Voltage Reg Simple Questions

Discussion in 'The Projects Forum' started by urb-nurd, Aug 15, 2014.

  1. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    hey guys!
    I am here to just make sure i am not missing anything with my fiddling.
    I have an LM317T regulator that i was going to use to power my 7.4v heater using a 9v battery.
    i hooked it all up - .1uf ceramic on the input - and a 220uf (16v) Electrolytic on the output.
    For my reference resistor (fixed value) i used 2 470ohm resistor in parallel to give me 230 (was 240 in the datasheet).
    This was then hooked up to a 10K potentiometer.
    I powered the circuit with a 9V battery and every time i connected my load (varying heaters at numerous voltage ratings) the output would drop to 0 volts.

    I just want to clarify that the issue is the inability for the 9v battery to produce the current necessary.

    When i use a 10mm LED i got i can turn it on and off with the circuit and vary the voltage from 2.2 (led off) to 3.4 led is on fully and all the way up to 14v (from a 9v - im confused!).

    So to clear this up, the 9V battery cannot drive my heater - this is why the output drops to 0v - Though i would still like an explanation for this.

    The Led's work due to their low current requirement. correct?

    Thanks for anything that can shed light on my dark dark times
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    how much current does your heater pull?
  3. bertus


    Apr 5, 2008

    What kind of 9 Volts battery are you using?
    The small 9 Volts block batteries are not capable of giving much current.
    Have a look at the following page for info on the 9 Volts batteries:

  4. crutschow


    Mar 14, 2008
    Your confused? Some am I. :confused: No way to get 14V from a 9V battery unless you have a switching boost converter of some type.
  5. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    The heaters pull about 1.5A+
    It tested two kodak 9v batteries, they read 13v roughly.
    I don't think i hooked anything up wrong, i tried with and without the capacitors.
    The pot in question is a panasonic 10k (i used for a cmoy amp, using input 1 and output 2 for my variable R)

    I have attached pics.
    One shows the battery voltage from my multi
    The other shows the pot at its highest setting
    The last the pot is at its lowest setting.

    As you can see - with any load the vout form the regulator goes from about 13 (dropped maybe two from the battery's erroneous 15v) to a max of about 3.4v with the LED in place.
    The lowest output voltage produced is 2.1 shown with the led off.
  6. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    Flipping the IC allowed me to get the output from 0 to 11.4 (NO load - multimeter to measure)
    Which seems better than the 2.4 to 14v range when the IC was per the pinout of fairchild!

    this does not fix my problem however, i still drop to 0V when i connect my heater (low resistance),
    Also when i drive the LED i get a limited range of 0 to about 4v.
  7. danielb33


    Aug 20, 2012
    First of all - 1.5A is a lot for a lm317 if you are not using the correct kind. Typically a 1.5A lm317 pushed to these limits will use a heat sink. LM317's do cut out when overheated.

    Second - 9V batteries are not meant for a flippen heater! Just look at any 9V battery datasheet on digikey. http://data.energizer.com/PDFs/EN22.pdf
    The datasheet above shows that at 300mA you will get 1 hour of life. If you are pushing 1.5A through two of them, I am not surprised your voltage drops! Try putting 5 in parallel. Or - just a better battery.

    I do not understand the LED statements. When using LEDs are you only using the LEDs?

    Have you verified the correct voltage output under no load?

    All in all I would say your whole circuit should be revised. New battery, new regulator. Did you verify the current draw of the heater with the DMM?
  8. danielb33


    Aug 20, 2012
    Also - keep in mind you are putting about 8 watts through that poor regulator. LM317s typically have around 32degrees C increase per watt at room temperature. This means your going to melt it if you could actually provide the current your heater needs (and if the regulator did not thermal limit)
  9. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    Yeah i quickly realised that the 9v battery is ridiculously insufficient, i was just trying to ghetto rig something until i get my 25500's today.
    Then when i saw some crazy outputs i just wanted to get to the bottom of it.
    I have a heat sink that i can clip on - however the vreg didn't get hot at all.

    I verified my output voltage with no load and got a range of 0-13 in one orientation, then flipped i got a range of 2.2 - 15v.

    Also when i had the led's i would use them soley, then put my heater in parallel and the led would shut off. no current through anything it seemed (or negligible).

    Im swinging by radioshack today so im going to pick up a better regulator and maybe a PSU.
    However i will be hooking this up to a PIC - im not even sure if my dev board can support the 3a output i had in my head for two heaters.
  10. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    UPDATE: OP is remedial.
    I dont want to admit my error, but my multimeter - yeah...... so i kept using AC voltage measurement settings.
    Here the deal now i got a new regulator thats good for 5A but the datasheet is so terrible!
    I picked up a pack of ceramic caps from maplins however they are all much lower values than i anticipated. lower than 1uf... all in the pici and nanofarad range.
    I grabbed some smaller electrolytics for the output as well.
    I managed to get better pots ranging from 5-10k so i can adjust the voltage of my output.
    The datasheet offers formulae for calculation, one of the values is Iadj and Vref.
    I am not sure how to obtain these values for calculation?
    Also with regards to the capacitors, the datasheet says 10uf tantalum caps, i only have electrolyrics and ceramic of low values.
    Will i need to source more components or will i get desired performance?
    I am using 4aa's to power a 3.2v heater with a current draw of about 1.5A

    Thanks again guys! You are always a great help.
    Forgive me for my brainfart
  11. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    UPDATE - i haven't used the variable voltage configuration yet as i am still not sure on the unknown in the forumla.
    However i have hooked it up as a fixed regulator and my 5v input drops to about 3.5 (seems correct) however when i connect my loads i still get a drop in vout dependent on the resistance of my load.
    If i use a 1.2ohm heater i get 2.5Vout where as when i use the ino .8ohm heater i get about 2V out.

    What is the issue here?

    before i even think about a variable output i need to get my head around this.


    (Regulator in use is a ts1084 - i have two with differing codes following that, one drops more voltage than the other)

    I am going to use a voltage divider with a pot to vary the voltage to where i need it for the time being.
  12. urb-nurd

    Thread Starter Member

    Jul 9, 2014
    Sometimes i question my ability - i really do.
    V divider is POO POO. output current way to large haha.
    I am not with it today :(