Battery charging via Solar pannel

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Discussion Overview

The discussion revolves around the charging of a battery using a photovoltaic (PV) module, focusing on the efficiency of power conversion under varying irradiance conditions. Participants explore the mechanisms involved in battery charging, including the role of resistance and control circuits.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that while a fixed resistance will not draw maximum energy from the PV module, the battery showed good power conversion under both high and low irradiance, questioning the underlying reasons.
  • Another participant suggests that the terminal voltage of the battery changes as it charges, affecting the current available from the PV module.
  • A different participant emphasizes that as long as the PV output voltage exceeds the battery voltage, charging will occur, and warns about potential battery drainage when the PV output drops.
  • Concerns are raised about whether the power conversion measurements during low irradiance were accurately attributed to the battery.
  • One participant proposes that using a simple regulator with a control circuit and a PNP pass transistor could improve charging efficiency, referencing the forward voltage drop of diodes in the context of battery charging.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of battery charging and the implications of varying irradiance levels. There is no consensus on the specific reasons for the observed power conversion efficiency, and questions remain about the accuracy of measurements taken during the experiment.

Contextual Notes

Participants have not fully resolved the assumptions regarding the battery's behavior under different charging conditions, nor have they clarified the impact of circuit design on efficiency. The discussion also lacks detailed definitions of terms like Maximum Power Point Tracking (MPPT) and the specific types of batteries being referenced.

rusty009
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Hey guys, I recently conducted an experiment which involved charging a battery via a PV module and also logging the I and V values to calculate conversion efficiencies. I also logged the I and V values from two other circuits with a fixed resistance. I understand that every irradiation has a Maximum Power Point (MPPT) so a fixed resistance will never draw the maximum energy yield from the PV module. But when I saw the results I saw that the power conversion for the battery was good under high and low irradiances. My question is why is this? Does a battery have some sort of control circuit to vary its resistance ? Thanks in advance.
 
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No, but depending on the battery type the terminal voltage and so the current availabel from the PV will change as it charges.

For everythign you want to know about batteries see here http://www.batteryuniversity.com/
 
I've looked through that but I still don't understand what is actually happening.
 
As long as the PV output voltage is higher than the battery it will charge the battery. When the PV output drops, the battery will drain through the PV circuit. Many sailors have woken up to find drained batteries from either leaving their solar charger on at night or not installing diodes to keep the current flowing only to the battery.

Are you certain that durring the low irradiance test the battery was not what you measured for power conversion?
 
MythUser said:
As long as the PV output voltage is higher than the battery it will charge the battery. When the PV output drops, the battery will drain through the PV circuit. Many sailors have woken up to find drained batteries from either leaving their solar charger on at night or not installing diodes to keep the current flowing only to the battery.

The forward voltage drop of a diode is roughly 0.6 volts, and is roughly 3 times the emitter-collector drop of a saturated PNP transistor, so using a simple regulator comprised of a simple control circuit and a PNP pass transistor on the + side of the charging voltage is better.
 

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