LM317 not regulating properly

[offroadheli]

Constructed Scott Henion's simple 2S Lipo charger. Charger was working for a awhile and could calibrate output with the pot to 8.4V using a 12v regulated input.

However, circuit fails after a couple charges and the LM317 doesn't seem to regulate at all. Output voltage is close to input voltage.

What could I be doing wrong? How can i test if the regulator is functioning properly?

Any clues people?

[Probedude]

How do you have it constructed? Are you making sure you hookup the +12V supply before hooking up the battery?

What happens if you ground the adjustment pin? (DON'T hookup a Lipo) That should limit the output to 1.2V.

[Unterhausen]

I have had nothing but unpleasant experiences with the LM 317. The circuit they show in the data sheet just barely works. You need to use smaller resistors in the voltage divider circuit.

[z-matrix]

i whouldn't use an lm317 for voltage stabilizer in a li charger,

though if you do so, you have to use a ballast resistor for the lm317 to work, or it will trickle your li pack until it ignites.

[poulsbobill]

Constructed Scott Henion's simple 2S Lipo charger. Charger was working for a awhile and could calibrate output with the pot to 8.4V using a 12v regulated input.

However, circuit fails after a couple charges and the LM317 doesn't seem to regulate at all. Output voltage is close to input voltage.

What could I be doing wrong? How can i test if the regulator is functioning properly?

Any clues people?
Recheck all your connections. When output voltage = input voltage one of your resistors (the one that changes the voltage 4.2, 8.4,12.6) is disconnected. I had it happen.

You could try another lm317. I fried one with a short circuit...remember the body of the lm317 is hot. Check to see if it or your heat sink is touching a ground.

I love this lipo charger. Have used for about a year now charging 1-3 cells from 25 mah up to 2.0 amps when properly cooled.

One thing that will make the charger more useful is using a trimmer instead of a pot for the voltage adj. to make it more precise.

Bill

[offroadheli]

Fellas, I goofed! My circuits on a (messy) project board and ended up connecting the output to the source voltage! :p

Circuits fine.

Otherwise, thanks for all the potentially useful and valid hints.

Cheers!!

[Unterhausen]

Fellas, I goofed! My circuits on a (messy) project board and ended up connecting the output to the source voltage! :p
Done that many times, the picture in the data sheet is less than clear. And I'm dyslexic