I recently installed a 15W solar panel & battery charge controller on my travel trailer. I have two new 12V deep-cycle batteries that I'm trying to keep charged while the camper is in storage, and something doesn't seem to be working.
I installed the solar panel & ran the wires down to the trailer's main electrical panel where I connected them to the charge controller & then plugged the charge controller wires into the main wire posts that connect to the batteries. When I measured the voltage at the end of the charge controller it read 16 to 17 V w/ full sun, so I figure it should be putting out enough to trickle charge my two batteries.
But when I came back a week later my batteries were down to 1/3rd capacity. So I figured my rig must be drawing more amps than what my puny little 15W panel is capable of putting out each day (even though everything was off).
To test that theory and make sure the batteries were capable of being fully charged by the panel, I pulled both batteries out of their boxes & put them inside the trailer next to the electrical panel then hooked up the solar panel directly to them. So in this configuration there's was nothing to drain the batteries and all the power the solar panel could muster would go into the batteries.
I came back several weeks later hoping to find my batteries would be fully charged. I put the two batteries back into their battery boxes, connected everything together & pressed the 'test' button on my tank/electrical status panel to find that my batteries were still only at 1/3rd capacity!
I'm completely at a loss. According to my voltmeter the solar panel is putting out more than 12V. My batteries weren't connected to anything but the solar charger, so shouldn't they be more charged after several weeks of mostly sunny days?
I thought a 15W panel & controller would be sufficient to keep a pair of new 12V batteries fully charged. Is this true? Or could the solar panel and/or controller be leeching electricity back out of the batteries at night? Supposedly the controller has a diode to prevent battery drainage when there's no sun. How can I test to see if there is a short or other defect in my controller?
Can't say how to test, perrhaps ask where you bought it?
We have a 15 watt panel on our SINGLE 12 volt battery, which is also connected to an ultrasonic mouse deterer. Panel keeps our battery topped up while running ultrasonic gadget 24x7. With no load it seems to me it should keep two 12's up easily.
But you are only putting in about one amp hour per sunny time, so say 6 amp hours per day assuming all sunshiney days (here we get some cloudy days in winter). In two weeks that is 84 amp hours, or 42 amp hours per battery. If batteries were 220 amp hours and were down to 1/3, they each need about 140 amp hours if I did that right. If all those assumptions are correct, which they likely are not, you need to wait about 6 weeks for a recharge with no load.
Chuck
Wonderful Wife
Lovely German Shepherd.
1999 Mercedes ML320 TV
2003 Wanderer 187TB Toybox (3620# UVW, 4800# loaded) Not yet camped in Hawaii, 2 Canada Provinces, & 2 Territories. I can't be lost because I don't care where this lovely road is going
15 watts will not charge the battery. You need to get the battery charged first and let the panel maintain them. The battery needs to be isolated from and draw.
I wired my 15 watt panel all the way to the battery compartment. I use a switch to disconnect the battery completely from the trailer. The 15 watt solar Battery Minder is however connected direct to the battery(no switch). Mine is lucky to get the battery to 13.2 volts and runs flat out this time of year. In the early summer it will get the battery to 14.2 and switch to float mode 13.2 volts. I have four golf batteries, 464 amp hours. I always fully charge the battery before storage.
2001 F150 SuperCrew 5.4 Lariat Offroad 4x4 Tow Package 4.10 Truetrac
2006 Keystone Springdale 249FWBHLS
12K SuperGlide, KGE3000Ti 2.3kw rated 2.6kw max
Frank's voltage booster, Prosine 1800 powered by 4 GC2 batteries
I've put the trailer on shore power for the next day or two to get the batteries up to full before I put it back in storage.
It sounds like I'll have to add a manual battery disconnect switch & reroute the charger wires to go to the boxes (since that's where I'll need to locate the disconnect). Hopefully that will keep the batteries fully charged.
Perhaps I don't understand batteries, but I figured that w/ no load attached & a 15W solar trickle charger that my batteries would be fully charged in only a few weeks.
How many watts would one need to fully charge two medium sized batteries in two to three weeks anyway?
It sounds like 1 of biggest problem you have is voltage loss over the distance you are running your panel from the batts. I would make sure you use at least 10 ga wire as a minimum and try to limit the distance you need to run said wires. 15 Watts may well be enough to keep a fully charged batt up..but not might not be enough to charge it when really down. Any shadow will cut your panels ability by 50% or more.
If ya can..go 6Volt. You'll love em.
Here is an excellent FAQ for all those that want to learn more on Batteries:
With a 15 watt solar panel, your output is only about 1 amp, so #12 or #14 wire will be oversized for that load.
You might want to add more 15 watt panels, skip the charge controller, or install a 50W or more watt solar panel. 15 watt solar charger will not damage your batteries even if they where full when you started to charge them. At the worst you might get in 14.2 volts and boil away a little bit of water, but you likely will not reach 14 volts even if the batteries started out full.
Here is a place that sells larger solar panels. SolarOnSale.com
You can also learn a lot about solar systems at this great website HomePower.com
My RV when the refrigerator, propane and carbon monoxde detectors are on, the RV is using 36 amp hours per day, about what one of my 120 watt solar panels can make each day.
Fred.
Money can't buy happiness but somehow it's more comfortable to cry in a Porsche or Country Coach!
Get a volt meter, those idiot lights aren't telling you anything. The batteries should be maintaining at least 12.6 volts. If not, you need more solar or something is wrong.
By your removing the batteries and eliminating any phantom loads, you shouldn't even need the solar charger to keep them up to snuff. Certainly a 15 watt solar connected would be a plus and should keep them at a high charge state.
I have a '57 Ford with a *9* year old battery in storage right now and it gets started every 3 to 5 months and sometimes not even driven at that time and the battery stays charged enough to start each time.
I know I'm on very borrowed time with a 9 year old battery, but......so far so good.
hershey - albuquerque, nm Someday Finally Got Here
My wife does all the driving - I just get to hold the steering wheel.
Expedition - Suzuki Grand Viagra
I've had a 7 watt (about 0.4 amp) solar panel on my boat for 20 years. It keeps two 12v group 24 batteries fully charged. However,
a) It's in sunny Southern California
b) No draw from the batteries from detectors, etc.
As a previous poster said. Don't worry about wire size with that little of charging current. Voltage drop is proportional to amps. Mr. Ohm proved that.
Ralph
2006 GMC 2500HD, XCab, SB, 6.0L w/2001 Lance 845
Firestone Air Bags, 125 watt solar
1970 Martin D18 Guitar My RV Travels Webpage and Campsite Map
Like Ramblin' Ralph, I've got a small (5 watt) panel that keeps my two 12 volt batteries charged. It's plugged into the 12 volt outlet at the antenna connection.
I was intrigued by your comment that you measured the voltage to be 16 to 17 volts with the solar panel connected to the battery? That's about what I'd get with the panel connected to nothing, or open circuit. Connected to the batteries I max out at about 13.5v. Makes me wonder if you were actually connected?
Offline
