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Anyone have experience with Renogy vs WindyNation PWM solar charge controllers?

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  • #16
    Originally posted by Bucho View Post
    With PWM controllers Amps in = Amps out.

    So those 250w panels have a Vmp of 30.4v and an Imp of 8.23a that's where the 250w comes from: 30.4 x 8.23 = 250.192

    This means that if you put them in parallel you get 8.23 x 2 = 16.46

    So you should be able to use a 20amp charge controller. It's only when we start talking about MPPT that watts in and watts out comes up.
    Does this suggest that I can use a PWM controller?
    I'm curious how this works so I'm going to restate what I think I learned, but correct me if I am wrong please.

    The 30.4V rating is more important than the 36V open circuit volt rating.
    With PWM at 30.4V and 8.23A, that's 250W in. But if the controller is converting it to 12V for the battery I only get 12V * 8.23A out = 100watts.
    So I can safely use this PWM controller, but there will be a lot of power loss, maybe a lot of heat?

    If I were to use an MPPT controller, for a 12V battery how does it deliver the full 250 Watts from 30V panels?
    Can someone show me the math please?

    Originally posted by Bucho View Post
    Glad I asked about batteries you can only charge batteries so quickly. Those batteries are way too small for your solar panels.
    You mean they'll charge so slowly that I'll need a larger capacity in case it runs out of charge?

    Anyway, this is for a school competition and we have constraints. 15Ah is the maximum allowed.
    There are several rounds, none of them use the solar panels and battery simultaneously. It's either purely solar or purely battery. I was just hoping to charge the battery in between rounds.

    Thanks.

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    • #17
      Most of the low price pwm are chinese made, the ones you linked you might be able to find cheaper on ebay under a different name. i've used the wincong brand 20 amp pwm charger on both 120 watt and my larger 240 watt panel and it worked like a champ 24/7 nonstop for almost a year till i upgraded to mppt. They do the job. From my expierence you dont need mppt on the larger panels example on my 240 watt panel pwm gets me 6 amps, mppt gets me 12 amps, but they both worked, one is more efficient but cost 5 times more, but if your on a budget pwm will work. the thing to watch is what your panel output voltage is and make sure your controller can handle it.
      The price of the wincong controller is less than 20 dollars but it has no LCD, but in my case I just bought a dc 90 volt 30 amp combo LED meter and wired it between controller and battery and can see at a glance from across the room how my battery is doing and the realtime charging current. The built-in LCD screens for voltage/amp readings are over rated and at best are only good for programming the parameters.
      For a 15 amp agm battery you would only need one 250 watt panel and pwm will easily keep it charged up, it will actually produce many times what is required. the harbor freight jump start packs are usually a 17 amp agm battery and cost about the same as the the 15 amp battery.

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      • #18
        Originally posted by jony101 View Post
        For a 15 amp agm battery you would only need one 250 watt panel and pwm will easily keep it charged up, it will actually produce many times what is required. the harbor freight jump start packs are usually a 17 amp agm battery and cost about the same as the the 15 amp battery.
        How long should I expect for it to take to fully charge the battery with 1 panel? With 2 panels?
        With 1 panel I can get 100W output, with 2 panels I can get 200W output I think.

        If I can wire 2 panels that would certainly be great!

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        • #19
          Originally posted by overtak3n View Post
          How long should I expect for it to take to fully charge the battery with 1 panel? With 2 panels?
          With 1 panel I can get 100W output, with 2 panels I can get 200W output I think.

          If I can wire 2 panels that would certainly be great!
          Like I was saying batteries can only be charged so quickly. Here's some info: http://www.solarpaneltalk.com/showth...eries-Tutorial

          It's generally c/8 some batteries could be c/4. c is your capacity, so for 15AH batteries c=15 therefore best possible case scenario with batteries that small 15/4 = 3.75. You can't charge/discharge greater than 3.75amps.

          You've been going about this whole thing backwards because you have those panels laying around. The first thing to do is figure out your load, that tells you what battery to get, that tells you what you need to charge it.

          If all you actually need is a 15AH battery then I'd suggest selling those panels to pay for what you actually need.

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          • #20
            Originally posted by Bucho View Post
            Like I was saying batteries can only be charged so quickly. Here's some info: http://www.solarpaneltalk.com/showth...eries-Tutorial

            It's generally c/8 some batteries could be c/4. c is your capacity, so for 15AH batteries c=15 therefore best possible case scenario with batteries that small 15/4 = 3.75. You can't charge/discharge greater than 3.75amps.

