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dimming 3 leds


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midwestoffroad 
Member - Posts: 8
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Joined: April 02, 2008
Posted: April 02, 2008 at 7:29 PM / IP Logged  

I have a pillar gauge in my truck. and each gauge has a white LED. i currently have them all running the the factory dimmer knob but when i get them to the desired brightrness the factory gauges are dark.

my question is can i dim all 3 in 1 shot or do i need a resistor on each lead.. or would a POT be better. i tried a 0-25 ohm dial resistor one and it didn't do anything  that was at the suggestion of the radio shack guy..  otherwise he has 1000k POT,s

midwestoffroad 
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Joined: April 02, 2008
Posted: April 02, 2008 at 7:54 PM / IP Logged  

if it isnt obvious i have no idea what i am doing ot talking about..

each gauge came setup with a led.. i just want to dim them.. any idea on a starting point with a resistor.  . one chart i found shows the resistor  on the - side . i tried the reostat on the +  ..

KPierson 
Platinum - Posts: 3,527
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Joined: April 14, 2005
Location: Ohio, United States
Posted: April 02, 2008 at 8:14 PM / IP Logged  

It doesn't matter which side you put the resistor on, as it will limit current either way.

25 ohms is really, really low.  I would look for a pot in the 0-25K range.

Kevin Pierson
midwestoffroad 
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Joined: April 02, 2008
Posted: April 02, 2008 at 9:34 PM / IP Logged  

thank you. 

i did find in our maintanace department  a 91 and 100 ohm resistor i may try to see way happens.

KPierson 
Platinum - Posts: 3,527
Platinum spaceThis member consistently provides reliable informationspace
Joined: April 14, 2005
Location: Ohio, United States
Posted: April 02, 2008 at 9:51 PM / IP Logged  

That 100 ohm resistor will limit current to 120mA, roughly 80 times more current the the LED can handle anyway - that 100 ohm resistor isn't going to help at all, it is too small.

Kevin Pierson
dudehitt 
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Joined: May 15, 2007
Location: Arizona, United States
Posted: April 02, 2008 at 9:52 PM / IP Logged  

I had a similar situation with some switches I swapped LED's in to match my dash (which were also swapped from factory).  I finally got noticeable results with a 5k resistor and left if at that.  They're still a little brighter than the others, but not by much.

I think the 25k pot. is a great idea.

midwestoffroad 
Member - Posts: 8
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Joined: April 02, 2008
Posted: April 02, 2008 at 9:57 PM / IP Logged  

OK i will try Radio shack again i think all he had was a 1k  pot maybe i am wrong

midwestoffroad 
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Joined: April 02, 2008
Posted: April 03, 2008 at 10:55 AM / IP Logged  
After I came home last night I tried some of the resistors from work , no idea on there size it is a blue resistor with 5 bands
Violet-Black Red Brown and sliver it ohmed to 409.5 and worked perfectly.. so i have no idea if it will work or for how long.
The color bands confuse me even after looking at the Resistor page
i am an idiot 
Platinum - Posts: 13,666
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Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 03, 2008 at 6:51 PM / IP Logged  
It will work pretty much forever.
midwestoffroad 
Member - Posts: 8
Member spacespace
Joined: April 02, 2008
Posted: April 03, 2008 at 9:02 PM / IP Logged  
That would be nice.
Can anyone decipher this resistor
orange,purple,yellow,black,brown
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