MPPT Design

Im working on a power supply board which takes power from solar cells, charges some batteries, and distributes power to 12 loads which can each be turned off and on independently. I want to maximize efficiency so I I’m trying to implement an MPPT circuit, but I’m not sure I fully understand the concept.

To the best of my understanding, the solar cells feed into a switching converter to produce the battery charging voltage. The duty cycle of the converter is varied to tune the output voltage until the maximum output power is achieved, measured by a power sensor at the converter output. Is this how it works?

Doesn’t the battery require a very specific voltage range to charge safely? The nominal charging voltage in the data sheet for my batteries is 4.2V. Would an MPPT circuit generally give a higher or lower voltage than that? Is there any danger to the battery?

I’m planning to have pairs of high efficiency cells (~%30) in series (max 5V, 500mA per pair) and have 3 to 6 pairs in parallel. The batteries will be four 18650 cells in series so I guess the charging voltage should be between 16 and 16.8V.

MPPT is all about matching a load to the solar panel; it has nothing to do with charging batteries, only indirectly.

Imagine that you wanted to heat water with a resistance heater powered by a solar panel. What would the resistance of the heater have to be to heat the water in the shortest time.? When you understand how to find the resistance value, you will understand mppt.

Knowing about mppt teaches you nothing about charging batteries. Two separate problems.

As Mike noted, MPPT and charging batteries are separate functions, but they can be combined in one circuit.
The MPPT circuit optimizes its input voltage and current for best efficiency in extracting power from the solar panel.
The battery charging circuit optimizes the output voltage and current for proper battery charging.
The input voltage from the solar panel and the battery charging voltage are, in general, different.
The MPPT circuit uses switching circuits to perform this voltage conversion.

If the battery can't take the full power from the solar panel, then the circuit will have to reduce the charging power to the battery and thus cannot operate at the MPPT point.

crutschow said:

If the battery can't take the full power from the solar panel, then the circuit will have to reduce the charging power to the battery and thus cannot operate at the MPPT point.

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Profound!

This happens any time the batteries are charged. (Full)

ronsimpson said:

Profound!

This happens any time the batteries are charged. (Full)

Click to expand...

Thanks for stating the obvious.

But I was referring to a battery that is charging but its maximum charge rate is below what the panel can deliver.

crutschow said:

Thanks for stating the obvious.

Click to expand...

I have had trouble explaining why MPPT and battery charging is two separate things.
What you said turn on the light. lol
If you can not store/use the entire power then MPPT can not function. Very simple. (there are many reasons why all the power can not be used)