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jlinga(at)mchsi.com
Guest

Posted: Fri Jun 30, 2006 4:37 am Post subject: Instrument lighting

Hey Guys,

     I have a simple problem that  most likely has a simple solution.  The solution, however, eludes me.   I have an internally lit g-meter on my instrument panel (Don't ask me why  ).  The g-meter's lighting is internal to the instrument, i.e. it's not  a lighting tray that is screwed to the top.  The instrument would have to  be opened up to get to the lamp.

  

     I purchased the g-meter from  Chief a while back ago, and when I received it, I realized it was a 5v  unit.  Chief didn't have any other lighting option listed or  available.  I thought about dropping the voltage with a resistor.   Before doing this I called the manufacturer Wultrad (aka Falcon Gauge).   They said they had a 12v unit in stock that they could swap for mine.  I  thought... "great problem solved."  They shipped me one back with a 12v  label over the original label.  In testing my instrument panel lighting, I  discovered that the g-meter is considerably brighter than the other instruments  to the point it would be annoying at night.  The interesting thing is the  light is nice and white and very uniform though out the face of the  instrument.  Anyway, I thought... "gee I'm back to putting in a resistor to  dim the light!"

  

     "OK, no problem.  I'll  figure out what size resistor I need and move on," I thought.  The problem  is the resistance of any incandescent lamp changes whether it hot or cold.   The lamp is drawing 0.56 A at 12.0 v.  Seem's like a lot to me.  From  that I deduced the lamp's resistance at 21.3 ohm.  The problem is that when  I figure out what size resistor I need to get say a 7 or 8 v voltage drop across  the lamp and add that resistor to the circuit, the current changes and so does  the resistance of the lamp.  So how does one figure this stuff out?  I  decided to purchase a potentiometer and install it in my circuit, adjust it  'till I got the brightness I wanted and then measure the resistance of the  pot.  In doing this I began to smell smoke, the little pot was beginning to  glow red as I dimmed down the light in the instrument.  I went back and  purchased a heavier pot.  This did the trick.  I decided a 20 ohm  resistor in series would be perfect.  I purchased a 22 ohm, 2 W  resistor, temporarily installed it, and the light was perfect.  The problem  was I was still smelling that familiar acrid smell.  I had a 7.4 v drop  across the resistor and a .34 A current giving me 2.5 W to dissipate.  I  later tried two 10 ohm, 2 W resistors in series.  Still, they got too  hot.  I purchased a ceramic 22 ohm, 5 W resistor and it still got too hot  to touch.  The small battery I was using for testing was putting out 12.2 v  under the load.  I had a 7.4 v drop across the resistor, So I deduced I  must be getting a 4.8 v drop across the lamp.  The light was just  right.  I wonder if I still have a 5v lamp inside the instrument!   I measured 0.34 A in the circuit.  The 5 W resistor ought to be  handling the 2.5 W I need to dissipate just fine.  Something is  wrong.  Do any of you smart guys know what I'm doing wrong?

  

 Jerry

 "Smelling smoke in  Georgia"

klehman(at)albedo.net
Guest

Posted: Fri Jun 30, 2006 5:02 am Post subject: Instrument lighting

Hi Jerry

I'd say you did it all correctly but you are just surprised at how much 

the 2.5 watts heats up a resistor. A 5 watt bulb is about what 

incandescent children's night lights are and does seem ridiculous for an 

instrument so I agree that is is the wrong bulb. I would leave it as is 

with your resistor. Second choice would be change the bulb to one that 

is really 12 volts. Third choice is a variable duty cycle circuit that 

pulses short 12 volt pulses to the lamp so that it averages the same 

power as running it on 5 volts. That avoids heating up a resistor and 

dumping the 2.5 watts but I doubt it is worth the trouble. Fourth choice 

is kind of silly but if you had another similar instrument you could 

wire them is series...

