MC34063 Battery charger

[dave_j_fan]

Trying to make 12v 7AH battery charger

added Booster circuit in attachment . Original MC34063  ic based booster circuit had TIP41 replaced with 2N2222

and 180E  to 220E , using 330UH coil inplace of 100uH

the circuit gives 14.2V after VR is adjusted
but direct connect to SLA battery ( lead acid) , i  goes like in a short circuit mode
(MY diy  800mA 20v power supply shows that ) .

on the output to I have checked adding 12E series resistor to battery .
This limits current to 50mA and circuit works but the current is too low .


Why this circuit?
common 12v adapters i want to use as a charger for LEAD acid


help needed to make a charger that gives atleast 200-300mA

[David Hess]

The peak current is configured to almost 3 amps by R1 at the 0.22 ohms but the 2N2222 is only rated to about 0.8 amps.  Either increase R1 to at least 1 ohm limiting the current to about 0.6 amps or use a higher current transistor for Q1 like the original TIP41.  I would start out with a lower current limit and just using the internal 1.5 amp transistor.

Also keep in mind that the inductor has to sustain the peak current without saturating.  It must be a power inductor.

[dave_j_fan]

Thank you . I will try that .
A dual 2n2222 will help

[schmitt trigger]

Thank you . I will try that .
A dual 2n2222 will help

Unless you make arrangements to make sure that the current shares equally among both transistors, it would be always a better idea to use a single, higher current transistor with adequate heat sinking.
The TIP31 should be available worldwide at a very reasonable cost.

[mikerj]

This isn't really a suitable circuit for charging a 12v (nominal) lead acid battery from a 12v source.  If the battery is fairly discharged it's voltage could easily be below that of the power supply, in which case the current will be limited only by the DC impedance of R1, L1, D1 and the battery being charged.  A standard boost regulator can not regulate or current limit output voltages below the supply voltage.

For situations where the output voltage could be above or below the supply voltage you need a different regulator architecture such as a SEPIC converter.

[dave_j_fan]

about to do shopping ... for that bigfat transistor

Info provided by David Hess helped !

Replaced the .22E resistor with 1.5E not good usable current flows
getting current of 200-250mA is enough for my need , the circuit will run over night till mid day

and will fill a 12V SLA battery

 
Will it top the battery if the O/P  is to 14.1V , i am assuming  no auto cut chrger circuit needed , this DCDC booster will do ?
 

[dave_j_fan]

Addressing mikerj comments

This isn't really a suitable circuit for charging a 12v (nominal) lead acid battery from a 12v source.  If the battery is fairly discharged it's voltage could easily be below that of the power supply, in which case the current will be limited only by the DC impedance of R1, L1, D1 and the battery being charged.  A standard boost regulator can not regulate or current limit output voltages below the supply voltage.

For situations where the output voltage could be above or below the supply voltage you need a different regulator architecture such as a SEPIC converter.

Here I have succeeded to make it work  at 9v input , battery went to 12.1V and started charging ...till 13.8V

yes may be 12.1V is greater than 9v . As as precaution i will limit supply via resistor . so all deep discharged till 10.5v cells it will charge .