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Confused with watts & amps calculation

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  1. 9th March 2012 04:13 AM Thread Starter #11
    skmdmasud skmdmasud is offline
    Quote Originally Posted by audioguru View Post
    The LM350 should be set for 300mA. You need one LM350 for each string of LEDs.
    If your LEDs are actually 3V each then you can connect 9 in series and in series with an LM350.
    If you connect only 5 LEDs in series then the LM350 has 13.75V across it and it will dissipate 13.75V x 300mA= 4.1W.
    is there anyway to use the led's in parallel. lets say 9leds in 3 strings etc.. and use only 1 regulator
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    Last edited by skmdmasud; 9th March 2012 at 04:14 AM.
  2. 9th March 2012 06:30 AM #12
    crutschow crutschow is offline
    Quote Originally Posted by MrAl View Post
    Carl,

    I think i covered that scenario :-) Also, he has 30v right?
    Yup you did. I missed that. Also somehow converted 30V to 20V. Guess it wasn't my day.
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    Zapper
    Curmudgeon Elektroniker

    --Inside every little problem is a big problem trying to get out.--
  3. 9th March 2012 10:44 AM #13
    MrAl MrAl is offline
    Quote Originally Posted by skmdmasud View Post
    is there anyway to use the led's in parallel. lets say 9leds in 3 strings etc.. and use only 1 regulator
    As i said before in this thread, if you use only one and you connect the strings in parallel you run the risk of one string drawing more current than another, and if one string blows open that might burn out all the rest too.

    If you already have a DC output that is regulated you can use resistors, you dont need a LM 3 terminal regulator.
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    One test is worth a thousand expert opinions, but one expert specification is worth a thousand tests.
    If i miss something you posted or something you think is important, feel free to PM me.
  4. 9th March 2012 11:21 AM Thread Starter #14
    skmdmasud skmdmasud is offline
    Quote Originally Posted by MrAl View Post
    As i said before in this thread, if you use only one and you connect the strings in parallel you run the risk of one string drawing more current than another, and if one string blows open that might burn out all the rest too.

    If you already have a DC output that is regulated you can use resistors, you dont need a LM 3 terminal regulator.
    Ok Sir got you loud and clear. I guess the LM regulator and led cost almost the same so why take the risk. 7 or 8 leds cost a lot more than a LM regulator. Better stay safe and cool.

    Thanks a lot.

    Regards
    Masud.

    I will post pictures of my project which is a Aquarium hood light. soon.
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    Last edited by skmdmasud; 9th March 2012 at 11:23 AM. Reason: had to say few things
  5. 9th March 2012 11:36 AM #15
    MrAl MrAl is offline
    Hi,

    OH yeah it would be nice to see some pics of the finished product.

    What kind of fish, fresh water or salt water, or other types of animals?
    0
    One test is worth a thousand expert opinions, but one expert specification is worth a thousand tests.
    If i miss something you posted or something you think is important, feel free to PM me.
  6. 9th March 2012 12:03 PM #16
    audioguru audioguru is offline
    Quote Originally Posted by skmdmasud View Post
    is there anyway to use the led's in parallel. lets say 9leds in 3 strings etc.. and use only 1 regulator
    That is what cheap Chinese flashlight manufacturers do. But the strings do not equally share the current. The LEDs last only for a couple of hours before they begin to burn out. When one or two strings burn out then the remaining strings get too much current and they also burn out.

    If you buy thousands of LEDs, measure the forward voltage of each one and sort them so that they are in groups having exactly the same forward voltage then one group can be connected in parallel or in parallel strings.
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    Uncle $crooge
  7. 9th March 2012 02:12 PM Thread Starter #17
    skmdmasud skmdmasud is offline
    Quote Originally Posted by MrAl View Post
    Hi,

    OH yeah it would be nice to see some pics of the finished product.

    What kind of fish, fresh water or salt water, or other types of animals?
    Its for freshwater planted tank. performance is good. i am running it at 300ma They are rated at 350ma.



    I am using 7 leds for testing. I plan to use 15 leds in the final design






    I have also attached a 12v cpu fan to keep the heat sink temperature low. It seems to be working very well. The heat sink is cold to touch. With 15 leds it may heat up a bit more.

    Installed in an empty tank which has a dark 3d background. The rocky background further decreases the light.


    with only 7 leds the light looks very bright. with 15 leds it will be more than enough for a planted tank of this size.



    Top view.
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  8. 9th March 2012 02:37 PM #18
    MrAl MrAl is offline
    Hi,


    Oh ok nice pics. So you're going to put fish in it then? What species of fish?
    0
    One test is worth a thousand expert opinions, but one expert specification is worth a thousand tests.
    If i miss something you posted or something you think is important, feel free to PM me.
  9. 9th March 2012 03:25 PM Thread Starter #19
    skmdmasud skmdmasud is offline
    Quote Originally Posted by MrAl View Post
    Hi,


    Oh ok nice pics. So you're going to put fish in it then? What species of fish?
    Hi.
    My aim is to make it a planted tank. I will put soil and put some foreground plants and then put some small tetra fish like neon's etc.

    Do you have aquariums or fishes in ponds etc?

    Regards.
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  10. 9th March 2012 03:44 PM #20
    audioguru audioguru is offline
    Are the fish blinded by the high power LEDs?
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    Uncle $crooge
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