Ken



Jerry & Ledy Esquenazi wrote:



 	  Quote: 	
		   Hey Guys,

     I have a simple problem that most likely has a simple solution.  

 The solution, however, eludes me.  I have an internally lit g-meter on 

 my instrument panel (Don't ask me why ).  The g-meter's lighting is 

 internal to the instrument, i.e. it's not a lighting tray that is 

 screwed to the top.  The instrument would have to be opened up to get 

 to the lamp.

  

     I purchased the g-meter from Chief a while back ago, and when I 

 received it, I realized it was a 5v unit.  Chief didn't have any other 

 lighting option listed or available.  I thought about dropping the 

 voltage with a resistor.  Before doing this I called the manufacturer 

 Wultrad (aka Falcon Gauge).  They said they had a 12v unit in stock 

 that they could swap for mine.  I thought... "great problem solved."  

 They shipped me one back with a 12v label over the original label.  In 

 testing my instrument panel lighting, I discovered that the g-meter is 

 considerably brighter than the other instruments to the point it would 

 be annoying at night.  The interesting thing is the light is nice and 

 white and very uniform though out the face of the instrument.  Anyway, 

 I thought... "gee I'm back to putting in a resistor to dim the light!"

  

     "OK, no problem.  I'll figure out what size resistor I need and 

 move on," I thought.  The problem is the resistance of any 

 incandescent lamp changes whether it hot or cold.  The lamp is drawing 

 0.56 A at 12.0 v.  Seem's like a lot to me.  From that I deduced the 

 lamp's resistance at 21.3 ohm.  The problem is that when I figure out 

 what size resistor I need to get say a 7 or 8 v voltage drop across 

 the lamp and add that resistor to the circuit, the current changes and 

 so does the resistance of the lamp.  So how does one figure this stuff 

 out?  I decided to purchase a potentiometer and install it in my 

 circuit, adjust it 'till I got the brightness I wanted and then 

 measure the resistance of the pot.  In doing this I began to smell 

 smoke, the little pot was beginning to glow red as I dimmed down the 

 light in the instrument.  I went back and purchased a heavier pot.  

 This did the trick.  I decided a 20 ohm resistor in series would be 

 perfect.  I purchased a 22 ohm, 2 W resistor, temporarily installed 

 it, and the light was perfect.  The problem was I was still smelling 

 that familiar acrid smell.  I had a 7.4 v drop across the resistor and 

 a .34 A current giving me 2.5 W to dissipate.  I later tried two 10 

 ohm, 2 W resistors in series.  Still, they got too hot.  I purchased a 

 ceramic 22 ohm, 5 W resistor and it still got too hot to touch.  The 

 small battery I was using for testing was putting out 12.2 v under the 

 load.  I had a 7.4 v drop across the resistor, So I deduced I must be 

 getting a 4.8 v drop across the lamp.  The light was just right.  I 

 wonder if I still have a 5v lamp inside the instrument!  I measured 

 0.34 A in the circuit.  The 5 W resistor ought to be handling the 2.5 

 W I need to dissipate just fine.  Something is wrong.  Do any of you 

 smart guys know what I'm doing wrong?

  

 Jerry

 "Smelling smoke in Georgia"

chaztuna(at)adelphia.net
Guest

Posted: Fri Jun 30, 2006 6:41 am Post subject: Instrument lighting

Jerry,

  I think that Ken's third suggestion is the best for your problem. A nice, inexpensive circuit for accomplishing this can be purchased below. FYI, this unit can be used to control a defroster fan motor, slow down electric trim servos or act as you wish to use it, to dim lights.



  http://www.mpja.com/productview.asp?product=4057+MD



 For your purpose, the reversing slide switch can be eliminated. I've built a number of these units. I'm using them for defrost fan speed control, MAC trim servo speed reducers and for panel light dimming. They are a lot cheaper than other items sold for these purposes. In addition, if I carry one spare unit, I can use it to replace a number of failed control devices. Heck, if it fails, I can simply go to Radio Shack and buy a replacement diode/resistor/capacitor to repair it.

