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battery charger

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kazem3d

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hi
i want to design a battery charger in constant voltage method .
but i have a question , when i want to measure the battery voltage should i disconnect power supply from battery terminal an then measure voltage or not?
 
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Answer depends on charging current and battery chemistry.
 
battery type is SLA and current is 0.5A.

Most SLA chargers use battery terminal voltage (during charging) to control the charging algorithm.

What is the AH capacity of your battery?

What voltage limit are you planning to use?

How long after reaching the voltage limit will you turn off the charger?
 
Most SLA chargers use battery terminal voltage (during charging) to control the charging algorithm.

What is the AH capacity of your battery?


What voltage limit are you planning to use?

How long after reaching the voltage limit will you turn off the charger?
battery capacity is 10ah and i want to stop charging in 13.8 volt but i dont know how long after reaching the voltage to 13.8 battery chrging must turn off, what is your recommend?
my basic question is : should i stop charging and then measure battery voltage or i can measure the battery voltage during the charging ?(i want to use avr microcontroler )
 
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As I already stated: Most SLA chargers use battery terminal voltage (during charging) to control the charging algorithm.

Here is the problem: If you connect an SLA to a 0.5A current-limited power supply whose open-circuit voltage is set to 13.7V, the battery voltage will initially be less than 13.7V, the voltage will rise as the battery accumulates charge. Upon reaching 13.7V, the supply will voltage limit, and the charging current will begin to drop. If you wait long enough (10-30 hours) after reaching 13.7V, the charging current will asymptotically decrease to ~10 to 50mA, which is the leakage (self-discharge) current for the battery. The battery is only about 80% charged when the voltage first reaches 13.7V.

I used 13.7V (not your 13.8V) because it is the correct float voltage at 25degC as specified by most SLA makers. At 13.7V (corrected for ambient temperature) the battery can be left on float charge for long periods. Read this reference for the correct temperature correction.

If you want to recharge the battery faster, you should be looking for a charger that uses the "three state charging algorithm" Your AVR will need a means of reading the charging current as well as the battery voltage.
 
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thanks
do you have any reference about charging SLA batteries.

I gave it to about three posts ago. Go read everything on "Powersteam". Also some good stuff on "Battery University"
 
the voltage will rise as the battery accumulates charge. Upon reaching 13.7V, the supply will voltage limit, and the charging current will begin to drop.
i want to use sloar panel to charge the battery that it's open circuit volatge is 21 volt .
should i use voltage regulator like lm317 for regulate voltage to 13.7?
 
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Are you asking about making a stand-alone charger, or are you going to control the charger with a micro-controller?
 
I want to make a circuit that store energy from solar panel to the battery and then use it for lighting when battery is full charged.
 
So are you planning to use the AVR as the "brains", or not?
 
Here is a simpe SLA charger circuit:

BatteryCharger12vSLA.gif
 
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Start with this. It is self-contained without intervention from the AVR. You can use the AVR as a supervisor, to disconnect the load to protect the battery when the sun doesn't shine. We can modify the circuit later to enable the AVR to speed up re-charging.

In the meantime, start simple. This basic circuit will limit initial charging current to ~ 1/2A (R5 = Vbe/Ic). It will also limit the maximum battery voltage to 13.7V (adjustable with R6) after the current tapers.
 

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i have a new idea :charging battery with solar panel (that have 21 volt open circuit) until battery voltage reach to the 13.7 and then stop charging .what is your opinion?
 
i have a new idea :charging battery with solar panel (that have 21 volt open circuit) until battery voltage reach to the 13.7 and then stop charging .what is your opinion?

Kazem,

That is EXACTLY what the circuit I posted above does!!!

You are either very inexperienced, or are a Troll.
 
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