Smart Car of America Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
861 Posts
Discussion Starter #1
i purchased 2 of the Festoon bulbs from ebay for $.99. they work good but yes it has residual current at nite although you can just barely see it.

i just don't understand how there can be juice when the switches are closed/open....almost sounds like a feedback short somewhere
 

·
Registered
Joined
·
333 Posts
i purchased 2 of the Festoon bulbs from ebay for $.99. they work good but yes it has residual current at nite although you can just barely see it.

i just don't understand how there can be juice when the switches are closed/open....almost sounds like a feedback short somewhere
I find the glow just barely perceptible at night and nonexistent during the day.

The dome light is driven by a circuit in the SAM. It is not a mechanical on/off switch or relay, but some sort of transistorized dimming circuit. While the residual current is not sufficient to produce a glow from the stock incandescent bulb, it does with the more efficient LEDs.

I seem to recall the voltage was just a little above the point where the LED would extinguish completely. A series diode may provide enough drop for those more OCD than me. :laugh:

~toaster
 

·
Registered
Joined
·
861 Posts
Discussion Starter #3
thanks toaster that makes sense

huh, whats a series diode and where do it go for us dumdums (didn't mean you toaster)
 

·
Registered
Joined
·
333 Posts
thanks toaster that makes sense

huh, whats a series diode and where do it go for us dumdums (didn't mean you toaster)
A series diode would go in series with the LED. The idea is to increase the forward voltage of the LED light by an additional diode drop of 0.6V - I think this might raise the 'ON' voltage of these LEDs to just above the done light's off voltage.

I suppose one could cut up the factory wiring and add it, but I abhor the thought of hacking up the wire harness. Maybe the crude automotive harnesses of the 50s, 60s & 70s... but not today's advanced harnesses. I cringe when people do so. I've had both the dealership and another shop cut up the harness on my truck, opening it up to water intrusion and corrosion and the problems which followed. It was not fun repairing their mess! :(

In this case I'd try adding it to the LED bulb... probably in series with the LED's current limiting resistor. But to do so, you'd need a fine tip soldering iron and the ability to work with tiny surface mount parts.

~toaster
 

·
Registered
Joined
·
2,947 Posts
I think most would be way too inexperienced with circuits to work on the tiny board on a LED. Would you be willing to sell your services??? (@ toaster)
 

·
Registered
Joined
·
333 Posts
Does a diode drop the voltage? I did not even realize that it does....
I think most would be way too inexperienced with circuits to work on the tiny board on a LED. Would you be willing to sell your services??? (@ toaster)
A typical silicon diode has a nominal 0.6V drop.

While I used to be able to read the numbers on an 0603 resistor unaided, not so any more... nor are my hands as steady as they once were... old age creeps up rather sneakily.

I find a microscope necessary for working on this stuff anymore. 0603 parts are easy, 0402 parts are tricky, but 0201 parts are dang near, but not quite, impossible to hand solder. I generally rely on the talented girls in the rework department, but in a pinch I can still manage.

~toaster

P.S. SMD component sizes are often expressed in "mils" which is 1/1000 of an inch, so an 0603 part is 60-mils by 30-mils.
 

·
Registered
Joined
·
2,947 Posts
Can we "pinch" you to get some neat soldering out of you? . Sadly I have to practice just to get wire together nicely, it helps to have high flux solder....

Someone once told me to ask my wife when I expressed concern about my ability to solder, even just wiring. Neat little secret! (Helpful to have small hands). Then once my sister-in-law was noting how in China they would try to hand repair PCBs. (I asked and she noted only if it were the top layer. She also noted that for automotive boards it would not be allowed because of reliability requirements. She's some sort of QC manager of sorts).

Sigh....
 
1 - 8 of 8 Posts
Top