Small Solar system for RV in Storage

keith32

Greetings, this is my first post -

I recently bought a 5 year old Outback 27RLS travel trailer. I'm looking to set up a small solar panel to maintain my single deep cycle battery when the RV is in an off grid storage lot (open parking lot, no shade). I already have a foldable pv (for backwoods kayak camping, recharges a pocket Brunton Li power pack). It's a 10W PowerFilm F15-600 (flexible amorophous 12V .6A, CLA socket). Since it is not totally sealed for weather, I was going to hang in a south facing window to trickle charge the single deep cycle batt (Interstate Mega-Tron marine-RV deep cycle, SRM-24, 550 CCA, 690 MCA SPR). There is no date code punched, so don't know the age. RV was serviced by the dealer before sold.

When working on the trailer, stocking etc., I have been connecting towing 7-blade plug to running pickup's tow socket via 10ga. 25ft. extension that I built. Mostly I would just be there for an hour or two, but may spend more time as I work on trailer sytems. Loads during this time are mainly lights, buy may run the radio/CD or a small tv, and sometimes other systems. The largest load is when I extend/retract the dinette slideout. Once getting ready for a trip, or after returning, I move from storage lot to my driveway, with full hookups.

The power center is a WFCO WF-8955AN-P, which the manual states has 3 modes: Absorbtion Mode for normal RV operation (13.6v), Bulk Mode when battery voltage is less than 13.2, and Float Mode if the RV has no demand. I have been reading on the NAWS site, and purchased a MorningStar PS30-M (PWM with Meter), thinking that I would use it with the 10W panel for now, and eventually install 100-200W of pv. That investment will have to wait for now, however. I do not have any immediate plans to go dry camping.

So at this point I am wondering how can I best use the PS30-M with the WFCO converter? What I wanted to do is to use the PS30 to control the SOLAR input for solar trickle charge, so that I could use the built-in meter to monitor the current. I would connect the BATTERY to it's terminals, with also the remote voltage sense wires and a BTS. There is also a separate LOAD connection, which allows monitoring current, and shutting off the load. I am not clear on how to connect this to the WFCO battery and load connections, or if I will need a load relay or switch to prevent changeover problems. I believe that this needs to be set up as automatic and foolproof as possible, although unplgging the solar panel before travel would not be a problem.

Any thoughts? Thanks for this great forum.

Keith

BB.

Re: Small Solar system for RV in Storage

Welcome to the Forum Keith!

keith32 wrote: »

I recently bought a 5 year old Outback 27RLS travel trailer. I'm looking to set up a small solar panel to maintain my single deep cycle battery when the RV is in an off grid storage lot (open parking lot, no shade). I already have a foldable pv (for backwoods kayak camping, recharges a pocket Brunton Li power pack). It's a 10W PowerFilm F15-600 (flexible amorphous 12V .6A, CLA socket). Since it is not totally sealed for weather, I was going to hang in a south facing window to trickle charge the single deep cycle batt (Interstate Mega-Tron marine-RV deep cycle, SRM-24, 550 CCA, 690 MCA SPR). There is no date code punched, so don't know the age. RV was serviced by the dealer before sold.

Your Interstate battery is around an 84 AH battery. And RV/Marine batteries tend not to be great deep cycle batteries--But since you have it, you might as well use it.

A 10 watt @ 15.4 volt solar panel is probably just fine for trickle charging. The Vmp~15.4 volts is really too low for use with a small solar charge controller. The Vmp of such a solar panel should be ~17.5 to 18.6 volts or so. Vmp falls as panels get to operating temperatures and there is the additional voltage drop of the charge controller. Not enough to "charge" a battery at 14.5 volts or so--But probably good enough to float it at 13.2-13.6 volts.

Just make sure you have the battery charged before storing the RV and make sure there is a 2 amp or so fuse to protect the solar panel wiring from shorts. Note if you wire the solar panel backwards, it will be ruined by the battery current/voltage surge.

Also note that a solar panel behind a vertical window will lose quite bit of output. And in summer, the panel probably would be better near horizontal.

In any case, the battery should be never be stored below ~75% state of charge. Normally, a flooded cell lead acid storage battery not on a trickle charger should be recharged about once a month.

When working on the trailer, stocking etc., I have been connecting towing 7-blade plug to running pickup's tow socket via 10ga. 25ft. extension that I built. Mostly I would just be there for an hour or two, but may spend more time as I work on trailer systems. Loads during this time are mainly lights, buy may run the radio/CD or a small tv, and sometimes other systems. The largest load is when I extend/retract the dinette slideout. Once getting ready for a trip, or after returning, I move from storage lot to my driveway, with full hookups.

