I have built a voltage regular circuit with LM317. Its input is connected to my solar panel.
As in many circuit examples, there is a voltage divider to bias the adjust pin. Also, I have connected a diode on output to prevent backward current flowing into voltage divider.
When no load is connected on output, I measure the output of my solar panel, it is also the input of LM317. It is generally over 18V. I set the output voltage to 8V by using a pot, and it works perfectly. In this connection, due to the voltage drop on diode, I get about 7.2V at the end.
Now, when I connect my 6V lead acid battery (it says 7.20V - 7.50V for charging), I measure the input of LM317, and see that it drops to about 4-5V and stays there. I don't have much experience with lead acid batteries, but some days it works perfectly, and output stays really high, other days, battery doesn't charge at all and above situation is seen. What is causing this? Is it normal?
P.S. After charging batteries, I use it to light hallway with white LEDs.
.. After a while ...
I used a 12V power adapter last night as substitution of solar panel, and measured voltage at different points. I saw the same effect. That means this effect is not about solar panel.