 Charlie Kuss



  	  Quote: 	
		  Hey Guys,

     I have a simple problem that most likely has a simple solution.  The solution, however, eludes me.  I have an internally lit g-meter on my instrument panel (Don't ask me why ).  The g-meter's lighting is internal to the instrument, i.e. it's not a lighting tray that is screwed to the top.  The instrument would have to be opened up to get to the lamp.

  

     I purchased the g-meter from Chief a while back ago, and when I received it, I realized it was a 5v unit.  Chief didn't have any other lighting option listed or available.  I thought about dropping the voltage with a resistor.  Before doing this I called the manufacturer Wultrad (aka Falcon Gauge).  They said they had a 12v unit in stock that they could swap for mine.  I thought... "great problem solved."  They shipped me one back with a 12v label over the original label.  In testing my instrument panel lighting, I discovered that the g-meter is considerably brighter than the other instruments to the point it would be annoying at night.  The interesting thing is the light is nice and white and very uniform though out the face of the instrument.  Anyway, I thought... "gee I'm back to putting in a resistor to dim the light!"

  

     "OK, no problem.  I'll figure out what size resistor I need and move on," I thought.  The problem is the resistance of any incandescent lamp changes whether it hot or cold.  The lamp is drawing 0.56 A at 12.0 v.  Seem's like a lot to me.  From that I deduced the lamp's resistance at 21.3 ohm.  The problem is that when I figure out what size resistor I need to get say a 7 or 8 v voltage drop across the lamp and add that resistor to the circuit, the current changes and so does the resistance of the lamp.  So how does one figure this stuff out?  I decided to purchase a potentiometer and install it in my circuit, adjust it 'till I got the brightness I wanted and then measure the resistance of the pot.  In doing this I began to smell smoke, the little pot was beginning to glow red as I dimmed down the light in the instrument.  I went back and purchased a heavier pot.  This did the trick.  I decided a 20 ohm resistor in series would be perfect.  I purchased a 22 ohm, 2 W resistor, temporarily installed it, and the light was perfect.  The problem was I was still smelling that familiar acrid smell.  I had a 7.4 v drop across the resistor and a .34 A current giving me 2.5 W to dissipate.  I later tried two 10 ohm, 2 W resistors in series.  Still, they got too hot.  I purchased a ceramic 22 ohm, 5 W resistor and it still got too hot to touch.  The small battery I was using for testing was putting out 12.2 v under the load.  I had a 7.4 v drop across the resistor, So I deduced I must be getting a 4.8 v drop across the lamp.  The light was just right.  I wonder if I still have a 5v lamp inside the instrument!  I measured 0.34 A in the circuit.  The 5 W resistor ought to be handling the 2.5 W I need to dissipate just fine.  Something is wrong.  Do any of you smart guys know what I'm doing wrong?

  

 Jerry

 "Smelling smoke in Georgia"

dcarter11(at)sbcglobal.ne
Guest

Posted: Fri Jun 30, 2006 4:40 pm Post subject: Instrument lighting

I can't resist:  "And what are you doing at  night that you need a g-meter for?"

 . . . How about not connecting a wire to the  g-meter light?

 David

 [quote]   ---

icubob(at)newnorth.net
Guest

Posted: Fri Jun 30, 2006 8:36 pm Post subject: Instrument lighting

 Since David cant resist neither can I. How  about a little piece of electrical tape over the meter at night? Like is used to  cover the idiot light in a car that says, ''service vehicle  soon''.!

                                                                            bob noffs

 [quote]   ---

etekberg(at)gmail.com
Guest

Posted: Tue Jul 04, 2006 6:34 am Post subject: Instrument lighting

I think what you did is fine, resistors are designed to get hot.  However, if you want to reduce voltage efficiently use a simple PWM (pulse width modulated) voltage regulator circuit - you can build them for a dollar or two, they just use one IC and 2 or 3 resistors, and sometimes a heatsink.  Look in one of the electronic catalogs.  You can do a google search and come up with the design examples. 

