Original led strip circuit:
Where the input is 12V
and R = 150 ohms:
And to make it work on 5.1V rail i removed the resistors and attach them 2 by 2 like so :
at the end i used a n mosfet to negative to control it with my arduino BUT my question is:
Is there any problem because i used no resistors on the leds ?
They are powered by a 5.1V wall adapter, obviously they are not at full brightness and they are not getting hot.
bump!
Not getting hot is a good sign. Led forward voltage drops with heat.
You could get a DC-DC boost converter to change 5V to 12V and not have to modify the strip. Biggest problem might be getting enough amps of 5V to power more than a meter of strip.
Didn't had access to a boost convertor and they are expensive in local shops the 5v can deliver 700mA and i have less then 50cm of led strip (modified)
For led use you might search on DIY converters and maybe but I'm not sure, a Joule Thief circuit.
This would be to save you having to modify a lot of led strip.
I feel for your restriction. I would not want the same. Here I have access to eBay.
Thanks for your replay man, i really appreciate you
I mean i have access to ebay and all of those but 30-40 days + christmas delay
The thing is i already modified it but i just wanted to be sure that everythings is going good,
the propose of those leds are for a mood lamp and the fact that they are not at full brightness (because 5.1V - 3.2V(led1) - 3.2V(led2) are not giving me a positive result) it's a good thing for a mood lamp
I don't thing you can understand much of this mess but there's a picure of it:
as i said, everything is cold and bright
Is there any problem because i used no resistors on the leds ?
Yes! That's a BAD thing to do! LEDs, like all diodes, are "non-linear and their resistance drops "suddenly" at their breakdown voltage ("operating voltage" for an LED). When resistance drops, current increases dramatically. If there's not something to limit the current, the LED will burn-up or the power supply (or other driver circuit) will burn-up.*
An LED can overheat and burn-up internally before it's hot enough to feel hot to the touch. But, if you're not getting full-brightness they are not getting over-driven.
obviously they are not at full brightness
It's not so obvious.** Either the breakdown voltage of the two LEDs in series is less than 5.1V, or you have a lot LED-pairs drawing lots of current and 5.1V is not holding-up.
** P.S.
(because 5.1V - 3.2V(led1) - 3.2V(led2)
It is obvious if you are sure the LEDs are rated at 3.2V... It depends on the color of the LED and the 'exact' breakdown voltage will vary with temperature and from part-to-part.
DVDdoug:
Either the breakdown voltage of the two LEDs in series is less than 5.1V, or you have a lot LED-pairs drawing lots of current and 5.1V is not holding-up.
My guess is the latter but I'm no expert on leds and I do have 12-led-disks that run 120-125F (not checked lifetime, likely reduced).
I'm a bit shady about this, the led should not conduct until forward voltage is reached?
Then after that the current flow has very low resistance?
Still, a white led has multiple junctions with differing VF? Or one junction and sumptin else?
prologikus:
I mean i have access to ebay and all of those but 30-40 days + christmas delay
Chinese New Year is another maybe bigger delay. 2 or 3 extra weeks last time I bought then.
DVDdoug:
Yes! That's a BAD thing to do! LEDs, like all diodes, are "non-linear and their resistance drops "suddenly" at their breakdown voltage ("operating voltage" for an LED). When resistance drops, current increases dramatically. If there's not something to limit the current, the LED will burn-up or the power supply (or other driver circuit) will burn-up.*
yes but what resistor shoud i use, because using the classic method like so :
R=V/I result in this:
R = (5.1-3.2-3.2)/0.01
R = -130 and resistence can't be on -, and this confused me
An LED can overheat and burn-up internally before it's hot enough to feel hot to the touch. But, if you're not getting full-brightness they are not getting over-driven.
It's not so obvious.** Either the breakdown voltage of the two LEDs in series is less than 5.1V, or you have a lot LED-pairs drawing lots of current and 5.1V is not holding-up.
DVDdoug:
__** P.S.__It is obvious if you are sure the LEDs are rated at 3.2V... It depends on the color of the LED and the 'exact' breakdown voltage will vary with temperature and from part-to-part.
I don't know for sure that the led is rated at 3.2V but doing the reverse ohm law on a part of unmodified led strip and that gave me 3.2V but even if the led is rated lower like 2.55 the resistor is still <=1 ...
What do you think ?
If you use a constant current circuit ....
Yes, they are connected to a 5.1V adapter and there is nothing else connected to it
The 5.1V adapter has a current limit that may suit how many leds you light.
A constant current circuit can be set to what current, not voltage, you decide.
The leds can burn up when too much voltage pushes too much current through, it is the excess current that you want to avoid. The resistors are about limiting current. The adapter has a current limit of its own but get another with bigger limit and your leds may get real bright for a short time.
How many mA does the adapter deliver? I have 1000mA and 2000mA 5V plugins. I have seen 500mA 5V adapters but didn't buy.
GoForSmoke:
The 5.1V adapter has a current limit that may suit how many leds you light.A constant current circuit can be set to what current, not voltage, you decide.
The leds can burn up when too much voltage pushes too much current through, it is the excess current that you want to avoid. The resistors are about limiting current. The adapter has a current limit of its own but get another with bigger limit and your leds may get real bright for a short time.
How many mA does the adapter deliver? I have 1000mA and 2000mA 5V plugins. I have seen 500mA 5V adapters but didn't buy.
It's from a old phone (charger) 500mA
I understand all of what you said but i'm very confused because even though i want to use a resistor or more for those i don't know how to calculate it (there are a few leds)