12vdc adapter for white led strip help - Page 1
Forum section: electronics / projects

author: Arcamax
author_rank: Regular Contributor
timestamp: May 13, 2015, 07:17:28 pm
content: so i've been getting different answers, How many amps on an adapter would be enough to light a 1m white 5050 non-waterproof led striphttp://www.ebay.ca/itm/371305992754?_trksid=p2057872.m2749.l2649&var=640425017958&ssPageName=STRK%3AMEBIDX%3AIT

author: rolycat
author_rank: Super Contributor
timestamp: May 13, 2015, 07:51:12 pm
content: White 5050 strips typically consume about 0.24W per LED. 1m has 60 LEDs, so roughly 14.4W or 1.2A.

author: Arcamax
author_rank: Regular Contributor
timestamp: May 13, 2015, 08:22:00 pm
content: ok then, so this should be good then

author: akis
author_rank: Frequent Contributor
timestamp: May 13, 2015, 11:32:17 pm
content: I have purchased a 5 metre 300 SMD 5050 LED white bright strip and tested it today. At 12V it draws around 2.8A, all 300 LEDs and resistors together.

author: rolycat
author_rank: Super Contributor
timestamp: May 13, 2015, 11:55:20 pm
content: Quote from: akis on May 13, 2015, 11:32:17 pmSounds a bit low. What's the voltage drop at the end of the 5M strip? Does it draw more current if you dual-feed it?

author: akis
author_rank: Frequent Contributor
timestamp: May 14, 2015, 09:18:07 am
content: Good point.I have plugged both ends of the 5 metre roll, and it draws 4A at 12V but it varies greatly with heat, as it is all rolled up it gets quite hot and the current shoots up, I stopped it at 4.5A. This is a worry actually, how hot will it get when opened up? I plan to use it inside 1 metre length, sealed acrylic tubes...

author: rolycat
author_rank: Super Contributor
timestamp: May 14, 2015, 10:56:14 am
content: Quote from: akis on May 14, 2015, 09:18:07 amAn LED is typically about 15-20% efficient, so your 1m strips will each generate around 12W of heat. It may be worth testing a tube with a temperature sensor inside.You should also check that your target environment can accommodate a constant 60W of additional heat.

author: akis
author_rank: Frequent Contributor
timestamp: May 14, 2015, 11:37:47 am
content: I have LEDs, 20mA rated, that produce perfect brightness at 10mA. I also have LEDs that are 10 times brighter at 0.5mA and that is all you need to give them.I surely hope that those 60 LEDs which draw around 16mA each are of the type that at 0.5mA would produce same bright light as my ordinary 0.5mA ones!

author: Zero999
author_rank: Super Contributor
timestamp: May 14, 2015, 12:43:11 pm
content: LED strips have the LEDs connected in strings of 3 for 12V to save power dissipation in the series resistors.If the strip has 300 LEDs and draws 2.8A from 12V, then that's 28mA per LED which sounds quite high.

author: rolycat
author_rank: Super Contributor
timestamp: May 14, 2015, 01:09:43 pm
content: Quote from: Hero999 on May 14, 2015, 12:43:11 pm[Edited figures]5050 strips use tri-chip units - 3 diodes in each housing - so technically a 5m strip has 900 LEDs and the current per LED chip would be only 9.3mA.The 2.8A figure is low due to voltage drop along the strip. Assuming the strip is split into 1m lengths which each draw 1.2A, the current per LED chip would be 1.2/60 or 20mA. Current per unit would be 60mA.

author: akis
author_rank: Frequent Contributor
timestamp: May 14, 2015, 01:18:20 pm
content: Wait. Real current (with less voltage drop) per 5 metres is over 4A, increasing rapidly with temperature. That is 13.33mA per LED, and assuming each LED is composed of three internally, then it is 4.44mA per LED. There is a lot of heat generated, all my other LEDs run very cool, maybe it is the resistors on the strip, I will have to check.

author: Zero999
author_rank: Super Contributor
timestamp: May 14, 2015, 01:26:52 pm
content: Quote from: rolycat on May 14, 2015, 01:09:43 pmNo.If it's 300 LEDs then it would be 100 strings of 3 LEDs in series, making 28mA per LED.If each LED has three per package connected in series, 900 LEDs, then it would be 9.33mA per LED.

author: akis
author_rank: Frequent Contributor
timestamp: May 14, 2015, 01:37:59 pm
content: That is true they are in groups of three, so three share the same current. So for 5 metres and 300 total LEDs, we divide by 3, thus 100 LEDs, and we have 4A total, so 4000mA/100LEDs = 40mA per LED.

author: rolycat
author_rank: Super Contributor
timestamp: May 14, 2015, 02:23:31 pm
content: Quote from: Hero999 on May 14, 2015, 01:26:52 pmDoh.You are right, of course. Brain fade, as our beloved Prime Minister would say.Anyway, 9.33mA sounds a lot more reasonable as a per-LED current. Even 13.3mA, assuming the larger current resulting from driving both ends of the strip.

author: Towger
author_rank: Super Contributor
timestamp: May 14, 2015, 06:38:17 pm
content: 5050 internal LEDS are in parallel, supplied separately by 6 pins on the package. From memory chinese strips need to be powered at 14v to achieve their rated power, leaving out the problems with voltage drop etc. However... They may/will not last long. I have two 2.3m strips lighting my conservatory, running at about 11v, fed from both ends without any problems for the last two years.

author: akis
author_rank: Frequent Contributor
timestamp: May 18, 2015, 07:52:52 am
content: I will cut mine is lengths of 1 metre. I will power them on one end with ~12V. It should be OK.