[PROJECT REPORT] August 24, 2010
CONTENTS
SL.NO.
TOPICS
PAGE
1
Introduction
2
2
24V lead acid battery charger circuit
3
3
FAQ s
7
4
Conclusion
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| Electronics Department
[PROJECT REPORT] August 24, 2010
INTRODUCTION A battery charger is a device used to put energy into a secondary cell or (rechargeable) battery by forcing an electric through it. The charge current depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 V car battery will be very different from the current for a mobile phone battery. There are many types of battery charger such as simple battery charger that works by supplying a constant DC power source to a battery being charged, trickle charger, time-based charger, intelligent charger, fast chargers that make use of control circuitry in the batteries being charged, pulse chargers using pulse technologies, solar battery chargers that convert light into DC current, inductive battery chargers that use electromagnetic induction, etc. This project discuss in detail about the 24V lead acid battery charger circuit, its specifications, construction, working, description and applications. This charger can be used to continue trickle charge a 24V battery 24hrs a day, ideal for UPS system to continue trickle charge a battery. Its efficiency is 72 %( min) at rating power, 115Vac 60Hz.
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[PROJECT REPORT] August 24, 2010
24V lead acid battery charger
Capacity Charge Current Input Voltage No Of Charge Stages
1.5 → 12Ah 0.5A 90 → 264Vac 3
Output Power Max
14.7W
Output Voltage
24Vdc
Type
Bench-Top, Switchmode
Weight
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| Electronics Department
0.115kg
[PROJECT REPORT] August 24, 2010
1. 2. 3. 4. 5. 6. 7.
230V primary, 35V/3A secondary step down transformer 1N5003 diode (5 nos.) Capacitors(220 ÂľF/50V,100ÂľF/50V) Variable voltage regulator IC LM 317 Resistors(100 ohm,.85 ohm/2W ,220 ohm,10K) 24V/7AH battery. BC547 n p n transistor
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| Electronics Department
[PROJECT REPORT] August 24, 2010
The circuit is assembled on a good quality PCB.T1 can be a 230V primary, 35V/3A secondary step down transformer. If 3A Bridge is not available, make one using four 1N5003 diodes.LM317 must be fitted with a heat sink.R2 = 0.85 ohm is not a standard value. It can be obtained by combining a 6.2 ohm and 1 ohm resistors in parallel. F1 can be a 2A fuse. To setup the charging voltage, power ON the charger and hook up a voltmeter across the output terminals and adjust R4 to make the voltmeter read 28V. Now the charger is ready and you can connect the batteries. This charger is specifically designed for two 12V/7AH/6 cell lead acid batteries in series OR a 24V/7AH/12 cell lead acid battery.
When two batteries are connected in series, the voltage will add up and the current capacity remains same. So two 12V/7AH batteries connected in series can be considered as a 24V/7AH battery. The circuit given here is a current limited lead acid battery charger built around the famous variable voltage regulator IC LM 317. The charging current depends on the value of resistor R2 and here it is set to be 700mA. Resistor R3 and POT R4 determines the charging voltage. Transformer T1 steps down the mains voltage and bridge D1 does the job of rectification. C1 is the filter capacitor. Diode D1 prevents the reverse flow of current from the battery when charger is switched OFF or when mains power is not available.
Since a battery charger is intended to be connected to a battery, it may not have voltage regulation or filtering of the DC voltage output. A battery charger can work as a DC power adapter for experimentation. It may, however, require an external capacitor to be connected across its output terminals in order to "smooth" the voltage sufficiently, which may be thought of as a DC voltage plus a “ripple� voltage added to it. There may be an internal resistance connected to limit the short circuit current, and the value of that internal resistance may have to be taken into consideration in experiments. This charger will charge any 12V lead acid battery including flooded, gel and AGM. It is fully automatic and will charge at a rate up to about 4A until the battery voltage reaches a preset point at which it will switch to a very low current float charge. If the battery voltage drops again the charger will begin charging until the voltage once again reaches the cut-off point. In this way it can be left connected to a battery indefinitely to maintain full charge without causing damage. An LED indicates when the battery is fully charged.
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| Electronics Department
[PROJECT REPORT] August 24, 2010
1. R2 will have to be adjusted to set the proper finish charge voltage. Flooded and gel batteries are generally charged to 13.8V. If you are cycling the battery (AGM or gel) then 14.5V to 14.9V is generally recommended by battery manufacturers. To set up the charger, set the pot to midway, turn on the charger and then connect a battery to its output. Monitor the charge with a voltmeter until the battery reaches the proper end voltage and then adjust the pot until the LED glows steadily. The charger has now been set. To charge multiple battery types you can mount the pot on the front of the case and have each position marked for the appropriate voltage. 2. Q1 will need a heatsink. If the circuit is mounted in a case then a small fan might be necessary and can generally be powered right off the output of D1. 3. T1 is a transformer with a primary voltage appropriate to your location (120V, 220V, etc.) and a secondary around 12V. Using a higher voltage secondary (16V-18V) will allow you to charge 16V batteries sometimes used in racing applications. If the circuit is powered off, the battery should be disconnected from it's output otherwise the circuit will drain the battery slowly.
1. Charging wheel chairs, bicycles, and scooters in a car, van or bus. 2. Microprocessor controlled 4-stage adaptive charging algorithm suitable for Gel, Absorbed Glass Mat, VRLA, or flooded lead acid batteries. Fully automatic without intervention. 3. Output short circuit and battery polarity protections. Input low voltage and high voltage connections. 4. Charging 24 volt batteries from a vehicle. 5. Charging 24 volt "jump start" batteries from a 12 volt tow truck or service vehicle. 6. Charging 24 volt electric bicycle from a vehicle. 7. Four stage charge--constant current, constant voltage, fill, and float. This charges your battery the fastest way possible without damaging the battery. It is suitable for any size 24 volt lead acid battery. 8. Charge efficiency is 95% for the SLA, VRLA, or Gel Cell battery and 85% for the charger, making a combined efficiency of 81%. So a 12 volt 100 AH battery would be able to charge a 24 volt 10 AH battery 4 or 5 times before the host battery needs recharging.
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[PROJECT REPORT] August 24, 2010
FAQs Q. Which resistor defines the output charging current and output charging voltage? Q. What prevents the reverse flow of current from the battery when the charger is switched off? Q. What gives the application feedback of 24volt lead acid battery charger? Q: Can the charger be left connected to the battery when the charger is not turned on, or when the input voltage of the charger has been cut off? Q. What happens when the two battery are kept in series? Explain with respect to voltage and current. Q. Which component in the above circuit is used as variable voltage regulator? Q: If the battery is discharged while the charger is attached will the charger maintain a full charge? Q: Can the charger be adjusted to lower currents?
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| Electronics Department
[PROJECT REPORT] August 24, 2010
CONCLUSION A battery charger can work as a DC power adapter for experimentation. It may, however, require an external capacitor to be connected across its output terminals in order to "smooth" the voltage sufficiently, which may be thought of as a DC voltage plus a “ripple" voltage added to it. There may be an internal resistance the short circuit current, and the value of that internal resistance may have to be taken into consideration in experiments. Most modern cell phones, laptops, and most electric vehicles use Lithium-ion batteries. Internal combustion engine vehicles, such as boats, RVs, ATVs, motorcycles, cars, trucks, and more use lead-acid batteries.
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| Electronics Department