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IV Curve with MPPT Charge Controller

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  • #76
    Originally posted by BackwoodsEE View Post
    We are in the thick of the smoke from British Columbia's forest fires right now. The max power from my three panels is about half what they'd be capable of in full sun.
    If I may ask, if the sweep identified the maximum power point as 318 W, from 3.84 A and 82.8 V, how come the live reading is showing only 183 W (1.91 A @ 95.9 V)? Was the sweep run under different atmospheric conditions than those at the time of the live reading? Or, are you not in bulk charging, so the controller is intentionally off the maximum?
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #77
      Dang smoke
      I'm not even reaching Absorb today, and that's with irrigation pump off. Generally I have 300+ min of float after 2 hr of absorb.
      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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      • #78
        And now it just dropped to 188 W, a little less than a third of available power under clear skies. It's interesting to see the visible effect of this haze so precisely quantified by the PV array.

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        • #79
          Originally posted by sensij View Post
          If I may ask, if the sweep identified the maximum power point as 318 W, from 3.84 A and 82.8 V, how come the live reading is showing only 183 W (1.91 A @ 95.9 V)? Was the sweep run under different atmospheric conditions than those at the time of the live reading? Or, are you not in bulk charging, so the controller is intentionally off the maximum?
          The latter. The charge controller was at the tail end of absorb, and the only real power being consumed was from the inverter.

          Incidentally, I've come to the conclusion that this charge controller (Morningstar TS-MPPT-150) tends not to bother with a sweep when it is receiving all the power it needs at its present voltage setting. That makes sense. I had to induce it to do this sweep by adding a big load to the inverter. It swept the voltage, although not that far down, and then put itself a bit to the right on the IV curve where it pulled less current than was available.

          When it gets closer to needing whatever is available, it does the sweeps fairly regularly, but I've seen it go hours without a sweep when it's in absorb and not needing much. (With my tiny 12V 100 Ah battery for this toy setup, and clear summer skies, that is most of the day.)

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          • #80
            I suspect it never sweeps when the draw on it is less than what is there. Just acts as a resistor (or battery) to raise it's resistance (or voltage) [not sure which model makes more sense in this case] until the power in matches the power out. Wasn't that the essence of what Sunking was trying to say early in the thread, that you need to ensure that it is in a mode which enables the MPP seeking algorithm(s)? I don't know, but still enjoying the presentation.

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            • #81
              Originally posted by BackwoodsEE View Post
              I've seen it go hours without a sweep when it's in absorb and not needing much. (With my tiny 12V 100 Ah battery for this toy setup, and clear summer skies, that is most of the day.)
              It will never sweep once in Absorb Mode because it is no longer MPPT and has switched to PWM mode operating as a Voltage Source between Vmp and Voc where Input Current = Output Current.

              Absorb, Float, and Eq are Voltage modes, there is no Current Boost or I should say no Power Conversion taking place any more. Once in Absorb, Float and EQ basically is just a plain ole series PWM voltage regulator.
              Last edited by Sunking; 08-05-2017, 11:20 AM.
              MSEE, PE

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              • #82
                Originally posted by BackwoodsEE View Post

                The latter. The charge controller was at the tail end of absorb, and the only real power being consumed was from the inverter.

                Incidentally, I've come to the conclusion that this charge controller (Morningstar TS-MPPT-150) tends not to bother with a sweep when it is receiving all the power it needs at its present voltage setting. That makes sense. I had to induce it to do this sweep by adding a big load to the inverter. It swept the voltage, although not that far down, and then put itself a bit to the right on the IV curve where it pulled less current than was available.

                When it gets closer to needing whatever is available, it does the sweeps fairly regularly, but I've seen it go hours without a sweep when it's in absorb and not needing much. (With my tiny 12V 100 Ah battery for this toy setup, and clear summer skies, that is most of the day.)
                Thanks. It is nice to have the real data you've shared to fortify against some of the nonsense that flies around here sometimes.
                CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                • #83
                  Just in case you were sitting at your computer hitting "refresh" waiting for another plot, here's one from just now. Bulk mode charging with about 200 W of inverter load. Charge controller is taking everything it can get. Full sun (clear skies with no clouds or smoke) coming in at a bit of an angle to the array.

