[rjgramps]

Yep, there is no light n the dimmer. BUT....there is a light in the fog light switch next to it. As I recall, that one is easy.

 

[JohnnyG]

Finally got curious enough to look up the suggested LED via the eBay link that rjgramps provided. I hate to say it, but I don't think these bulbs are going to last very long in this application! IF the bulb has a built-in resistor as they claim (big IF!), it will burn out pretty quick with no way to dissipate the heat. Also, I don't believe there is any such thing as a "5-15" volt LED?! If 5V makes it light up, then it's a 5V bulb and anything more than that is over-driving it. They say you can add an extra resistor...ok, what value?! Just beware - it's a lot of work to replace these and it would suck if they don't last.

 

[rockinpirate]

Finally got curious enough to look up the suggested LED via the eBay link that rjgramps provided. I hate to say it, but I don't think these bulbs are going to last very long in this application! IF the bulb has a built-in resister as they claim (big IF!), it will burn out pretty quick with no way to dissipate the heat. Also, I don't believe there is any such thing as a "5-15" volt LED?! If 5V makes it light up, then it's a 5V bulb and anything more than that is over-driving it. They say you can add an extra resistor...ok, what value?! Just beware - it's a lot of work to replace these and it would suck if they don't last.

I'm really happy with this for backup light.

https://www.autozone.com/electrical-and-lighting/back-up-light-mini-bulb/p/silverstar-mini-bulb-3157st/232887_0_0

 

[rjgramps]

I hate to say it, but I don't think these bulbs are going to last very long in this application!

IF the bulb has a built-in resistor as they claim (big IF!), it will burn out pretty quick with no way to dissipate the heat.

It's a lot of work to replace these and it would suck if they don't last.

I hope you are wrong because it would really stink if these LEDs don't last. I will find out one way or the other. So far so good but admittedly we don't drive the car on a regular basis so it will take some time to find out.

 

[JohnnyG]

Believe me, I hope that I'm wrong too! Looking at the wiring diagram, it seems possible to insert a single resistor in-line somewhere (but what value without knowing the "real" spec of those bulbs?), or even better, turn the dimmer into a Pulse Width Modulation control so they can be dimmed properly.

Technically, LEDs are not dimmable by reducing voltage unless they are being over-driven. The rated forward voltage is where they light up to rated output, and anything less than that might not light them at all.

 

[TomatoSoup]

Technically, LEDs are not dimmable by reducing voltage unless they are being over-driven. The rated forward voltage is where they light up to rated output, and anything less than that might not light them at all.

You are the second person to post this incorrect info recently, not sure where you all are getting this from. Of course LEDs ARE dimmable by reducing forward voltage (and hence current, given a series resistor). Just look at an LED datasheet. See the extract below, second graph. Luminosity is directly (linearly) proportional to forward current.

 

[JohnnyG]

In that 2nd graph, Y axis (luminance) is relative to 20mA, so it's saying that at 20mA (its rated forward current), you get 1.0 rated luminance, at 10mA you get 50% less luminance, and at 30mA, you get 50% (1.5) more luminance.

This doesn't change what I said though. Technically, if you find the current that lights the LED, everything above that is overdriving it, but that doesn't mean it isn't still within the manufacturers spec. They could take the same bulb and say "lasts forever" at 10mA, or "lasts for 10 years" at 20mA. These specs tell you that if you drive it at 30mA it will put out 50% more light, but the datasheet does not suggest at all that it can be driven continuously and safely at that level (think PWM).

 

[JohnWR]

In that 2nd graph, Y axis (luminance) is relative to 20mA, so it's saying that at 20mA (its rated forward current), you get 1.0 rated luminance, at 10mA you get 50% less luminance, and at 30mA, you get 50% (1.5) more luminance.

This doesn't change what I said though. Technically, if you find the current that lights the LED, everything above that is overdriving it, but that doesn't mean it isn't still within the manufacturers spec. They could take the same bulb and say "lasts forever" at 10mA, or "lasts for 10 years" at 20mA. These specs tell you that if you drive it at 30mA it will put out 50% more light, but the datasheet does not suggest at all that it can be driven continuously and safely at that level (think PWM).

