5v/12v battery is charged with auto cut off.

what is auto cut off battery charger?

some off charger maybe can't stop charging when the battery is fully charged.

So we want to show you a simple circuit for the charger when the battery is fully charged, the charging automatically stops,

This is a circuit of the auto cut off battery charger, it has only:-

- one NPN transistor such as c1815 to control the charging,

- relay for cutting off this current path through the battery after fully charged,

- 10 kilo-ohm variable resistor connected to the base of the transistor,

The variable resistor is used to restrict the voltage from how many volts you want to stop charging!

DIYers...We have all been through the situation when our high end chargers are busy charging those lithium polymer batteries but you still need to charge that 12v lead acid battery and the only charger you got is a blind one…. Yes a blind one as it never knows when it kills the battery by overcharging it…. Same goes while discharging the battery as you have no idea what charge state it's at.

Well I have got a solution for that situation as we are going to built a battery capacity level indicator by using a LM3914 IC and we are also going to add an important feature to our existing charger to cut off the charging current when the battery is fully charged

The basic idea is to design a battery level indicator but after going through the data sheet I found that we can easily control the overcharging problem by adding a relay that switches off the supply to the charger when the battery hit the max charge level.

Even though its not exactly what controlled charging is but its better to cut off the charging current before we jump above the max voltage limit stated on the battery pack thats 14.4v.

Since we are going to use 10 LEDs to indicate the battery capacity level so each LED represents approximately 10% charge.

Moreover the current through LEDs is limited using the resistor across pin 7 of LM3914 IC so we don’t need to use individual resistors for each of them.

Besides that the variable resistors R3 and R4 are used to set the upper and lower voltage levels for the battery pack that you are going to use. For the lead acid battery its usually 10.8v fully discharged and 14.4v fully charged. More on that later.

The rest you see are a bunch of complimentary components as advised in the data sheet.

I have also added the Gerber file for the PCB in this step so be sure to check it out.

Well I love it when I make it neat and that's the one thing that I always prefer. So instead of messing up everything on a perfboard I decided to build this circuit over a PCB, so I designed one. Well this step is not mandatory but these extra efforts are going to pay off later and I must say you should give it a try.

As the layout is finalized I went to PCBWAY, checked out all the options that I wanted and uploaded the gerber files. The best part about their services is that they review your design within an hour and let you know if there is any issue with it.

We received the PCBs within a week and the quality pretty much talks about its own so guys have a look at their website as they made this project possible by sponsoring it.

After receiving the PCBs, we have decided to gather the tools and components that are used in this project.

LIST OF TOOLS USED:

Soldering Iron

Soldering Wire

Multi Meter

Pliers