Hello friends,in our country there is often a shortage of electricity especially in the rural areas. So one of my friend wants an emergency light and also wants a socket for mobile charging for his village with a good battery backup.So this project came up here.Here it is..
Step 1: || Electronics & Hardware ||
1. 6 Volt / 4.5 Ah Rechargeable Battery: Four in numbers
2. 0-12 Volt / 3 Ampere Transformer
3. 1 watt led with heatsink: 64 in numbers
4. LM 2596 dc-dc buck converter
5. 6 Ampere diode: 4 in numbers, 1N5408( 3 Ampere Diode), 1kilo ohm resistance(1/4 watt or 1/2 watt), 5mm red Led
6. 1000 uf/25 volt capacitor: 4 in numbers OR 4700 uf/ 25 volt capacitor also be used.
7. SPST switch(One way switch): 5 in numbers
8. USB female socket, Two pin power socket , Main lead
1. Plyboard of 0.75 inch thickness is preferred.
2. Wood of 1.5"X 0.75" is preferred for better supporting.
3. 2.3 mm MDF is used .
4. 26 gauge aluminum sheet is used for led base .You can use 22 gauge to 28 gauge aluminum also.
5. 0.75" and 1 " four head screws are used for framing the build. Separate Nut and Bolts are used for mounting transformer and handle.
6. 1"x1" Aluminum Angle are used , you can use any dimension of angles which is thick enough to support the total weight.
7. 4 " Handle is used here and 1" buffer is used at the base.
Step 2: How to Build
Step one: Make two base with wood and plywood for the mounting of battery pack and the transformer and another one is for handle,sockets etc.
Step two: Connect the batteries in Series -Parallel fashion as shown in Circuit. Then using double sided tape fix battery first.Then apply RTV silicon sealent or Thermal Paste on transformer and place the wood above it for heat absorbing.
Step three: Cut Four Aluminium sheets and MDF in equal dimensions and join them with adhesive, here 10"x6" dimension is used.
Step four: Place Heatsink first with adhesive,then make series of four heatsink as shown in picture and then led's are soldered.
There are 16 parallel strings of 4 series strings of led's are to be construct.
Step five: Make a cut in aluminum sheet for placement of switches.See figures above for reference.
Step six: Place Mini switch,usb socket and power socket and also an indication led on upper base. Ensure proper cutting and fixing of sockets.
Step seven: As shown in figure mount the handle,LM 2596 module and rectifier pcb on upper base.
Step eight: Make connections according to circuit diagram.
Step nine: With the help of angles make frame around the structure and place buffer on the lower base.It is time consuming process but have to done for durability of project.
Step 3: Why and How
::When battery are connected in series,there voltage is equals to the double i.e when two 6 volt batteries are joined in series ,there total voltage because of combination is greater than 12 volt.
:: When these are added in parallel, there Ampere rating becomes doubles i.e two 4.5Ah batteries in parallel combination is equivalent to 9 Ah.
::For taking both advantages and for building 12 Volt/9 Ah battery pack,these are connected in series-parallel combination.
:: To charge a 12 volt / 9 Ah battery we need a charger.
Maximum charging current which was mentioned on the battery is 1.35 Ampere. So the parallel combination takes maximum 1.35 x 2 = 2.7 ampere.
So 3 Ampere rating transformer is used to minimize heat losses although it heats up moderately.
:: Voltage of transformer is matched with battery voltage i.e 12 Volts.Transformer voltage is always greater than 12 volt after rectification and filteration.
:: Upto 2.7 ampere current is to be rectified so we use 6 ampere diode for making bridge.If we use 1N5408 diode for making bridge it will heat up,so it is only used here for making the current direction to battery .
:: Combination of four 1000uf /25 volt capacitor is used which is necessary for filteration of pulsated dc of around 2 ampere.
:: Why 7805 voltage regulator is not used although this is shown in figure.
So when 7805 was used for obtaining 5 volt dc to usb socket,two things happened
~Burning smell came up when there is a lot of heatsink is already mounted approx. of 10 mm in thickness.
~ For an output current of 400 mA it wastes the battery power in the form of tremendous heat,so there is very little efficiency obtained.
:: Why LM 2596 module is used instead of 7805.,
so obviously because of conversion efficiency.
:: LM 2596 is simple switcher ic having capable of giving 3 Amp max. current to load with over 85% efficiency.
:: When tested at 5 volt to the connected load as mobile,input current to ic is around 250 mA and it's output current is found to be 450 mA,so there is no heat generated and negligible amount of loss in conversion from 12 volt to 5 volt which is far better than linear regulator.
Step 4: Charging and Discharging Time
**When it is tested for 3 and half hours ,the output current from battery is going down from 1.5 amp to 0.8 amp and light output is going down from 16 watt to 10 watt.
** When it is charged ,the transformer current initially jumps at 2.2 amp and slowly it saturates at 1.6 amp. The batteries are charged within 1 hour having 12.8 as float voltage.
** Expected Backup based on testing would be approximate 5 to 6 hours.
Step 5: Pros,Cons and Scope
Let's read Pros
1. Good battery backup.
2. Adequate Light Output.
4.No resistance is used,i.e no loss.
1. Doesn't have automatic cutoff Charging system.
3. Let me know
Scope of Improvement
1. Should have small mounting analog voltmeter and ammeter on the panel.
2. Damage proof cut off circuit.
3.Should have more efficacy of Led's.
4.Let me know