Solar Panel-Battery Charging *Deep Cycle Recommendations*

[shootr]

My question is, will 18v and 340mA for 6 hours a day hurt the battery over the long run? Does leaving the panels connected in the dark actually discharge the battery? Would a 1N5822 diode wired into the positive lead prevent this? (Read about that on the internet too)

I can get a simple charge controller like this from HF, but prefer not to - just another link to break in the chain...
http://www.harborfreight.com/7-amp-solar-charge-regulator-96728.html

I had one of these panels for the longest time, just for messing around with:

http://www.ebay.com/itm/VW-Volkswagen-12V-Solar-Panel-Battery-Maintainer-OBD-Plug-USED-/271300142952?pt=Motors_Car_Truck_Parts_Accessories&hash=item3f2abfa768&vxp=mtr

(Basically it is a small 3W panel that specs out at 18V max / 170mA - I can vouch for the voltage, but no way to measure the amperage)

My new-to-me teardrop came with one as well, the previous owner used it to keep the battery up while in storage (direct wired to the battery). I wired the two panels together to see how much I can get in a typical AZ day - possibly enough to bring the battery up after a night of running the roof vent fan. (The fan draws the battery down from 12.5v to about 9.5v overnight). One panel in 6 hours of partly cloudy skies brought it from 10.5v to 11.6v, not bad for a little bitty panel.

I have a small battery charger that I can plug into an inverter-supplied outlet in the bed of the truck and top off that much in a couple hours of running the engine - so this isn't a huge deal - more of an ongoing experiment/study. I have no need for a generator and don't want bigger panels - these store neatly in the battery box on the tongue.

As always, thank you for your input/expertise!

[bdosborn]

(The fan draws the battery down from 12.5v to about 9.5v overnight). One panel in 6 hours of partly cloudy skies brought it from 10.5v to 11.6v, not bad for a little bitty panel.

Ouch! You're drawing your battery down too far; ideally you wouldn't ever go lower than 12V.

The 3W panel can be connected to your battery without a controller, its too small to overcharge your battery. The panel has an integral diode (or least mine does) so you don't need to add one. I think think the rule-of-thumb is you don't need a controller for anything 10 watts or less. 3 watts isn't very much when you consider that a Fantastic Fan will draw around 2 amp-hrs on low. You would need around 18 days at 8 hours a day of full sun to recharge your battery from 12V back up to 12.7V.

Bruce

[shootr]

Hello and thanks Bruce,

I just threw the charger on it again, and when it's topped off I have a Snap-On load tester I'm going to check it with to see if it's just worn out and tired. Heck, there isn't even a label on it showing the basic specs, but it's dark and it might be my imagination and I just didn't pay attention before - but I think it may be bulging too.

What would be a good one to replace it with?

Just another thing when you buy a used one. I'm still in love with it, this is just another lil hiccup on the way to teardrop happiness.

[Kharn]

How many amp-hours is the current battery rated for?
It must be either very worn out or extremely undersized for the fan to draw it down that much.

[shootr]

That's the thing - there are zero labels on this battery - I couldn't tell you what group it's from, age - nothing. I'm going with the theory it's old, neglected, and tired - Walmart here I come for new one.

[Kharn]

Could you measure the height, width and length? Group size would tell us the approximate capacity, and that would also determine your options for replacement.

[noseoil]

Some people are using folding panels to do the charging chores. They are pretty compact & can be set up or knocked down in a minute and range anywhere from 6 watts (a cell phone charger) to 120 watts (all you need here in a day to fully charge a bigger battery). I'm seeing more of this type of setup now & am planning on a fixed 100 watt panel for my roof on the build, but I'm not there yet.

It sounds like you will need a fresh battery in your "new" teardrop, and perhaps a bit more solar power than you have now to take things on the road. For now, just use what you have and monitor what happens with the battery and your panel. I'd be curious to see if that small panel is even able to charge up the battery after draining it down so far. Usually, there's a cut-off in most battery systems to automatically keep a battery from discharging that far. It will ruin a battery if you do that regularly. A deep cycle battery will help, but that's pushing the envelope a bit too far at 9v!

