Got some LEDs and resistors now a question...
Thread Starter
TECH Junkie
iTrader: (6)
Joined: May 2005
Posts: 3,185
Likes: 3
From: Highland, Indiana
Got some LEDs and resistors now a question... Ok I got some 8,000 MCD Red LEDs on ebay a good deal 100 for like 10 bucks shipped and 100 330 ohm 1/4 watt resistors for like 4 bucks shipped . So here the problem the lead on the resistors is a considerable smaller gauge than the leads on the LEDs. I did a TEST setup ...
note: this will NOT look anything like my final product
It is obvious that the gauges are much different... especially after turning it on, the resistor leads get quite warm ( too hot to touch ). I left it on for a while and they didnt melt off or anything like that but I couldnt get an actual temperature on it.
My question is, will this heat issue dissapear when I solder these together especially if I solder the leads as close the actual resistor as possible or should I start looking for different resistors?
note: this will NOT look anything like my final product
It is obvious that the gauges are much different... especially after turning it on, the resistor leads get quite warm ( too hot to touch ). I left it on for a while and they didnt melt off or anything like that but I couldnt get an actual temperature on it.
My question is, will this heat issue dissapear when I solder these together especially if I solder the leads as close the actual resistor as possible or should I start looking for different resistors?
Last edited by Luna; Dec 7, 2005 at 08:20 PM.
Thread Starter
TECH Junkie
iTrader: (6)
Joined: May 2005
Posts: 3,185
Likes: 3
From: Highland, Indiana
Ok , thats kind of what I was thinking anyway. Now what the hell am I going to do with 100 resistors
Will these do the trick ?
http://cgi.ebay.com/ws/eBayISAPI.dll...MEBI%3AIT&rd=1
Will these do the trick ?
http://cgi.ebay.com/ws/eBayISAPI.dll...MEBI%3AIT&rd=1
Last edited by Luna; Dec 7, 2005 at 09:18 PM.
There's not much your going ot be able to do with the resistors. I always use resistors that are rated at 1/4 watt. LED's pull around 20 mA or .02 A of current. So the amp. ratign must be very small on those resistors. Here's the formula you use to figure out the OHM value of the resistor you should use for the LED. Say you have a 12 volt supply voltage and the resistor has a voltage rating of 2.8 volt's and a amp. rating of 20 mA which is common. Different colors will have different voltage ratings. What you do is
Source Voltage (12V) - LED voltage (2.8)
---------------------------------------------- = 460 OHMS
LED amp rating 20mA which is (.02)
You can use this formula to figure out the proper resistor to use with any LED
Hope this helps
Source Voltage (12V) - LED voltage (2.8)
---------------------------------------------- = 460 OHMS
LED amp rating 20mA which is (.02)
You can use this formula to figure out the proper resistor to use with any LED
Hope this helps
It's not the wire gauge, it's the heat being shed
in the resistor. You're running them right at the
rated power dissipation. If you give them adequate
air for cooling, OK (barely). If you put them inside
a little closed space they'll cook. Of course running
voltage is higher than 12V so you may end up on
the wrong side of it.
If you stack 2 LEDs in series then that resistor
will put you at about 20mA (check the forward
current rating, and try to run about 75% of it to
avoid damage) and the resistor itself will be running
about 0.1W. The LEDs will vary in brightness a bit
more, with line voltage but maybe this is a tolerable
solution (like, free).
in the resistor. You're running them right at the
rated power dissipation. If you give them adequate
air for cooling, OK (barely). If you put them inside
a little closed space they'll cook. Of course running
voltage is higher than 12V so you may end up on
the wrong side of it.
If you stack 2 LEDs in series then that resistor
will put you at about 20mA (check the forward
current rating, and try to run about 75% of it to
avoid damage) and the resistor itself will be running
about 0.1W. The LEDs will vary in brightness a bit
more, with line voltage but maybe this is a tolerable
solution (like, free).
Trending Topics
Thread Starter
TECH Junkie
iTrader: (6)
Joined: May 2005
Posts: 3,185
Likes: 3
From: Highland, Indiana
Well my DC source right now is the power supply from a model train and where i have it set right now is about 13.5 volts which I would say is a good estimate of what it would be in the car?