This is the manufacturer's description of the LEDs referenced by @rjgramps :

Here we have a newer style LED to the scene! We've got a 12v 3mm cool / clear white round top led. This is a special style of LED because it will on 12v with just the LED you see. It will actually work between lower voltage of about 5v to 15v. You will lose some brightness if you are using at a lower voltage than 12v, but it will still work well. If you've worked with LEDs much in the past you will be familiar that most LEDs that are around the 20mA range will only work on approximately 2-3v without a resistor, depending on the color and technical specifications. These LEDs are particularly special because they have a current limiter inside the actual lens itself. What makes these even more rare is that we have taken it a step further and designed them so they will work with voltages up to 15v. While we don't recommend running them continuously at 15v, they will be ok with occasional spikes. This is something you will definitely not find in other LEDs similar to these out there. This is particularly useful in automotive applications where the charging systems see these higher voltages. With all of this said, we still recommend using the good old fashion LED with an external resistor added in, if possible. It keeps the heat further away from the diode itself and that is always a good thing. We know this is not always possible, so we have brought the 12v 3mm cool / clear white round top LED to you for such applications. You can't go wrong with the 12v 3mm cool / clear white round top LED.

They state clearly that they will work at reduced brightness below 12V, down to the specified 5V.

The note about not recommending their continuous use at 15V is somewhat concerning, because the car's electrical system operates at 14.2V when the engine is running. It would be interesting to see what the maximum actual voltage supplied to these LEDs is.

Also of interest is the comment about a separate LED and resistor being preferred when it is possible.

 

[load97]

With vehicle off. I have tested the voltage at low, med, high of the dimmer. I am not worried about longevity. With how bright the LED is, I will be running the dimmer on low, or just above at most. eBay seller also told me there wouldn’t be an issue.

I had checked out a few older car forums of people either using same seller or same type bulbs and didn’t see any complaints (besides X amount of bulbs being bad brand new). <— which is why I bought a bulb tester. I uploaded photos of the various dimmer settings, along with photo of my fluke showing voltage.

 

[JohnnyG]

So the question is, is there really such a thing as a 5-15V 15mA LED? I think not. How can you vary the voltage yet maintain the amperage with the same value resistor? How can the LED light with 5V if it's rated forward voltage is higher than that? Plus check Digi-Key or Mouser...no such listing that I've found.

Fact is, you can connect a 3V LED to a 9V battery and it'll light for days - maybe months - maybe even years. But it's a bit of a game of chance because another of the exact same LED might die instantly.

 

[rjgramps]

This is at home with standard screw-in 120V LED light bulbs.

I don't know why, but two 25W equivalent light bulbs in a particular light fixture, blink at random. I heated one bulb up using my heat gun thinking maybe a cracked solder joint would stop the blinking, but that lasted about a week. The problem is the fixture has 8 bulbs in view and I cannot find exact replacements, so changing one requires changing all 8.

When buying LEDs for a particular application, I suggest buying extra bulbs.

 

[TomatoSoup]

So the question is, is there really such a thing as a 5-15V 15mA LED? I think not

Yes, and No! An individual LED will have a forward voltage drop, depending on color, of between ~1.7V (red) and ~3.2V (white/blue). Without a built-in or external resistor, exceeding this forward voltage by more than ~20% will blow the LED in short order. HOWEVER, LED bulb assemblies often include a series resistor (and sometimes diodes or bridges) that allow them a much greater voltage supply range, given that at higher voltages, the resistor drops the voltage enough to save the LED. Some fancier LEDs even include a constant current converter allowing a much greater applied voltage range, while still applying a constant "cruising" current to the LED that allows for max life/brightness.

You most likely will not find these on Digikey/Mouser etc, as they are not standalone components.

I don't know why, but two 25W equivalent light bulbs in a particular light fixture, blink at random.

Do you have a wall dimmer for that fixture? Many wall dimmers and LED bulb combinations do not work happily together, resulting in just the symptoms you describe.

 

[rjgramps]

Do you have a wall dimmer for that fixture? Many wall dimmers and LED bulb combinations do not work happily together, resulting in just the symptoms you describe.

No dimmer here, only straight 120V 100% of the time.

I agree with you concerning dimmers with LED bulbs that are not designed to work with dimmers.