Is there a battery box in your rig, or does it just sit there? Can you add a "bigger" battery, a group 27 for example will give you about 100 amp-hours. That's usually plenty for overnight, especially here where there's lots of sun to re-charge. There's a Tearjerkers meet here in Tucson this weekend (Catalina State Park) if you can come down, I'd enjoy meeting you and seeing your rig. Welcome, tim

[bdosborn]

It's getting pretty tough to find a true deep cycle battery that doesn't cost an arm and a leg. Walmart has marine batteries, which aren't the best deep cycle type batteries but they're cheap. I just bought golf cart batteries for my trailer but you need two of those. I'd do a forum search on "deep cycle" and see what others have picked lately. The last time I bought a 12V deep cycle battery (as opposed to the 6V GC type) was in 2008 and I think prices have gone up a little since then...

Bruce

[shootr]

Apparently Tim is some kind of Seer! Hit the nail on the head of just about everything he mentioned.

Yep, the battery is a dud. Put the charger on it one last time all day yesterday, then hit it with my Snap-On battery tester last night and it only showed 20% capacity.

The battery has no markings but measures out to a standard automotive starter battery, not a deep cycle or marine type. Others have guided me on acceptable and unacceptable discharge rates and this one has seen it's last days long ago. It is in a battery box that is inside the tongue box. It's plenty big enough for a group 27 battery to fit.

Walmart has this one for a heck of a deal http://www.walmart.com/ip/EverStart-27D ... y/16795212 , and since all I plan on running is a couple LED reading lights, the kitchen LED lights when needed, and the roof vent fan - I have to believe that is enough for a couple days. (OK, maybe the margarita blender but that's getting ahead of myself).

I'm still going to bring the multimeter and the solar panels to see how things work out (sun/clouds, tree's, etc) in the real world, and I'll bring my 120V charger that can run off the outlet/inverter in the bed of the tow vehicle just to be safe too.

I appreciate the offer of the gathering this weekend. I joined the Tearjerkers site and saw that, but we're just going to do a quick trip to Payson, which is just 1.5 hours, and get some experience in the manner we expect to use it. I'm looking forward to a future event though to meet up, visit, learn, and enjoy some good company.

[tony.latham]

That battery should (while it's new) give you about 50 useable amp/hours before you start damaging it. I've got a Group 27 marine I bought at COSTCO and use a similar amount of amperage as you do (plus a 12v, 4 amp/hour, electric blanket when it's chilly for preheating the bed) and I've got more amperage than I need. But where I camp, I don't need to run my Fantastic fan all night. It's more of a napping tool.

I've got a 60 watt homemade folding setup, see Bruce's page here for the details: http://home.comcast.net/~bdosborn/Boxca ... Solar.html

I prefer it to the on-the-roof panels so I can camp in the shade.

I bought one of these for $20 to monitor my usage: http://www.amazon.com/Power-130a-Precis ... B0090YW78U It works great.

Tony

[Kharn]

I'm still going to bring the multimeter and the solar panels to see how things work out (sun/clouds, tree's, etc) in the real world, and I'll bring my 120V charger that can run off the outlet/inverter in the bed of the tow vehicle just to be safe too.

That's not a great way to go about charging your battery, a 7-pin RV-style trailer plug to do DC-to-DC charging (or a set of jumper cables) would be more efficient.

[shootr]

I guess I mean that in the morning if the battery is 12.0V or lower, I'd fire up the truck and use the 110 outlet it has factory installed in the bed to plug in the small 2/6/10 amp battery charger I have and top it off - I figure an hour or two would be sufficient but it's all guess work until I get into the field.

Unless there is just no other way, then I would consider a bigger PV array or a generator.

[Kharn]

The 10 amp charger will deliver exactly that, 10 amps.
RV plug or jumper cables would give you 20-40 amps, which would reduce your charging time significantly, plus avoiding the losses in the inverter and charger.

[bdosborn]

Or just try a bigger portable PV panel. 3 watts it's really too small to do much more than maintain the battery. I have two portables, a 60 watt and an 80 watt. Either one would easily keep up with the usage you've described.



They're better than roof top panels when you want to camp in the shade:



Of course, you might go overboard with the PV like I did and end of with 550 watts worth of panels:



Or worse yet, go completely off the deep end like OVTTCT and get thousands of watts of panels!

Bruce

[MtnDon]

I heartily second the idea of using a connection between the truck 12 volt system and the trailer rather than a charger powered by the inverter on the truck ....

There are 10 gauge 2 pole connectors available that can handle heavier loads.
http://smile.amazon.com/CES-Gauge-Quick ... uge+2+pole