Official: Powering your rig

[admin]

I wanted to start a thread for the neverending debate on how to power your rig. Anyone is welcome to join in here but I plan to start adding posts and comments from other threads that relate to generators and solar options, as well as other issues related to power for the RV world.

At this point the posts are in no specific order.

[admin]

[quote source="/post/7001/thread" timestamp="1424378306" author="@david"][p]I have cruised on sailboats for about 20 years while managing to live on DC only and have used solar panels for almost 15 years to power my DC needs. I am going to skip the physics, ie watts=amps*volts, but here are some rules of thumbs, facts and opinions. It is long and probably confusing so I apologize. It is full of data.

1. A 100 watt solar panel when mounted horizontally will generate about 33 amp hours of power on a sunny day in moderate latitudes when operated with an MPPT controller.  A PWM controller will drop it to 25 amp hours fixed horizontally. If you tilt it perpendicular to the sun manually several times a day then you might get 50 amp hours with a MPPT controller.

2. Most refrigerators again in moderate climates (80 deg daytime highs) will operate on a 50% duty cycle. I will measure the draw on my 6 cu foot fridge on my 16TBS when I get a chance but I am guessing 1/2 amp or less. So the amp hour draw for a typical fridge would be 24*.50*.5 or 6 amp hours. That does not account for frame heaters on the bigger units.

3. For best life, you should not routinely draw down your batteries more than 50%. A typical dealer delivered group 27 trailer battery has 80 amp hours of capacity. A couple of golf cart batteries has 220 amp hours.[/p][p]
[/p][p]4. If you only use lights in the evening (and we rarely use more than an hour's worth) a low power stereo system for ambiance, recharging your cell and iPad, a few amphours for the water pump and heater and 6 amphours for the fridge, then you can live on 10-12 amp hours each day. That is 3-4 days on our Group 27 batteries to stay above 50%. We never camp longer than that without hooking up the TV and moving. The TV will replace 40 amp hours at about 10 amps an hour average rate while driving- more at first and tapering off as the battery gets almost fully charged.

5. But some people want more- microwave or even the furnace at night. Charlie corrected my misimpression of microwaves in a previous post- I thought that they were rated as input power and that the CLs had a 600 watt unit so that a 1,000 watt inverter would run one fine. But even using Charlie's numbers a couple of golf cart batteries could easily run a microwave for 5-10 minutes each day with a 2,000 watt inverter. It would draw about 25 amp hours to do so, but due to the high 150 amp draw it would take down the batteries quite a bit and would probably take 50 or more amp hours to replace it. That is more you can expect from a 100 watt solar panel on a sunny day.[/p][p]
[/p][p]The furnace blower  probably takes at least 5 amps and at a 25% duty cycle (lows in the 40s) you might draw another 10-15 amp hours overnight.

6. But solar panels are really cheap. I just bought a Renogy 100 watt unit for my boat and it cost $150. You could put together a system consisting of two 100 watt panels for $300, a 12 amp rated Morningstar PWM controller for $70 ($150 for MPPT), a couple of golf cart batteries for $200, a 2,000 watt inverter for $200 (Chinese/Chinese) or $380 (American/Chinese) and $50 for wire and fittings. That system will power everything discussed above almost indefinitely.[/p][p]
[/p][p]You could cut that about in half for a single 100 watt panel and use your existing Group 27 battery. That would power everything above except the microwave and recharge it on a 2 out of 3 sunny day basis.

