Thursday, February 12, 2015

Top Solar Battery Charger Circuit Schematic using LM317T

Eltronicschool. - Here is Top Solar Battery Charger Circuit Schematic using LM317T. This is the most simple and affordable solar battery charger that the hobbyist can make. It has a few drawbacks over other similar controls, but offers numerous advantages. It is intended for charging lead-acid batteries, but may also be used for charging any battery at a constant voltage. Voltage output is adjustable. The circuit schematic Top Solar Battery Charger using LM317T like in figure 1 below.

Circuit Schematic

Figure 1. Top Solar Battery Charger Circuit Schematic using LM317T

Component List

  1. C1 0.1uF
  2. U1 LM317T
  3. R1 220
  4. R2 680
  5. R3 2K Variable
  6. D1 3A, 50V Schottky


Circuit schematic like in figure 1 above is Top Solar Battery Charger using LM317T. When you apply the circuit in real condition you will get many advantages as follow:

1. Minimum Head Voltage

This is also referred to “drop-out voltage.” The input voltage must exceed the output voltage by about 2.75V @ 1.5A. Fortunately, when the battery discharged, the output voltage is lower so the solar panel voltage will also be lower.

2. Maximum Power Dissipation

In this solar battery charger project the power is limited by the thermal resistances of both the LM317T and the heat sink. To keep the junction temperature below the 125°C Max, the power must be limited to about 10W. If a smaller or less effective heat sink is used, the maximum power dissipation must be de-rated. Fortunately, the LM317 has internal temperature limiting so that if it gets too hot, it shuts down thus protecting itself from damage. Max power comes into effect when charging a 12V battery @ 1.5A: e.g. battery voltage = 12V, solar panel = 18V. P = (18V – 12V) * 1.5A = 9W. So thermally, it is carefully matched to the current rating.

3. Current Limiting

Current limiting is provided by the solar panel—it is not a commonly understood fact that the solar panel tends to be a constant current device. For this reason, a solar panel can withstand a short circuit.

4. Float Charge of Lead-Acid Batteries

This control charges the battery at a constant voltage and also maintains a charged battery (float charge). The float charge voltage specification is a little lower, so to accommodate both charge and float charge voltage, a compromise is reached by simply reducing the voltage slightly—that is how ALL automotive systems operate. To obtain maximum charge in a 12V battery, set the control to 14.6V. Automotive systems further reduce voltage to 13 to 13.5V in order to accommodate high temperature operation as the battery is usually located in the hot engine compartment—battery has a negative thermal coefficient of voltage.

5. Solar Battery Charger Protection

C1 provides substantial protection against static discharge.
There is no protection against reverse polarity or mis-wiring. It is protected if solar panel is connected reverse without battery connected, or if battery is connected reverse without solar panel connected.

The Original Article : "Solar Battery Charger Circuit"

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