Cool invention, John, and one that I'm sure you'll get lots of fun use out of (watch your eyes everyone). But what I love most about this Gadget Freak example is that John is 15 and motivated enough to pursue his interest in engineering and science to experiment with new technologies like LED. Keep it up and let's hope there are lots more Johns out there today honing their engineering skills for tomorrow.
Beth, I agree, what a cool Gadget Freak video! John is definitely passionate about LEDs and I can see him becoming the next Thomas Edison of the 21st century. I have a couple students in my Electrical Engineering Technology program (I'm Dept. Chair) at ITT Tech want to share this video with to get them motivated about their field of study. Very Nice work John!!!
I also would like to note that yesterday the LEDs I used were re-specced by the distributor (DX.com) , thus the light isn't quite 3000lm. Not by much, of course, but about 2700lm-2800lm.
John: I am impressed with your results and would like to talk to you about your future. My name is Frank Rudolph and you can reach me on Linked-In under that name. You can reach me on Linked-In or directly at docrudolph@gmail.com, or at rudolph@beaconpower.com. At Beacon Power, our corporate charter focuses on alternative energy and sustainability.
Incidentally, if you don't already have a Linked-In account, you should get one now!! Judging from what I have read here, you have a brilliant career ahead of you, and making contacts with a network of people in the industry should start for you right now! Good job! Keep on thinking of new stuff.
I shared your Gadget Freak video with a group of DC-AC Electronics students at ITT Tech to get them motivated about Electrical-Electronics Engineering Tech. I wanted to illustrate the importance of doing homework, which you elegantly demonstrated, in the video based on your LED research. Keep the good work!!!
To aid in your LED lighting research experiments, here's a cool online circuit simulation website called Circuit Lab. Nice way to do paper analysis first and then model it using software. Here's the link below. Enjoy!!!
You are correct that three 10-watt resistors in parallel will make a 30-watt resistor that is one-third the resistance. But then adding three of these 30-watt resistors in series will only result in a resistor of the original value, but STILL only capable of dissipating 30 Watts, not 90W as you stated.
Huh?!? Better go back and study Ohm's Law again, my friend!
Paralleling three equal 10W resistors will, as you agreed give you a 30W equivalent.
Placing three equal 30W resistors *however achieved* in series will indeed give you a 90W equivalent. If all nine resistors are of the same value, the combination will have the equivalent resistance of a single resistor, with nine times the power rating.
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.
@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.
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.
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.
It's actually even less than that, and it's 90W of power handling. The Cree XM-L datasheet puts 2.5A at 3.25V. (12-(3.25*3))V^2/1Ohm=5W. 5W/9=1/2W per. Better get those resistors some airflow John. You got them wrapped in insulation or something?
My humble apologies. I just cranked through the numbers (Using E^2/R, 90W across 1-ohm means voltage of ~9.48V, and current of ~9.48V; break that into thirds, carry the zero, hold yer tongue right, etc...) and John (along with the rest of you) is correct! Somehow, 30 years as a BSEE and all, I let my mind take over before doing the (full) analysis.
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.)
Nice project;it's great to see this lad working hands-on on this project. Perhaps a good follow-on project would be to design a switching regulator and avoid the power loss in the resistor bank. Keep up the the good work you've started.
Best regards,
Myron Boyajian
Congratulations again, John. You've got the makings of a great product here. For those who haven't seen John's earlier work in Gadget Freak, look here:
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.
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.
Not sure whether you meant that those are better, or this is, but I did notice that they were over $600 and $1000usd respectively. This was about $50, and runs cold. Those, just judging by size, would run VERY hot, and would probably not run for the claimed ~2 hours without overheating. Either way, I wasn't claiming that this is the brightest possible light, just that it is very bright.
John: Nearly as impressive as your design is your knowledge of the different specifications and attention to using that data as part of a process around design tradeoffs. Looking under the covers and considering the pros and cons of different materials and different design choices is all part of the game and you are well on your way to becoming quite a diligent and thoughtful engineer.
You're clearly well on your way to an elustrious career in electrical engineering. Do take a look at the ol' LM317 (LM117,217,317) voltage regulator datasheet. Somewhere in the back is a constant current regulator circuit that you will find very useful in your line of research. Also, check out Natsemi's (now TI) boost switching regulators. Just add an inductor, a FET, a diode and a bunch of caps to nake a voltage step-up constant current regulator. I just finished a controller design to drive those ebay 100W modules (33V @ 3A) off of 12V power. Keep having fun.
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 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
@laserdudephil, thanks, but I generally, (except on DX), can only really buy stuff from stores, and constant current switching supplies arent exactly cheap or common. I just used resistors becasuse radioshack carries them for about $1 each.
As for the power dissipation of the resistors, they are sinking a lot more than 1.6W each, and it is definately not much more than 3A, or else the LEDs would burn out. Also, I'm not sure if heat is solely dependent on wattage, I believe current is generally more important (not sure though...) since high voltage at low current (estimated 100,000V@~20mA) should be about 2000W, but the resistor didn't break a sweat.
Naw, the power being dissipated IS the heat being given off. Remember that law of thermodynamics? Energy shall neither be created nor destroyed. Here elecrtrical energy (the power x the time it is applied to the resistor) is entirely converted to heat.
First off let me give John a thumbs up for the good work.
I have been reading this article over and over and cannot understand how Design News publishes a project that falls into a category of a flash light that can cause eye damage if looked at accidentally. This is not a novice project and Design News should considered not publishing projects of this type.
