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

[tasmod]

Thanks for your parience Hank. Sometimes I wonder where my head is. I know all this, but I've been in a blank place since having the head cold, amazing how I can't think straight.

As for the heat, I realised later that the .1 was in series with regulator which runs quite hot, there was heat transfer. The .47 is in the ground leg which is nowhere near the reg.

The unit is running fine now and the basic (sic) software works, now I need to add the frills such as logging to eeprom, temperature compensation etc.

For the larger unit I have in mind making it multi battery, nicad, nimh etc. with menu choices.

[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.

[Ramius]

Hi Rob,
The link I gave you accurately measures the current from .02 amp upto 70 amps and using the ACS758 takes care of the shunt resistor as it is part of the device. The program gives you the actual current as a digital number you can use for anything you wish as well as the voltage. http://www.picbasic.co.uk/forum/showthread.php?t=16387 Best, Ed