Extra Solar Storage Options?

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Hi Folks - I'm new to the forum. It looks great! I have a small RV trailer (T@B) is only 12' long x 6'. It has only one Deep Cycle battery, but lots of electric gadgets (Stereo, TV, 3 way fridge, water pump, furnace, sensors, etc). I have 3 - 20 watt solar panels that seem to recharge the battery daily quite easily (on good solar days), and was trying to devise a simple means of recharging a 2nd (floater) deep cycle battery once the built-in battery is full. I often use 2 computers and can use the additional battery storage for heavy use & cloudy weather.
I have purchased a 2nd Diehard Platinum battery and wired the posts to a 12 volt extension cable (male / female cigarette ligher ends) so I can plug into a simple inverter and use to power 110 volt equipment. The male end (I'd assumed) would simply plug into my 12v outlet connected to my built-in battern and recharge itself while my panels recharged the built-in battery. It looks like my wattage in that 2nd battery is dropping however, rather than rising.... What is wrong with this theory?
Any thoughts would be welcome!
What else might be a better approach?
Thx! SteveM
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: Extra Solar Storage Options?

    firstly, the battery you bought if i read it rightly is made for starting cars or other vehicles even though it is an agm style battery. starting batteries do not fair well in deep cycle applications. it is unknbown to me how this battery will fair in your applications.
    another point would be the thin wire you've got as this would limit the current into the battery while the inverter is surely sucking the battery down at a good pace.
    i do have to admit that i had trouble picturing it all, but one comment disturbs me and that's when you said, "recharge itself". nothing can recharge itself without heavy losses and so it is a losing battle with no such animal.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
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    Re: Extra Solar Storage Options?

    60 watts of solar, will just not power much at all. You are lucky to see your batteries charging at all, as you may only be harvesting 30W, without being at a "good" angle to the sun.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • System2
    System2 Posts: 6,290 admin
    #4
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    Re: Extra Solar Storage Options?

    Niel, thx for comments! The Diehard Platinum is a deep cycle battery (one of the best available I've been told), but most folks likely relate to the 'Starter' type Diehards. The 60 watts is very adequate for recharging my one built in battery to near 14 volts each and every day - even if the furnace runs all nite. That is why I was thinking there was more 'recharge potential' that I wasn't harvesting. In Colorado we get good sunshine. I'm the trailer is 'small'.
    The 'floater' battery does use small 12 volt wiring - but my thought was 'trickle charging' only requires a small wire. How do you add images-I thought that might explain better... Again Thx!

    Here are some images of my setup...
    See image of solar setup on trailer to follow:
    TabAndPanels.jpg
    The Floater Batter is set up as follows - see image (I hope this works!)
    FloatingBattery.JPG
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  • System2
    System2 Posts: 6,290 admin
    #5
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    Re: Extra Solar Storage Options?

    Mike90045,
    Thx for Comments! It is a trickle charge and does a fine job of restoring all lost over nite (the 12 volt, lights, running furnace, propane fridge, water pumps, etc.) just doesn't keep up with multiple computers and 110 TV, etc.
    See image of solar setup on trailer to follow:
    TabAndPanels.jpg
    The Floater Batter is set up as follows - see image (I hope this works!)
    FloatingBattery.JPG
    Again Thx! Steve
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
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    Re: Extra Solar Storage Options?

    Just because the batteries "get to 14vdc" every day doesn't mean they are getting fully charged. To determine state of charge you have to check voltage "at rest" after a prolonged (couple of hours) on neither charging nor discharging. The at rest voltage should be something on the order of 12.7 when fully charged at rest.

    It is a simple matter of doing a couple of calcs. to determine what your harvest should likely be.

    I use a simple back of the napkin calc that says,, take your panel wattage, divide it in two to account for all system losses, multiply that number by the number of hours of expect GOOD sun. In you case,, 60X.5X4=120 watt/hours a day,,, or ~10 ah at 12vdc. Enough to light a 15 watt CFL for 4 hours.

    Tony
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