            You've been going about this whole thing backwards because you have those panels laying around. The first thing to do is figure out your load, that tells you what battery to get, that tells you what you need to charge it.

            If all you actually need is a 15AH battery then I'd suggest selling those panels to pay for what you actually need.
            I agree. With a maximum charging current of 3.75amps for that 15Ah battery the biggest panel he can safely use would be about 60 watts with a Vmp ~ 17v and Imp ~ 3.5amps and a 10amp PWM CC.

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            • #21
              The Math

              You've got 20V nominal panels to charge a 12V nominal battery. I go through all of the details in the video I was telling you about, I suggest checking it out. For the Readers Digest version, simple math without losses and other variables is below"

              A PWM will not convert the voltage, just pass through the current and the voltage will be pulled down to the battery voltage. So for 1 panel 8.23A for 5 hours will give you 41.15 amp hours, 8.23A x 5 hours. An MPPT will convert the voltage down, and in doing so, because of ohms law, will increase the current. 20V / 12V = 1.6. 8.23A x 1.6 = 13.16A x 5 hours = 65.8aH. That's 24.3aH more than if you used a PWM.

              However, since you are using such a small battery, you won't be able to use all that power any ways. I agree with the idea of just buy a small panel and PWM charge controller. The free panels are going to cost you more than you save.

              Amy
              Last edited by Amy@altE; 12-15-2014, 12:36 PM. Reason: oops, need more coffee
              Solar Queen
              altE Store

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              • #22
                Originally posted by Amy@altE View Post
                You've got 20V nominal panels to charge a 12V nominal battery. I go through all of the details in the video I was telling you about, I suggest checking it out. For the Readers Digest version, simple math without losses and other variables is below"

                A PWM will not convert the voltage, just pass through the current and the voltage will be pulled down to the battery voltage. So for 1 panel 8.23A for 5 hours will give you 41.15 amp hours, 8.23A x 5 hours. A PWM will convert the voltage down, and in doing so, because of ohms law, will increase the current. 20V / 12V = 1.6. 8.23A x 1.6 = 13.16A x 5 hours = 65.8aH. That's 24.3aH more than if you used a PWM.

                However, since you are using such a small battery, you won't be able to use all that power any ways. I agree with the idea of just buy a small panel and PWM charge controller. The free panels are going to cost you more than you save.

                Amy
                You mean MPPT?

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                • #23
                  Thanks Paul, yes, MPPT. Fixed post. Making myself more coffee now.
                  Solar Queen
                  altE Store

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                  • #24
                    Originally posted by Amy@altE View Post
                    An MPPT will convert the voltage down, and in doing so, because of ohms law, will increase the current. 20V / 12V = 1.6. 8.23A x 1.6 = 13.16A x 5 hours = 65.8aH. That's 24.3aH more than if you used a PWM.

                    Amy
                    If the specs say the maximum power current is 8.23A (and short circuit current is 8.81A) can an MPPT really increase the current by lowering the voltage? Will the solar panel be able to generate more current? If the current increases when the voltage lowers, and 8.81A is the short circuit current, I thought the short circuit current is the highest current you can ever get regardless of the voltage. At short circuit the voltage is nearly 0V?
                    I hope to understand these questions as this is my first time dealing with solar panels so I don't really know how if their currents are limited.

                    Thanks for all of the responses!

                    Just to clear things up a bit, these solar panels were given to be used on the competition. Every competitor is using the same panels. After the competition we must give them back. We are restricted to just the 2 panels, no other source of power generation is allowed and we can't use extra panels. The battery constraint is limited to 15Ah. Charging the battery is not a requirement, I was just wondering if it would be possible to charge it in between rounds with these panels.

                    Thanks again for all of the help and sorry for any confusion.

                    Comment


                    • #25
                      Originally posted by overtak3n View Post
                      If the specs say the maximum power current is 8.23A (and short circuit current is 8.81A) can an MPPT really increase the current by lowering the voltage? Will the solar panel be able to generate more current? If the current increases when the voltage lowers, and 8.81A is the short circuit current, I thought the short circuit current is the highest current you can ever get regardless of the voltage. At short circuit the voltage is nearly 0V?
                      I hope to understand these questions as this is my first time dealing with this.

                      Thanks again for all of the help and sorry for any confusion.
                      The MPPT controller act like a step down transformer, it convert the high voltage low ampere current to lower voltage higher amperes current. so if you have 30 volt and your batteries is 12 volts it will double the charge current on the battery side, if you have 8 amps in then you will get over 16 amps out to 12 volts.

