MC34063 Battery charger  - Page 1
Forum section: electronics / beginners

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 19, 2017, 06:40:09 am
content: Trying to make 12v 7AH battery chargeradded Booster circuit in attachment . Original MC34063 ic based booster circuit had TIP41 replaced with 2N2222and 180E to 220E , using 330UH coil inplace of 100uHthe circuit gives 14.2V after VR is adjustedbut 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 acidhelp needed to make a charger that gives atleast 200-300mA

author: David Hess
author_rank: Super Contributor
timestamp: December 19, 2017, 02:04:02 pm
content: 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.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 19, 2017, 02:23:51 pm
content: Thank you . I will try that .A dual 2n2222 will help

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 19, 2017, 02:31:20 pm
content: Quote from: dave_j_fan on December 19, 2017, 02:23:51 pmUnless you make arrangements to make sure that the current shares equally among both transistors, it would be always a better idea to usea single, higher current transistor with adequate heat sinking.The TIP31 should be available worldwide at a very reasonable cost.

author: mikerj
author_rank: Super Contributor
timestamp: December 20, 2017, 07:49:19 am
content: 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.

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 20, 2017, 11:37:44 am
content: about to do shopping ... for that bigfat transistorInfo provided by David Hess helped !Replaced the .22E resistor with 1.5E not good usable current flowsgetting current of 200-250mA is enough for my need , the circuit will run over night till mid dayand will fill a 12V SLA batteryWill 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 ?

author: dave_j_fan
author_rank: Regular Contributor
timestamp: December 20, 2017, 11:47:54 am
content: AddressingmikerjcommentsQuoteHere I have succeeded to make it work at 9v input , battery went to 12.1V and started charging ...till 13.8Vyes 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 .