RV Power!! summer school project and need a few ideas :)

[Derspower]

Hi i'm new here to solar forums and just bought a small RV last month and would like to mont solar panels on the roof for some extended power when i will be with out hook ups for 3 ish days at a time. I am primarily living in this RV yet am frugal with power and mostly use it for lights at night, a water pump when i need it and the stereo which is in the house battery circuit and some charging of phones, laptops, ext.... I know I will use more power in the winter, but can always hook up more to make sure i keep a good charge but want to plan ahead to use more power.

I am in school training to be an electronics technician and am interning as a wind turbine technician for GE. I am still learning but am figuring out this electronics thing but really just need the practice and more experience to feel that i know what i'm doing . That saidI would like to do this right the first time to save money from costly mistakes so i'm willing to spend a little more up front to do it right and need a little help with some suggestions of what to do.

Right now my plan is to buy 1 100 watt 12v solar panel, mppt charger found one for $100 at 20A, cabe, and hardware, i'm figuring about $240 for all this amazon pricing maybe more. I have already bought 2 15 watt 12v solar panels and then did research and figured i would need more power then that to charge my 95 amp hr battery that is most likely in poor condition based on its history, assumptions of previous owners, and myself who have discharged it way more then I should have knowing how bad it is for the batteries. Iv just been getting a feel for the power im dealing with... Any way iv been thinking about the 100 what in parallel with the two 15 watts that would be connected in series with each other and then to the mppt controler. and here the questions lie..

Should i upgrade and get a larger battery or maybe another in parallel with it ? I would need to do some retro fitting for two batteries but for more power in the bank it could be nice.

Should I connect the pannels in a parallel circuit before it hits charge controller? I feel this is best practice but am wondering what happens if you can have two solar circuits going to 1 charge controller. Meaning hook everything strait there.. I ask this because there is already 10' of cabbel on the 15W's that would be awkward to strip and connect to the more legit solar cabal of the 100 watt. Also should i just pay the 13ish $ to just return the 2 15 w solar panels and save myself the troubles if a 100 would be fine and maybe get a as well 50w to be sure?

All suggestions appreciated!
Thanks!

Anders,

[DanKegel]

It's good to know that your goal is
"lights at night, a water pump when i need it and the stereo which is in the house battery circuit and some charging of phones, laptops"
for 3 nights. Next step is to figure out how many watt-hours that is. Can you measure your power / energy consumption?

[Sunking]

You have no need for Solar. The very first thing you should regardless if you solar or not is install an Electronic Battery Isolator to charge the House battery from the Alternator. Your alternator can generate more power in 10 minutes than a 100 watt panel can generate in 3 days. It ill be a lot less expensive and allow you to buy a larger battery that will easily last 3 days in between charges when you drive. Get a pair of 6 volt golf cart batteries. Use an Isolator that takes the voltage regulator out of the Alternator. Sure Power made by Cooper Industries makes the best. You would need a 2-port 70 Amp Isolator. 1 port for the RV SLI battery, and one port for the House Battery.

If you insist on solar use the two toy panels you already have and not waste anymore money for something you have no use for. The 70 amp isolator is less than $30

[44toy]

I know this may be a stupid question but here goes. My motorhome currently has the CS144 140 amp alternator on it. So if I was riding down the road on a sunny day and the alternator was kicking out 100 amps into battery bank would the charge controller see what appeared to be a charged bank and put little or no of the solar into the bank? I was just wondering because I would prefer the solar to charge over alternator. Or would the output from isolator be ran into the input of CC? know it takes about 5hp to turn a loaded alternator and that is extra gas on a 8mpg rig.

[ewarnerusa]

If you're living in the RV, then I assume you're also using a fridge? A modern RV absorption fridge running on propane will still consume about 1A DC continuously to power the control panel, so keep that in mind. There are other parasitic loads such as propane detectors and stereo clocks, so just keep in mind that even if you have no lights on and the RV is just sitting there it is still discharging your battery. A week off of shore power and the battery would probably be totally dead without some type of recharging happening.
First I would replace your battery. You already know it is suspect, don't bother limping along with that weak source of power that is critical to your RV appliances. 2x6V GC are a great suggestion for performance and price, but if you've only got space for one battery then get the largest and heaviest 12V one you can fit in there. Insist on a true deep cycle, don't be sold on the dual purpose marine batteries that RV dealers supply OEM.
Next I would change all RV living space lighting from incandescent to LEDs. Ebay is your friend, they are cheap enough that you can buy extras to counter the potentially suspect consistent quality. This will reduce your already minimal energy use by a lot. Plus they give off way less heat.
A 100 watt panel should be adequate for <100Ah battery capacity, but not by much. With a single 12V nominal panel as the workhorse, the more-expensive MPPT controller isn't going to provide a whole lot more amps than a comparable PWM one. But if you're planning for future upgrades, don't cut corners with the controller. Get one that has fully programmable charging voltages and that offers temperature compensation. I like my Morningstar Tristar controller as an example.
You sound like you probably know more electricity than I do, but in case it is relatively new to you I recommend googling "12 volt side of life" parts 1 and 2 and reading up on how the RV's DC and AC systems operate.
If you rely on the charging by vehicle alternator, I suggest upgrading the path between the alternator and house battery with large gauge wiring.

[Sunking]

44toy the charge source with the highest energy state does the charging. In the case of a Alternator vs a Solar Panel, the Alternator always is the higher order source. When the engine is running, and if the battery demands a charge, the Alternator will provide it and the controller does basically nothing because the panel cannot supply enough voltage to overcome the Alternator.

Keep in mind when a battery is fully charged, makes no difference what the charge source is available, the battery will not take any more. Panels will only charge or supply power when the engine is off and the panel is in direct sun light. Its all automatic and not something you need to worry about.

[44toy]

Thank you for the ino