  

 eric

 do not archive

 

 On 6/30/06, Jerry & Ledy Esquenazi <jlinga(at)mchsi.com (jlinga(at)mchsi.com)> wrote:  	  Quote: 	
		      Hey Guys,

     I have a simple problem that most likely has a simple solution.  The solution, however, eludes me.  I have an internally lit g-meter on my instrument panel (Don't ask me why ).  The g-meter's lighting is internal to the instrument,  i.e. it's not a lighting tray that is screwed to the top.  The instrument would have to be opened up to get to the lamp.

  

     I purchased the g-meter from Chief a while back ago, and when I received it, I realized it was a 5v unit.  Chief didn't have any other lighting option listed or available.  I thought about dropping the voltage with a resistor.  Before doing this I called the manufacturer Wultrad (aka Falcon Gauge).  They said they had a 12v unit in stock that they could swap for mine.  I thought... "great problem solved."  They shipped me one back with a 12v label over the original label.  In testing my instrument panel lighting, I discovered that the g-meter is considerably brighter than the other instruments to the point it would be annoying at night.  The interesting thing is the light is nice and white and very uniform though out the face of the instrument.  Anyway, I thought... "gee I'm back to putting in a resistor to dim the light!" 

  

     "OK, no problem.  I'll figure out what size resistor I need and move on," I thought.  The problem is the resistance of any incandescent lamp changes whether it hot or cold.  The lamp is drawing  0.56 A at 12.0 v.  Seem's like a lot to me.  From that I deduced the lamp's resistance at 21.3 ohm.  The problem is that when I figure out what size resistor I need to get say a 7 or 8 v voltage drop across the lamp and add that resistor to the circuit, the current changes and so does the resistance of the lamp.  So how does one figure this stuff out?  I decided to purchase a potentiometer and install it in my circuit, adjust it 'till I got the brightness I wanted and then measure the resistance of the pot.  In doing this I began to smell smoke, the little pot was beginning to glow red as I dimmed down the light in the instrument.  I went back and purchased a heavier pot.  This did the trick.  I decided a 20 ohm resistor in series would be perfect.  I purchased a 22 ohm, 2 W resistor, temporarily installed it, and the light was perfect.  The problem was I was still smelling that familiar acrid smell.  I had a  7.4 v drop across the resistor and a .34 A current giving me 2.5 W to dissipate.  I later tried two 10 ohm, 2 W resistors in series.  Still, they got too hot.  I purchased a ceramic 22 ohm, 5 W resistor and it still got too hot to touch.  The small battery I was using for testing was putting out  12.2 v under the load.  I had a 7.4 v drop across the resistor, So I deduced I must be getting a 4.8 v drop across the lamp.  The light was just right.  I wonder if I still have a 5v lamp inside the instrument!  I measured  0.34 A in the circuit.  The 5 W resistor ought to be handling the 2.5 W I need to dissipate just fine.  Something is wrong.  Do any of you smart guys know what I'm doing wrong?

  

 Jerry

 "Smelling smoke in Georgia"

rd2(at)evenlink.com
Guest

Posted: Thu Jul 06, 2006 10:31 am Post subject: Instrument lighting

Would PWM be suitable for LEDs also?



Rumen



_____________________Original message __________________________

                  (received from Eric Ekberg; Date: 09:32 AM 7/4/2006

-0500)

________________________________________________________________

I think what you did is fine, resistors are designed to get hot.  However,

if you want to reduce voltage efficiently use a simple PWM (pulse width

modulated) voltage regulator circuit - you can build them for a dollar or

two, they just use one IC and 2 or 3 resistors, and sometimes a heatsink. 

Look in one of the electronic catalogs.  You can do a google search and

come up with the design examples. 