 

[JohnnyG]

LED house bulbs are a different beast. They need a bridge rectifier to convert AC to DC, plus a transformer and other components to deliver current and voltage specs that meet the needs of the LED(s). The LEDs don't create heat, but these other components most certainly do, which is why most bulbs say "not for use in enclosed fixtures". Too much heat will kill components in the circuitry and cause this flashing. In most case, the LED itself is fine, but the driver is damaged. Even in open air, there are a number of ways to create the driver and cheap components will lead to early failure - still usually caused by heat.

 

[JohnnyG]

HOWEVER, LED bulb assemblies often include a series resistor (and sometimes diodes or bridges) that allow them a much greater voltage supply range, given that at higher voltages, the resistor drops the voltage enough to save the LED.

We are talking about a specific LED here...it's not a bulb assembly but a discrete component. It claims to have an integrated resistor but doesn't specify the value, or the forward voltage - only the forward current.

If I do this mod (and there's a decent chance I will), I would use standard off-the-shelf LEDs and find a way to turn the dimmer into a control for a PWM module. Here's a suitable unit on Amazon Canada for under $10 - DC 12V-14V 8A LED Bulb Dimmer Switch Brightness Controller, Dimmer Switches - Amazon Canada

 

[TomatoSoup]

We are talking about a specific LED here...it's not a bulb assembly but a discrete component. It claims to have an integrated resistor but doesn't specify the value, or the forward voltage - only the forward current.

If it includes a resistor, then it is an assembly by definition (LED+resistor) - exactly what I was talking about. A discrete component would be an LED only.

 

[JohnnyG]

An electronic assembly can typically be disassembled. This cannot be, nor would it be considered an integrated circuit.

But who cares! Let's call it an assembly!

 

[JohnWR]

We are talking about a specific LED here...it's not a bulb assembly but a discrete component. It claims to have an integrated resistor but doesn't specify the value, or the forward voltage - only the forward current.

If I do this mod (and there's a decent chance I will), I would use standard off-the-shelf LEDs and find a way to turn the dimmer into a control for a PWM module. Here's a suitable unit on Amazon Canada for under $10 - DC 12V-14V 8A LED Bulb Dimmer Switch Brightness Controller, Dimmer Switches - Amazon Canada

It does specify a forward voltage for the assembly: 5-15V, although it states that anything over 12V is not recommended for extended periods. Read the lines that I underlined in my quote from the manufacturer's specification page here: LED Interior Lighting, Bight Daylight Color Throughout...

Also, my service manual indicates that the lights in the switches and the IPC are dimmed by PWM in the supply from the BCM.

 

[JohnnyG]

Last things first. Yes! I was looking at the wiring diagram last night myself and the dimmer is not on the same circuit as the bulbs and does not directly control dimming. The value from this variable resistor is sent to the BMC. I don't see any direct evidence that it controls dimming via PWM but it's really the only thing that makes sense. I'd check it with an oscilloscope but I don't currently have one (yeah, a new tool!)

Now back to that LED. From what we know, it seems to be a "regular" LED, but with a resistor added within it. A typical "regular" white LED has a forward voltage value of 3.6V, and the device spec states the forward current as 20mA. With a 5V supply, the resistor value would be 93 Ohms, with power dissipation at .021 Watts (an 1/8 watt resistor would do). With a 15V supply, the resistor value would be 760 Ohms, with power dissipation of .171 Watts (a 1/4 watt resistor required). So assuming it doesn't have some magical voltage sensing resistor that automatically changes it's value, how does it SAFELY handle this voltage range? Answer is, it can't. Why any of you would side with wild marketing claims on eBay is beyond me!

Now that said, assuming the Sky/Solstice is indeed using PWM, these LEDs should provide a long service life. I'd still like to measure the duty cycle with a scope at full low and full high brightness (to ensure full brightness is not constant voltage), but it seems likely that my initial concerns are not valid given the configuration, and I apologize for any undue stress and 2nd guessing I may have caused!

 

[JohnWR]

The "Logic" block shown in the service manual for light dimming has a square wave pulse train illustrated, and that is a common designator for PWM.

The LED assembly is rated for 20 mA, and the wording indicates to me that it is at the design voltage of 12V. The description further states that it will operate as low as 5V, but will have lower output. That by definition means that the current will be less than 20mA. It can also operate as high as 15V, but that is not recommended, so that indicates more than 20mA.

No magic, just math.