Solar on RV question

BaddogyBaddogy Registered Users Posts: 4
Good afternoon, I’m new to the forum and find it informative. I'm a newbie and could use some help. I have a 36 foot 5th wheel that I am planning to add solar. I plan on starting with 2 140 watt panels with a charge controller and 2 t105s. Now my question is how do you run your 110 items from you batteries? I understand that I need an inverter but, do I need to go directly to the panel or through a switch? Sorry I can't remember the name. Also is there a back feeding problem when you hook up to power?

I would be great full for any information. and picture would really help.

thanks

Tom

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar on RV question

    Welcome to the forum Tom.

    I've moved this to its own thread to make it easier to keep track of who's talking about what.

    So far you're doing okay: 280 Watts of panel will just about charge 220 Amp hours @ 12 Volts. If those are Kyocera KD140's they have a 7.9 Imp so with a PWM type controller you'll be right around 7% for a peak charge rate. All good.

    The inverter will be wired directly to the batteries through an appropriate sized fuse or breaker. The size of the wires and circuit protection will be determined by the particular inverter you use.

    You are right that there can be problems when connecting to "shore power". For one thing you definitely need to switch AC loads from 'inverter' to 'shore' so that there is never any connection between the two AC power sources. There's more than one way to do this, and again the particular inverter used comes in to play. One of the big issues is the problem of neutral-ground bond on AC. The easiest way to avoid those issues is to avoid MSW type inverters.

    Mainly you're looking at a transfer switch for the AC. Some inverters have one built in, other don't.

    Did that help any?
  • BaddogyBaddogy Registered Users Posts: 4
    Re: Solar on RV question

    thank you it helped allot. i currently have a transfer switch between the generator and shore power. i will have to look and another one to be safe. now how would you connect the inverters to the electrical panel? or would it go through the transfer switch? also what is a good ratio for battery to panel?

    thanks for your time

    Tom
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar on RV question

    For AC it is necessary to keep all power sources separate. Usually you have a transfer switch that switches loads between shore power and generator. When you add a third source, the inverter, it becomes necessary to decide where that will come in the mix. Again the exact inverter will make a difference; one with its own built-in transfer switch is very easy to integrate. One that needs a separate switch not so easy; you have to decide what order the switching will go. Usually this will be a switch for "generator or inverter" connected to the "generator" side of the existing transfer switch.

    A good "middle of the road" panel to battery ratio is one that provides a peak charging current of around 10% of the total battery capacity. For the 220 Amp hour battery bank this is 22 Amps. With panels that produce 7 to 8 Amps that makes three "ideal", but you can use less. You just have to remember that it will be necessary to start the gen to charge the batteries a little more often.

    On those lines, many RV's have what they call "power converters" in them. These are basically big DC supplies that power the 12 VDC equipment and recharge batteries when generator or shore power is available. Be aware that they can be a real headache when you add an inverter, especially if the AC wiring gets out of line: the inverter can end up powering the converter which tries to charge the batteries that are running the inverter. All this gets you is dead batteries. You have to be sure the converter is only powered by shore power or generator. Most people get rid of them in favour of an inverter with built-in charger; it makes things much easier. Unfortunately it costs more money.
  • BaddogyBaddogy Registered Users Posts: 4
    Re: Solar on RV question

    Very interesting info. I'm not sure about the inverter what do you think about the Japanese pure sine ones on eBay they are cheaper?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar on RV question
    Baddogy wrote: »
    Very interesting info. I'm not sure about the inverter what do you think about the Japanese pure sine ones on eBay they are cheaper?

    Japanese? Do you mean no-name import specials? How much of a gambler are you?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar on RV question

    japanese? no, you mean chinese as japan in general has better quality.
  • kellylippkellylipp Registered Users Posts: 21 ✭✭
    Re: Solar on RV question

    I have a five page "paper" that I wrote about the solar install I did on our fiver. 735W, Morningstar CC, Inverter, etc. I am happy to share this with anyone that wants it. Private email me and I will send it to you. It contains photos of various install points and a good diagram of all wiring connections. Two installs are highlighted. One a pure 12V systems (panels and charge controller) and a larger system using MPPT and a good inverter. Small system cost around $1500 all in including professional install and the large about $4K installed myself. One can easily wiggle either of these to fit a budget.