  

eric

do not archive

  

On 6/30/06, Jerry & Ledy Esquenazi

<<mailto:jlinga(at)mchsi.com>jlinga(at)mchsi.com> wrote: 

Hey Guys,

    I have a simple problem that most likely has a simple solution.  The

solution, however, eludes me.  I have an internally lit g-meter on my

instrument panel (Don't ask me why ).  The g-meter's lighting is

internal to the instrument, i.e. it's not a lighting tray that is screwed

to the top.  The instrument would have to be opened up to get to the lamp.

  

    I purchased the g-meter from Chief a while back ago, and when I

received it, I realized it was a 5v unit.  Chief didn't have any other

lighting option listed or available.  I thought about dropping the voltage

with a resistor.  Before doing this I called the manufacturer Wultrad (aka

Falcon Gauge).  They said they had a 12v unit in stock that they could swap

for mine.  I thought... "great problem solved."  They shipped me one back

with a 12v label over the original label.  In testing my instrument panel

lighting, I discovered that the g-meter is considerably brighter than the

other instruments to the point it would be annoying at night.  The

interesting thing is the light is nice and white and very uniform though

out the face of the instrument.  Anyway, I thought... "gee I'm back to

putting in a resistor to dim the light!" 

  

    "OK, no problem.  I'll figure out what size resistor I need and move

on," I thought.  The problem is the resistance of any incandescent lamp

changes whether it hot or cold.  The lamp is drawing 0.56 A at 12.0 v. 

Seem's like a lot to me.  From that I deduced the lamp's resistance at 21.3

ohm.  The problem is that when I figure out what size resistor I need to

get say a 7 or 8 v voltage drop across the lamp and add that resistor to

the circuit, the current changes and so does the resistance of the lamp. 

So how does one figure this stuff out?  I decided to purchase a

potentiometer and install it in my circuit, adjust it 'till I got the

brightness I wanted and then measure the resistance of the pot.  In doing

this I began to smell smoke, the little pot was beginning to glow red as I

dimmed down the light in the instrument.  I went back and purchased a

heavier pot.  This did the trick.  I decided a 20 ohm resistor in series

would be perfect.  I purchased a 22 ohm, 2 W resistor, temporarily

installed it, and the light was perfect.  The problem was I was still

smelling that familiar acrid smell.  I had a 7.4 v drop across the resistor

and a .34 A current giving me 2.5 W to dissipate.  I later tried two 10

ohm, 2 W resistors in series.  Still, they got too hot.  I purchased a

ceramic 22 ohm, 5 W resistor and it still got too hot to touch.  The small

battery I was using for testing was putting out 12.2 v under the load.  I

had a 7.4 v drop across the resistor, So I deduced I must be getting a 4.8

v drop across the lamp.  The light was just right.  I wonder if I still

have a 5v lamp inside the instrument!  I measured 0.34 A in the circuit. 

The 5 W resistor ought to be handling the 2.5 W I need to dissipate just

fine.  Something is wrong.  Do any of you smart guys know what I'm doing

wrong?

  

Jerry

"Smelling smoke in Georgia"

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Thu Jul 06, 2006 11:45 am Post subject: Instrument lighting

On Jul 6, 2006, at 1:53 PM, rd2(at)evenlink.com wrote:



 	  Quote: 	
		   



 Would PWM be suitable for LEDs also?


	


Yes.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

klehman(at)albedo.net
Guest

Posted: Thu Jul 06, 2006 12:14 pm Post subject: Instrument lighting

Yes that works very well but as a rule you still need the current 

limiting resistor. LED's draw so little power that a simple linear 

regulator may be a bit easier and cheaper and may not even require a 

heatsink. While you can put LED's and incandescant lamps on the same 

dimmer they are unlikely to dim evenly so two different dimmers might be 

required if you are picky about uniformly dimming panel lights. There 

are ways of controlling multiple dimming circuits from one knob but of 

course then one circuit failure can kill all the lights if that is a 

concern.