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                      • #26
                        Well said Paul. So it's not that the panels are putting out a lower voltage and higher current, they are sending the 32V 8.23A into the charge controller, and the charge controller is converting the charge controller's voltage output down to about 17V and increasing the current.

                        The event is providing the equipment and the battery restrictions, but not an MPPT charge controller? Hmmm, trying to find something nice to say about that. Failing.
                        Solar Queen
                        altE Store

                        Comment


                        • #27
                          Originally posted by Amy@altE View Post
                          Well said Paul. So it's not that the panels are putting out a lower voltage and higher current, they are sending the 32V 8.23A into the charge controller, and the charge controller is converting the charge controller's voltage output down to about 17V and increasing the current.

                          The event is providing the equipment and the battery restrictions, but not an MPPT charge controller? Hmmm, trying to find something nice to say about that. Failing.
                          What this Posting shows is the lack of good knowledge of solar battery systems by the people putting on the event.

                          It also reinforces my feelings that the majority of people coming to this forum have preconceived ideas on what solar and batteries can provide in the way of power.

                          I feel they need to be given good & clear guidance to help them understand that what "they want" may not be what "they need" and the associated costs to build a good balanced system.

                          Comment


                          • #28
                            Originally posted by Amy@altE View Post
                            Well said Paul. So it's not that the panels are putting out a lower voltage and higher current, they are sending the 32V 8.23A into the charge controller, and the charge controller is converting the charge controller's voltage output down to about 17V and increasing the current.
                            I didn't know converters/transformers work that way. Thanks for the info.

                            Originally posted by Amy@altE View Post
                            The event is providing the equipment and the battery restrictions, but not an MPPT charge controller? Hmmm, trying to find something nice to say about that. Failing.
                            Haha yup when I figured out about the restrictions I thought it would be harder than I intended. We're constructing a solar boat and using it to race.

                            Originally posted by SunEagle View Post
                            What this Posting shows is the lack of good knowledge of solar battery systems by the people putting on the event.

                            It also reinforces my feelings that the majority of people coming to this forum have preconceived ideas on what solar and batteries can provide in the way of power.

                            I feel they need to be given good & clear guidance to help them understand that what "they want" may not be what "they need" and the associated costs to build a good balanced system.
                            I already mentioned it, a charge controller is not required. In this event it's purely solar and pure battery in various rounds. I don't think they lack good knowledge. In fact, I think if they required charging then the restrictions would be different. Hey I'm still learning.

                            Comment


                            • #29
                              Originally posted by overtak3n View Post
                              If the specs say the maximum power current is 8.23A (and short circuit current is 8.81A) can an MPPT really increase the current by lowering the voltage? Will the solar panel be able to generate more current? If the current increases when the voltage lowers, and 8.81A is the short circuit current, I thought the short circuit current is the highest current you can ever get regardless of the voltage. At short circuit the voltage is nearly 0V?
                              I hope to understand these questions as this is my first time dealing with solar panels so I don't really know how if their currents are limited.

                              Thanks for all of the responses!

                              Just to clear things up a bit, these solar panels were given to be used on the competition. Every competitor is using the same panels. After the competition we must give them back. We are restricted to just the 2 panels, no other source of power generation is allowed and we can't use extra panels. The battery constraint is limited to 15Ah. Charging the battery is not a requirement, I was just wondering if it would be possible to charge it in between rounds with these panels.

                              Thanks again for all of the help and sorry for any confusion.
                              It sounds like they gave you the panels to use in this project but not necessarily to use them to recharge the battery. Kind of confusing for me.

                              So to help you maybe you can provide the full description of what you have been asked to do and why.

                              Comment


                              • #30
                                Originally posted by SunEagle View Post
                                So to help you maybe you can provide the full description of what you have been asked to do and why.
                                We are to design a solar boat that will be used to race and tests its endurance. We are using an electric motor that we must find our selves. The specs of the motor are not restricted, however given a limited budget we will use what we have: a 12V minn kota motor with 55lb thrust. Two solar panels were provided for every competitor, 250W each. Battery we must find can be no more than 180 watts: 12V with 15Ah or 24V with 7.5Ah. We will have several rounds that include races and the distance the boat can travel in a given time (either time runs out first or the battery dies). Each round is either purely solar or purely battery. Having the solar panels connected to the battery during the rounds is forbidden. There were no requirements of charging the battery with the solar panels, that was strictly my own idea to charge in between rounds. I wanted to implement it just for learning purposes so I didn't know what to expect when I started this thread.

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