12v Battery Charger Circuit with Auto Cut off

[muhammad59]

1-what will be the voltage on( cv or pin 5)coz it internally connect to voltage divider


**broken link removed**
Working

• Positive terminal of the upper comparator of 555 is connected with reference voltage in order to turn OFF the charger if the battery charges above 13.8V.
• why they said Positive terminal ?????? i think ( cv or pin 5) is negative terminal

 

[alec_t]

The voltage on the CV pin will be 5.1V because of the zener diode.
They said 'positive terminal' meaning 'non-inverting input'.
BTW, if a standard NE555 is being used in that linked circuit then it will probably fail because its rated absolute maximum supply voltage is 18V (as per the TI datasheet) and the diode bridge is supplying 19.8V peak (15*√2-1.4).

 

[muhammad59]

The voltage on the CV pin will be 5.1V because of the zener diode.
They said 'positive terminal' meaning 'non-inverting input'.
BTW, if a standard NE555 is being used in that linked circuit then it will probably fail because its rated absolute maximum supply voltage is 18V (as per the TI datasheet) and the diode bridge is supplying 19.8V peak (15*√2-1.4).

thanks for replay : but i think( pin 5 or cv )always inverting input not inverting input

 

[audioguru]

Another student in your class asked about this same horrible circuit on another website forum and I answered:
"Like many circuits from that website, this circuit is WRONG.
The reference voltage for the pin 6 comparator is 5.1V by the zener diode so when the battery voltage is 5.1V or higher then the charger turns off. Stupid!
The pin 2 voltage is the battery voltage divided down by the pot so when the battery voltage becomes lower than the pot divider setting then the charger turns on. That works fine."

 

[gary350]

I assume your talking lead acid car battery?

Lead acid batteries are self controlling. When the battery is low it suck in the amps at a very high rate but when the battery has a 90% charge the battery charges at a very low rate. When the battery is full it wont charge.

Wire resistance if very important at low voltage trash those 14 gauge battery charger wires and replace them with 8 gauge stranded copper wire and keep the wires short as possible. A small voltage drop on the wires can make a big difference at this low voltage.

Charge load voltage needs to be 15 volts when connected to the battery. If you charge a battery at 14v the 1 volt difference can make a big difference, battery might never get a full charge. Worse thing you can do to a battery is let it get below 50% charge and NEVER give it a full charge. It is like trying to put 30 psi air pressure into a car tire with a 25 psi air compressor it can not be done.

Put a GOOD meter on the battery. It will suck in a lot of amps if it is low but 24 hours later it wont be sucking in many amps. Battery voltage might be 13.4 volts when you start then 13.7 volts tomorrow. Watch your meters when voltage is at its highest voltage about 13.8 the amps will be lowest, about zero. Let the battery rest 1 hour before you test it or use it.