Led Dash lights are they dimmable?
Discussion
I'm after a new set of T10 /194 dash Leds for my old motor, have some but they don't dim and need to fit the correct polarity to work no problem really with polarity, but I want dimmables but I can't quite work out if modern canbus 5050 Leds would do this.
After much searching I found a US site that does dimmable and polarity but looking a little expensive as need approx 10 leds plus shipping https://www.superbrightleds.com/moreinfo/miniature...
I see loads for sale on Ebay uk for more modern cars ie Audi BMW that work with canbus etc, i would hope that you could still dim on modern cars would something like these dim? http://www.ebay.co.uk/itm/4x-ERROR-FREE-CANBUS-8-S...
Any info greatly welcome
After much searching I found a US site that does dimmable and polarity but looking a little expensive as need approx 10 leds plus shipping https://www.superbrightleds.com/moreinfo/miniature...
I see loads for sale on Ebay uk for more modern cars ie Audi BMW that work with canbus etc, i would hope that you could still dim on modern cars would something like these dim? http://www.ebay.co.uk/itm/4x-ERROR-FREE-CANBUS-8-S...
Any info greatly welcome
Edited by 69 coupe on Monday 17th November 16:41
I'm not sure how the CANBUS stuff works, but assuming it is what it sounds like then I'd guess it's actually receiving instructions from the Canbus, sourced from the brightness control, to work out what the nominal brightness should be.
If that's the case then simply plugging them into the existing lighting on an old car wont work as the brightness will be controlled by PWM either at the bulb or on its circuit.
If dimmable LED's are available then it's probably the easiest route, although if you're feeling adventurous then you could use the rheostat as an input for a PWM controller like so:
http://www.ebay.com/bhp/pwm-dimmer
However you will need to isolate the ground for the dash lighting and feed it back into the controller.
If that's the case then simply plugging them into the existing lighting on an old car wont work as the brightness will be controlled by PWM either at the bulb or on its circuit.
If dimmable LED's are available then it's probably the easiest route, although if you're feeling adventurous then you could use the rheostat as an input for a PWM controller like so:
http://www.ebay.com/bhp/pwm-dimmer
However you will need to isolate the ground for the dash lighting and feed it back into the controller.
Edited by The Wookie on Monday 17th November 16:15
I think I read somewhere that dimmable LEDS, aren't really dimmable, just that when "dimmed" they flash very rapidly (imperceptibly fast) for a very short period of time. It's the circuitry of the device that does this, so if the aforegoing is correct then a bulb by itself* won't dim via a drop in voltage as does an incandescent bulb.
Suppose however circuitry on board the bulb could be designed to respond to the drop in voltage to translate into the appropriate flashing.
Suppose however circuitry on board the bulb could be designed to respond to the drop in voltage to translate into the appropriate flashing.
- i.e. plugged into an old car's socket not designed to cause the led to dim
Edited by 996TT02 on Monday 17th November 16:17
996TT02 said:
I think I read somewhere that dimmable LEDS, aren't really dimmable, just that when "dimmed" they flash very rapidly (imperceptibly fast) for a very short period of time. It's the circuitry of the device that does this, so if the aforegoing is correct then a bulb by itself* won't dim via a drop in voltage as does an incandescent bulb.
Yep, it's called Pulse Width Modulation. Effectively it varies the speed at which the LED switches on and off, giving the impression of variable brightness.Hmm good to know modern LED car dashes do dim and guess they do that by powering/cycling on/off
Re question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
Re question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
69 coupe said:
Hmm good to know modern LED car dashes do dim and guess they do that by powering/cycling on/off
Re question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
I'm guessing that does exactly what 996TT has suggested which uses the circuit voltage as an input for a little PWM controller on the boardRe question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
69 coupe said:
Hmm good to know modern LED car dashes do dim and guess they do that by powering/cycling on/off
Re question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
That ic is just a voltage regulator with 22ohm resistor 4 diodes and a capacitor on the pcbRe question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
Edited by Pesty on Monday 17th November 17:02
Pesty said:
69 coupe said:
Hmm good to know modern LED car dashes do dim and guess they do that by powering/cycling on/off
Re question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
That ic is just a voltage regulator with 22ohm resistor 4 diodes and a capacitor on the pcbRe question about circuitry specifically designed to do this, in my original post the link for LED that does dim it looks like it has an IC circuitry on the board.
https://www.superbrightleds.com/moreinfo/miniature...
