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Complete Newcomer, 100W system, help with loss of power through controller

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  • Complete Newcomer, 100W system, help with loss of power through controller

    Hi there, I am a complete newcomer to solar power so please forgive my ignorance! I am having some problems getting things going as I had expected and wondered if anyone could be of help.

    I have recently purchased a 100W 12V panel and a 22Ah 12V battery. I have the panel connected to the battery through a PWM charge controller (the cheap blue Anself 10A one available on Amazon) and all appears to be fine, controller reads battery voltage (11.9V) and implies that it is charging the battery when the panel is in sunlight. However it seems to be taking an age to charge the battery, in fact after more than 1 week albeit in grey UK weather conditions but without any load it has not gained as much as 0.1V so I am suspicious something is not working right. I noticed that the open circuit voltage and current direct from the panel is approximately 20V and 1A respectively (I assume this to be normal for a sunny winter day in the UK). However when I measure what is being supplied to the battery I see that it is only just over the present battery voltage (approx 12V) but worse the current is less than <0.1A. So my question is where has all the power gone? I was suspecting at very least my battery would be charged at 1A and ideally higher (due to the change in voltage). Are PWM controllers really that inefficient, could something be faulty? or am I simply being stupid and this is normal? I had hoped I had overspec'd my panel enough to provide power to a small security camera even through the winter in the UK but at this rate i;ll be charging the battery myself every few days! I have charged the battery via the mains to test the battery and although I couldn't seem to fully charge it it does seem to comfortably hold steady around 12.4V. Any help and advice would be much appreciated.

  • #2
    Solar panels need full sun (sharp crisp shadows on the ground) or they produce very little power.
    In cloudy weather today, my 5,000 w of pv panels produce 200 w not very good.
    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 assume you have some method to measure current. Connect The panel directly to the battery through the amp meter. This is what the PWM does. That would rule out the controller. Assume the current measurement was made with the panel short circuited. This can be a false reading. I've had panels go bad that still produced near rated amps but had weak cells. Try the shorted test with a 10-15 0hm resistor in series ( two 5 ohm 10W in series would be a common part). If current drops dramatically it could be a panel problem. And bad days, welcome to the world of solar.

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      • #4
        Once the sun comes out remember that one should always connect the battery to the controller first, and the panels last. If you reverse this procedure, controllers can get confused thinking you have a zero-volt battery and refuse to charge. Or some may go into a failsafe float-only mode.

        And at 11.9v ocv, your agm is practically dead and is now sulfating. Grab a CTEK or Tecmate-Optimate charger which should be available close to you and save that thing.

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        • #5
          Many thanks all, so I connected the panel briefly to the battery and got a current reading of 0.5A compared to my open circuit reading of 0.5A (the weather is even cloudier today). Hopefully this means the panels are OK (they are brand new after all). With the controller back in place the current going to the battery was 0.4A so much improved, perhaps due to being careful to do as you say PNjunction. Would this appear to be working normally now? My understanding is that the panels are producing approx 10W (20V x 0.5A) of power but yet the controller is using only 4.8W (12V x 0.4). I know this voltage drop and the controller use power but less than 50% efficiency seems pretty poor. What are others experiences?

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          • #6
            No, the battery will lower the panel voltage. It will nearly be exactly the same voltage as the battery. The panel produces 20V now because when it is really hot it will drop down to 16V. You are also mixing terms, current can not be measured open circuit. It is not that the controller is inefficient. Current that goes in is the same as the current that goes out. MPPT is like a transmission that exchanges higher voltage for higher current. The most power, volts X amps, is generated at about 18V depending on panel temperature.

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            • #7
              Originally posted by tinted View Post
              Many thanks all, so I connected the panel briefly to the battery and got a current reading of 0.5A compared to my open circuit reading of 0.5A
              Let's see if we can get you on the right track by you finding the problem yourself. First you did not read 0.5 Amps in an Open Circuit as that is impossible because no current can flow in an open circuit. Otherwise no switch or anything electrical would work.

              With PWM Controllers Output Current = Input Current. This is what makes them so inefficient of 66% - 68% at best. Look at your panel ratings and look for Imp which is Current @ Maximum Power should be around 5.8 amps right. 5.5 amps into a 12 volt battery = 5.5 amps x 12 volts = 66 watts.

              One clue you gave and you did not know is when you said your panel connected to the controller had an input of 20 volts @ 0.5 amps or 10 watts makes no sense., or a bad test result. A PWM Controller is really nothing more than a SWitch that is either Open (off) or Closed (on) like a light switch. Assuming your battery voltage is low like you indicate of 12 volts, with the panel and controller connected and operating correctly, the Controller Input Voltage = Battery Voltage approximately. Input should be ever so slightly higher of .1 volts or less. Now as the battery becomes fully charged around 14.4 volts you will see the Panel Voltage go higher toward Voc or Voltage Open Circuit. When no current flows then you should read Voc at the input of the Controller, and battery voltage should read around 14 volts and no charge current because current cannot flow in an open circuit. So if you see 20 volts on the input of your controller and 12 volts on the output with battery properly terminated, you know you have a problem that needs to be isolated and resolved. So let's get to work and find it.

