3 Terminal Regulator Heatsink Question

Discussion in 'The Projects Forum' started by Robertw55, May 20, 2009.

  1. Robertw55

    Thread Starter New Member

    May 20, 2009
    4
    0
    I have a 7805 3 terminal regulator.

    I'm sending out 32V, 2A (from small solar panels) through a +5v 1A 7805 to a 5v 2A playstation PSP

    I'm having trouble finding the correct dimensions I need for the heatsink. there are so many different types!

    would this one work by chance?

    http://www.radioshack.com/product/index.jsp?productId=2102856

    also from what i understand, i should use thermo grease (is that whats its called) between the regulator and heatsink? if possible, could you provide a link to this grease to make sure i get the right stuff?

    many thanks
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    This is very small. You need one which is able to dissipate about 40W.
     
  3. Robertw55

    Thread Starter New Member

    May 20, 2009
    4
    0
    is their a particular dimension I need with the 40w heatsink? are there a lot of different sizes or is there a standard size?

    i'm looking for a 40w heatsink, but having no luck. (im googling "TO-220 40W heatsink")

    thank you
     
  4. Robertw55

    Thread Starter New Member

    May 20, 2009
    4
    0
    what is the C per watt for a heatsink dissipating 40W?
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Try the biggest you can find. If the LM7805 shuts down due to overthermal detection try to cool it with a fan.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Depends on permitted temperature rise and ambient temperature. Will this be in an air-conditioned space, or out in the summer heat?

    Personally, I would use a switching regulator instead. Dissipating 40W in order to use 10W seems like a big waste to me.
     
  7. Robertw55

    Thread Starter New Member

    May 20, 2009
    4
    0
    I'm doing a project where I'm taking the small solar panels off of some solar landscape lights that I have. they are 4v 250mA 1watt a piece approx.

    I'm hooking them together to make a charger for my PSP which is 5v 2A

    I was going to use a L7805 and a heatsink to regulate.

    I'm not sure the given information changes what you said, but you think I should get a switching regulator? like a LM338 for example?

    thanks
     
  8. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    Bob Pease has an old motorcycle engine block for such heavy-duty heatsinking. But you'd still need a meatier regulator, as the L7805 is only good for 1.5 A, and the Vmax of 35 V is perilously close to your 32 V.

    Off-the-shelf switching regulator modules are available for a reasonable price from suppliers like Farnell, RS, Digikey, Mouser, Newark etc. Search under DC-DC Converter.
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Why not simply use a 2 x 8 array to generate 8v 2A instead of a 8 x 8 array to generate the unneeded (and problematic) voltage? Better yet, you could create a 2 x 32 array, increasing available current to compensate for overcast days.
    The linear regulator would indeed be a simple and feasable solution in such case. Dissipation would be only 6W.
     
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