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  • OT: Voltage Adjuster for Solar Panel

    I had a solar panel that could output 12 volts (for a portable radio) but it no longer works. Most of the current crop of solar panels are usb (5 volts) oriented.

    Would the various circuits (or kits) offered to change/regulate a power supply be suitable to accept a solar cell input and consistently output the desired (12 volts) power? Would a battery act as a buffer help (solar panel charges battery then battery serves as power source for the voltage regulator that, in turn, supplies the radio)? What happens when the sun is cloud-covered? Does the voltage output of the solar panel decrease or is it the current?
    Assuming this is possible, would it be a lost cause because I would lose most of the power available due to circuit inefficiency? Are some circuits more efficient than others?
    While I can hook stuff up I come up short when it comes to the theory side.
    Thoughts appreciated. Thank you.

  • #2
    You're basically talking about an MPPT controller, which takes the output from a solar panel and manages it to provide an optimum power into a battery bank. As it does this it operates the solar panel at its most efficient point, which for a '12 volt' panel is about 17 volts or so, and it turns the product of that voltage and whatever current is provided into the 'maximum' power. That will be converted by the controller into a battery charge voltage and current, which will be regulated to prevent over-charging.

    It's likely that these controllers would not work from a 5 volt source, though there's no technical reason why it couldn't be done. There are available switching power supplies which will translate one voltage into another, though many of these won't boost a voltage into a higher one.

    Efficiency is another matter- some switching supplies I have will run quite cool at rated power outputs, and while idling, yet others warm up considerably even when idling. So it's quite possible to have an efficient controller with some smarts, and to design it to work with a wide range of voltages.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

    Comment


    • #3
      Most solar power regulators these days , at least ones for significant power output, are made to charge lead-acid batteries, 12V & 24V being the most popular voltages.

      Most of those are not made to regulate voltage, the MPPT types are made to put the most current possible into the battery, while regulating the PANEL voltage to the maximum power output.

      It generally is not possible to combine MPPT with a fixed voltage output. There are all sorts of voltage regulators that can produce 12V, 5V or any other desired voltage from a higher voltage. They vary in efficiency, and also (very important) in maximum voltage input. A "12V" panel setup can put out 17 to 18 V at full load, but when not loaded, or very lightly loaded, may put out anything from 20V to almost 30V. The regulator must be able to take that.

      The ordinary "linear" (analog) voltage regulators work, but are inefficient, and going from 17V to 5V would be VERY inefficient, the heat output would be larger than the electrical output at 5V.

      A "switching" type regulator may be quite efficient, often over 90% efficient. Their problem is that many have a minimum load, they do not regulate well if the output current is too low. But they will work effectively and provide any voltage needed. Some types can handle light loads, or even no load conditions and still maintain a good regulated output.

      But, again, the MPPT characteristic is not compatible with a fixed voltage output and varying load. The best that can be done for that case is to not allow the panels to be overloaded.

      1601

      Keep eye on ball.
      Hashim Khan

      Comment


      • #4
        The output of a solar cell will vary in both Voltage and current when the available light changes. This is more or less due to Ohms law: the equivalent circuit of any Voltage source will include both an ideal Voltage source and a series resistance. And the effective load resistance also limits the current available at any Voltage level.

        First, it is possible to "transform" DC Voltages both up and down with the proper circuitry. With all the battery powered, electronic devices being built and sold today, this is a hot area of electronics.

        Yes, most of the easily available devices will be oriented around charging batteries. And output Voltages around 12 and 24 Volts will be popular due to the ready availability of rechargeable batteries in those sizes. So, you should be able to find one for a 12 Volt rechargeable battery. But almost any input and output Voltage combination is possible. You just have to search.

        Using a battery is probably a good idea in any case. For one thing, it will allow your radio to work after dark. And these charging devices will expect a battery to be connected. They will use that battery as a big capacitor to smooth out the intermittent nature of their output. Sending that very noisy output directly to a radio is only asking for trouble. So, do use a battery. You can get rechargeable batteries in small sizes if you need to keep the weight down: D cells, C cells, even AA and AAA sized cells are available.

        If you do not want to have a battery, then you may need some extra capacitors to filter the Voltage. There are a host of DC to DC converters out there. I am talking about complete modules that only need to be mounted in an external case: no circuit design work is necessary. Just connect and use. A search on sites like Digi-Key, Newark, Mouser, and other electronic suppliers will yield results; almost too many. Your search term should be "DC to DC converter". You need to drill down the specifications until you have one with, at least, the correct input Voltage range, the correct output Voltage, the needed output current, and one which will work over a large range of input Voltages, not just one. Other search terms you may want to use are "step up" or "boost". The high end electronic sites that I mentioned make this spec selection process easy; a lot easier than going to Amazon or EBay or other run-of-the-mill web sources. Just like finding something at McMaster is a lot easier than on WalMart.

        You asked about efficiency. There is a large number of ICs that these DC to DC converters can be based on and one of the ratings for these ICs is the conversion efficiency. It will vary with Voltage and current, but numbers in the 80s and 90 are possible with modern chips and a good circuit design. There is no reason for settling for a low efficiency, like below 50 or 60 percent.
        Paul A.
        SE Texas

        Make it fit.
        You can't win and there IS a penalty for trying!

