Hooking up LED lights to 12V battery

Discussion in 'OnBoard Electronics & Controls' started by Nickpontoon, Oct 5, 2012.

  1. Don H
    Joined: Apr 2012
    Posts: 52
    Likes: 4, Points: 8, Legacy Rep: 45
    Location: Queensland Australia

    Don H Junior Member

    Hi Rx I have been away on a job for a few days so i will try to answer your comments.

    Yes i agree it may be getting a little technical but at the same time many members are doing their own work so an understanding of the way LED lighting can work may give an option for their own applications. I should mention my degree is in Electrical Engineering and i own an Electronics OEM manufacturing company. As i mentioned earlier we no longer build Hi power LED products but we do have several thousand units or various types in service.

    Yes you are correct they are current devices and a small rise in voltage will cause a large increase in current. However , you do not need to be limited by the steep current curve . One of my designs used a 12v low dropout regulator with 4 x Cree 1 watt leds. Nothing else!! The unit was specified as a 12volt 4 watt driver for RED high power led. The reason it works with so little parts is that the leds are not able to run at the full 350ma rating so they are slightly less bright but well within tolerance. The regulator protects the leds against voltage spikes and rises.

    I would agree that the low current leds(20ma) in the data sheet you attached should have a current limiting resistor for each led. i would even agree that for the superflux leds at 70ma this would also apply. For true high powerleds of 350ma and above parallel conection is common.
    The article of PWM operation might explain that 4 times the current for a quarter of the time produces the same power as the original current all day long.They do not explain that the losses from FET junction resistance or lack of transistor saturation are the reasons for less heating occurring. None of this reduces the heating that occurs at the LED junction.

    The ic is a 5 pin TO252 Package. The heatsink is the tab at the top. Most probably Michael's pcb has an aluminium layer to get rid of the heat from both the driver and the LEDs

    Yes we do multiplex 7 segment displays but not in individual segments. We set the segments all at once then sect the digits. Matrix displays are different in that we multiplex a 7 x 5 character and the multiplex characters. The individual pixel in these displays can be 9 leds each. In this case we do a combination of series and parallel to get a compromise between voltage and current . This combination ensures a failure doesnt mean and entire segment or pixel is lost

    We may just have to agree to disagree on some points but i do think it important to point out some of the options available especially since many on here are building and LEDS will be the fitting choice for sure.

    Thanks Don
     

    Attached Files:

  2. rxcomposite
    Joined: Jan 2005
    Posts: 2,307
    Likes: 324, Points: 83, Legacy Rep: 1110
    Location: Philippines

    rxcomposite Senior Member

    Glad to know we rode on the same boat. I have an Electronics degree and have worked in electronics manufacturing LED/LCD watches, IC, Discrete and Hybrid devices, and design of programmable large panel displays. That is past now as I have changed career. It was becoming too crowded in there.

    No offense was intended and I apologize if I caused any. I was limiting myself to practical design.

    Since you mentioned it, and I also did, paralleling LEDs, is only for manufacturing environment for all practical purposes. The LED watches we made were segmented displays etched on the same chip less than 2 mm. tall yet we have manufacturing problem of uneven segment brightness.

    Even on large discrete display, we did have problem of uneven brightness, color shades because of different bin numbers, even mechanical problem such as chip bonding or soldering of leads. The eye is so sensitive it can discern different shades or perceived brightness. I still have hundreds of these red button with six LEDs inside (attached) because they are of mixed bin numbers that I cannot use. Some are deep red, some red orange. Not good enough. Used as a pixel in a dot matrix display, the eye can see the difference. It being red, I could not find a use for it. Good for experimenting but not for commercial use.

    I agree well regulated voltage IC power supply WITH a load resistor to the LED will work. So does a current regulator IC and a resistor to bias the IC. For all practical purposes, it should be biased so as not to squeeze out max power from the LED. Need allowance for temperature variation.

    And yes, I did blew up Michael’s pics and noticed it is not a mini pack.
     

    Attached Files:


  3. Don H
    Joined: Apr 2012
    Posts: 52
    Likes: 4, Points: 8, Legacy Rep: 45
    Location: Queensland Australia

    Don H Junior Member

    Hi Rx, no offence taken and certainly no apology needed. Its good to hear other ideas. Nothing wrong with a different point of veiw. Without it nobody would learn anything new. Led technology has been changing significantly in the last 10 years, we do very little in new led driver designs but i still take an interest in whats happening. From what i have seen the tend seems to be going slightly away from even the high power leds to the superflux ones.A fair amount of energy is wasted in heat in the LED and until that gets better i think there will be more superflux fittings coming on to the market. They are not quite as bright but with enough of them they are getting good brightness results on low current drain. Great news for boaties trying to keep the load down.

    Thanks Don
     
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