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Replacing bulb for window button switch on main console

starLED

Member
I need to replace bulb that's inside of a button for car window.
The bulb is 12V T1 1/4 80mA and because it's a bit difficult to find it in a store, I decided to put orange LED 2.5V 50mA.
Is it safe to put LED with resistor 1/4 watts 270 ohms?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Ignoring the LED voltage, the resistor would dissipate (V^2 / R) almost 1W at 15V, which is what the electrical system may run at from the alternator.

You need a much higher power resistor (or combination of resistors), or use an ultra-bright LED that will give adequate illumination at rather lower current, so you can use a higher value resistor.

Edit:
Or would one of these be a drop-in replacement for the original bulb?
 
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Diver300

Well-Known Member
Most Helpful Member
50 mA through an LED is a lot. That will be far brighter than the original lamp. I would start at 10 mA or less, with 1200 Ohms, and then you will only get around 130 mW in the resistor.
 

starLED

Member
Or would one of these be a drop-in replacement for the original bulb?
I am not sure that I can find it.
This is what I have available in store:

I guess I could use 12V, 50mA, 0.60W without resistor?
 
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starLED

Member
This is what bulb looks like
1615021856964.png

I'd prefer to use LED diode instead of T1 because they can last longer.
 
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Diver300

Well-Known Member
Most Helpful Member
This is what bulb looks like
View attachment 130131

I'd prefer to use LED diode instead of T1 because they can last longer.
Just use an LED of the right colour that fits in the space, get the connections the right way round, fit a resistor in series, make sure that the current rating of the LED is not exceeded, and that the power rating of the resistor isn't exceeded.

Do you have an LED that you intend to use?
 

starLED

Member
Just use an LED of the right colour that fits in the space, get the connections the right way round, fit a resistor in series, make sure that the current rating of the LED is not exceeded, and that the power rating of the resistor isn't exceeded.

Do you have an LED that you intend to use?
Orange LED:

or white LED:
 

JimB

Super Moderator
Most Helpful Member
Be aware that most of the light emitted from an LED comes from the domed end of the LED package, as a narrow beam.

An incandescent lamp as shown in post#5 emits most of the light from the sides of the cylinder shape, in an omni-directional pattern.

Replacing the lamp with an LED may not give the result that you require.

JimB
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Is there enough room in that housing to use eg. three 3mm LEDs in series, such as with the leads on each bent 90' out, trimmed and soldered directly to each other?

That gives three times the light for a given current and reduces the voltage across the series resistor, so that is producing less heat.
 

starLED

Member
Be aware that most of the light emitted from an LED comes from the domed end of the LED package, as a narrow beam.

An incandescent lamp as shown in post#5 emits most of the light from the sides of the cylinder shape, in an omni-directional pattern.

Replacing the lamp with an LED may not give the result that you require.

JimB
Yes, you are right, it crossed my mind too.

Can I use 12V, 50mA, 0.60W without resistor?
 

starLED

Member
Is there enough room in that housing to use eg. three 3mm LEDs in series, such as with the leads on each bent 90' out, trimmed and soldered directly to each other?

That gives three times the light for a given current and reduces the voltage across the series resistor, so that is producing less heat.
I doubt it, maybe just 2, but that's not for sure either.
Case is about 5 x 20 mm.
Maybe LED SMT is an option.
 
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starLED

Member
I have replaced bulbs in three of four buttons with 12V, 50mA, 0.60W.
Fourth button bulb have to be desoldered/soldered but I am not sure how to pull out circuit board out. It doesn't lift up, it seems like it's soldered inside to something and it holds it back.
I am not sure that I can lift it up if I desolder all leads.
IMG_20210312_124708.jpg
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Can I use 12V, 50mA, 0.60W without resistor?
That's commonly called a "grain of wheat" lamp. it's a filament lamp. Essentially what you have.

It depends on which way the light has to face. From your pic, it seems it has to face toward the paper. the lens will mess it up. So, yellow LED with yellow lens. there might be some right angle LEDs or axiel leds that can work. Just size R correctly.

examples:

1615600654790.png

1615600691766.png




1615600777728.png

Series wiring would not be too bad, just alternate them.
 

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