Lead Acid Battery Charger 1

Posted on Feb 6, 2014

Except for use as a normal Battery Charger, this circuit is perfect to `constant-charge` a 12-Volt Lead-Acid Battery, like the one in your flight box, and keep it in optimum charged condition. This circuit is not recommended for GEL-TYPE batteries since it draws to much current. The above circuit is a precision voltage source, and contains a tempe

Lead Acid Battery Charger 1
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rature sensor with a negative temperature co »ficient. Meaning, whenever the surrounding or battery temperature increases the voltage will automatically decrease. Temperature co »ficient for this circuit is -8mV per °Celcius. A normal transistor (Q1) is used as a temperature sensor. This Battery Charger is centered around the LM350 integrated, 3-amp, adjustable stabilizer IC. Output voltage can be adjusted with P1 between 13. 5 and 14. 5 volt. T2 was added to prevent battery discharge via R1 if no power present. P1 can adjust the output voltage between 13. 5 and 14. 5 volts. R4`s value can be adjusted to accommodate a bit larger or smaller window. D1 is a large power-diode, 100V PRV @ 3 amp. Bigger is best but I don`t recommend going smaller. The LM350`s `adjust` pin will try to keep the voltage drop between its pin and the output pin at a constant value of 1. 25V. So there is a constant current flow through R1. Q1 act here as a temperature sensor with the help of components P1/R3/R4 who more or less control the base of Q1. Since the emitter/base connection of Q1, just like any other semiconductor, contains a temperature co »ficient of -2mV/ °C, the output voltage will also show a negative temperature co »ficient. That one is only a factor of 4 larger, because of the variation of the emitter/basis of Q1 multiplied by the division factor of P1/R3/R4. Which results in approximately -8mV/ °C. To prevent that sensor Q1 is...

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