Solar charging batteries.

Discussion in 'Motorhome Chat' started by Humsafer, Aug 10, 2016.

  1. Humsafer

    Humsafer Funster

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    I unfortunately have to run a C-pap machine during the night and when off mains I use a separate 12 car battery to power it, so as not to deplete the batteries in the motorhome. At Misterton I purchased a TOPRAY SOLAR 12 watt charger which has a cable and two crocodile clips. The question is can I connect this directly to the battery terminals. This is a stand alone battery totally divorced from the Motorhome electrics. Help/advice appreciated as we are off hook up this long weekend .
    Cheers Fred
     
  2. Lenny HB

    Lenny HB Funster

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    Yes, 12 watt will be OK anything bigger would need a regulator but don't expect to get much of a charge out of a 12 watt panel. on a very clear bright day you will get an amp for a couple of hours around midday, either side of that output will fall off rapidly. If you are relying on that battery you really need a minimum of 40 watts and then only OK for the summer months.
     
  3. scotzsue

    scotzsue Funster

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    John uses Cpap too, 2 leisure batteries and solar, can manage 5 nights in fair weather, don't watch a lot of TV though. usually find that power used overnight has been recharged by midafternoon. We do carry a generator 'just in case' only used a couple of times, and that was before getting a second leisure battery.
    Last van solar was sufficient even in th snow.
     
  4. PhilandMena

    PhilandMena Funster

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    I have a 125W good quality German Solar Panel and the best I can get in the UK is about 5A and this is on a very bright day and for short periods. That's 10 times bigger than your 12W solar panel and I think you will struggle to get 1 Amp.

    These are very good S.P. and can be connected directly to your leisure batteries, or stand alone battery.

    http://www.photonicuniverse.com/en/catalog/list/category/folding-solar-kits
     
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  5. Humsafer

    Humsafer Funster

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    Thanks everyone, I guess the answer to the question is yes I can connect (which I will) but it will only help if I am lucky with the weather
    I do have 2x 100watt Batteries and for emergency use only a 1kilowatt Honda which I hate cos they can be so antisocial.
    Anyone want to buy a 12watt solar panel
    Cheers Fred
     
  6. ludo

    ludo Funster Life Member

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  7. PhilandMena

    PhilandMena Funster

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    I thought it worth mentioning, (as you may not be fully conversant with Solar Panels (S.P.)). The S.P. I have refereed to in my last post comes with it's own controller so you can connect it directly to your battery/ies and it immediately starts to work and requires no further attention/add on's or modification.
    If you are going to purchase from elsewhere make sure it's an all embracing version and can be safelt attached to your batteries without requiring additional add on's etc.
     
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  8. seanoo

    seanoo Funster

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    hi phil, thats a very low output from a 125w panel . thats more like the output of a 80w panel. you should be seeing 8 amps ish in direct sunlight. have you got any shadows on the panel from anything on your roof? any shadow whatsoever will dramatically reduce the output.
     
  9. Lenny HB

    Lenny HB Funster

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    Agree on a good day get over 5 amps out of each of our 100 watt panels, maybe not a very good regulator.
     
  10. PhilandMena

    PhilandMena Funster

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    Seanoo, I cant understand how you arrive at that figure.

    The specification for my S.P. is as follows.

    Solar panel 125W: Compact & Powerful Mono crystalline solar panels are made of Q-cell solar cells
    -->Power: 125W
    -->Dimensions: 1135 x 660 x 35 (mm)
    -->Voltage: 17.2V
    -->Open-Circuit voltage: 21.6V
    -->Max Current: 7.26A
    -->Short circuit current: 8.13A
    -->Max voltage: 1000V
    -->Weight: 8.8kg
    -->Efficiency: >18%
    -->no of cells: 36

    As you can see the maximum current is only 7.62 Amp and this is a high quality S.P. Also, no S.P. is going to achieve anything like the maximum output and considerably less in the UK, even in good sunlight. The most I have ever obtained is 5.6 Amp and this is when in Morocco. I do not know where you are getting your facts from but ||I would advise you re- check as they make no sense.
    As for an 80 W S.P. maximum current around 4.5 Amp so expect to get about 3 Amps in the UK at best.
     
