# Charger - Supply

• posted

Greetings,

I am wondering if someone has or knows of anyone who has used a 12vdc charger as the foundation of a power supply? I have a 12v, 2 or 6 amp charger that I would like to use for this purpose.

My Idea is to build a module that I could run the output from the charger into and vary the voltage and amperage from 0 - 12vdc and, 0 -

6adc respectively. Simplicity is my goal, precision is a concern but not a priority. Can someone help me with the circuit?

Randy

• posted

After some thought and a lot of math,

I am looking at a new approach. Dividing the voltage would have been simple, if we put the power dissipated aside ( 72 watts ). The problem comes with stepping the voltage up incrementally. Each step in voltage would require a current division circuit ( dedicated ) to sustain the

0 - 6A output in that range. Thats 12 circuits with resistors ranging from a few watts up to 60 watts, we're digging deep in the pockets now! Unrealistic!

Instead, I've settled to keep the 12vdc constant and vary the current:

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12vdc R1 R2 R3 R4 R5 6A 12 ohm 6 ohm 4 ohm 3 ohm 2.4 ohm 72W | | | | |
• posted

OK! Back to the future.

I think I've found a regulator that might fit the application. It is the LM338. There is only one concern I have with applying it to my purpose, the 6amp input. According to the LM338 datasheet, the regulator has an output range "in excess" of 5A but, I could'nt determine how much, sustained. The LM338 can handle surges up to 12A but I'm thinking this is momentary. Could I parallel two LM338s' to split the current and adjust them with one var. res. as in the following circuit:

---------- | LM338 | ----|I O|------ | | A | | | ---------- | >----------------| |______ |---------------> | | | | | | 12 vdc | | ---------- | | R R1 | | | | LM338 | | | R 120 | 6A | ----|I O|------ R | | | A | | | +| CAP ---------- | | CAP .01mf |------- | 1mf | |-------------- | | | +| | | R2 R 5K CAP | | --R-> 10mf | | R | | | | | | --GND----------------------------------------------

or, can I increase the value of the current set resistor ( R1 ) to lower the maximum current through the regulator.

Randy

• posted

I don't know whether parallel LM338s will work. It might work properly.

However, here is a 5A adjustable voltage/current regulator that might work for you. Look on pg 16.

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