Thursday, 10 April 2014

Intelligent Automatic Battery Carger circuit

How to Make the Intelligent Fully Automatic Fast, Efficient Battery Charger circuit at home.


While i was searching for fully automatic battery charger or fast diehard battery charger what i found on google was only crap but nothing, I dont know either most of the people dont know what exactly fast battery charger is or they dont want to share that with public. Today i am going to explain How to make a intelligent fully automatic battery charger(6v 12v 48v or any) circuit.

First you should know that, we can not charge the lead acid batteries faster because Lead acid batteries are not designed to accept high current level continuously.

How fast charging is Done:

For charging the batteries faster we apply the full dose of  high current specified for that battery and when full charged automatically switch off the charging to prevent battery from overcharge. It works best for Li-ion batteries

The bottom line with Lead Acid batteries is that these can not be charged quickly unless a intelligent Automatic circuitary is incorporated.

Fast charging, It should be done in step wise mechanism means initially we charge using X1 rate and then gradually reducing the rate of charging to X1/10
as battery is getting charged we need to slow down the charging rate to prevent battery from damage and overheat. And when battery becomes full charged that need to autocut the charging operation.

The steps should be divided in 4 to 6 steps for the battery sake and its safety.

We are going to apply 4 step charging automatic circuit. you can also apply 5 steps or 6 step charging after understanding this circuit.

For stepped charging method we are using the IC LM324 for sensing the different voltage levels for switching the rate of charging according to the level of charge appearing on battery and making it  automatic or intelligent charger.

Below diagram show a automatic battery charger with 4 step intelligent battery charging 

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Components required:

R1---R4 = 10k ohm
P1---P4 = 10k ohm presets or potentiometer
T1---T4 = BC547
RL/1---RL/4 = SPDT 12V relays( 10amp contact rating)
D1---D4 = 1N4007 diode
Z1 = 6V, 1/2 watt zener diode
A1---A4 = LM324 IC

Circuit Diagram:


Here IC LM324 is a quad opamp ic whose all the four opamp here is used for sequential control or switching charging level.

Here A1 and A2 is optimised for sensing and switching the charging at different voltage levels and switching the rate of charging.

All the non-inverting input of the op-amp are refrenced to the ground voltage via a zener voltage.

The inverting input is connected with the positive supply of the circuit via the corresponding presets or potentiometer.

If we assume that the battery is a 12V battery having a discharge level of 11V, P1 may be set such that relay just disconnects when the battery voltage reaches to 12V, P2 may be adjusted to release the relay at 12.5V, P3 may be done for the same at 13.5V and finally P4 could be set for responding at the battery full charge level of 14.3V.

Rx, Ry, Rz having same values and are optimized to provide battery with the required amount of current during the various charging voltage levels.

The value can be fixed such that each inductor allows a current supply rate that may be 1/10 of the battery AH(Ampere Hour).

It may be determined by using ohm's law R = I/V;

The values of Rx, alone or Rx, Ry together can be dimensioned a little different for allowing relatively more current to the battery during the initial stages as per individual preferences, and is changable.

Working of above intelligent fast charging:

When charger is switched on and a fully discharged battery is connected across the output then:

All op-amps inverting inputs senses a corresponding lower voltage levels than the reference level of the zener voltage.

This makes all the outputs of the op-amps to become high and activates the relays RL/1, RL/2, RL3 and RL/4.

Now the full supply voltage from the input is passed to the battery via the N/O contacts of RL1 (Relay1).

Now battery starts charging at a high current rate and rapidly charges the battery upto a level above the discharged level until the set voltage at P1 exceeds the zener reference voltage.

Now the above condition forces A1 to switch OFF T1/RL1.

Now the battery is restricted from getting the full supply current but keeps charging with the parallel resistances created by Rx, Ry, Rz via the corresponding relay contacts.

It makes sure that battery is now charged to the next higher setted current level determined by the the three parallel inductors net value (resistances).

As the battery charges increases further, A2 shuts down at the next predetermined voltage level, then switching OFF the Rx and make switch on  Ry, Rz only with the setted charging current to the battery. This makes sure that the current level is correspondingly reduced for the battery as we have planned earlier.

Following the same mechanism as the battery charges to the next predifined higher level, then  A3 switches OFF allowing only Rz to maintain the required required current level for the battery, until it gets fully charged.

When it get fully charged, then  A4 finally switches OFF making sure that the battery is now gets completely switched off after attaining the required full charge.

Our method of 4 step charging ensures a rapid or fast charging with automatic or intelligent charging without harming the battery and makes sure that the battery's charge reaches at least at 95%.

Rx, Ry, Rz may be replaced with equivalent wire wound resistors, but it would mean some heat dissipation from them compared the inductor counterparts.

Normally a lead acid battery need to be charged for about 10 to 14 hours to charge 90%. 
By using above fast automatic intelligent efficient battery charger circuit the same can be done within 5-6 hours of time, that's 50-60% quicker.

Enjoy fast charging.

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