Hi, everyone! I'm a novice hobbyist, not a student, so please don't laugh too loudly when reading this and please be kind and don't use big words in your replies! ;) I want to use my two old 14.4VDC @ 4Amp batteries from two old drills as a supplemental power source for my laptop when I go camping. I have two battery packs and two charges, so this is convenient and helps keep things out of the landfill. After searching Google for project ideas, I decided to use an LM317 because I have them and I am on a tight budget. Laboring through various manufacturers datasheets on the LM317 to boost up current output, I have come up with this design. I'm sure I've messed up the calculations somewhere. About the circuit: Transistor Q1 and resistor R1 form the short-circuit protection portion of the schematic.
I don't know what the value of R1 should be, since the diagram I pulled it from only listed the value of Q1 and said the resistor causes it to conduct when the load drops (of course, I can't find the website where I pulled this from, so I can't give the exact explanation).
I'm leaving the circuit as adjustable, so that with the use of my DMM, I can adjust R4 so that I get exactly 19vdc.
The output amperage is critical, my laptop's PSU calls for 19vdc @ 4.74amps. My questions/problems: I'd like to keep Q1 & R1 in the circuit, but if no one can help me determine the value of R1, then I can live without the added protection of Q1 & R1. Are my other values correct? (I realize that an LM338 will give me 5A out, but my local supplier doesn't stock them and I do have all the above components in my parts collection). Thanks in advance for your assistance!