8. So for not much more than the Hyundai generator mentioned above, you could have a completely quiet, self sufficient, solar powered RV that would cover your needs almost indefinitely. But you could not run your A/C of course. And that assumes that you are not shaded. We like to camp in shade.[/p][p]
[/p][p]9. Moving the panels to a sunny spot doesn't really work for me. A 100 watt panel weighs about 30 lbs, is about 40"x20" and needs to be securely mounted to the rooftop. I had a 30 watt panel that I could store in the basement, take it out and set it up 20' away from the camper in a sunny spot. But in the places we like to camp that spot quickly moved and I never got more than a few hours worth of sun.[/p][p]
[/p][p]Finally let me talk about PWM and MPPT controllers. So called 12V panels have an open circuit voltage of 21 volts and a maximum power point voltage of 17 V. A 100 watt panel is rated at its MPPT of 17 volts approximately and its current at that point is 5.9 amps which gives 100 watts output. Solar panels are pretty much constant current sources, ie it doesn't vary much from 12 to 20 volts. So if you connect it directly to a half charged battery of about 12 volts, you will see only 12*5.9= 71 watts, increasing to 80 or so as it gets recharged and the charging voltage rises.[/p][p]
[/p][p]PWM (pulse width modulation) controllers simply take the solar panel's output and when the battery gets pretty well charged and no more current is needed they pulse the output to average 13.5 volts. Otherwise the battery would continue to charge and start to gas (disassociate water to hydrogen and oxygen) which is very bad for batteries.[/p][p]
[/p][p]MPPT controllers work differently. While charging, the controller adjusts its input impedance to keep the solar panel loaded at its optimum power point of 17 volts. It then electrically converts that 17 volts to whatever voltage  the battery needs to charge efficiently- starting at 12 or so for a 50% charged battery and rising to 14+ as it gets fully charge and finally cutting back to about 13.5 when fully charged. But except for internal losses you are still getting 100 watts output so the amps go up to 8 or so at 12 volts. So the MPPT controller is about 17/13= 31% more efficient less its internal losses of about 5% for an overall improvement of maybe 25%.[/p][p]
[/p][p]But in the two 100 watt system discussed above, the price difference between a PWM and MPPT controller is about half or more of the cost of another panel. If you have the room, just add another panel up to a point.

David[/p][/quote]

[admin]

[quote timestamp="1421812600" source="/post/6124/thread" author="@mitch"]So here's what works for me and the why's and hows of the setup, if you're only interested in the actual parts to use skip all the talk and go straight to the links below.

First I've only ever boondocked so my outlook is guided by the thought that I have to be self-sufficient. Second, I don't like to park right out in the sun because the camper heats up a lot so I knew I would need a solar panel I could move around a little.   Finally I didn't want to modify the camper structure (no holes or brackets) but I also didn't want to have to lug around and set up to much extra equipment.  

Based on some math and my actual experience I know that my 13QBB with the 5 cf refrigerator on propane, the hot water heater on propane and normal usage of all of the "stuff" (I don't have a TV and I replaced the incandescent light bulbs with LEDs) uses about 19 AHrs per day of battery power probably a little less.  My camper battery is 85 AHrs capacity but the rule of thumb is try to not draw it below 50% charge so that gives me 42.5 usable AHrs so the math (I like math, can you tell?) says I can go 2.2 days before I'm in the dark or more importantly until the beer starts to get warm.

With all this information you can start putting together a system, there are only 3 components: the panel, the charge controller and some wire.  Everything else is gravy, meaning it might be nice but you don't need it for the system to work.

 Panel size is pretty much dependent on how much sunlight you think you'll get and how much power you think you need.  I assumed a very conservative 5 hours a day of sun and the 19 AHrs based on my usage.  Panels are sized in Watts and without getting technical about it higher watts means more Ahrs of charge in a shorter period of sunlight.  A 50 watt panel will generate 14.2 Ahrs in 5 hours of sun.  Not enough for my needs, a 70 watt panel will give me almost 20 Ahrs in that same 5 hours of sun and that would be enough so that's the size panel I got.   

I wanted a charge controller from a reputable company so I went with Morningstar. Charge controllers are sized in Amps, the higher the wattage of the panel the more amps it will put out so the controller has to be able to handle slightly more amps then the panel will deliver. A 70 watt panel only puts out 4 amps so a 10 amp controller is plenty.

