. My camper has NO space for wall mount. You could say that it has no walls at all. They fold onto each other. I am considering a two part system which will require two controllers serving two separate battery banks.

In the interest of keeping my posts terse (a hopeless endeavor), I will come back with defined usage profiles.

Craig

icarus · April 2009

Re: Small System for Pop UP RV

Kamala,

A couple of notes.

If your fridge is a Dometic and it is blowing the 3 amp fuse you probably have a bunged control board,,,should be covered under warrantee. Dometic boards are notoriously bad. There are aftermarket boards (Dinosaur) that perform way better over time. If you ever have fridge issues look here: http://rvmobile.com/wb/default.asp?action=10&boardid=2&fid=2 In addition to the forum the home site is a treasure trove of LP fridge info.

Second,, regarding the Bluesky controller and RF noise. In point of fact it is not an issue for me at all. We don't run the computers on a wireless net. I do pick up some considerable RF from the CFL ballasts AND and the inverter on the AM broadcast band,, but since we get no AM,, except late at night,,, and then why listen? it is not a problem.

FM broadcast band is clean as a whistle,,, as is Sat Radio. We have no broadcast Tv either. If you are a Ham,, who knows what bands might be effected.

As I say,, the biggest noise is from the CFLs followed by the inverter,,, but only on the am.

As a point of observation as one who has been there,,, as you are calculating loads, ad thereby system hardware,, remember a couple of things. Your loads WILL increase with time. Having 24/7 power allows you to use 24/7 power. Second you will probably generate somewhat less than you expect as you calculate your input.

If I was starting over again,, I would start with the biggest controller that I could envision,,that made sense in a smaller system. 20-25 amp would be about right. I don't think I would worry too much about MPPT and it's gains and I might favour a cheaper PWM. Since your batteries aren't likely to be drawn way down,, nor your normal usage at very cold temps,, so mppt gain may not be worth the cost. (Let SG answer that definitively!)

Remember, adding panels is always an option (assuming you have head room with the controller) adding batteries is not an option, as mixing new batteries with old is a no/no. If you guess that the batteries are going to have a struggle to get charged over the week, you could always throw them on the genny for a couple of hours before you leave on Sunday,, which would be a much better way of doing it than leaving them ~80 for five days and then charging them. You panel arraingment will be more effective at doing absorb/float charge than bulk charge if you are under paneled relative to the battery ah cap.

Good luck,

Tony

Kamala · April 2009

Re: Small System for Pop UP RV

The fridge is indeed a Dometic and is under warranty. The camper is at the dealer now and they are working on it. I'm not happy to hear that the Dometic board is notoriously bad. Thanks for the link.

The camper is really very small so future expansion is not much of a concern. I looked at the Xantrax XW controller and can't think of where I could mount it. The only available space is under the bed. So access and ventilation are a problem. Wall mount in the living area is not possible. I could wall mount a remote panel but now I've got that extra cost and a pricey unit with more power than I *expect* to need. I'm pretty committed to MPPT since peak usage will be during summer.

My original plan was to build a PV system that would serve as a 120V hookup one would find in a campground. I abandoned that plan when I learned that my DC power supply's stand by current draw was 8 amps. I could look for a different PS but why? I'm already producing 12VDC. So when parked I would pull the flooded battery, that came with the camper, put it on a charger in my sister's garage (1/2 a mile from the campsite), connect the load output of the controller to the cables that the flooded battery was connected to and then connect the inverter to the AGM bank. The 8A PS would be shut off.

Initially, I will build the PV system as a stand alone unit. That is, not connected to or mounted on the camper in any way. I want to be sure the system works the way I want before I start making modifications to my new toy. If all goes well, I will eventually incorporate the PV into the camper.

I am considering going with 6 batteries (675AH) and three 180 watt panels. There is not enough roof space for the 205 watt panel. In fact, there is only enough room for one of the 180's.

The only reason to move the PV system into the camper is that, one day, we may want to take it on the road. Sometimes we will be at campgrounds with 120V service but at other times we will be at a primitive site to "dry" camp. The flooded battery would be returned to service and would be charged by the tow vehicle. It's a group 24 so that's, what, maybe 65AH. Not enough for an extended "dry" camp. We can trim our 12V usage to 325WHr/day and 120V usage to 180WHr/day. So, one 180W PV, a controler, a couple of 225AH AGMs, an inverter, some switches...

I'm getting ahead of myself... I'll keep you informed.

K

icarus · April 2009

Re: Small System for Pop UP RV

You could wire the whole system together with a series of Anderson Connectors : http://www.andersonpower.com/products/

You could design the panel array to ground mount in one situation but hang on the camper if you are traveling for example. The controller could mount in a weatherproof box outside the camper. All you would have to do then is plug the output leads from the PV system into a pigtail Anderson poking out of the camper. Making up a number of different Anderson "patch cords" would allow you great flexibility going forward.