  11. pappajohn

    pappajohn Funster Life Member

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    As a rule of thumb, any panel less than 20watts doesn't need a controller......unless you have a very small battery.

    20w (around 1A to 1.5A charge output) cannot overcharge your battery
     
  12. John Laidler

    John Laidler Funster

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    The 7.26 current figure is from the panel and at a voltage of around 17 volts. The controller will reduce the voltage and increase the current, assuming it isn't a basic shunt type controller. Ignoring losses in the controller a 125W panel should be capable of producing 10 amps at 12.5 volts for example.
     
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  13. seanoo

    seanoo Funster

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    i u
    i use a mppt charge controller with my current setup and have 210 watts on the roof , i can pull in 14 amps on a clear day in the uk no problem if my batteries are down. so thats 7 amps per 105 watt ..
    before i had just an 80 watt panel and a pwm regulator and i still got close to 5 amps in the uk on a clear day in summer.
    in summer the midday sun in morocco and in uk are virtually no different for a small solar installation apart from the pollution in the uk of course (and clouds lol)
    looking at your link to your solar panel it shows the regulator on the back of the panel which means that it has already dropped the voltage and then this reduced charge has to travel along the 5 meters of cable to your battery via crocodile clips . it would be more efficient if you put the reg next to the battery and had short cables to the battery
     
    Last edited: Aug 11, 2016
  14. Lenny HB

    Lenny HB Funster

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    Not quite, you won't get any charge at 12.5 most regulators need around 16 volts to produce a chargeable output so 125 watts should produce around 7.8 amps. I said most regulators as MPPT ones and some clever ones like the Schaudt LR1218 can boost the voltage coming in to still give a charge when sunlight levels are low but that can not increase the total power available.
     
  15. John Laidler

    John Laidler Funster

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    I was describing the battery end of things and how the controller can increase the current by dropping the voltage from the panel. Essentially, power into the controller will equal the power going to the battery less the losses which are low. V x A in the panel cables equals V x A at the battery. It can't be otherwise, ignoring the losses in the system.
     
  16. PhilandMena

    PhilandMena Funster

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    The specification I posted refers to the S.P. on my roof, not the one in the link. I am impressed to say the least, that you can obtain 14 Amps from 210 W.
     
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  17. PhilandMena

    PhilandMena Funster

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    I was not aware of this and this is not the case with my system. I will explore in more detail.
     
  18. PhilandMena

    PhilandMena Funster

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    Sorted ! Your are spot on! If my batteries were low or flat I would have seen a much bigger Amp reading from my control panel.
     
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  19. John Laidler

    John Laidler Funster

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    It's easy enough to work out what current you might get by just thinking of the wattage. V * A = W, so your 17.2 * 7.26 = 125W (more or less) If the panel was actually producing this full amount then this power can't get lost as it makes its way to the battery, apart from a few percent lost in the wires and the controller. Lets assume 5W is lost as heat somewhere so at the battery terminals there is a potential 120W to charge the battery. The same V * A = 120 applies so if the voltage was say 13v then the current would be 120/13 = 9.2 A Of course if the battery is fully charged then the controller will more or less stop charging and the current might reduce to say 0.1 amp at which point your panel will also stop putting out all but minimal current too. The only complication of course is if there is a load on somewhere this could divert power from the charging.

    This current increase at the batteries does not of course apply to very simple controllers which simply connect the panel output directly to the battery which is why MPPT controllers are generally considered the best as they will maintain the panel voltage at the optimum to generate the most watts - or maximum power as the name implies. :)
     
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  20. PhilandMena

    PhilandMena Funster

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    This is the regulator that came factory fitted with my Motorhome. My interpretation, after reading your comments is that this regulator would allow up to 10A from my S.P. to be directed to either the Hab or Cab batteries if called for by the batteries. (I never allow my batteries to discharge much which is probably why I have been seen more than 5.5 A from my S.P. on the control panel.
    https://sargentltd.co.uk/shop/product/10amp_solar_regulator/122
     
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