Newbie project needs constructive criticism

Discussion in 'The Projects Forum' started by Patrick Brown, Aug 6, 2009.

  1. Patrick Brown

    Thread Starter New Member

    Aug 2, 2009
    2
    0
    Hello,

    I am new to the field and am looking for some constructive criticism and a few answers to some questions.

    My goal is regulate from 12v DC to 6 and 9v DC. I have motion activated cameras which use either 4 or 6 "C" or "D" cell batteries and I want to power them using a 12v rechargeable SLA battery which can be charged using a solar panel.

    I found a schematic for a voltage regulator using an LM317T here: http://www.reuk.co.uk/Using-The-LM317T-To-Regulate-Voltage.htm

    I have created the circuit on a printed circuit board from radio shack and plan to house it in a project box also from radio shack. The resistors I used will regulate to 6.32 in one circuit and 9.58 in the other. These values are based on a chart found here: http://www.reuk.co.uk/LM317-Voltage-Calculator.htm. In the 6.32v circuit I will use two resistors in series for R2, 150 ohms and 220 ohms, to reach the required resistance of 370 ohms.

    I have attached a photo of the 9v board with all components, but not in its final state. I plan to attach a larger gauge wire which will run through the ends of the box. I have tested the 9v circuit on a camera and it worked.



    Questions I have:

    1. The schematic I found was quite simple (only requiring 3 parts) but I have found others a bit more complex (using capacitors and other parts). Is the design I used suitable for my application? Seems too easy.

    2. Do I need a heat sync? If I used and read my multimeter correctly, the draw of the 9v camera was .1 amp during standby and .4 amps for a few seconds after the flash went off. The camera will be on standby for the majority of the time and only take 3 flash photos about 10 sec. apart, every minute (presuming there is activity to be photographed).

    I tested the temperature of the LM317T while using the camera and the temp would be at about 120F during normal operation. When manually firing the camera (once every 10 seconds, faster than normal operation) the temp of the LM317T rose to about 170f.

    3. The LM317T is just slightly too tall for the box so I will need to bend it a bit to make it fit. Will this be an issue?

    I appreciate any guidance and instruction you can provide to help make my project better. I know this must be pretty simple and mundane for most, but the process has been super exciting for me and I've learned a lot so far. I'm already thinking about other, more complex, projects to tackle.

    Thanks,
    Patrick
     
    Last edited: Aug 7, 2009
  2. steinar96

    Active Member

    Apr 18, 2009
    239
    4
    For some regulators the capacitors are needed. But according to your link they arent for this one. They do however increase the load regulation.

    Well, i find it likely that your regulator is gonna explode (or worse catch fire) if you dont add a heatsink on it. That depends however on the load. These regulators are linear and dissipate alot of heat. So even small loads can cause it to overheat and large loads (even within the device specs) can cause it to litterally explode;).

    Better safe then sorry if you ask me, these devices often have internal current limiting in the case of shorting so with a heatsink they can withstand temperoral shorting. A non-heatsinked chip like that however will instantly fail or explode if accidentally shorted.

    Bending the voltage regulator should pose no proplem. You'll notice that if you buy a heatsink you most likely have to bend it for it to lie firmly against the heatsink.
     
    Last edited: Aug 7, 2009
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    With the regulator heating so much inside a plastic case, it's going to be difficult to shed heat. A metal box would seem to be a better choice. With an insulator, the regulator may be mounted to the case for a heat sink effect. A cast aluminum case is good for shedding heat and protecting the contents.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Those boxes usually have a metal cover, he could use that as a heat dump.
     
  5. Patrick Brown

    Thread Starter New Member

    Aug 2, 2009
    2
    0
    Thanks for the tips. I'll figure out a way to attach the regulator to the metal cover of the box like Bill mentioned.
     
  6. Tahmid

    Active Member

    Jul 2, 2008
    344
    25
    Hi,
    For 6v and 9v, you could use 7806 and 7809. The circuits require less parts than LM317.
    And heatsinking is required.
     
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