IR flood light - Page 1
Forum section: electronics / beginners

author: shane_95
author_rank: Regular Contributor
timestamp: June 27, 2012, 08:00:54 am
content: If you have read my my other post, you would know I'm trying to get a start into electronicshttps://www.eevblog.com/forum/beginners/17-soon-and-i-want-to-get-into-electronics/I'm thinking about making an "IR flood light" from scratch. I was wondering would this work?LED'shttp://www.digikey.com.au/scripts/dksearch/dksus.dll?vendor=0&keywords=hir7393cBattery cliphttp://www.digikey.com.au/product-detail/en/BS6I/BS6I-ND/32055Switchhttp://www.digikey.com.au/product-detail/en/S201031MS02Q/CKN9891-ND/2055169

author: Rerouter
author_rank: Super Contributor
timestamp: June 27, 2012, 08:07:58 am
content: just a few small beginner mistakes,your leds have a voltage drop of 1.45V each, 10 of them will need 14.5V just to turn on the diodes,also they are 100mA diodes, and 0.1x90 means your resistor would be dropping 9V,you take your supply voltage, - the diode drops in your loop, devide that voltage by your current, and you would end up with 35 ohm if you ran it off 2x 9V batteries in series,edit: also you can upload image directly to this site under attachments at the bottom

author: Rerouter
author_rank: Super Contributor
timestamp: June 27, 2012, 08:17:56 am
content: also it might cost a few cents more, but for something your likely to be swapping batteries commonly on, use a solid clip like thishttp://www.digikey.com.au/product-detail/en/84-6/84-6K-ND/304014and fair game, most 9V batteries at 100mA are only going to last about 4-5 Hours,http://www.electronics-lab.com/blog/wp-content/uploads/2012/02/test_data2.jpg

author: david77
author_rank: Frequent Contributor
timestamp: June 27, 2012, 08:19:42 am
content: I'd like to add that - depending on what you want to do with it - running a flood light like that of 2x9V batteries might not be a good idea. At 100mA current your typical 9V battery will be empty pretty quick, I'd say about 3-4 hours give or take.

author: shane_95
author_rank: Regular Contributor
timestamp: June 27, 2012, 08:25:04 am
content: Ok, so a new resistor, and an extra 9V battery.I wouldn't be running this hours on end, its just a bit of fun I came up with

author: david77
author_rank: Frequent Contributor
timestamp: June 27, 2012, 08:29:04 am
content: You also have to take the power dissipated in the resistor into account. 3.5V x 0.1A = 0.35W.So the absolute minimum you should use is a 0.6W resistor, better get a 1 or 2W type.

author: notsob
author_rank: Frequent Contributor
timestamp: June 27, 2012, 08:30:29 am
content: Here's how to string a few LEDs together

author: Rerouter
author_rank: Super Contributor
timestamp: June 27, 2012, 08:39:11 am
content: personally i would reccomend this design,note its only good for 2 new matched batteries, but it gives you the most bang for your buck on your batteries,

author: shane_95
author_rank: Regular Contributor
timestamp: June 27, 2012, 08:58:09 am
content: Quote from: Rerouter on June 27, 2012, 08:39:11 amis that 4.7 ohm or what?

author: Rerouter
author_rank: Super Contributor
timestamp: June 27, 2012, 08:59:59 am
content: yes, ohm, sorry about that

author: shane_95
author_rank: Regular Contributor
timestamp: June 27, 2012, 09:06:28 am
content: Quote from: Rerouter on June 27, 2012, 08:39:11 amwhat did you use to draw that up

author: Rerouter
author_rank: Super Contributor
timestamp: June 27, 2012, 09:07:22 am
content: falstads circuit simulator, then just captured a screen shot and cropped, (my prefered image export for small circuits)edit:http://www.falstad.com/circuit/

author: Flávio V
author_rank: Regular Contributor
timestamp: June 27, 2012, 10:02:51 am
content: Using 9V batteries on that does't seems like a good idea...For those than love ideal components i may say than they never exist.Batteries have a large resistance of near 200m ohm so that means than a 9V has more than a ohm of resistance.(Not sure about the certain valours for the alkaline ones but they are higher than the NIHM ones...and 200m are a little ones than a usual medium capacity battery.For those types of infra-red LEDs(i wonder what you will do with then)it would be recommended to use rechargeable batteries for less use expenses..