My guess is that using the trailer cabling for charging the RV battery is not really "that good"... I would be surprised if you get ~14.5 volts at 8-10 amps. Most vehicle alternators are setup for ~13.8 to 14.2 volts which is pretty low voltage for charging a deep cycle battery and then add 25 feet of 10 awg cable with more voltage drop--especially if it has been deeply cycled (say 80% to 50% state of charge range).

Your RV's "converter" should charge the battery at 14.4 to 14.6 volts or so (bulk/absorb set point)--For probably 4-8 hours after cycling. 13.6 volt Float is fine when in storage and you have AC power.

The power center is a WFCO WF-8955AN-P, which the manual states has 3 modes: Absorption Mode for normal RV operation (13.6v), Bulk Mode when battery voltage is less than 13.2, and Float Mode if the RV has no demand. I have been reading on the NAWS site, and purchased a MorningStar PS30-M (PWM with Meter), thinking that I would use it with the 10W panel for now, and eventually install 100-200W of pv. That investment will have to wait for now, however. I do not have any immediate plans to go dry camping.

I don't know anything about the WFCO--But the specifications look OK as a basic converter. It does not do "equalization" (around 15 volt charging at ~5% of battery bank AH capacity)--Which is really a good idea if you replace the existing battery with a true Deep Cycle Battery and you want to get more than a few years of life from the battery bank (although, even 2-3 years with an inexpensive deep cycle battery and the existing converter may be an "OK" cost effective solution too).

If most of your camping is with shore power (and/or a small genset)--Then you should be OK too with this setup.

So at this point I am wondering how can I best use the PS30-M with the WFCO converter? What I wanted to do is to use the PS30 to control the SOLAR input for solar trickle charge, so that I could use the built-in meter to monitor the current. I would connect the BATTERY to it's terminals, with also the remote voltage sense wires and a BTS. There is also a separate LOAD connection, which allows monitoring current, and shutting off the load. I am not clear on how to connect this to the WFCO battery and load connections, or if I will need a load relay or switch to prevent changeover problems. I believe that this needs to be set up as automatic and foolproof as possible, although unplgging the solar panel before travel would not be a problem.

You can put charge controllers in parallel to a single battery bank just fine--The one with the highest output voltage will "win".

As I mentioned before, you probably do not need a charge controller at all with the 10 watt panel--especially if it behind a window. And this panel does not really have a high enough operating voltage to drive a charge controller (especially one that large). If you still want to try a charge controller, I would go with something much smaller--Such as: SunGuard 4.5 Amp 12 Volt Solar Charge Controller

If you want to measure charging current, and just have a good tool for debugging general electrical problems... I would get a DC/AC Current Camp DMM (digital multi meter) such as this one. DC current clamp meters are much easier and safer to use than the other meters where you have to "cut the wire" and insert a meter/current shunt. The downside is with the clamp meter is you cannot just leave it hooked up.

You might also want to read a couple of deep cycle Battery FAQs:

Battery FAQ
www.batteryfaq.org

If you decide to do some dry camping, you can put a 140 watt solar panel and a 15 amp charge controller on your RV and keep the battery pretty happy (assuming you don't use a lot of power--always conservation with solar power).

-Bill

Shadowcatcher

Re: Small Solar system for RV in Storage

I will second many of Bill's recommendations particularly the two links for information. I will add http://handybobsolar.wordpress.com/
WFCO has a very poor reputation as a converter and if you google WFCO problems...
We have a large teardrop trailer designed to begin with for solar with serious boondocking in mind. It has a 185W fixed panel and a 140W flex panel with its own controller that can be unrolled in the sun on an extension cord.
You will eventually be replacing the marine battery and for storage purposes you might want to consider using an AGM battery which self discharges much more slowly as long as there are no parasitic loads. One other trick is to actually hook up jumper cable to recharge rather than rely on a long too small wire.
As Bill said if you plan on being off grid, conservation is the name of the game i.e. LED lights and monitoring usage.

keith32

Re: Small Solar system for RV in Storage

Thanks for the excellent info, BB and Shadowcatcher. I had just found HandyBob site last night, so I will digest what you have posted along with his puzzle paper.

In the meantime, will just float with the 10w pv and no cc, and try to angle inside of window. I'll drop back to jumper cables for charging from truck, which I originally considered. I also have an AGM Blue top (not being used, in home on batt maintainer), which I had set up in a batt case for trolling motor, with jacks and fuses. I may add same 50A jack to my RV batt case to allow jumper cable from truck directly into RV batt jack. May carry the AGM as a spare, but keep it off/separate from wet cell, either unconnected or on batt switch. No immediate upgrades to trailor for now, but will plan on wiring an e-panel inside front cargo hatch near tongue RV batt to allow later adding one large panel and the cc that I got when I can. Any thoughts on the 100w Grape pv thru HD? It's a good fit on roof, with room to grow from one to 2-4 panels.