I have two of my panels roof mounted,, but wired with Anderson's so I can pull one off if I need to,,, or add one more. I have several other panels that move over the course of the year,, connected to the home run to the controller through Anderson's. A series of "Y" cords with Anderson's allow me the flexibility to do a number of things.

540 watts of panel for such a small camper IMHO would be huge! We live,, full time with ~300 watts!

Tony

Kamala · April 2009

Re: Small System for Pop UP RV

I've looked at the Anderson connectors. That might be an idea. I'm still sizing this system. Up and down. Down and up. Haven't really gotten to heavily into that "conserve a watt is cheaper" thing yet.

Kamala · April 2009

Re: Small System for Pop UP RV

I think I have a plan. Will be tested off rig but if all goes well many options for installing totally on rig. I have attached a jpg of a block diagram of the electrical plan and a crude (not to scale) mechanical schematic of the camper.

The electrical plan provides for three modes of operation: In tow, parked dry and parked wet.

In all modes the AGM bank is connected to PV. This never changes.

In tow, all AC loads are disconnected. All DC loads (fridge only) are connected to the 65AH flooded charged by the tow vehicle.

At wet camp the AGMs are charged by a smart charger (Battery Tender,) AC loads are powered by the campground, 12VDC loads are powered by the DC supply (also powered by the campground) and the 65AH flooded is charged by the same unit.

In dry camp the DC loads and inverter (a DC load) are powered by the AGMs. Which are, as always, charged by the PV system.

To make it convenient, two switches are required. Blue Sea makes a 305ADC battery selector that can be used for the DC systems. And I think a regular 30A wall switch can serve for the AC selector. In wet camp the inverter is switched off at it's front panel. Otherwise it would draw a standby current. In dry camp the DC supply is switched off since it would draw 8ADC through the inverter.

There are two potential problems. 1. Can the smart charger and the solar controller be connected in parallel to feed the AGMs? IOW can one damage the other? 2. The combined weight of the PV panels is about 73 pounds. The camper roof is raised by hand. There are torsion springs in each corner to assist in this maneuver. It's already an effort for a man of my prodigious strength.;) The alternative is to stow the panels in the RV when towing. On the bed, between pillows, etc. Or mount them on the collapsed camper to be removed before roof raising. A simple (relatively) rack mount system could also be stowed for travel and then set up at optimal angle in camp. Might have to be staked down for wind. As you can see from the mech schematic, the roof angle is too high for 45°N in summer.

The cargo doors, (there are three of them,) are a convenient place to put the controller and inverter.

This forum is essential. Glad I found it.

Craig

icarus · April 2009

Re: Small System for Pop UP RV

At first glance,, it looks pretty good.

Iota makes a nice 30 amp automatic transfer switch that would work great for the ac switch. http://store.solar-electric.com/ioitauactrsw.html Would automatically transfer from shore ac to inverter ac. It would default to the inverter until there was shore powe, then switch over.

For a DC switch consider a battery isolator switch.http://store.wardmarine.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=WMOS&Product_Code=SCP11501&Category_Code=BS

There is no reason that the solar charge controller and the smart charge can't be wired in together in parallel.

It does beg the question however,, why use a dual battery system at all? If all you are doing is running the fridge for the few hours a day you are rolling why not run the fridge off of LP, or the Agm's for that time period? The other thing you could do wire the fridge to run off of 12vdc from the tow vehicle. I would posit that the only time you are going to run the fridge on 12vdc is while being towed. A simple transfer switch to the control board of the fridge so that it gets it 12vdc from either the tow vehicle or the agms as needed. (I shouldn't have worried you about Dometic control boards in the previous post,,, in fact they are quite reliable,, easy to replace and not very expensive. In fact,, in 10+ years with several Dometic electronic control fridges I have had to replace 1 board,,)

Tony

Kamala · April 2009

Re: Small System for Pop UP RV

The Iota is EXACTLY what I need. I was going to say that I preferred the Blue Sea Switch because you could switch from Bat 1 to Bat 2 without going through both. But then I realized that with the Blue Sea in order to go from one to two you had to go through off. Now it's a question of make-before-break or break-before-make. I guess in this power transfer scenario I would go for MBB. So thanks again Tony!

niel · April 2009

Re: Small System for Pop UP RV

if memory serves me correctly, that switch also has a position of both so it does not need to go through off. may be different now or different switch, but check that.

Kamala · April 2009

Re: Small System for Pop UP RV

This was the Blue Sea switch I was thinking of. Looks like it could go either way. Anyway the question remains, should I use M-B-B or B-B-M? My guess is that it doesn't matter much.

niel · April 2009

Re: Small System for Pop UP RV

i don't much know if it will much matter as the switch has a high amp rating, but going through both may ease sparking somewhat.

Kamala · April 2009

Re: Small System for Pop UP RV

That's what I thought, and as we say here in the TC's "It's a *non-factor*." I like the more symmetrical look of the Blue Sea.

Small System for Pop UP RV

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