There are various battery chargers for selling in the market. Most of chargers are to rely on the fusing of fuse to provide over-current protection and its positive and negative poles need to be distinguished when used. It would be a very dangerous thing if user reversed the polarity of charger and battery, It might fuse the fuze, or even burn down the transformer and rectifier bridge.

    A charger circuit with protective function and automatically distinguishing battery polarity was introduced in the article. Everyone can DIY or modify other ordinary charger. (Article was reproduced from the network, copyright owned by the author, if any infringement of your rights, please contact us, we will delete the information at first time.)

    Following is the circuit picture.

    After connected to the charger power, if the charger’s output port does not connect the battery, then the relay J1 and J2 don’t work, the charger’s output port doesn’t have voltage to output. As we all know, there would be 8 to 10V residual voltage between the electrode port even after a fully discharging. When A connects battery’s negative pole and B connects battery’s positive pole, photocoupler U2 cut off, Q4 cut off, relay J2 does not work, photoelectric coupler U1 breakover, the circuit’s output is a voltage that A negative and B positive after U1 breakover. It just meets the battery charging conditions and can charge the battery normally.

    When B connects battery’s negative pole and A connects battery’s positive pole, photoelectric coupler U2 berakover, Q4 also breakover, relay J2 works, then the photoelectric coupler U1 breakover, the circuit’s output is a voltage that A positive and B negative after U1 breakover. It just meets the battery charging conditions and can charge the battery normally.

     When the current during the charging process is too high, the voltage between the R13 rise, Q2 breakover, and Q5 breakover forced by R4, Q1 cut off after Q5 breakover, relay J1 off, the charger at this time has no output, thus protecting the battery and charger, the fault indicator light LED2 lightens after the machine protection. Working indicator light LED1 extinguished, then the charger power and the connecting line of battery and charger need to be disconnected, the machine would work normally after connecting charger power and battery again.