I just try wiring the LEDs in series but it doesnt seem to effect the amount of heat the resistor is generating.
Here are the exact specs for the LEDs and resistors I am using so maybe someone can pinpoint what is wrong here.
Resistors:
- 330 ohm 1/4 Watt ±1% Axial Lead Metal Film Resistors
- I did not see an amperage rating for the resistors but it does say they can be used for:" two InGaN based 3.0~3.3V LED @ 20mA from a 12V source."
LEDs:
Material : InGaN
Size(mm) : 5mm
Lens Color : Water Clear
Emitted Color : Red
Intensity Typ : 8,000mcd
Viewing Angle : 20°
Forward Voltage : 1.9v-2.2v
Forward Current : 20mA
I just try wiring the LEDs in series but it doesnt seem to effect the amount of heat the resistor is generating.
Here are the exact specs for the LEDs and resistors I am using so maybe someone can pinpoint what is wrong here.
Resistors:
- 330 ohm 1/4 Watt ±1% Axial Lead Metal Film Resistors
- I did not see an amperage rating for the resistors but it does say they can be used for:" two InGaN based 3.0~3.3V LED @ 20mA from a 12V source."
LEDs:
Material : InGaN
Size(mm) : 5mm
Lens Color : Water Clear
Emitted Color : Red
Intensity Typ : 8,000mcd
Viewing Angle : 20°
Forward Voltage : 1.9v-2.2v
Forward Current : 20mA
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
TECH Enthusiast
Joined: Sep 2005
Posts: 717
Likes: 0
From: Georgetown, DE
IMHO you should use 680 Ohm 0.5 watt resistors. Ohms Law is a rough calculation. You always want some overhead. In addition, you have to factor in tolerances. Common resistors usually have a tolerance of 20%. You can find you can get resistors with tolerances as low as 1% if want them. But that's probably not necessary.
At this resistance, 0.25W are on the hairy edge of being adaquate. They will work, but they won't last as long as they should. A lower resistance will also work, but your going to be driving more current thru your LED than it was designed for, plus disipating a full 1/2 watt thru the resistor. Again this shortens the life of the components.
At this resistance, 0.25W are on the hairy edge of being adaquate. They will work, but they won't last as long as they should. A lower resistance will also work, but your going to be driving more current thru your LED than it was designed for, plus disipating a full 1/2 watt thru the resistor. Again this shortens the life of the components.
The heat will be the same but the surface area,
roughly double. Still the dissipation has to be
supported by airflow convection, or conduction
to some hard heat path.
13.5 is a good enough estimate of normal. For a
product that you would warranty, you probably
want to margin it up some, like 15V. Here is what
various diode stacks should do for the same 330
ohm resistor (I was figuring more like the 3V I see
on white LEDs, but this is for a 2V drop):
Batt LEDs VdropL VdropR PdissR I_LED
13.5 1 2.0 11.5 0.40 35mA
13.5 2 4.0 9.5 0.27 28mA
13.5 3 6.0 7.5 0.17 23mA
13.5 4 8.0 5.5 0.09 17mA
15.0 4 8.0 7.0 0.15 21mA
Your LEDs will vary more in current and output
with line, the more diodes are stacked in series
(relatively invariant drop leaving variation to
the current-setting resistor).
roughly double. Still the dissipation has to be
supported by airflow convection, or conduction
to some hard heat path.
13.5 is a good enough estimate of normal. For a
product that you would warranty, you probably
want to margin it up some, like 15V. Here is what
various diode stacks should do for the same 330
ohm resistor (I was figuring more like the 3V I see
on white LEDs, but this is for a 2V drop):
Batt LEDs VdropL VdropR PdissR I_LED
13.5 1 2.0 11.5 0.40 35mA
13.5 2 4.0 9.5 0.27 28mA
13.5 3 6.0 7.5 0.17 23mA
13.5 4 8.0 5.5 0.09 17mA
15.0 4 8.0 7.0 0.15 21mA
Your LEDs will vary more in current and output
with line, the more diodes are stacked in series
(relatively invariant drop leaving variation to
the current-setting resistor).