              The first two test are done with the panel and a DMM capable of measuring both Voltage and Current up to at least 10-Amps. This is done outside, around noon, with bright Sun, and panel facing directly at the Sun. You are going to measure the panels Voc (voltage open circuit) and Isc (current short circuit). Catch that? Open Circuit and Short Circuit? To do this requires you to fully understand how to set your meter up to read Current or Voltage. Most every DMM has 3 Input ports: Common (negative) is used for all measurements and usually color coded BLACK which you plug your BLACK Test Probe into. For current measurement up to 10 amps should be clearly marked and you plug your RED test probe into this port to measure current ONLY. The 3rd port is for all other measurements including voltage which you plug your Red test probe into. Make sure you understand how to use your meter especially for CURRENT. Understand????

              OK to do the test click here for instructions how to perform VOC and ISC Test. Note Voc should be very close even with cloudy skies. For Isc you will never measure what the spec is even if you are on top of a mountain, located at the earths equator, with crystal clear bright blue skies at solar noon. Just not going to happen. Solar panels are current sources and current is directly proportional to the amount of sunlight striking it surface. In doomy gloomy England summer you will not even come close to Isc. In winter even on a clear day at noon I would I not expect more than 30% of Isc spec. If that checks out OK, time for the next test.

              Next for fun let's connect the panel to then battery directly using your meter set up to measure Current use din place of a wire. Real easy and a great method to measure actual current in a circuit. Sorry no drawings here but super simple now that you have mastered setting up your meter to measure current. Take your battery outside with you when you start the Isc and Voc test above. Once Isc/Voc test are completed and passed, connect the panel Negative wire directly to the battery Negative Term Post. Now take the Panels Positive Wire and connect it to your meter's Red wire, and then connect the meter's Black wire to the battery Positive Term Post. Make sure the meter is setup for CURRENT. As soon as you complete the connections, you should see positive current flowing from the panel into the battery Your meter is used as a WIRE when measuring current. Just like your PWM controller is a switch that is turned on or a short circuit. In fact you can charge your battery this way.

              If all the above test pass, time to connect the battery to the Controller first, then connect the panel. In fact use your meter set up to measure current in in the battery circuit to test the system as a whole. Perform the above test, and you will find your problem all by yourself. It is the only way.
              Last edited by Sunking; 01-08-2017, 01:06 PM.
              MSEE, PE

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              • #8
                Sorry as I said I am new to this and yes I meant short circuit current.

                Thanks for the explanation Sunking, I think you misunderstood me as I have already done everything as you said, measured open circuit voltage and short circuit current, connected directly to the battery and measured more or less the same current and voltage just above that of the battery voltage. With the controller connected I am now getting similar results to that of the direct connection to the battery. So it seems everything is working as it should and I just need to wait for some more sun and hence more amps!. So if PWM controllers are so inefficient, and I guess I didn't appreciate the concept of current in = current out, would you recommend using MPPT? It was my understanding these were only really useful for high voltage applications. I'm guessing as the current goes up and the voltage goes down this loss will be less of an issue for me but I'd be interested to know what kind of efficiency increase I'd be looking to get under my current conditions. Can anyone recommend a cheap MPPT controller if so?

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                • #9
                  Why don't we wait for full sun, and get what you already have up and running....

                  Newbie caution when measuring ISC and VOC - have some spare fuses handy. In your zeal to measure voltage, and then current, it is tempting to just rock the multimeter knob without disconnecting AND MOVING THE METER LEADS on the multimeter itself first. POOF. This is assuming you are doing this with nothing but the panel and a multimeter with nothing else attached.

                  How critical is this 22ah battery application? What are you doing with it? Also consider that mppt for you at this point means an additional purchase of a higher voltage panel than the "nominal 12v" panel you have now.

                  Also try to avoid going "cheap" with anything solar. If that is your prime motivation, then you can easily be sold a "cheap and cheerful" mppt controller, which is nothing but a fake, and only a simple pwm inside. A quality PWM controller obviously beats a fake mppt controller, and in many instances, cheap mppt's with absolutely horrid buck-boost algo's and hardware make them a ripoff too. Quality mppt cost$.

                  So keep the real world in mind - are you just charging up cellphones with that battery?

                  How about that charger? I guarantee you that agm is sulfated to a point, and could really use a reliable charge to start out with.

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                  • #10
                    I have some Morningstar SL controllers and I swear they don't do anything for the first five minutes they are connected to a battery as they figure out state of charge or whatever. That also might have been what you were seeing in some of your testing.

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                    • #11
                      MPPT controller is a Power Converter, not a Series Regulator. With MPPT Output Current = Panel Wattage / Battery Voltage.

                      Assuming your batteries are demanding current, Panel voltage is at Vmp of the panel. With a 100 watt panel roughly 18 volts. As the battery charges and curent tapers off the voltage will rise toward Voc.

                      MPPT can be used with battery panels but you loose the benefits of a higher voltage. Example let's use two 100 watt panels. One like yours with a Imp = 5.55 amps, and Vmp = 18 volts. Panel 2 is 100 watts with an Imp = 1 Amp, and Vmp = 100 volts. Other than voltage what changed? With both setups the controller output current is 8.33 amps.

                      The advantage of High Voltage is obvious. The 100 volt panel with 1 amp would use much smaller wire and will eliminate most of the Power loss on the wiring between panels and controller. You can buy a 600 Volts controller to charge a 12 volt battery.

                      To your question if you should use MPPT, at 100 watts is not really worth the effort because your battery is grossly undersized for 100 watts. Even with PWM at 5.5 amps is more than your battery can handle.

                      Almost forgot, another excellent reason to use MPPT is so you can use Grid Tied panels which are higher voltage than a battery panel like you have. Here is the catch $/watt a battery panel cost 2 to 6 times more than GT panels per watt. You could have bought a 200 watt panel, for the same money.
                      MSEE, PE

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