Why a Constant Current Charger
A constant current charger is highly recommended as far as maintaining safety and long battery life is concerned. Using the IC L200, a simple yet a very useful and powerful lead-acid battery charger providing constant current output can be built.
I have already discussed many useful battery charger circuits through my previous articles, some being too accurate and some much simpler in design.
Although the main criteria involved with charging batteries largely depends on the type of the battery, but broadly it’s the voltage and the current which particularly needs appropriate dimensioning to ensure an effective and safe charging of any battery.
In this article we discuss a battery charger circuit suitable for charging lead acid batteries equipped with visual reverse polarity and full-charge indicators.
The circuit incorporates the versatile but not so popular voltage regulator IC L200 along with a few external complementing passive components to form a full fledged lead acid battery charger circuit.
Let’s learn more about this constant current charger circuit.
The IC L200 produces a good voltage regulation and therefore ensures a safe and a constant current charging, a must for any kind of chargeable battery.
Referring to the figure, the input supply is acquired from a standard transformer/bridge configuration, C1 forms the main filter capacitor and C2 being responsible for grounding any left residual AC.
The charging voltage is set by adjusting the variable resistor VR1, with no load connected at the output.
The circuit includes a reverse polarity indicator using LED LD1.
Once the connected battery becomes fully charged i.e. when its voltage becomes to the set voltage, the IC restricts the charging current and stops the battery from over charging.
The above situation also reduces the positive biasing of T1 and creates a potential difference of above -0.6 volts, so that it starts conducting and switches LD2 ON, indicating that the battery has reached its full charge and may be removed from the charger.
The resistors Rx and Ry are the current limiting resistors required to fix or determine the maximum charging current or the rate at which the battery needs to be charged. It is calculated using the formula:
I = 0.45 (Rx + Ry) / Rx.Ry.
The IC L200 may be mounted on a suitable heatsink to facilitate consistent charging of the battery; however the built-in protection circuitry of the IC virtually never allows the IC to get damaged. It typically includes built-in thermal run away, output short circuit and over load protections.
Diode D5 ensures that the IC doesn’t get damaged in case the battery accidentally gets wrongly connected with reverse polarities at the output.
Diode D7 is included to restrict the connected battery from getting discharged through the IC in case the system is switched OFF without disconnecting the battery.
You may quite easily modify this constant current charger circuit to make it compatible with the charging of a 6 Volt battery by doing the simple changes in the value of a few resistors. Please refer the parts list to get the required info.
Parts list for the proposed constant current lead acid battery charger circuit.
Voltmeter, 0-12Volt FSD
How to Set up the CC Charger Circuit
Connect a variable power supply to the circuit.
Set the voltage close to the upper threshold volt level.
Adjust the preset so that the relay remains activated at this voltage.
Now raise the voltage slightly more to upper threshold volt level and again adjust the preset such that the relay just trips off.
The circuit is set, and can be used normally using a fixed 48 volts input for charging the desired battery.
A request from one of my followers:
I got your email from a website www.brighthub.com where you shared your expertise with regards to construction of a battery charger.
Please i have a little problem that i hope you could help me out:
I am just a layman with no much knowledge of electronics.
I have been using a 3000w inverter and recently i discovered it doesnt charge the battery (but inverts). We have no much experts around here and for fear of further damaging it, i decided to get a separate charger to charge the battery.
My question is: the charger i got has an output of 12volts 6Amps will that charge my dry-cell battery with 200ahs capacity? If yes, how long will it take to full and if no, what charger capacity do i get to serve that purpose? I have had experience in the past where a charger damaged my battery and i dont want to risk that this time.
My Answer to Mr. Habu
The charging current of a charger should be ideally rated at 1/10 of the battery AH. That means for your 200AH battery the charger must be rated at around 20 Amps.
At this rate the battery will take around 10 to 12 hours for getting fully charged.
With a 6 amp charger it may take ages for your battery to get charged, or simply the charging process might fail to initiate.
Thanks and Regards.