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Cars radio's light bulbs, 12v or 14v?

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BigB9k

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I ordered up some 12v light bulbs to fix the burnt bulbs in my radio.
Then I saw a thread here mentioning the car being at about 14.7v.

Did I buy the wrong bulbs? Should I have just gotten some 14v's?
Or do you think the radio has some kind of regulator within?
 
The 12V system in your car is actually slightly higher than 12V. It can be ~13.5V - 14.5V. If you bought automotive bulbs designed to work with a 12V system, you'll be fine.
 
Car batteries (lead acid) are 13.8V fully charged, nominally 12V, and a bit lower than that when dead. Should be fine. My exact numbers may be a bit off since I don't know them for sure.

The radio has a regulator but for other things thst need it and probably not for the bulbs since bulbs are rugged relatively voltage insensitive devices. Not like a CPU or LEDs for example.

EDIT:

Lead acid is pretty rugged and one side effect of that is tolerance to overvoltage or overcharging. The max charge voltage can be chosen for longer life or more peroformance. 13.8V is the conservative long life max voltage. 14.7V is the aggressiv, life shortening but peformance increasing max charge voltage. All voltages slowly drop as the battery empties out. How fast and what voltage is considered dead depends on chemistry.
 
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What you're missing dk is that when the car is ON the battery voltage will always be 13.8 volts (unless the car is idling) as the alternator will be providing most of the power and the battery is just used as a buffer and it's constantly being float charged. It shouldn't hurt anything, but if the bulbs aren't rated for automotive use they might not last very long. Automotive components are often drastically derated on their actual potential outputs to compensate for the rough use and wide range of conditions they see.
 
Light bulbs operate at an extremely high internal temperature (white hot) so of course they burn out soon. That is why LEDs are used today because they last 100,000 hours or more.
 
I have several mobile ham rigs that use the small "grain-o-wheat" 12V lamps as illuminators. Those damn things are always burning out. The reason is that with the car's alternator charging, the system voltage goes as high as 14.5 V or even higher, and those little lamps have a very short life even at 12.0V

Since I have to open up the radios to solder in new lamps, I fix the under-lying issue (12V lamps running on 14.5+V) by wiring a resistor in-series with the lamps to drop the voltage about 15%. I have actually modified a couple of the radios by replacing the lamps with LEDs (several in series) in series with a current-limiting resistor.

Off the top of my head I cant remember what resistor value I used, but it extends the life of the bulbs to where I am not having to get into the radios very often...

Here is one I converted to LEDs. I cut the dome off the water clear red LEDs to get a more diffused light.
 

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Cant dim the LED's though, correct?

I'm thinking about just getting some 13v or 14v bulbs

Actually, since I'm running 4 or so Red LEDs in series (Vf=~2V), they dim quite nicely...
 
The dash lights in most good car radios do have dropping resistors on them on unless thay are to cheep. Even if you add a ohm or two you will incress the bulb life dramatically. Andy
 
Had done the LED swap inm a car radio but did for the lighted push buttons. Used blue LEDs looks really nice. just added a resistor in series as the bulbs were already in series using pcb. LEDs are cheaper than them grain of wheat bulbs and will last really long. I computed resistor for 12ma. At 18-20 ma the light was too bright.
 
Never mind. The LED was to bright at 20ma. So you used 12ma.
 
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Yes the LEDs were to bright (this was on a friends car radio) so I used a resistor with a higher resistance using ohms law
 
Put it in the DC mA mode. You may have to move the red lead plug to a different hole. Connect the meter leads in series with your lamp, polarity doesn't matter, and then connect one meter lead and the other lamp lead to the 12V power supply. The lamp should light, and meter will read the current required to operate the lamp. When you put the meter in current measurement mode, and hook it in series with the lamp, the voltage drop across the meter is so low that the lamp will not know the meter is there...
 
Cant dim the LED's though, correct?

I'm thinking about just getting some 13v or 14v bulbs

hi,
A range of 14V miniature lamps are available, often used in 12V mobile applications eg: boats/cars etc in order to cater for a 14V charging source.

**broken link removed**
 
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Unfortuately, the ones I have to replace are directly soldered into the PCB with wire protruding from the glass.
 
obtain some solder wick, remove the existing bulbs, insert LEDs into the holes (determine which hole is ground and + and insert LEDs as per)
the bulbs are most likely in series (removing one bulb should disable the rest of the bulbs or one is burned out and none of the bulbs light)
determine either the + or ground side of the series circuit, count number of LEDs needed (most likely 4 or 5 LEDs) (number of bulbs removed) then using ohms law determine resistor value needed for 12-15ma. solder into series circuit. you should be done.
If only one bulb is burnt out and all the rest are lit then a resistor per led is needed but it is easier for manufacture to go with series circuit. Just follow the printed circuit board traces.
 
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