staged dimming

[etlsport]

anyone know how the staged dimming on the dome light works? i ordered a dome light consisting of 36 high intensity LEDs and the circuit board in the stock dome light didnt have the power to light it up right.. so i added a relay activated by the circuit board.. problem now is when the light goes out (when the dimming would occur) the relay freaks out and buzzes... anyone know how this feature works, how i could disable it or how i could just stop the buzzing?

[Kenny]

anyone know how the staged dimming on the dome light works? i ordered a dome light consisting of 36 high intensity LEDs and the circuit board in the stock dome light didnt have the power to light it up right.. so i added a relay activated by the circuit board.. problem now is when the light goes out (when the dimming would occur) the relay freaks out and buzzes... anyone know how this feature works, how i could disable it or how i could just stop the buzzing?

Funny, I was in the process of getting a cluster LED dome light myself and was curious about this too. I also ran into some fun with the circuit board when I tapped into it for the LEDs I placed in the cargo area. I drilled and placed a bunch of LEDs with resistors in the upper cladding to light up the cargo area with the dome light and found that the LEDs don't dim on the second stage (12V drops to 7V). LEDs with resistors don't like voltage fluctuations.

In answer to your question, you need to bypass the circuit board AND add a relay. The two wires that come to the dome light are BOTH 12V and the frame is ground. The red wire with the green stripe (on my 2001) is the control wire based on door ajar, unfortunately, it's HOT when the door is closed - there is no voltage when the door is ajar. The other red wire with silver dots is always hot. So you need a relay to switch the dome light ON when control power is OFF.Unplug the dome light, wire a relay to the incoming wires and ground to the frame. Send the HOT wire from the relay to the drivers side tab of the dome light the passenger side will be grounded when you screw the dome back to the frame.

That's the easy but messy way. You could be more clean if you found the door ajar relay and do the switch there to send 12V when the door is ajar...
At least with the easy way you can always go back to a bulb and plug the dome circuit board in place.

Let me know how it goes, I'll be doing the dome LED soon too, once I find a small relay...

cheers.

[etlsport]

thanks kenny... i wanted to keep the circuit board so i would still have a switch to turn the light on by pressing the dome light lens... whatta pain ill let u know what i decide to do

[WyrreJ]

I bought a similar board, can't remember quite where online I purchased it, but it was only like $5-$10. It came with an adapter that plugs in where the normal bulb goes and runs a wire to the circuit board.

This one works just fine, I didn't even attach it, just kind of stuck it in and put the dome-light cover back on. It slides around a little bit but not enough to cause much of a problem. It's much brighter than the original incandescent bulb

[etlsport]

ok just talked to a buddy of mine who is an EE major... told me that all i need to do is open up the dome light and remove the capacitor on the board that is responsible for the dimming.... sounds easy enough, so next time i see him he'll be lookin at it and figuring out how to stop the dimming while still retaining the switch


wyrrej -yea i had an LED setup similar to that before that i liked a lot.. it was 9 LEDs which was pretty bright... i stepped up to 36 now though... heh should be enough to land an airplane by! even in full daylight they light up the seats.. cant wait to see them at night ill be sure to post pics tonight

http://www.vehicross.info/gallery/data/500/medium/dome_003.jpg (http://www.vehicross.info/gallery/data/500/dome_003.jpg)

[tom4bren]

Remember when it was OK to have your dome light come on when you opened your door and turned off when you closed it - AAHH the good ol' days.

I guess you've already realized that LEDs don't dim (that's the Diode part of LED) and that you're OK with that. You are only concerned with the buzzing of the relay.

Your dweebish EE friend (I can say that cause I are one) was on the right track with removing the capacitor. Before you remove it though, you might just try putting a BFC (Big F%%%ing Capacitor) across the power leads of your relay. It should hold the switched voltage long enough (in theory) for the dimming action to finish and then bleed off fast enough so that the switch in the relay doesn't 'bounce'.

[etlsport]

hehehehehehe
http://www.vehicross.info/gallery/data/500/medium/night_light_009.jpg (http://www.vehicross.info/gallery/data/500/night_light_009.jpg)
http://www.vehicross.info/gallery/data/500/medium/night_light_021.jpg (http://www.vehicross.info/gallery/data/500/night_light_021.jpg)

[WyrreJ]

I guess you've already realized that LEDs don't dim (that's the Diode part of LED) and that you're OK with that.

What are you talking about? Of course LEDs dim. In fact, it takes special circuitry (voltage regulator) to prevent them from dimming when running from a battery - as voltage decreases so does brightness.

[tom4bren]

WyrreJ,

"Because the voltage versus current characteristics of an LED are much like any diode (that is, current approximately an exponential function of voltage), a small voltage change results in a huge change in current."

It can be done but shouldn't be done. All of the benefits of an LED go down the toilet when you try to dim them. If you feel the need to dim LEDs then you should seriously consider PWM (Pulse Width Modulation) as they react very well to that scenario. Of course the effectiveness of PWM is very dependent on the color of the LED you are using as your eye will integrate the different colors at different efficiencies.

OOOPPSS - Just looked in a mirror and saw a dweeb. Sorry 'bout that.

Tom

BTW ETL - the pix look great

[WyrreJ]

PWM requires a much more complicated circuit. If you want to run at peak efficiency than PWM may be the way to go, but not always. But in applications like this, there is hardly any need for it - reduced efficiency for a few seconds isn't going to hurt anyone. Which is all really beyond the point, as an engineer I'm sure you can appreciate my desire for precision -- "LEDs don't dim" is just simply incorrect.

[tom4bren]

PWM is definitely too complicated for this application.

LEDs can dim - a little. If you want to retain the dimming though, keep the incandescant setup (I meant to make that statement in my earlier comment but forgot). If you try to dim LEDs (especially in an array like ETL is using) you'll end up frying it or the circuit. LEDs try to be constant power so the current will increase dramatically as the voltage drops ... and the LEDs are NOT protected by the fuse.

The more pertinent question is: can ETL debounce his relay so that it doesn't buzz?

[Lizardmen3477]

Wow where did u get that and how hard is it to install i would love to buy that please send me website and how it was to install. Thanks Lot.

[WyrreJ]

LEDs can dim - a little.
No, they can dim a lot.

Here is just one of many graphs of the output of an (unregulated) LED flashlight brightness versus time starting with a fresh set of batteries:

http://www.flashlightreviews.com/reviews/img/mag_minimagled/mag_minimagled_010.gif

They pretty much all look like that - 50-75% dimming.

Here's a ton of discussion on PWM versus current-control for LED lighting.
The general consensus seems to be that current-control is preferred.
http://www.candlepowerforums.com/vb/showthread.php?t=152185