To get the most out of the panel you need wire that allows the current to flow easily.  I went with 25 feet of 10 gauge flexible wire because I hate fighting to coil up wire for travel.  I just want to be able to use the stuff and put it away easily. The wire that comes for pre-configured for solar setups is not very flexible and a pain in the butt. Because of this I had to add the proper connectors on the panel end of the wire (The panel itself already has connectors on it) but that's not very hard. The only other things you need are an inline fuse, I used 10 amp automotive, and a couple alligator type clips to hook the wire from the charge controller up to the battery

That's it for equipment, in a nutshell here's the configuration.  There are 2 wires coming out of the panel that connect to two 20 foot wires that plug directly into the charge controller.  There are two 5 foot wires that come out of the charge controller that connect to the battery via clips.  There is an inline 10 amp fuse spliced into the positive wire between the charge controller and battery.  That's it, done. You may want a little water tight box for the charge controller to sit in near the battery, you could even use a cheap fishing tackle box and just drill a few holes in it for the wires.  You may want to build some sort of tripod to prop up the panel so you can maximize the way the sun hits it. You can get very fancy or you can stay really simple but that's all gravy.  No matter what you do you really only need the panel, the controller and some wire. On to the actual parts, this is what I would buy today if I were going to start over again.

[a href="http://smile.amazon.com/RENOGY-Monocrystalline-Photovoltaic-Battery-Charging/dp/B009Z6CW7O/ref=sr_1_3?ie=UTF8&qid=1421812008&sr=8-3&keywords=renogy+solar+panel"]This panel[/a]

[a href="http://smile.amazon.com/Morningstar-SunSaver-SS-10-12v-Charge-Controller/dp/B002MQW3H8/ref=sr_1_2?ie=UTF8&qid=1421812101&sr=8-2&keywords=morningstar+charge+controller"]This controller

[/a][a href="http://smile.amazon.com/Cord-10-Gauge-Conductor-SOOW/dp/B003FOBLHY/ref=sr_1_2?ie=UTF8&qid=1421812299&sr=8-2&keywords=wire+cord+10+gauge+4+conductor"]This wire[/a]  (you'll only use 2 of the 4 wires)

[a href="http://smile.amazon.com/gp/product/B00A8TRKJW/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1"]These connectors[/a]  (you'll only use 2)

[a href="http://smile.amazon.com/Attwood-In-Line-Holder-ATO-ATC-Gauge/dp/B003EEX5XS/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1421812441&sr=1-2-catcorr&keywords=10+amp+inline+fuse"]This in-line fuse[/a]

[a href="http://smile.amazon.com/Shoreline-Marine-Battery-Clips-Pair/dp/B004UOUTIK/ref=sr_1_3?s=sporting-goods&ie=UTF8&qid=1421812514&sr=1-3&keywords=battery+clips"]These battery clips[/a]

With this equipment you only need 3.5 hours of sunlight to generate 20 Ahrs of power.  Or you can run more "stuff" and use the power knowing you have plenty of time to recharge. I hope this helps and wasn't to wordy but I wanted to give enough of an overview that you might be comfortable enough to try it. Fire away with questions.


[/quote]

[david]

[p]Mitch:

Your system is very good and handles your DC power needs well. I just hooked up a very similar system for my boat and used the same or similar components. A couple of comments:

Morningstar makes outdoor epoxy potted controllers in 6 and 12 amp versions in the Sunkeeper line. It avoids having to install everything in a junction box. I had a Sunseeker controller like yours and kept it outdoors but mounted on the back of the panel somewhat protected from the rain. It failed after a few years.[/p][p]
Ten gauge wire is pretty big to carry 4 amps 25 feet. I used 16 gauge two conductor cable for my installation. Four amps with 16 gauge cable and a 25' length causes a voltage drop of 0.8 volts. Since extra voltage is wasted with PWM controllers you aren't losing anything. Genuinedealz.com is a great place to buy tinned, stranded wire by the foot or by the roll.

Enjoy your solar installation. The only downside is camping in or near the sun. That isn't a problem on my boat ;-).

David[/p]

[mitch]

Hey David,

Thanks for the comments, the setup does seem to work remarkably well.  I did a bunch of research before I built it out and I'm sure that led me to overspec some of the things, wire most especially.  There's a blog by a fellow named Handybob who specializes in RV solar setups. He's very insistent about wire gauges and the importance of every little scrap of power you can get.  As far as the controller enclosure, I actually built out a NEMA enclosure with a couple voltage gauges (panel and battery) an amp meter and then some switches.  It's way overkill but it was a fun project and it accommodated my nerdy instincts.

I'm trying to work with wind power now but not having much luck, it's a tougher nut than solar.
Take Care.