                  Capture.PNG

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                  • #84
                    Originally posted by Sunking View Post
                    Absorb, Float, and Eq are Voltage modes, there is no Current Boost or I should say no Power Conversion taking place any more. Once in Absorb, Float and EQ basically is just a plain ole series PWM voltage regulator.
                    Nope. The switchmode power converter is still running, and you still get all the benefits of an MPPT controller (i.e. bucking a 120V array down to 58 volts, at up to twice the current) while in absorb. It does NOT switch to series PWM controller type operation. The only difference is that the MPPT algorithm is no longer running; the voltage of the panels is allowed to rise until it hits the limits of its own VI curve.

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                    • #85
                      Originally posted by jflorey2 View Post
                      Nope. The switchmode power converter is still running, and you still get all the benefits of an MPPT controller (i.e. bucking a 120V array down to 58 volts, at up to twice the current) while in absorb.
                      Jeff you might fool most on here, but not me.

                      MSEE, PE

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                      • #86
                        Originally posted by jflorey2 View Post
                        Nope. The switchmode power converter is still running, and you still get all the benefits of an MPPT controller (i.e. bucking a 120V array down to 58 volts, at up to twice the current) while in absorb. It does NOT switch to series PWM controller type operation. The only difference is that the MPPT algorithm is no longer running; the voltage of the panels is allowed to rise until it hits the limits of its own VI curve.
                        This really does agree nicely with the data shown in post 75. The controller is in absorb, and ran a sweep showing that 318 W was the maximum power point, at 82.8 V and 3.84 A. The power conversion circuit drove the operating voltage up to 95.9 V, producing 1.91 A and 183 W. There is no way Input current = Output current in that condition.

                        What if we assert that the OP's data collection is only picking up *average* voltage and current, not instantaneous (which is unlikely based on the sample rate, and the resolution with which the 120 Hz ripple is shown in some of the early posts)? The 95.9 V could be the average of a square wave bouncing between Voc and Vbat, but you'd have to explain how 183 W could be delivered to a 12 V battery if the controller is operating in that simple PWM mode. With the battery at 14.4 V, to get to 183 W you'd need 12.7 A from a single string of 3 panels in series, with an Isc rating <10 A. Not possible under these conditions.
                        Last edited by sensij; 08-18-2017, 01:40 PM.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                        • #87
                          Both my Classic and Morningstar will display MPPT Float under certain conditions. MPPT seems to be more "on demand" than only in bulk.

                          However, in the case of cheap imported controllers, MPPT or a crude version of it, likely only operates in bulk

                          Float-MPPT_classic.jpg
                          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

                          Comment


                          • #88
                            Riddle me this. What happens when Controller Input Current = Output Current

                            One thing you know for sure, you are not operating @ MPPT Vmp. Something has changed. There is no current Boost and most likely not using a chipset that does Buck.
                            Last edited by Sunking; 08-18-2017, 03:14 PM.
                            MSEE, PE

                            Comment


                            • #89
                              Originally posted by Sunking View Post

                              One thing you know for sure, you are not operating @ MPPT Vmp. Something has changed. There is no current Boost and most likely not using a chipset that does Buck.
                              In the data shown in post 75, the controller is in absorb. The current is boosted from 1.91 A to something around 12 A. The output current isn't shown, but the input power is shown, battery voltage is approximately known, controller efficiency can be accounted for.

                              You are right, it isn't operating at Vmp, but the controller still ran enough of an IV curve sweep to show what Vmp would have been. The 95.9 V operating point is between Vmp and Voc, as we'd expect, and is efficiently converted to the constant 14.4 (or whatever) battery voltage that is being held for absorb. I don't understand why you are fighting this.
                              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                              Comment


                              • #90
                                Originally posted by Sunking View Post
                                Riddle me this. What happens when Controller Input Current = Output Current
                                In an MPPT controller, the voltage at the panels is very high (close to Voc) and the buck converter is running at a relatively low duty cycle.
                                In a PWM controller, the voltage at the panels is very low (close to battery voltage) and the switch remains closed.
                                One thing you know for sure, you are not operating @ MPPT Vmp. Something has changed. There is no current Boost and most likely not using a chipset that does Buck.
                                The buck converter is still running, just at a lower duty cycle, sufficient to maintain the voltage at the output at a lower current. That's how they work. Power electronics 101.

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