Trying to determine dc current - 12v lead acid battery charger

[tasmod]

OK I've given up on this board and I'm going to design my own and start again. There's something peculiar happening with it. I had it working just fine and left it to one side running but not connected to the test battery for a while. I was busy on the bench making up a temperature and memory board.

Later I connected the test battery and nothing happened to the current but the output was suddenly 7.9v ?? So I disconnected it, switched off and then tried again a minute or so later. It powered up fine gave the correct output but now the current routine was way off. I checked against a multimeter.

I suspect the LM317 is playing up.

On another tack, this months (June) QST has an interesting article on carrying batteries in a cooler box. What interested me was the authors use of a steel 3/16th (4mm) setscrew to make a high current shunt.

He used nuts and wire tags to make the shunt and calibrated against a multimeter by adjusting the nuts along the thread length till he got it correct. At the head end he used two nuts to clamp two tags tight, then at about 1 inch (25mm) he used two nuts again to clamp two tags. This end he screwed along the thread length to get the right reading. Quite novel.

Pic added with acknowledgemen to QST.