question on panel lamps?

crippledchicken · 18th May 2007, 02:33 PM

hi, this is a little off topic but, the back light panel lamps on my home base police scanner have burnt out and, i can't order replacements as they are not available any more . the voltage present for each of the 4 bulbs is 5v. dc. the scanner has three brightness settings bright,dim and off. i used some 6v. dc bulbs from Radio Shack that worked but, burnt out within a few weeks? should i be adding a resistor in series with thes replacement bulbs which are rated 25ma.dc? i'm not sure of the current rating of the original bulbs or, should the bulbs regulate the current that goes through them according to the resistance through them? http://www.radioshack.com/product/in...tId=2102814&cp these are the bulbs i'm trying to use. any help would be greatly appreaciated! Thanks

BWRX · 19th May 2007, 01:52 PM

I don't see why those 6V 25mA would have burned out, unless they're just really crappy bulbs which could be the case. The current draw rating is how much current the bulb will draw with 6V across it. It should be able to handle slightly higher or lower voltages without any problems.

What are the voltages for the bright and dim levels? You could probably replace the bulbs with LEDs and series resistors and get good results.

crippledchicken · 19th May 2007, 03:45 PM

Hi, and thanks for your help. i haven't measured the bright and dim settings but i will. are you familiar with any of the leds Radio Shack stocks that might be a good choice and resistor value that would work well? my eyes aren't what they used to be due to my diabetes problem so, the better the back lights, the better for me. thanks again for your help!

i assume, the red wire on the bulbs is the positive, and the white goes to ground?

Sonusthree · 19th May 2007, 04:37 PM

Hi,
Regular bulbs don't have a polarity so anyway round is good but it might be useful to follow convention and have the red at positive,

LED's:
The longest leg of the LED is positive and you can use this handy calculator: http://led.linear1.org/1led.wiz to find the correct resistor. Just punch in the supply voltage and LED specs and away you go. There is another calculator on that page for using multiple LED's. The rest of the site is good reading too if you have the time.

Best regards,
Martin.

crippledchicken · 19th May 2007, 11:12 PM

hey, thanks for the great link and advice! i'll see what i can come up with. thanks again!

18th May 2007, 02:33 PM	#1
crippledchicken diyAudio Member Join Date: Dec 2003 Location: south east mo.	question on panel lamps? hi, this is a little off topic but, the back light panel lamps on my home base police scanner have burnt out and, i can't order replacements as they are not available any more . the voltage present for each of the 4 bulbs is 5v. dc. the scanner has three brightness settings bright,dim and off. i used some 6v. dc bulbs from Radio Shack that worked but, burnt out within a few weeks? should i be adding a resistor in series with thes replacement bulbs which are rated 25ma.dc? i'm not sure of the current rating of the original bulbs or, should the bulbs regulate the current that goes through them according to the resistance through them? http://www.radioshack.com/product/in...tId=2102814&cp these are the bulbs i'm trying to use. any help would be greatly appreaciated! Thanks

19th May 2007, 01:52 PM	#2
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	I don't see why those 6V 25mA would have burned out, unless they're just really crappy bulbs which could be the case. The current draw rating is how much current the bulb will draw with 6V across it. It should be able to handle slightly higher or lower voltages without any problems. What are the voltages for the bright and dim levels? You could probably replace the bulbs with LEDs and series resistors and get good results. __________________ Brian

19th May 2007, 04:37 PM	#4
Sonusthree diyAudio Member Join Date: Dec 2005 Location: Brighton,UK	Hi, Regular bulbs don't have a polarity so anyway round is good but it might be useful to follow convention and have the red at positive, LED's: The longest leg of the LED is positive and you can use this handy calculator: http://led.linear1.org/1led.wiz to find the correct resistor. Just punch in the supply voltage and LED specs and away you go. There is another calculator on that page for using multiple LED's. The rest of the site is good reading too if you have the time. Best regards, Martin. __________________ Martin + + =

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19th May 2007, 03:45 PM	#3
crippledchicken diyAudio Member Join Date: Dec 2003 Location: south east mo.	Hi, and thanks for your help. i haven't measured the bright and dim settings but i will. are you familiar with any of the leds Radio Shack stocks that might be a good choice and resistor value that would work well? my eyes aren't what they used to be due to my diabetes problem so, the better the back lights, the better for me. thanks again for your help! i assume, the red wire on the bulbs is the positive, and the white goes to ground?

19th May 2007, 11:12 PM	#5
crippledchicken diyAudio Member Join Date: Dec 2003 Location: south east mo.	hey, thanks for the great link and advice! i'll see what i can come up with. thanks again!

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