Workings Of A MPPT Controller

[tx2sturgis]

That link provides the answer Jim, but its kinda buried in the technobabble...I was aiming to answer Weight's question with a simple answer:

Since solar panels are not themselves voltage regulated: as the load increases, the voltage sags.

If you dead short a solar panel, current is at maximum (or nearly so)  and voltage will be at minimum, in other words, zero.

At the other end of the spectrum, with no load at all (open circuit) you will see maximum voltage for that panel and zero current.

With a carbon pile adjustable load tester, which is used to test power supplies and batteries, I could vary the voltage of any solar panel with no fancy MPPT technology at all.

Our fancy MPPT controllers find a happy intermediate range (between no load and full load) where the load applied can extract the maximum power for a given amount of sunlight.


Just FYI, PWM controllers simply switch the solar input on and off rapidly, and vary the duty cycle, to achieve 'brute force' charging.

 

[tripper]

I have slowly (over time) swapped out 3 PWM controllers for MPPT controllers, I saw a marked increase in amps (= more watts) to my 12v from the existing solar panels each time. I just spent nearly two weeks at Burning Man, I had 2 other RVs besides my own and a sound system plugged into my Solar System/inverter, with a constant pull of 600-1000 watts for at least 8 hours a day. If I let my batteries get fully charged before plugging in the other RVs, my MPPT controller would hold the voltage in float mode (putting out 600-1000 watts) all day, otherwise it would stay in absorb mode. I am 100% sure good MPPT controllers (in this case Victron) put out more total watts than PWM controllers. My RV has 3 separate solar systems feeding the 12v system.

As a side note Victron has an excel spreadsheet that will tell you how high the panel voltage can get in respect to low temperatures. My system is pushing it on the 3 big panels around -20 degrees, I think I would cover a couple of cells with duct tape in really cold temps to reduce the voltage.

 

[Weight]

What you are measuring is voltage drop across the load. The controller does not change the voltage available from the panels. It can only reduce the voltage going out of the controller. The MPPT controller can manipulate the amps when there is sufficient need from the battery. But that is limited.

 

[John61CT]

"voltage available" does not equal "voltage extracted"

Manipulating panel voltage is fundamental to how MPPT works.

Is my understanding.

 

[tx2sturgis]

What you are measuring is voltage drop across the load. The controller does not change the voltage available from the panels.

They are one and the same....voltage 'available' (when unloaded) does not matter, what matters is what the panel voltage has been pulled down to under that load. 

This is a basic fundamental principal in electronic circuit design.

If I have a small unregulated DC power supply, set for 14 volts with no load, and hook up a load, lets say a light bulb, that pulls enough amperage that the power supply voltage drops to say, 12 volts, then 12 volts IS the voltage read across the load, AND the voltage 'available' with that load.