    To me, the thing about RV installs isn't quite as much about loads (which is critical in home sites) but about how much real estate you have on the roof. You can certainly calculate a fairly significant load requirement and not be able to meet charging requirements with the real estate you have. It then becomes a how much do I want to spend and what sacrifices am I willing to make to go solar? For instance the first sacrifice for a pure solar (ie. no generator) is the honking air conditioner you have on the roof! Frankly I'd rather have the real estate than the AC!

    The key to a good RV system IMHO is correct installation with correct wiring. The down drop wire size between the panel header and the charge controller and the wire size and length between the CC and the batteries is critical. Mess that up and it won't work. Since you are very limited to the number of panels you can have any losses created by wire are problematic. The overall wire runs are typically reasonably short (and if they aren't make them short) so the cost delta between wire that is too small and wire that is too big is minimal. Oversize within reason.

    Enough Soapbox from another newbie? Certainly.

    Thanks,

    Kelly
  • BB.BB. Super Moderators, Administrators Posts: 31,765 admin
    Re: Solar on RV question

    Welcome to the forum Kelly.

    By the way, have you ever read this site--From our host NAWS:
    For 12 Volt & RV Systems - HandyBob's long discussion and rant is about 99% right on how to make RV and similar 12 volt systems work correctly. One of the few "non NAWS" articles that we recommend.

    Have you seen/worked with any systems using Lithium Ion type rechargeable battery banks yet? Lead Acid are a bit on the heavy/bulky side if there were better options available.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: Solar on RV question

    I will second the HandyBob recomendation. My system is much smaller since we have a a large teardrop trailer and because of a mistake on my part in purchasing a high voltage 185W panel which required an MPPT controller, but the trade off is that it works better in low light.
  • kellylippkellylipp Registered Users Posts: 21 ✭✭
    Re: Solar on RV question

    Yes, I am aware of HandyBob. He is actually a friend and he helped (OK, I helped Him) me install my first 430W system on travel trailer last January. We sold that rig and purchased a fifth wheel and he and I worked on the design and I installed it. We went to see him at his home base late last summer. He picked over my install pretty thoroughly! I passed!

    Handy is right on. Start there if you are building an RV system. Most of us really don't understand how batteries charge. My main take aways from working with him: most of the time the downwire size is not adequate and/or the wire size from the CC to the batteries is not adequate or both! The threads from the moderator beat this point home in many responses and are right on. Copper is expensive but not that expensive but having a system that does not work is even more expensive.

    I also think that load calculation is less important than rooftop real estate in RV solar installations. You can't completely ignore it but you may find that you can't put enough panels on the roof to charge your batteries no matter what the calculations say!

    The post right before this one is also another key: for small systems try to stay with 12V (or LV) panels and a PWM controller. If you can put several panels on the roof you may require and or benefit from the higher cost MPPT controllers. Remember, though, that you don't get something for nothing. HandyBob has a lot to say about MPPT as well. My first install had two LV panels and PWM. The second has three HV panels and MPPT. The cost of the MPPT was "spread" better across the panels and I got those at less than $1/watt (this was early last year) so figured it made good sense.

    Thanks,

    Kelly
  • BaddogyBaddogy Registered Users Posts: 4
    Re: Solar on RV question

    well i did this earlier, not sure were it went. Todays update on my system. i have installed a trimetric 2025 rv, added 4 more Trojan T105s for a total of 6. Installed a Morningstar 45a ppm charge controller and two 260 w 12 volt panels. i would like to thank Handy Bob for a great artical and Kelly lipp for all his great advise.

    Here are some picks:

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