Edited by Pesty on Monday 17th November 17:02
(electronics not my thing!
)Do the diodes set the polarity on that LED so they work if fitted 180 degrees as most leds need correct polarity? and the regulator cycles power on/off and the capacitor keeps a charge to the SMD when as in my case I turn the headlamp switch with built-in rheostat.
The Poster "Totalled" on this thread is what I'm trying to do. http://www.7173mustangs.com/thread-what-can-i-do-t...
Not sure what you are asking there. No the diodes don't change the polarity of the LEDs. All LEDs and diodes are polarised.
God knows what the diodes are there for, stopping reverse current Or something maybe on the output side
Not much better at electronics either, my two years at college doing an OND were forgotten the week after I left.
God knows what the diodes are there for, stopping reverse current Or something maybe on the output side
Not much better at electronics either, my two years at college doing an OND were forgotten the week after I left.
Pesty said:
Not sure what you are asking there. No the diodes don't change the polarity of the LEDs. All LEDs and diodes are polarised.
God knows what the diodes are there for, stopping reverse current Or something maybe on the output side
Not much better at electronics either, my two years at college doing an OND were forgotten the week after I left.
Ha Ha, I don't know what I'm asking either God knows what the diodes are there for, stopping reverse current Or something maybe on the output side
Not much better at electronics either, my two years at college doing an OND were forgotten the week after I left.
all I know early mustang dashes are exceptionally dim with standard filament bulbs. I wanted dimming in case by some exceptional miracle the dash lights up like a lighthouse if they have 5050 SMD's.
Edited by 69 coupe on Monday 17th November 19:48
Those diodes are configured in a bridge.
That enables the (+) or (-) to be connected any way around, effectively making the LED work with any polarity.
The LM317 regulator is there to stabilise the voltage (or current - depending on how it's connected) to the LED to maintain even brightness.
ETA: looking at the circuit board in more detail, the LM317 is indeed wired as a current regulator, so it'll be reducing the LED current to a safe value.
It'll look something like this:
That enables the (+) or (-) to be connected any way around, effectively making the LED work with any polarity.
The LM317 regulator is there to stabilise the voltage (or current - depending on how it's connected) to the LED to maintain even brightness.
ETA: looking at the circuit board in more detail, the LM317 is indeed wired as a current regulator, so it'll be reducing the LED current to a safe value.
It'll look something like this:
Edited by TonyRPH on Monday 17th November 18:53
TonyRPH said:
Those diodes are configured in a bridge.
That enables the (+) or (-) to be connected any way around, effectively making the LED work with any polarity.
A bridge if diodes would convert's ac to dc wouldn't it. That enables the (+) or (-) to be connected any way around, effectively making the LED work with any polarity.
Anyway I'm pretty sure an led only works in one polarity. It's nothing to do with the supply but the orientation of the n an p type semi conductor it's made of.
Drastically trying and failing to remember his theorie.
Not trying to be an arse by the way just trying to understand as this stuff interests me but I'm dim.
Pesty said:
A bridge if diodes would convert's ac to dc wouldn't it. <snip>
If AC were present, yes it would indeed convert it to DC - however in this case the bridge is simply being used to ensure that no matter which way the DC input is connected, the diodes will direct the DC in the correct manner.If you look at the bridge below - a diode will flow (positive) DC from (1) to (2)… (1) -->|--- (2) negative will flow from (2) to (1)
So the diodes will simply "steer" the DC in the correct direction.
The Wookie said:
I'm not sure how the CANBUS stuff works,
That put you in the same boat as the canbus LED sellers!Most cars have bulb checking capabilities, and when the light control module spots a blown or unusual bulb, it'll then send a message to the dashboard on the canbus which links everything together.
Someone then got hold of the wrong end of the stick, and the name "canbus" started appearing on LEDs.
Calling LEDs "canbus" is like calling buckets of water "non-999".
TonyRPH said:
If AC were present, yes it would indeed convert it to DC - however in this case the bridge is simply being used to ensure that no matter which way the DC input is connected, the diodes will direct the DC in the correct manner.
If you look at the bridge below - a diode will flow (positive) DC from (1) to (2)… (1) -->|--- (2) negative will flow from (2) to (1)
So the diodes will simply "steer" the DC in the correct direction.
Got you. If you look at the bridge below - a diode will flow (positive) DC from (1) to (2)… (1) -->|--- (2) negative will flow from (2) to (1)
So the diodes will simply "steer" the DC in the correct direction.
