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  • 5v solar system

    Hi all!

    I'm building a system to run a low powered USB device 24/7 (it draws 1Ah at 5v per day).

    Originally I was going to use a 6v solar panel -> USB powerbank (with an 'always on' mode) -> device.
    However, the 6v panel doesn't put out enough juice, and larger wattage 6v panels are almost non-existant.

    I'm trying to make the system as lightweight as possible, and my best idea currently is 12v 20w panel -> charge controller -> 20aH motorcycle battery -> 12v to 5v buck converter -> device.

    I've considered using a li-ion battery to get the weight/size down, but it seems like the controllers for small batteries only charge at low current (for example: https://www.adafruit.com/product/390)

    My question is, is there a better way of achieving this than my current 12v setup? Perhaps a li-ion type solution that I am missing?

    I have also seen some charge controllers that have a USB output on them, would I be better to use one of those, rather than a separate buck convertor?

    Another thought - could I use a 12v charge controller with USB output, have no 12v battery connected, and just hook the USB connector to a powerbank? (I *think* that controllers always need a battery connected, but may be wrong).

    Thanks!
    Last edited by alfredo; 05-25-2020, 06:16 AM.

  • #2
    My educated guess, is that any Charge Controller with a USB output, would need a battery to provide power overnight. (and daytime too ! ) I know of no CC that doesn't need a battery,
    Also small and lightweight, are Li-Ion vehicle Jump Starter packs. Those often have a USB port, and most will charge from a car, some may even charge from solar.
    here's one less than $50 but small, 12aH amazon.com/Nekteck-Starter-Portable-External-12000mAh
    Ask the sellers of these, if you can wire a small PV panel to charge it. They all have internal regulation to charge from a running car ( 15V ) but maybe 25V from solar panels might be too much
    Powerfab top of pole PV mount (2) | 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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    • #3
      I really don't understand why the product you're asking for is not available.

      I also realize that any solar powered system that draws serious amounts of power would need a load like a battery. If this load was not a battery, it would not be able to give power when the panel did not produce it, like the panel enters the shade from a cloud or a tree in the way. Without the battery, the power would be turned on and off quite a bit. This is not good for a lot of devices, but if I wanted to use it to boil the water, and I don't mind replacing my electric kettle frequently, hey its my money. In your case, your iPhone or digital camera might be plugged on and off several times. Can't be good for it.

      But hey, if I wanted to buy 4000 watts of panels to power a 2000 watt inverter so I could boil my water in a 1700 watt 1.7 liter electric kettle, than I think that should be available. I can guarantee that most or all would consider this system wasteful, but I can guarantee most could design this system better than me. But you know, if I wanted to drop the cash to make that happen, I think I should be able to, or at least see some technical article on why its not available.

      There's a company that marketed microinverters for the purpose I mentioned, but they seem to be out of business.

      For the panel you mentioned, I have one that charges my cell phone, but that can take four hours to charge my phone. So those type of panels are not practical for charging larger items like laptop or probably even iPad.

      I got a 100 watt panel, a 92 amp hour battery, which is a big RV battery, put a PWM charge controller on it. The PWM charge controller has two ports for USB at 2 amps and 5 volts each. Each port would draw 10 watts. Those two ports alone with the battery I have, once fully charged would power those two ports for 13 hours discharging 25% of the battery, 75% left, giving me about two days I could use those charge controllers to charge two USB ports for 13 hours.

      Charge controllers are made to be hooked to batteries. The setup is usually hooking to the battery first. If you hook the solar panels up, bypassing the battery, you can fry your charge controller.

      Comment


      • #4
        Originally posted by chrisski View Post
        I really don't understand why the product you're asking for is not available.

        There's a company that marketed microinverters for the purpose I mentioned, but they seem to be out of business.
        Connect the dots. No demand for such a product. Dead simple to make, but no use for it.. Two people are not a market.

        MSEE, PE

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        • #5
          Originally posted by Sunking View Post

          Connect the dots. No demand for such a product. Dead simple to make, but no use for it.. Two people are not a market.
          You're starting to make me think that solar energy is the least efficient form of renewable energy every created by man.

          I guess I could get a 2000 watt 12 VDC zener diode to regulate the DC power to the inverter.

          Comment


          • #6
            Originally posted by chrisski View Post

            You're starting to make me think that solar energy is the least efficient form of renewable energy every created by man.

            I guess I could get a 2000 watt 12 VDC zener diode to regulate the DC power to the inverter.
            Good luck finding a 2000 watt Zener and the product you are looking for. .

            This has been talked about here for 15 years. A product or two even appeared on the market and disappeared (bankrupt) just as quickly. Some I helped have even wasted time building them. I can tell you how to build one easily. just cannot sell any.
            MSEE, PE

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            • #7
              I would certainly like to see what it takes to build one. I would not want to sell it. If I did build it, this system would definitely not be attached to grid power nor even in the same building.

              Comment


              • #8
                Originally posted by chrisski View Post
                I would certainly like to see what it takes to build one. .
                15 years ago you could make one that would have limited appeal. Back then USB charging standards were primitive with very low power demand. Back then 5 volts @ 500 ma charge current or 2.5 watts. Today, will not charge much of anything, and what it does charge is painfully SLOW. Yep you could use a little fold up 4 watt panel with nothing more than a diode for electronics as long as you had a full day to bake in the sun. Sure was cool to be seen with.

                Today USB charging standards have changed considerably, and there is more than one. Most notable voltages and currents have gone up. The 5-volt model still exist but current has now gone up to 4 amps or 20 watts. No longer can you use a passive diode. It requires active processing and communications with the device. Active electronics have minimum power requirements. If it is demanding 20 watts, it must have it or will malfunction or self destruct trying. Lots of IC's made to do it, but it has minimum power requirements that must be met.

                That means today is going to require a fairly large panel, and a battery when you fat arse or a leaf shadow blows by. A big ugly very expensive cell phone charger no one would buy just like its predecessor. Sure is cool though, useless, but cool like James Dean.
                MSEE, PE

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                • #9
                  I've done the 5v thing - just off the shelf, even easier today for a 5v solar setup. No sense making it yourself. Not heirloom quality, but camping style stuff.

                  You'll need:

                  1) The typical "20 watt flexible folding solar panel". Not the rigid ones. They include the 5v regulators. Get one that has TWO usb outputs if you like. Even better, get one that has a voltage and current meter included if you like. Saves you from having to use a dongle-checker.

                  2) Quality li-ion battery from Anker. 20000mah (or more) type. It has two usb inputs. Use them with the two panel outputs for fastest charge.

                  Problems:
                  Isn't cheap, but that's not your goal if you want to do it right. The folding panels can differ in quality, but don't lowball it. Use good cabling. Keep it short, typically with battery shaded by the panel.

                  Personally I use the folding panels that also include "legs" that foldout so I can at least angle it properly during the day, and also shade the battery. That is until the wind takes it.

                  SOLAR RESET: This is one of the bigger issues, and the Ankers "IQ" circuit typically take care of that (along with figuring out what your actual internal cabling connections really are) Many lesser batts or crappy cabling will just idle once a shadow crosses the panel and the sun comes back out. Go super cheap, and this is the result.

                  As of late, this is something that is tested here:

                  http://www.candlepowerforums.com/vb/...eries-Included

                  Op "HKJ" does a fantastic job measuring stuff like this.

                  But yes, for a more DURABLE setup, go inefficient with the typical Panel > controller > lead-acid > 5v regulator to charge up the li-ion batt. No shame in doing that as long as you've done your power-budget homework in advance.


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