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120VAC to 12VDC Power Quality Problem? HELP!

Discussion in 'General Electronics Discussion' started by MaNa, Jun 15, 2016.

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  1. MaNa

    MaNa

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    Jun 15, 2016
    In my camper, I have a 120 VAC to 12 VDC converter. I installed some LED strip lighting that came with an plug-in power supply (like a laptop computer). Power supply output is 12VDC. I cut the power supply cord and wired the 12 VDC side into a 12 VDC circuit that powers another small, incandescent light.

    LEDs work fine off of their own power supply. Also work fine when powered directly off the 12VDC marine battery. Lights will not work when I plug the camper into 120VAC power. They blink once and will not turn on.Other 12VDC incandescent lights work just fine. I suspect "dirty" DC power. Any ideas how I fix that? I verified proper polarity and voltage.

    Thanks!
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Welcome to Electronics Point!

    Have you compared the current drawn by the LED strip lighting against the current rating of the 120 VAC to 12 VDC converter? It's possible the latter device is automagically shutting down when the LED load is added. Easy solution is to add a largeish electrolytic capacitor across converter output to provide some filtering. Size depends on load current expected, but you might start with 10,000 μF rated 20 WVDC (Working Volts Direct Current) and work up from there. This won't work if the LED string is overloading the converter, so measure the LED load current when powered off the 12 VDC marine battery and compare with the rating of your converter..
     
  3. MaNa

    MaNa

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    Jun 15, 2016
    Thanks a lot. I don't believe the power supply is overloading. The current draw for the LEDs is around 1 to 2A based on the cut sheet and the converter is protected by 15A fuses which haven't blown. However, I will try to measure the current just to be sure. I'll give the capacitor a try and let you know how that goes.
     
  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    It is important to measure the LED current when they are powered on with a stable DC source, like your marine battery. Some switch-mode power supplies will shut down if they "think" they are being overloaded, although a 120 VAC to 12 VDC converter properly protected with 15 A line fuses is likely more than capable of providing a few amperes of DC output without complaining. Are those the recommended fuses, or just something your circuit-breaker panel for "shore power" has in-line with the 120 VAC power receptacle?
     
  5. MaNa

    MaNa

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    Jun 15, 2016
    Good point about the stable power. The 15A fuses are the recommended fuse. Thanks again!
     
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    I suspect you mainly want to run your LED strip lighting off the marine battery when parked out there enjoying the wilderness, hopefully without running a motor-generator set into the wee morning hours, but would also like to run from "shore power" when the camper is connected to a 120 VAC RV park service. Why not use the original LED power pack for that? You could use a pair of Schottky diodes to isolate the power pack DC output from the marine battery to prevent over-charging the battery when the camper has 120 VAC power available... what am I missing here?
     
  7. MaNa

    MaNa

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    Jun 15, 2016
    NO MOTOR GENERATOR! That would be heresy in the woods! I would like to run them on "shore power". I don't think you are missing anything either. I did a nice, neat job of wiring in the DC connector to the lighting circuit so I DIDN'T have to run the power pack but I think I may be coming to the point of accepting that option. 95% vs 100% is good enough! I will still probably try the capacitor, just in case it works. Thanks for all you attention!
     
  8. BobK

    BobK

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    Jan 5, 2010
    Are these LED strips wired directly to the power supply, or is there some kind of controller in between?

    Bob
     
  9. MaNa

    MaNa

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    Jun 15, 2016
    There is a controller that takes an IR input from a remote into which the 12VDC power goes.
     
  10. BobK

    BobK

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    Jan 5, 2010
    That I suspect that controller is what is acting up.

    Bob
     
  11. globecollector

    globecollector

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    Jun 27, 2011
    It does help if you have an oscilloscope, because then you can see of the "power" is "dirty" or pure DC.
    Bob does have a point about the converter....it will be a constant current converter as LED's require a current (which is proportional to their brightness) and they develop a fixed voltage drop.

    A large capacitor in parallel with the input to that "converter" and a couple of Shottky diodes, like those dual ones you find in switchmode supplies (with about 30v peak inverse rating) should work.

    If not, then you need to draw the circuit diagram of EVERYTHING, all the camper wiring, all the stuff inside all converters and power supplies, all battery chargers involved etc., then apply a holistic approach to the whole lot.

    I can't count the number of times I have encountered these "black box" solutions that never quite work as they are expected to because people make assumptions as to what is inside the "black boxes". i.e. Power Supply Unit, LED control unit, Battery Charger Unit, Inverter Unit etc.

    This seems to be a very prevalent issue with people who have campers or boats and one recurring issue is the discontinuity of the 0v reference or "Eatrh" line. If you are using solar panels and MMPT's, (Maximum Power Trackers) with the panels, many designs of these do active things with MOSFETS and Diodes on the COLD SIDE, so the negative of the panels is not "Earth"....this catches many out and is also poor design by the "black box" manufacturers. "Earth" discontinuity can also sometimes be an issue with chargers and power supplies too, so it is always a good idea to draw the circuit diagrams of everything before you proceed, then you can see how to fit it all together and if anything is producing an output, requiring an input, has a different reference other than "Earth" or lacks input-output isolation that is NOT what you had assumed initially bey reading the product's brochures!

    I feel that many manufacturers of such products "deliberately" make the brochures vague, use poor design practice or are just plain ignorant of design issues such as input-output isolation that cause end-users endless headaches, catastrophic failures and loss of time and money.

    If I were to have a camper or boat, based on my past experiences with the campers and boats of others I have been called to attend to...I would purchase good quality complex black boxes like MMPT's, with very good manuals...and for all the less complex stuff, i.e. constant current LED drivers, DC-DC converters, chargers and the like...I would build all of them myself using design apps supplied by chip manufacturers like ST. I would ensure that "Earth" is always the reference line and that isolation, where required would be very high and reliable.
     
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