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Looking for advice on a panel for camping/charging RC battery

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  • Looking for advice on a panel for camping/charging RC battery

    So without doing any research I bought two 35AH solar batteries from Harbor Freight and a 4.8W schumacher solar panel and used them with pretty good results while charging some RC batteries in a field. I have now added a cheap solar charge controller from amazon https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 and now I am looking for a bigger solar panel. I have a 300W/600W inverter to run my laptop (max 150W charger) but probably not much else, and not very often. I usually run two chargers, which may pull as high as 20A each, at full tilt, but more likely less than 10A total from the 12V batteries.

    I am looking at replacing the 4.8w panel with a 100W from amazon https://www.amazon.com/gp/product/B0...KIKX0DER&psc=1 but its huge, and with all the stuff I bring it would be a huge pain to bring this panel. Is there anything smaller that would work well, or is this the best option (or is it even big enough?) for me?

    Any projects similar to this one? I am going to rewire everything with fuses and probably somehow integrate an ampmeter. This will probably get used maybe 10 times a year, if that.

  • #2
    You can connect smaller wattage PV Panels in parallel and/or series to get the volts, amps and watts that you,.
    It does not need to be one PV Panel.

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    • #3
      There are folding solar panels rated from 80 to 120 watts. They cost more but since they fold in half they are easier to transport.

      Here are a couple of pictures of my "portable system". It has an 80watt panel (I should have gone with a 100w panel), 65Ah battery, 15amp cheap CC (it came with the panel), a 200watt inverter and a hand cart I purchased from HF modified with some ladder hangers to support the panel.

      It does not produce a lot of power but it is handy and portable.

      Oh by the way. I built this system to charge my RC batteries. It also works for other small loads when power is not available.
      Last edited by SunEagle; 08-01-2017, 09:31 AM. Reason: added last sentence

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      • #4
        Was hoping to keep the total cost low, is there a decent 100w panel that folds up and costs less than say 200$?

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        • #5
          Originally posted by phillyb View Post
          Was hoping to keep the total cost low, is there a decent 100w panel that folds up and costs less than say 200$?
          Most companies hit you hard because of the ability to fold the panel so getting a 100 w unit for less than $200 may be hard to do.

          I did see one from Renogy for $280. I would check amazon or eBay to see what you can get. Be careful because there are some that come from Asia and you may get an import fee added on to the total price.

          My 80watt panel came from Eco-worthy about 4 years ago and cost me ~ $250. They now have that 80W panel for about $188 and a 100w panel for $230 although there might be shipping costs added to those values.
          Last edited by SunEagle; 08-01-2017, 06:38 PM.

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          • #6
            Originally posted by phillyb View Post
            So without doing any research I bought two 35AH solar batteries from Harbor Freight and a 4.8W schumacher solar panel and used them with pretty good results while charging some RC batteries in a field. .
            Pardon me please, speaking as a RC Pilot, but a 4.8 watt panels will not charge up any RC Battery. Your panel did almost nothing. it was the 2 12 volt 35 AH batteries doing everything. Example say a 4S 2200 mah LiPo charged at 1C or 2.2 amps is using 33 watts. That 4.8 watt panel is not doing anything. If you only used the solar panel power to recharge that same battery would take 2 to 4 days to charge.

            Your 12 volt batteries are way to small to do much serious field charging. Combined they are 12 volts @ 70 AH. Not much as that is roughly 840 watt hours with only 420 watt hours usable. Once you factor in the Peukert Effect and that is down to 300 watt hours usable or 25 AH usable battery. Well it takes 30 to 50 watt hours to charge a RC battery depending on its size. that is 6 to 10 recharges in the field. The panel at 4.8 watts is useless. At best it can only generate 10 to 15 watt hours in a day. A 200 watt panel will at least get you 400 to 500 Watt Hours per day which is 10 to 15 recharges without draining your batteries.

            At bare minimum to even be useful for RC Planes or Ground Vehicles in the field is:
            • 200 Watt Solar Panel
            • 15 Amp MPPT Controller
            • 12 Volt Golf Cart Batteries, a pair of 6-volt 225 AH GC Battery
            • Favorite RC Hobby Charger that works from 12 volts.
            Sorry but you are just wasting your time and money with what you have. A 4.8 Watt Panel will not even charge a cell phone.If you know and understand a couple of things, you will know 4.8 watts is useless. A LiPo battery has a Voltage and AH specification. RC LiPo's only give cell count, but we know the voltage of 3.7 volts per cell. So a 4S battery is 14.8 volts. Say the AH spec is 2200 mah = 2.2 Ah's

            To find the energy in a battery is called Watt Hours. To find Watt Hours in a Battery is: WH = Battery Voltage x Amp Hours. So a 4S 2200 mah battery has 14.8 volts x 2.2 AH = 32.56 Watt Hours. There is another way

            Watt Hours = Watts x Hours.

            Now if you wanted to recharge that 4S 2200 mah in 1 hour or less would mean we need to charge with 32.56 Watts right? Absolutely correct because we known Watt Hours = Watts x Hours. So how many amps did we charge at? Well at the 1C Charge rate with 2.2 Amps.

            Amps = Watt Hours / Battery Voltage

            32.56 wh / 14.8 Volts = 2.2 Amps exactly.

            But who the heck wants to charge at 1C in the field that takes an hour. Not me I charge at 2C or 3C so I am back in the air in 30 minutes or less. Well that means double or triple the Wattage. Now you are charging at 65 and 97 watts.

            So what good is a 4.8 Watt Panel?

            Not much good at all. In fact does little to nothing. So insignificant you would not miss it as it is not even capable of charging 1 RC LiPo battery in day with full sun.
            Last edited by Sunking; 08-01-2017, 11:30 PM.
            MSEE, PE

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