Calling on Solar Techies
I have been thinking of going solar for some time and decided to pull the plug. My wants are a 400 to 500 watt system. I have four 12 volt batteries with 340ah. I am not planning on changing b...
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The MPPT is operating as it always does - as a buck (or in some cases a boost) converter, regardless of the charging phase. The difference between this and PWM is that current in != current out. With PWM I_in = I_out, always.
This is often not a big deal, but if you have loads running while in float, it can be. You want to support the loads off of the solar as much as possible. If you can't convert the extra panels volts to current then you are throwing away power that then has to be put back into the batteries by the solar panels. So in short, MPPT is working even in float.
On technical note, a buck converter has a large inductor in it, so while you are PWM'ing a transistor on the input side, as long as the inductor isn't saturated you won't see the voltage move as the field collapse in the inductor is holding the voltage up. This is different from PWM where you will see the voltage oscillate up and down based on the state of the transistor.
This is often not a big deal, but if you have loads running while in float, it can be. You want to support the loads off of the solar as much as possible. If you can't convert the extra panels volts to current then you are throwing away power that then has to be put back into the batteries by the solar panels. So in short, MPPT is working even in float.
On technical note, a buck converter has a large inductor in it, so while you are PWM'ing a transistor on the input side, as long as the inductor isn't saturated you won't see the voltage move as the field collapse in the inductor is holding the voltage up. This is different from PWM where you will see the voltage oscillate up and down based on the state of the transistor.
BFL13 wrote:
In Float the MPPT controller keeps the voltage to the battery at the Float set-point, but the issue is the controller wrt the panel voltage.
The panel voltage that you can measure is actually a sort of average between on and off farther down (higher voltage) the IV curve knee than Vp and it varies with the load changes during Float.
If you don't want to call that on/off "PWM" give it another name, but some or all MPPT controller booklets call it PWM.
