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John Duffy
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Platinum
Re: Nice work John
John Duffy   10/22/2012 3:51:28 PM
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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. 

John Duffy
User Rank
Platinum
Re: Go John!
John Duffy   10/22/2012 3:47:44 PM
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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. 

  

dbell5
User Rank
Platinum
Re: Go John!
dbell5   10/22/2012 2:43:50 PM
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@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.

 

Dave

RICKZ28
User Rank
Platinum
Tinkering
RICKZ28   10/22/2012 2:24:43 PM
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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).

RudySchneider
User Rank
Iron
Re: Go John!
RudySchneider   10/22/2012 2:04:43 PM
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@Dave ---

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.

Eddy Current
User Rank
Iron
Re: Go John!
Eddy Current   10/22/2012 1:06:47 PM
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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. 

What's next for you?

-Eddy

mrdon
User Rank
Platinum
Re: Go John!
mrdon   10/22/2012 12:55:20 PM
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Hi John,

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!!!

https://www.circuitlab.com/

mrdon
User Rank
Platinum
Re: Go John!
mrdon   10/22/2012 12:39:20 PM
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Hi John,

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!!! 

dbell5
User Rank
Platinum
Re: Go John!
dbell5   10/22/2012 12:16:11 PM
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Great job, John! Keep up the good work.

 

Rudy Schneider:

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.

 

Dave

RudySchneider
User Rank
Iron
Re: Go John!
RudySchneider   10/22/2012 11:50:24 AM
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Just a quick correction, John...

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.

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