You didn't include a schematic of your light, so I had to infer from your math bit.
It appears that you are wiring the three 10W LEDs in series, and estimating 9.5V for the set, or ~3.2V each. That sounds correct, so far.
Powering that off of 12V, you need to drop (12 - 9.5) or 2.5V, as you showed.
Then, you place the LEDs in series with a power resistor, and switched 12V battery.
If all the above is true, then the (composite) resistor will see a 2.5V drop, and pass 2.5A. P=IE, for 6.25 Watts total dissipated, or ~1.6W per resistor.
If the 40W of resistor was getting to 200°C, then there it seems like must have been more than 3A in the circuit. If you were dissipating 40 Watts in 1 Ohm, then: P = I^2R, and I = sqrt(40), or 2 sqrt(10), or 6.3 Amps.
Thanks John, I've just checked it out. Did you notice that they only have line voltage drivers for them? Trust me on this, once you start playing with constant current switching power supplies, you'll never look back at those burning hot power hungry resistors and linear regulators. ...and in spite of what I said earlier, do take your time and get a proper BSEE from an accredited university. There are all too many people out there who would take advantage of your ingenuity to the detriment of your youth and education. Best, -Phil
I'm sorry but you're way off. You're thinking in terms of a fixed voltage. An n watt resistor is rated for n watts no matter what's next to it (except for a heat gun.)
Eddy, yes I really do enjoy making these kinds of things, even before I knew about Gadget Freak. For my next one, I'm thinking either audio or integrated computing.
Also, laserdudephil, I would recommend looking at DX.com, as they have some even higher power LEDs, one of them 150W. I'm actually looking to get one of those myself, to make a miniature spotlight. Problem is, I have to find some even stronger goggles first, and a way to keep it cool.
Thanks for all the feedback, I do have one question about engineering jobs and such though, specifically, what kind of jobs are there in building stuff, and what kind of college majors exist for jobs like that? I have recently started looking into colleges and such, and am not sure what to major in (I still have two years, of course, but it doesn't hurt to look ahead).
As for the debate over resistors, yes, more resistors means more power dissipated. It has to dissipate about 30-35W (2.5-3A@12V). Even though the LEDs drop the voltage, the ammout of power dissipated is still big, as when I had 40W resistors (4x10W), they got to about 200C, at which point it started melting the plastic around them. Also, yes, that does dissipate 40W. If you think about it, then it makes sense that the whole resistor block, be it 90W or 10W will always have 3A through it. Since each resistor (for the 4x20W configuration) will contain 1/2 of the ammount of resistive material between the two ends, each will recieve 1.5A@12V. If you put two in series, then each only needs to sink 1/2 the voltage. It is then 1.5A@6V, or 9W per resistor.
Anyway, thank you all for your support and suggestions about this, I really do appreciate it.
@Rudy - Hey, no problem - I love a good technical discussion! :{)
In the series/parallel arrangment John used (3x3 of 10 W originally, and I have to assume 2x2 of 20W in the parts list), both the current and the voltage divide among the 9 resistors. 1/3 I x 1/3 E = 1/9 P in each resistor. Doesn't matter a whit, if they are all in series, all in parallel, or in groups like this.
It's all a bit overkill, though. Unless I haven't had enough coffee yet this morning, dropping 2.5V at 2.5A is only 6.25 Watts. Still a bit much for a single 1 Ohm/10 Watt resistor, but should be no sweat for a single 1 Ohm/20 Watt, as in the parts list.
It's great to read about this young man "tinkering" with stuff...nice project! John Duffy, keep up the great work, and consider an engineering or science degree, and career!
All too often, interviewing engineering personnel candidates, I found that many young degreed engineers have never worked with/on anything while growing up (or currently). They have not had projects building gadgets, fixing things, or modifying stuff. They say things such as they like cars, but have never attempted any work on cars. I wonder if they can even hammer a nail, or screw-in a screw...use a tool. Installing software and playing video games does not count to me as a project or tinkering.
By age 18, my list of projects and accomplishments was huge, a lot of practical experience...including advanced auto and motorcycle mechanics, and Hot Rodding (modifying to be powerful and fast). Growing up, I helped my dad with numerous house and car repairs, my dad was an engineer (now retired).
I don't mean to argue, but I think you need to re-think that. If I place two 1K, 1-Watt resistors in series, I end up with a 2K, 1-watt resistor. The same holds true for three series 1/3-ohm, 30-watt resistors, as in John's example. It ends up being a 1-ohm, 30-watt resistor.
If John had started with nine 9-ohm, 10-watt resistors, and placed them ALL in parallel, I agree that he would end up with a 1-ohm, 90-watt resistor. That's not what he describes, however.
From your video we can see that you have done some experimentation with other batteries and LEDs. Enjoyable video and it looks like you are having fun.
By refining topologies and using new fluid technology, Moog's new peak sine drive controller increases available power without increasing controller volume.
Lantronix Inc. has expanded its line of controllers for sensor networks with the release of a rugged controller that improves management of automation systems used in a number of industries, including manufacturing, oil and gas, and chemicals.
Inspired by the hooks a parasitic worm uses to penetrate its host's intestines, the Karp Lab has invented a flexible adhesive patch covered with microneedles that adheres well to wet, soft tissues, but doesn't cause damage when removed.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
6 
