Question about Windynation "PWM" controllers

Discussion in 'Charge Controllers' started by J Stanley, Sep 18, 2020.

  1. OK, I understand electronics, SMPS, etc, and have designed quite a number of PWM devices. And I have had Solar for in excess of 20 years. I am a retired EE. Just saying this to clear the decks of assumptions and un-needed explanations.

    So, looking at the specs, with no particular explanation of how the specific units work, I see that the input voltage of the units, from the PV panels, is allowed up to around 48 or 50V, depending on model. These models are intended to use with 12 or 24V systems, considerably lower in voltage.

    Yet I see in another thread, that "Tom", Windynation engineer, suggests that the panels must be connected in parallel, with output voltage close to battery voltage. This makes no sense to me.

    What is the "PWM" control technique used for in these controllers supplied by WindyNation?

    "PWM", to me, suggests that the chargers are "buck regulator based", and can accept the higher voltages while converting them to the selected charging voltage. In the process, converting to, say, 13 volts from a 34 volt source, would lead to a charge current over double the panel current, due to the voltage change, and preserving the panel power.

    In that case, since panels typically put out around 17V at rated performance point, one would logically put two in series, for around 34V at rated performance. a 100W panel would produce 5.8A at 17V. A typical flooded battery is around 12.3V at 60% of full, and might become 13V under charge. So that would convert 34V /5.8A to 13V at about 14.4A.

    Just using the panels in parallel without conversion would charge at only 11.6A under the same conditions. That is a significant difference.

    I suppose that an alternate meaning of "PWM" is that the regulation of voltage is simply done by switching a "pass" device on and off, with no attempt at converting voltage. While possible, that would make no sense as far as maximum voltage, since most of the panel power at higher voltages would be wasted, unused. You might get only 75% of the actual power of the panels,

    Note I am NOT confusing this with MPPT, which actively seeks for a voltage that will produce maximum charge current. MPPT is just a way of controlling a PWM type "buck regulator based" charger so as to find the maximum possible power point as sun conditions change, or potential panel shading, etc occur throughout the day. It is NOT the same as voltage conversion. An MPPT controller may improve over the standard voltage converter type by another 15% to 20% as sun conditions change.

    I would assume that the "ordinary PWM" (NON MPPT) charger would simply be set to an expected panel voltage, which it would hold the panels to, adjusting current to maintain that voltage, and accepting whatever increased current that can provide at the lower charging voltage coming out of the converter.

    A smarter charger would read the open circuit voltage, and set itself to hold the panels to a FIXED voltage some amount under that, varying current draw to achieve the result.

    In contrast, an MPPT charger would actively vary the panel current draw and resulting panel voltage for max power, instead of holding a fixed voltage.

    But I see "explanations" that suggest the "PWM" controllers are not actually using the power at the higher voltage, and are therefore not able to convert power and charge at any current higher than what the solar panels produce. They may simply be turning the charge current off and on at a duty cycle to provide the desired charge current.

    Using such a device would not provide any advantage in charge current from putting panels in series, and is really just a solid state replacement for a "voltage sensitive relay", with the only significant advantage being some added metering.

    So, what is the true situation? Do the "PWM" chargers (not the MPPT unit) do actual voltage conversion, or do they just control the panel current to vary charging?
     
    Last edited: Sep 18, 2020
  2. Confirmed that these chargers from Windy Nation do NOT use the series panels, series panels in excess of the nominal 12 or 24V cannot be used with them (not unless you don't care if you get power from all of them). The MPPT version does, but is 5x higher cost vs what I paid.

    So, while I have a flush mount 30A charger, I will be replacing it with a different brand that will accept series panels.

    The "PWM" and the high voltage limit (48 or 50 V) are misleading. There is no point to accepting higher input voltage when the charger is not going to use it.

    Not recommended.
     
  3. Tuicemen

    Tuicemen Solar Guru

    The high voltage limit on a PWM controler is just that. Many panels supply higher peak voltage then they are sold as. My old shell 12 V panels supply a peak of over 20 volts on a good day. MPPT controllers use that extra voltage making them worth the extra coin.
     
  4. Yes they do. However, it is not necessary to have actual MPPT function in order to have that feature.

    Before MPPT, there were charger that had the high voltage capability and used it, employing a "PWM" buck regulator technique. Then MPPT came along as an improvement to it.

    So the current crop of "PWM" (so-called) controllers have virtually all the functionality to do the voltage step down, only they do not do it. They lack the inductor and a rectifier, but already have the control means.
     
    TomT likes this.
  5. TomT

    TomT WindyNation Engineer

    SolarPWM.png Things change but the one I have.
    Sinks the panels to 2 volts over battery voltage to a max of 14.4 DC.
    So if you did 2 panels at 22 volts this is where we get the problem.
    If the panels are 120 watts. we would get 5.45 amps at 44 volts.
    PWM would be 14 volts X roughly 5.45 A or 76.3 watts.
    Or in series 14 volts X roughly 10.90 amps or 152.6 watts.
    So mine are run in series. With PWM.
    The way they work as explained to me long ago.
    Is pwm keeps the amps and sinks the voltage to battery level.
    I have both MPPT and PWM. The PWM was just a test.
    I just haven't hooked them to MPPT controller yet.
     
    Last edited: Sep 24, 2020
    Tuicemen likes this.
  6. Tuicemen

    Tuicemen Solar Guru

    Things sure have changed since my first Trace 40 controler and mostly for the better.
     
  7. That would be about right, although the 30A flush mount here pulls down to much closer to the battery voltage, as indicated on the display (usually in error by about 0.1V, not unexpected). That will be dependent on the current being controlled. In bulk charge mode, probably nearly zero drop (for less heat loss) while when charge rate is being controlled, the voltage will rise considerably.

    The MPPT would have panels in series, and use an algorithm to find the max power point. It should do perhaps 30% or so better (adds about 1/3 more) than the ones that require panels in parallel.

    Old style non-MPPT series compatible PWM types were set to an average voltage and did perhaps 20-25% better, so MPPT adds another 5% or perhaps a bit more over what the old style PWM series compatible chargers did.

    The whole issue comes from solar panels acting as voltage limited current sources. That allows simple chargers to ignore the voltage and rely on the "current source" nature of the panels.
     
    TomT likes this.

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