Solar Charging / How Long From Flat ?

Discussion in 'Solar Power' started by RS_rob, May 29, 2015.

  1. RS_rob

    RS_rob Funster

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    This is a theoretical question prior to actually putting it in to practice.
    My MH has a solar panel possibly 100 watt I don't know fer sure as there are no markings to determine the size.
    My leisure battery is 85amp & I only have the one for now.

    So assuming the above & taking into account I have flattened my battery overnight say using a plugged in fridge (& this is not a question of how long my cool box will last on battery)

    How long would my battery take to charge on solar alone...................?
     
  2. Minxy Girl

    Minxy Girl Funster Life Member

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    .... how long is a bit of string! Depends on how much light there is for a start ... and whether you've totally stuffed your batteries in the process of letting them go flat ... best to get a second battery fitted to take advantage of all the power the solar panel is producing on a good sunny day then you won't ever have to find out! :D
     
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  3. BwB

    BwB Funster Life Member

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    As a rough guess I'd allow a week of average summer weather and assuming no other draw on the battery during that time.

    But, as stated already, lots of other factors and equipment efficiencies involved.
     
  4. Munchie

    Munchie Funster Life Member

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    A plugged in fridge?

    It would be flat in no time!!! That is why m/home fridges only run on 12v when engine is running!
     
  5. John Laidler

    John Laidler Funster

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    The question is further complicated by the fact that whatever drained the battery overnight might also be running during the day, diverting the solar power.

    The panel also won't produce 100w, perhaps only 30 averaged over a 12 hour period, it depends on the season, weather and latitude.
     
  6. Wildman

    Wildman Read Only Funster

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    well at midday your solar may produce 5 amps the est of the day 2-3amps, assuming you only depleted the battery by 50% i.e. 42.5 amp/hrs then I'd guess on average 2 days to really recharge it, not just to show 13.8V which would only be the charge voltage anyway. If the fridge or cool box is still plugged in the you have probably killed the battery anyway. Should only be on 12v when the engine is running. If you must run a compressor fridge or cool box on 12v then it should be connected to the load terminals of the solar controller so that the controller protects the battery and switches off before any damage is done and then remains switched off until the batteries have recovered a bit.
     
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  7. mickyc

    mickyc Read Only Funster

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    Wildman's figures are a good guide.

    In my experience with a 100w panel a sunny day will give you 20-30 AH's worth of charge.

    Scotland less so, the South of France more so :)
     
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  8. Don Quixote

    Don Quixote Funster

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    Sorry guy's, but UK sun you have NO chance of fully charging a battery.
    Average UK day 100 watt panel 15/20 amps MAX, why watch your solar charger ( that is if you have one with an amp read out ) 1 second you have 3 amps next second you have .5 of an amp because of cloud or angle of sun to your panel on the roof. So if NOTHING is connected to battery at all other then solar panel it would at best take 5/6 days, however as it is connected to the MH and drawing amps however little that is it WILL never charge ONLY "Top up" the battery.
    Average MH draws 3 amps an hour ( lights, pump, etc ) but most these days draw around 5 amps an hour (lights, pump, TV, DVD, phone the list goes on and on ) so: 5 hours at 3 amps is 15 or 5 hours at 5 is 25 amps.......... but your UK 100watt panel is only giving you 20amps.......... So to answer the OP'er NOT A CHANCE of CHARGING BATTERY alone. Sorry
     
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  9. Wildman

    Wildman Read Only Funster

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    solar has accounted for 100% of my motorhome charging for the past 5 years, whilst there is less sun than spain it does work in the UK. My 2nd battery bank is not connected to the alternator only the solar. Batteries are normally fully charged by lunchtime even when overcast. It is a matter of how much battery power and how much solar you have.
     
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  10. Don Quixote

    Don Quixote Funster

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    Removed by me.....
     
  11. Brian and Jo

    Brian and Jo Funster Life Member

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    correct me if im wrong but I didn't think solar panels would charge a battery ,only trickle current to keep them topped up.if the battery has been totally flattened then there is no chance of the solar panel bringing it back to life.
    Brian & Jo
     
  12. Wildman

    Wildman Read Only Funster

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    4-5 amps is a decent charge rate, I suppose it all depends just how low a battery has been discharged, below 10.5v irreparable damage has been done anyway. Plus you cannot charge a "dead" battery any more than a conventional charger can.
     
  13. Don Quixote

    Don Quixote Funster

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    C
    Correct.................
     
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  14. Don Quixote

    Don Quixote Funster

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    4 or 5 amps at 14.4 volts is charging at 13.???? is topping up.
     
  15. oldfozzie

    oldfozzie Funster

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    from a different view, when not in our MH we live on a narrowboat, this boat is fitted with 4 * 110 AH leisure batteries, it also has a 100 Watt solar panel.
    If we leave the boat moored up and go elsewhere, like a funster meet and the batteries are flat! when we come back 3 days later the batteries are fully charged and that is with a 12 volt fridge running all the time.
    I can assure you the boat seldom goes anywhere other than UK ( sorry England) and thus that is the sunshine levels we are used to.:)
    I base my evaluation of battery state on a fairly sophisticated battery management system and good number of years living at the mercy of battery state.
     
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  16. Wildbill

    Wildbill Funster

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    I don't know what I have done wrong but I made my solar panel lest year flattened my battery's completely dead after leaving the light on when it was in storage over winter
    I replaced the controller after I got out of hospital six days later the battery's were fully charged and all green in the indicator window.
    Wee have ben away for a full week using TV lights DVD's game stanchion's was off grid no power problems
    bill
     
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