Please how do I make the current of this cct to vary between 2-15A. I want to be using the charger for both lead acid and deep cycle batteries.

 

Besides the mains transformer being uprated for the required current, transistor Q1 will need to be mounted on a heat sink capable of handling the power dissipation*.

Diodes D4, D5 & D6 will need to be uprated to handle the maximum charge current and the value of resistor R5 will need to be reduced such that at the maximum charge current 0.68V appears across it (to switch on transistor Q5).

You will probably need to increase the capacitance values of C1 & C2 by a factor of at least 10.

* with a flat battery and maximum charge current it is unlikely that any size heat sink will be adequate for the power dissipation – so you will need some other arrangement (probably involving an additional 2N3055 transistor to share the power dissipation).

 

Besides the mains transformer being uprated for the required current, transistor Q1 will need to be mounted on a heat sink capable of handling the power dissipation*.

Diodes D4, D5 & D6 will need to be uprated to handle the maximum charge current and the value of resistor R5 will need to be reduced such that at the maximum charge current 0.68V appears across it (to switch on transistor Q5).

You will probably need to increase the capacitance values of C1 & C2 by a factor of at least 10.

* with a flat battery and maximum change current it is unlikely that any size heat sink will be adequate for the power dissipation – so you will need some other arrangement (probably involving an additional 2N3055 transistor to share the power dissipation).

This is really helpful, thanks

 

Mind your input (the voltage doubler has less efficiency on high loads also the el.-lyths get hot and blow - either by overvoltage or overcurrent)
= use ready made power supplies starting from about 18V 15A . . . and NOT -- PS! you do not want to charge PbSO with high amps!!

 

That has been my major fear. Thanks for the advice @ci139

 

it's where to be cautious ... not a solid rule ... depends on specific transformer (inductance, core) , rectifier diodes (junction capacity reverse leak/-brakedown) and electrolytic capacitors (ESR , thermal characteristics ...) in combination