Note that Bob has a LM-117 or LM-317 based linear regulator circuit for 

a lamp dimmer on his aeroelectric site. Linear regulators are 

essentially a solid state variable resistor and they dissipate as much 

heat as a resistor would. But for panel lighting that may not be much 

heat. I setup four of them in a row for panel dimming and they merely 

get a bit warm. The efficiency is not much of an issue in an application 

that doesn't require much power. A neat characteristic of these linear 

regulators is that they protect themselves rather well from overheating 

or short circuits so they are fairly resistant to abuse and they don't 

generate noise. A PWM circuit may generate some electrical noise as it 

rapidly switches the current on and off. I have seen some high end ANR 

headsets that are sensitive to noise from some PWM panel dimmers.



Ken



rd2(at)evenlink.com wrote:



 	  Quote: 	
		  



Would PWM be suitable for LEDs also?



Rumen



_____________________Original message __________________________

                  (received from Eric Ekberg; Date: 09:32 AM 7/4/2006

-0500)

________________________________________________________________

I think what you did is fine, resistors are designed to get hot.  However,

if you want to reduce voltage efficiently use a simple PWM (pulse width

modulated) voltage regulator circuit - you can build them for a dollar or

two, they just use one IC and 2 or 3 resistors, and sometimes a heatsink. 

Look in one of the electronic catalogs.  You can do a google search and

come up with the design examples. 

  

eric

snip

Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Thu Jul 06, 2006 6:44 pm Post subject: Instrument lighting

In a message dated 07/06/2006 1:33:31 PM Central Daylight Time, rd2(at)evenlink.com writes:

  	  Quote: 	
		  Would PWM be suitable for LEDs also? 	


 >>>

  

 Absolutely- I've been using one of the Marlin P. Jones PWM motor speed control kits (as recently mentioned by Charlie Kuss) on my panel lights for 3 years with most satisfactory results.  All LEDs (many!) thus fed appear to be happy so far...

  

 From The PossumWorks in TN

 Mark

_________________
From The PossumWorks...

rd2(at)evenlink.com
Guest

Posted: Fri Jul 07, 2006 4:47 am Post subject: Instrument lighting

Thanks to all who responded.

Rumen

do not archive



_____________________Original message __________________________

                  (received from Fiveonepw(at)aol.com; Date: 10:41 PM 7/6/2006

EDT)

________________________________________________________________

   In a message dated 07/06/2006 1:33:31 PM Central Daylight Time,

rd2(at)evenlink.com writes: Would PWM be suitable for LEDs also?

jlinga(at)mchsi.com
Guest

Posted: Sun Jul 09, 2006 6:23 pm Post subject: Instrument Lighting

Hello Guys,

     At the suggestion of another  lister I googled the LM317K.  It took about  $6 for the components and  hour worth of work.  I didn't even have to go to Radio Shack;  I have  an excellent electronics supply store 5 minutes from the house.  Not bad  for a town of only 45,000!  Anyway the regulator works like a champ.   The reason I needed this is because my g-meter light was a lot brighter than the  rest of the instruments.  It has a 3 lamps built into the instrument unlike  the other instruments that have a simple light tray.  A simple resistor in  series was getting too hot.  

     Since my main control for my  lights is the LC40 4 ch dimmer, I did away with the pot in the LM317K circuit  and replaced it with a fixed resistor of appropriate size.  The g-meter  lighting is powered by the LM317K circuit which in turn is wired to the rest of  my instrument lighting circuit via the LC40.

  

 Try it.  It is easy, cheap, and  effective.

  

 Jerry

  

  

  

  

  

  

 Hey Guys ...



Are you really willing to spend $75 for a simple  dimmer?  As I stated before, 

as much as I dislike Radio Shack you can  build this dimmer for $15 to $20 

with all parts and instructions available  from the $hit Shack.



LQQK for the LM-317



Barry

"Chop'd  Liver"

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