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arima avatar image
arima Suspended asked

How does MPPT charging controller work?

Compared with ‘shunt controller’ and ‘PULSE width modulation’ (PWM), ‘maximum Power point tracking’ (MPPT) is a more efficient DC-DC converter technology.

Using a non-MPPT charging controller is like connecting a battery directly to a solar module. A conventional charging controller can charge a battery at the voltage specified by the battery. Essentially, the voltage of a fully charged battery is higher than that of a discharged battery. As a result, an empty battery usually consumes less power than a full one.

The problem comes when we notice that we don't use power loss when our batteries are dead. Where are my powers?

The MPPT utilizes the power of the entire module by means of a voltage indicating the state of charge of the battery. The charging controller keeps voltage and current at optimal levels, enabling the module to provide the most juice.

Let's use an example to illustrate:

Suppose we use Newpowa 210w solar panels with a Vmp of 18.3 volts and an Imp of 11.48 amps. (11.48A x 18.3V = ~210 watts)

An empty 12V battery might typically have 12.2 volts. So the battery will charge 11.48A x 12.2V = 140 watts. It is significantly lower than the module's maximum usable output (210 watts).

The function of MPPT charging controller is to improve the voltage and current of the system, close to the I-V curve of the module. In this case, the MPPT charging controller charges the battery at A voltage of almost 18.3 V and 11.48 A, while maximizing the use of the solar panel.

Finally, it is important to note that maximum power point tracking is independent of solar tracking. MPPT is just the control function of the battery charger

mppt charging
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4 Answers
hjohnson avatar image
hjohnson answered ·

Well, by definition, the battery circuit will be operating at the voltage of the batteries at whatever state of charge they’re in. If your batteries are down at 12.2v, the MPPT controller will also be at 12.2v (neglecting wire losses, which are negligible). This is basic Kirchoff’s Voltage Law. (Total voltages in a circuit always sum to zero).

What the MPPT does is uncouple the voltage of the PV cells from the battery voltage so they can operate at a (much) higher voltage where they’re far more efficient. It basically loads the solar cells down until they deliver their maximum power (hence the name) and converts that power down to the battery voltage.

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Mike Dorsett avatar image
Mike Dorsett answered ·

Also please note: The maximum power point of a solar module is a function of irradience, and therefore not unrelated to tracking. This is further complicated by the possibility of two or more modules in series - if one is part shaded, this can create a kink in the maximum power curve which can only be found by 'sweeping' the tracker. The best way of looking at an MPPT unit is as an impedance matching circuit. The MPPT units behave best when operating near the high end of the input voltage range. This also reduces the current in the PV string cabling, which if long can cause significant loss.

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kevgermany avatar image
kevgermany answered ·

Also, when a battery is at 12.2V standalone, to charge it the MPPT has to apply a higher than 12.2V to force more charge in. The charging voltage is limited by available PV power (as Mike said) as well as the programmed battery/charging parameters.

MPPT regularly adjusts the current it draws from the panels (hunts) to determine the available power at that time.

There's a good graph of the fall off in PV voltage as current rises in the Victron MPPT manuals.

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steffen-graap avatar image
steffen-graap answered ·

An MMPT is not a shunt regulator with an MPPT algorithm, but a DC-DC converter with an additional MPPT control algorithm.

Like every DC-DC converter, it keeps the power constant (with the deduction of the loss due to the efficiency) when the voltage is reduced from 18.3V to 12.2V, on the other hand, it increases the charging current from 11.48A to 17, 22A (theoretically without losses). So input power equals output power (210W).

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