LM317 constant current charger are quite popular as it seems. I made one for my 12v 7Ah Lead Acid battery. I used a 2.2 ohm 10 watt resistor and calculated that it would give a decent amount of constant current to charge my battery. To my surprise, I noticed that the battery is drawing only 20 - 30mA current when charging. Currently the battery is little over-discharged to 11.8v.
I had an impression that LM317 Constant current mode pumps constant amount of current, no matter what the load is. Was my understanding wrong? If so, should the constant current value, i.e 1.25/R is actually the max current value? Because when I sorted the output terminals of the power supply, it reached upto desired current level, i.e (1.25/2.2) * 1000 mA
And if my understanding of LM317 constant current supply is correct, why is the battery drawing only 20mA current?
My circuit is as simple as following.