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.
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!!!
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!!!
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.
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.
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 firstname.lastname@example.org, or at email@example.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.
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.
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.
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.
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