1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

80 volt, 1500ma, LED light string powered by 117 AC

Discussion in 'General Electronics Chat' started by kinarfi, May 18, 2017 at 10:15 AM.

  1. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,482
    Likes:
    29
    Location:
    P. G., Utah, United States of America
    Is there a practical way to power a 80 volt, 1500 ma Led string of lights from 117 volts AC ? My thoughts are to use a 24 vac transformer to buck the 117, rectify that and use a current limiting circuit to hole the current at 1450 ma.
    Anyone have any suggestions?
    Thanks,
    Jeff
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,186
    Likes:
    916
    Location:
    Canada, of course!
    117V - 24V= 93V.
    93VAC rectified and filtered produces 129VDC.
    129V - 80V= 49V.
    49V x 1.5A= 73.5W of heat that will need some liquid nitrogen for cooling.
    If you don't filter the rectified AC then the LEDs will flicker and there will be less heat but still too much heat.

    Try the calculations by bucking away 48VAC or more.
     
  3. Mosaic

    Mosaic Well-Known Member

    Joined:
    Jun 3, 2010
    Messages:
    2,484
    Likes:
    123
    Location:
    Caribbean
    ONLINE
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,482
    Likes:
    29
    Location:
    P. G., Utah, United States of America

    I thought 24 vac would be a little low when I posted the idea, I have lots of nitrogen at hand, it's just not liquid, :)
    Thanks,
    Jeff
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,186
    Likes:
    916
    Location:
    Canada, of course!
    Mosaic's idea to use a capacitor to replace a transformer is used for very low power circuits like a low brightness LED indicator.
    For the 80VDC that you need, an AC signal of about 58VAC is needed to be rectified and filtered.
    The capacitor feeding the rectifier will have 117V - 58V= 59V across it . With a current of 1.5A then the reactance of the capacitor must be 59V/1.5A= 39.3 ohms. The value of the capacitor must be 67.8μF. it must be non-polar with a rated voltage of about 200V. At the moment when the AC is applied, there will be a huge current spike as this capacitor charges that might burn out your LEDs.
     
  7. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    6,834
    Likes:
    901
    Location:
    Loveland, CO USA
    Here is a crazy circuit: Buck down PWM. 150V to about 80V but regulates current not voltage.
    80V of LEDs 1.4A
    The "150 volt source" is a full wave bridge and capacitor on the power line.
    The PWM IC is LT1242 which is like the UC3842.
    D3,D4 should be removed.
    Q3, Q4 watches the LED current.
    It needs some work. There are things I would change. Just a first try circuit.
    upload_2017-5-19_18-32-12.png
     

    Attached Files:

  8. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,482
    Likes:
    29
    Location:
    P. G., Utah, United States of America
    The last line in the article states that the circuit is good for 1 - 100 ma but one of the other articles I saw while reading this one was this one, I haven't done any work on it yet, but it looks interesting.

    I believe I have a UC3842 on hand, I'll have to check this out.

    What I'm using this on is 8 of the 15 w white 6000k, they run at 10v, 1500 ma http://www.ebay.com/itm/10W-COB-Bar-Led-Chip-15W-LED-Strip-COB-Diodes-12V-White-Warm-White-Diy-Lamp-Bead/201485088299?_trksid=p2481888.c100675.m4236&_trkparms=aid=111001&algo=REC.SEED&ao=1&asc=20160908105057&meid=109355c00d614fff987c2959b87bb9a4&pid=100675&rk=1&rkt=15&sd=201485088299&_trkparms=pageci%3A77cb0b26-3d07-11e7-ba8c-74dbd180809a%7Cparentrq%3A23c5f20e15c0aa1302ee7214fffdc697%7Ciid%3A1
    Thanks,
    Jeff
     

    Attached Files:

  9. Colin

    Colin Member

    Joined:
    Sep 25, 2003
    Messages:
    269
    Likes:
    13
    Location:
    Australia
    The best is to start with half wave rectification and a resistor and an electro.
     
  10. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,482
    Likes:
    29
    Location:
    P. G., Utah, United States of America
    I'm sure this is NOT what you meant by electro, please elaborate,
    Thanks,
    Jeff
     

    Attached Files:

    • Funny Funny x 1
  11. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,482
    Likes:
    29
    Location:
    P. G., Utah, United States of America
    One of the key words in my opening post was PRACTICAL! Several hundred dollars for capacitors is NOT practical, IMHO.
    Thanks for your work on this,
    Jeff
     
  12. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,482
    Likes:
    29
    Location:
    P. G., Utah, United States of America
    So far, the best I have come up with is Untitled.png , but it is only 33% efficient. Looks like it's time to figure out some switch mode design.
     

    Attached Files:

  13. Colin

    Colin Member

    Joined:
    Sep 25, 2003
    Messages:
    269
    Likes:
    13
    Location:
    Australia
    Something like this

    LEDs.gif
     

Share This Page