Wondering why it would be needed are possitive and negative earth cars? Actually forget that depending on the standard bulb conections replaced it could be 180 out couldn't it.
Doh. I really should be better at thus.
Edited by Pesty on Tuesday 18th November 00:25
TonyRHP, Pesty, anyone else 
Interesting stuff learning how things work, so another question.
How does that voltage regulator work then, assuming that LED's needs to pulse on/off to give the dimming effect just reducing the voltage wouldn't work on its own would it? Does the Voltage regulator also do the pulse or is that all it does? What function does that capacitor & 22k resistor do/have on that LED circuit?
Early Mustangs reduce the voltage prior to the LEDs via a wire-wound rheostat on the headlamp switch they look like this. https://www.youtube.com/watch?v=MuwrwaiKPpQ
Interesting stuff learning how things work, so another question. How does that voltage regulator work then, assuming that LED's needs to pulse on/off to give the dimming effect just reducing the voltage wouldn't work on its own would it? Does the Voltage regulator also do the pulse or is that all it does? What function does that capacitor & 22k resistor do/have on that LED circuit?
Early Mustangs reduce the voltage prior to the LEDs via a wire-wound rheostat on the headlamp switch they look like this. https://www.youtube.com/watch?v=MuwrwaiKPpQ
The regulator is configured as a constant current source, so the LED brightness will remain the same regardless (almost) of input voltage, so the simple rheostat would not vary the brightness of it.
If you could add a variable resistor on that board (in series with the existing resistor) you could change the brightness (by changing the current) using that variable resistor - but this wouldn't help in your particular case.
The other option if you could build it yourself - would be to build a transistor controlled dimmer or buy an off the shelf PWM controller as somebody mentioned in a previous post.
With a little ingenuity, either one could be made to work with the rheostat (a rehostat is just a high powered variable resistor in case you didn't know).
At a pinch you could just vary the LED brightness directly with a variable resistor, but it's a crude way of doing it and you would need to ensure you don't provide too much current.
If you could add a variable resistor on that board (in series with the existing resistor) you could change the brightness (by changing the current) using that variable resistor - but this wouldn't help in your particular case.
The other option if you could build it yourself - would be to build a transistor controlled dimmer or buy an off the shelf PWM controller as somebody mentioned in a previous post.
With a little ingenuity, either one could be made to work with the rheostat (a rehostat is just a high powered variable resistor in case you didn't know).
At a pinch you could just vary the LED brightness directly with a variable resistor, but it's a crude way of doing it and you would need to ensure you don't provide too much current.
Hi Tony, thanks for your info, the only query I would still have is with those particular LEDs, in the "poster" "Totalled" reply on this thread http://www.7173mustangs.com/thread-what-can-i-do-t...
If as he suggests on the last page he points specifically to those LEDs as been dimmable seemingly through the standard wiring which will be controlled via a 12v DC wire-wound rheostat.
Thoughts?
If as he suggests on the last page he points specifically to those LEDs as been dimmable seemingly through the standard wiring which will be controlled via a 12v DC wire-wound rheostat.
Thoughts?
Looking at the spec for that LED, I suspect it will work, but I also suspect that the rheostat will not give you fine control of the brightness.
You may possibly find that all the control will be at one end of the rheostat, and the change from bright to dim will be rapid, rather than being gradual across it's rotation.
Without knowing the resistive value of the rheostat, it's difficult to be sure though.
IIRC - typical dash bulbs are around 3W, which would draw 250mA at 12V.
Those LEDS are rated at 35mA (0.42w), which is roughly 1/10th of a regular bulb. Therefore I'm pretty sure you can expect some odd behaviour with the rheostat.
It also depends how many lamps there are - but of course the calculations remain the same, e.g. 10 lamps / 10 LEDS or 5 lamps / 5 LEDS the result will be the same.
You may possibly find that all the control will be at one end of the rheostat, and the change from bright to dim will be rapid, rather than being gradual across it's rotation.
Without knowing the resistive value of the rheostat, it's difficult to be sure though.
IIRC - typical dash bulbs are around 3W, which would draw 250mA at 12V.
Those LEDS are rated at 35mA (0.42w), which is roughly 1/10th of a regular bulb. Therefore I'm pretty sure you can expect some odd behaviour with the rheostat.
It also depends how many lamps there are - but of course the calculations remain the same, e.g. 10 lamps / 10 LEDS or 5 lamps / 5 LEDS the result will be the same.
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