For the most part, it is eye-safe. I wear sunglasses for the final test, and welding goggles while building becasue I am right next to the lights. More than a foot or so away, and it's not very dangerous for a short glance. Only when you are RIGHT on the LEDs does it really start to cause damage (I used a light-sensitive resistor and the threshold of a 3mW laser to determine what would cause eye damage).
Basically, if you don't have something right in front of the LEDs, and no one is looking directly at it, it isn't dangerous.
I disagree with the statement that Gadget Freak articles are just for novices. I'm a retired electrical engineer and I don't miss a single one. Even an experienced engineer can sometimes learn something.
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).
"it is definately not much more than 3A, or else the LEDs would burn out"
I wonder. They can probably take dobule the nominal current for a while, and BTW, put out considerably over 1000 lumens each while doing so.
This could be explained by looking at a few assumptions. Your battery voltage is probably actually more like 12.6 V or even a bit higher, at full charge, which will drive up both the current the LEDs draw and the resulting power. The I/V curve for these devices increases pretty sharply! And - the LEDs are in series, correct?
As Phil commented, power = heat, and is not dependent upon either voltage or current more than the other. In the case of the 100 kV at 20 mA load, what's the source? It could be that what you are driving with has limited current capbility, and the terminal voltage drops drastically under a 20 mA load. Otherwise, you would be dissipating 5 Megawatts!!
In response to the nasty criticism about this being so very dangerous. Most of the readers drive cars, which are far more dangerous than this flashlight. Almost everything requires a bit of wisdom and good judgement to use. The safety rules designed to protect drunks bent on self destruction are a needless burden on most of society. What I am referencing is the european safety regulations for electrical equipment, by the way.
At some point an individual must take responsibility for the results of their actions, and a big part of that responsibility is understanding what one is doing. I know that is offensive to those who abhor personal responsibility, go ahead and be offended.
Those who produce my designs are confident in my level of responsibility, and know that I will not deliver a design that will not meet the project requirements. That would be a big risk if I were not responsible enough to assure that the design was adequate. Certainly there are many other engineers in a similar position, who are responsible for doing their job correctly. Those are the good engineers, the others need to have fifty people check their work for errors, oversights, and other types of goof-ups.
Good Job Duffy ! Keep your thinking cap on...innovate or perish!
Regarding "dangerous" LED light; Anyone who works with LEDs has inevitably received 'retina burn' from looking directly at a lit source. Being an evolved human, the typical person quickly looks away to mitigate the effect....which is annoying at worst. (seeing spots)
"it hurts when I look at the sun"
"so, don't do that, stupid."
Here's a biological safety report from Lumileds for an LED comparable to the one John used. www.philipslumileds.com/uploads/292/AB81-pdf
Result: Low risk to damage the eye from white LEDs. I've read elsewhere that exposure to Risk group 1 is comparable energy-wise to looking at the horizon line on a bright sunny day at high-noon in the desert, without sunglasses. In other words, peanut butter is probably more dangerous.
That said, good call on the sunglasses/welding mask...those 'after-image' spots are truly annoying, especially if you're trying to work a solder iron!
Note: blue or royal blue LEDs present a higher biological hazard because of the narrow bandwidth and high energy content of blue light...so if you're developing a remote phosphor system or a weaponized blue LED stun light, keep your welding goggles handy.
That's 3 leds, and 1 heatsink (referring to parts list). Also, it would be fairly simple to add a dimming circuit using a MOSFET and the LM555 as a PWM controller. Good job..
Im am new at this, can you spell out a few things for me,
If you were to try to make the brighest lamp why would you not use 4 of the leds and not use the droping resistors
How do you calculate the size (resistance and wattage) of the resistors if you were to use 1,2,3,4 of the led elements
The dimming circut you spoke about sounds interesting,can you give me more info on how to do that,or take the same aproach as in the led desk lamp #230 It seams to be a different aproach
sorry I took so long to respond, I haven't checked this in a while. I could have used four LEDs, but the minimum voltage to keep up output is 3V, so if I run four, it would only work as long as its above 12V. A deep cycle battery will drop the voltage a bit when a load like that is applied, and though ohms law will drop the current going to them based on the resistors, the effect would be way more significant if each gets <3V.
As for a driver circuit, I could have, but I was pressed for time initally, as I had intended to bring it to a gadget competition at a camp I was attending. Unfortunatealy, the LEDs didn't ship in time, and I didn't see much of a need to redesign. Another light I made just a few days ago using two LEDs does use a driver circuit. As for calculating the resistors, each LED has a frop of 3V, and thus for each LED, just subtract 3V from 12V, then use ohms law for 3A. I ran three, thus a drop of 9V, leaving 3V. I needed 3A, thus 1ohm. two would leave 6V, thus needing 2ohms, and one would leave 9V, needing 3ohms four would leave 0V, thus 0ohms, but leaving the problems mentioned before.
As for the safety issue mentioned, most of that was precautionary. From more than a few inches it won't burn. Becasue it has a ~120 degree spread, the power will very rapidly dissipate, so it's NOT like a laser, but is powerful enough to distract or irritate someone from afar. Basically, I just meant don't shine it at cars or in peoples eyes. It, and almost all things should just be treated as though they are more dangerous than they really are.
And finially, does anyone have any advice on easy to build 3D printer extruders, specifically, something light that doen't require fabrication access (no milling, latheing (lathing?) 3D printed parts, etc.), just hand tools and such? I'm building a cheap 3D printer/wax CNC device, and the only problem I haven't fixed so far is the extruder, mainly becasue it will likely be fairly expensive (I'm looking for <$50, though), and thus I don't want to experiment more than I have to, as that will get expensive fast.
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