        Comment


        • #5
          I like it when people are talking about that i= not machining, well it is. No way I could afford the electric bill. Just the 3ph motor eats. Start welding? Edison wanted to put me out due to costs. F- Them!! Put some perfectly South facing panels three to keep Edison off my azz. Still charge me 10 bucks A month delivery?? Taxes no ral bill, should be about 450-320. Its paid for itself now.

          P.S. Oh I Forgot to mention. The Large Brain Trust...
          Last edited by JRouche; 02-15-2020, 05:12 AM.
          My old yahoo group. Bridgeport Mill Group

          https://groups.yahoo.com/neo/groups/...port_mill/info

          Comment


          • #6
            Could use one of thease a
            Find many great new & used options and get the best deals for DC-DC 2-24V to 5-28V 6V 12V 24V 2A Adjustable Boost Step Up Converter Module at the best online prices at eBay! Free shipping for many products!
            Helder Ferreira
            Setubal, Portugal

            Comment


            • #7
              Originally posted by Noitoen View Post
              Could use one of thease a
              Biggest problem with that exact unit is this statement in the advert:

              "10. This module is a step-up module, the output voltage is larger than the input voltage."

              As I understood the OP, that is not what was wanted, the wanted system would be from a higher to a lower voltage.

              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                J, Read it again. He HAD a 12 V panel. It stopped working but he still wants 12 V. He says that the panels he is finding are mostly 5V. He needs to step the Voltage UP: 5 V up to 12 V.

                Modern, switching chips will go either way. Many will go both ways. What he wants is out there. He just needs to search in the correct places.



                Originally posted by J Tiers View Post

                Biggest problem with that exact unit is this statement in the advert:

                "10. This module is a step-up module, the output voltage is larger than the input voltage."

                As I understood the OP, that is not what was wanted, the wanted system would be from a higher to a lower voltage.
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there IS a penalty for trying!

                Comment


                • #9
                  Makes no sense to me. 12V nominal panels are possibly the most common ones there are, and they exist in any power level. I have NEVER SEEN a 5V panel in my life. Not even one.
                  1601

                  Keep eye on ball.
                  Hashim Khan

                  Comment


                  • #10
                    How big is your panel- or what is the current rating? The specs on Noitoens module suggest that it could take as little as 2 volts and still provide up to 26 volts to the load. It implies that even a 2 volt input can deliver 12 voIts output- I wonder how true this is- it's also unclear how that efficiency rating is calculated- probably at its most efficient operating point, wherever that is on the curve. I'd like to see the curve. It's going to be important to know if it has a low idle current or not- a significant idle current will suck all the power from the solar cell at lower light levels, and will not pass anything to the load. Again it depends on how much current is available from the panel.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                    Comment


                    • #11
                      Ok, I looked at a few curves- there's one module, an MT-3608, that works from 3v and up- it's 80% efficient at 3 volts input, and that rises to 90% at 4 volts. Seems reasonable enough. This module will handle 2 amps. I'd be looking to make sure the module you select already has the input and output capacitors on board- otherwise you may have to find some first, then add them.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                      Comment


                      • #12
                        Originally posted by darryl View Post
                        Ok, I looked at a few curves- there's one module, an MT-3608, that works from 3v and up- it's 80% efficient at 3 volts input, and that rises to 90% at 4 volts. Seems reasonable enough. This module will handle 2 amps. I'd be looking to make sure the module you select already has the input and output capacitors on board- otherwise you may have to find some first, then add them.
                        You will need to have a capacitor, size depending on the pulse frequency, unless you draw from a battery.

                        And, for a boost converter, the in[ut current is much higher than the output current. All "SMPS" are really "power converters", they transform power at one voltage into power at another, with a smallish loss in the process.

                        So, if you need 1A at 12VDC, you will have to have the ability to provide 3A (plus losses) at 4VDC. And, the power is taken in pulses, with a time between them depending on the boost ratio. Each pulse is larger than the average current. So it would not be unusual for the 1A at 12 V to take pulses of 4 to 5 A. That has to come from somewhere, and the "somewhere" is the input capacitor.

                        The efficiency is usually lower for a boost converter, just because of the higher currents involved, especially with high boost ratios. The mentioned efficiency was better at 4V than at 3, for that reason. A converter to 12V operating from a higher voltage might be well over 90% efficient. (almost as good as a transformer!)
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          We haven't heard from the OP again-

                          At any rate, there's one option which we haven't talked about- that is replacing the non-working 12 volt panel. I bought a number of panels that Volkswagen used to put in vehicles to maintain the battery during shipping. I also have others which I've found at thrift stores, etc. I bought another non-working panel and reattached the wire and it works again.

                          The idea to use a 5 volt panel to get 12 volts is interesting, but since you would have to spend some money anyway, why not look for another 12v panel instead. More efficient, less trouble prone- might be more dollars, but probably a better solution. Use your 5 v panel where that's all the voltage you need.

                          I have a 5 volt panel- it came out of a car window fan unit, designed to exhaust hot air out of the car. It has a little CD player motor in it turning the fan- probably one of the more useless gadgets I've acquired.
                          Last edited by darryl; 02-16-2020, 05:12 PM.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                          Comment


                          • #14
                            Originally posted by darryl View Post
                            We haven't heard from the OP again-

                            At any rate, there's one option which we haven't talked about- that is replacing the non-working 12 volt panel. ...
                            I would say that was a plan...... There are lots of them available.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment

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