Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reiland Pickups
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reilander Pickups
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reilander Pickups
Join TDPRI Today

Laptop 18VDC scavenge for pedal power

Discussion in 'Burnt Fingers DIY Effects' started by Fatknuckle, Jan 8, 2014.

  1. Fatknuckle

    Fatknuckle Tele-Holic

    Posts:
    972
    Joined:
    Jun 28, 2012
    Location:
    Gainesville FL
    I acquired a typical 18-volt DC laptop supply that had its cable mangled. Opened it up and set it up for some test fiddling, and it puts out a nice 18-19VDC. I have a 0.1uf cap from B+ to ground before the last terminal strip and the regulator circuit I am building.

    In my experimenting, I have rigged up a LM317T voltage regulator with a 5K linear pot as R2, two 680-ohm resistors in parallel (~330 ohm) for R1, one N4001 diode across the input and output , and a 10uf non polarized cap on the output, basically along the lines of the standard instructions (Radio Shack), plus some other web input.

    I had it working well yesterday with only one 680-Ohm resistor, but getting a range of 1.4 to 10.5 volts. Trying to get a bit over the 12-volt mark at least. The calculator I used said 330-ohms would get my range closer to 18-20volts at the top, but it works for a moment with everything cool, and then gets VERY hot on the sink, and I get nothing on the output.

    I am wondering if the range I am seeking is limited with R1 needing to be more around 560-ohm, thus I am overloading something. Or another diode? Or a different cap? Or a new hobby?


    image-3935970341.jpg



    image-1754636823.jpg



    image-4112557749.jpg

    The white goo is high-strength marine sealant. They didn't want anything moving around in there....
     
  2. luckett

    luckett Tele-Holic

    Posts:
    888
    Joined:
    Jun 14, 2011
    Location:
    United States
    The heatsink is not able to dissipate enough power and it's causing the overload circuit in the LM317 to shut it off. How much current are you supplying and at what voltage?
     
  3. Fatknuckle

    Fatknuckle Tele-Holic

    Posts:
    972
    Joined:
    Jun 28, 2012
    Location:
    Gainesville FL
    The DC supply is 19.5v at 4.62A. It occurred to me in a dream that the current was an issue. A bigger (much bigger) heat sink maybe? It looks like it is heating up at the wire connection at the regulator input.
     
  4. Forum Sponsor Sponsored posting

  5. Jubal81

    Jubal81 Tele-Meister

    Posts:
    353
    Joined:
    Apr 17, 2009
    Location:
    Wilmington, NC
    Current overload. It's more about what you're supplying (the load) than the rating of the laptop brick. Too much power is getting sucked to your ground.

    It's a design problem. A bigger heatsink isn't the answer.

    If you could draw out a schematic of exactly what you've built I could be more help.
     
  6. Fatknuckle

    Fatknuckle Tele-Holic

    Posts:
    972
    Joined:
    Jun 28, 2012
    Location:
    Gainesville FL
    Here is the basic approach. I left out D2, R1 is effectively 340-ohms.


    image-2817283851.jpg

    So I don't know if adding another N4007 will work, as D2 or elsewhere. D1 is a N4007, 1000v/1a, not a N4001.

    Thanks!
     
  7. Jubal81

    Jubal81 Tele-Meister

    Posts:
    353
    Joined:
    Apr 17, 2009
    Location:
    Wilmington, NC
    I guess first thing is to check that your diodes are oriented correctly for polarity. Replace the ones you already used with fresh ones. And check for any shorts, of course.

    You can also add a cap in parallel with the pot like:
    [​IMG]
     
  8. Fatknuckle

    Fatknuckle Tele-Holic

    Posts:
    972
    Joined:
    Jun 28, 2012
    Location:
    Gainesville FL
    I redid the circuit board following the example you provided, less the extra rectification diodes and the 1000uf cap,as I believe the power source already has provided something appropriate. It is working fine in voltage test mode, with a range from 1.25 to 19.4v. Runs much cooler too. Some pics:

    image-3444210905.jpg



    image-1051641858.jpg



    image-435251425.jpg



    image-1131842684.jpg

    Now to find a suitable enclosure.
     
  9. Fatknuckle

    Fatknuckle Tele-Holic

    Posts:
    972
    Joined:
    Jun 28, 2012
    Location:
    Gainesville FL
    Running it on a chain with 4 or 5 pedals at 9 to 10.5 v seems fine, no noise whatsoever. However , the heat sink still gets pretty warm to the touch. I am wondering if additional diodes in series, or a diode with higher current rating might make a difference. Works very steadily though.
     
  10. Fatknuckle

    Fatknuckle Tele-Holic

    Posts:
    972
    Joined:
    Jun 28, 2012
    Location:
    Gainesville FL
    I added some additional heat sink and that seemed to help. LED voltage display too, 6$ off EBay with free shipping from Georgia ( the State), not China.

    image-1338694305.jpg
     
  11. Jubal81

    Jubal81 Tele-Meister

    Posts:
    353
    Joined:
    Apr 17, 2009
    Location:
    Wilmington, NC
  12. limbe

    limbe Tele-Afflicted

    Posts:
    1,452
    Joined:
    Sep 4, 2009
    Location:
    Stockholm,Sweden
    As you may know Fatknuckle,D1 and D2 are not there for rectification,they are there to protect the regulator when you switch off the power supply and the output capacitor(s) discharges.You should be fine though,as long as the output voltage stays beneath 25 volt and the capacitor isn´t too big.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


Share This Page