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led, surface mount resistors.


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sallc5 
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Posted: January 28, 2010 at 4:27 PM / IP Logged  
I wanted to also give you the specs for the 5mm LEDs and 3mm LEDs I will be using. This a link to the exact ebay auction. The 3mm are identical specs.
sallc5 
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Posted: January 28, 2010 at 4:33 PM / IP Logged  
[url]http://cgi./ws/eBayISAPI.dll?ViewItem&item=370199470254&ssPageName=STRK:MEWNX:IT[/url]
oldspark 
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Posted: January 28, 2010 at 6:07 PM / IP Logged  
You're not having much luck with links! But I FINALLY got to use eBay's (advanced) search for "item number".
The electrical specs seem typical. (The rest look good too - especially the price from what I have read hereon or elsewhere!)
So the other bulbs are 12V. I suspected so - it would be unusual (if not bad design if linear power conversion etc) to run "bulbs" off 5V etc. And I think 5V bulbs are rare - 6V is common, but the they'd probably run 2 in series.
And it's rare for a dimmer (rheostat, pot, variable resistor) that controls cabin or dash lights to "mix voltages" - ie, 5V & 12V bulbs etc. (Unless PWM, else buffered etc.)
BTW - only 16 posts to go and you can "edit" your posts UNLESS someone has since replied.
On the meantime, do you "Preview Post" and test the links? (I right-click links to open in new tab etc.)
sallc5 
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Posted: January 28, 2010 at 6:25 PM / IP Logged  
Yes, most of the time I will preview the post but at the time the tinypic links were working. Once submitted it says deleted.
Any way. I will re-probe one of the twist lock style bulbs tomorrow while recording the setting the dimmer switch is on.
Did you have time to review the diagrams? I was really hoping you would pull something out of them. I included the ones I thought were crucial.
I am also not sure if the earlier decision of replacing the 5mm LEDs in HVAC control board is right now either? Just makes sense that they are 5v and not 12v+ granted the tiny 147 ohm resistor for the current factory LED.
oldspark 
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Posted: January 28, 2010 at 6:44 PM / IP Logged  
Wot? Review? Diagrams? Surely you confuse me with someone who gives a damn, or an impression they do stuff?
Yeah - I just looked and it suggests all illumination is +12V - at least the dimmer controlled stuff.
But I thought the existing LEDs were 5V - that made sense with the 147R & 20mA etc. They are not dimmed are they? (If they are, it may be via some interface to the dimmer pot, or some other mechanism (maybe an optic sensor)...?)
Maybe I need to re-read.... I thought/assumed LEDs for indication else maybe panel backlighting etc, and the (12V) bulbs for illumination - hence dimmer etc.
Ah - mid-30s tomorrow (~95F) - maybe a swim with the rays & noahs (sharks) will refresh me......
sallc5 
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Posted: January 28, 2010 at 6:56 PM / IP Logged  
The LEDs do NOT dim, they are either on or off. Regardless of interior light dimming. So, with those diagrams i thought we have confirmed replacing the LEDs was alright with the factory 147 ohm resistor. So, let's close that topic.
I am still just curious about twist-lock filaments bulbs, which you now know do dim. If they are 12v+, which is what you have gathered from the diagrams, how do I go about dropping in an LED into the bulb base safely. Where would I put a resistor? I would like to avoid spending $1.30 USD on each individual 9-14.4v Neo-Wedge LEDs
Keep in mind the bases of the twist-lock filaments in my car are identical to those pictured at link above.
Not sure if I should put a resistor on each individual twist-lock bulb (if even possible) or in line somewhere between the dimmer switch and the respective lamps.
I do appreciate your help! Look forward to hearing your suggestions.
I must say I am jealous which I was near a beach! Hopefully I got all the links and everything right without needing to edit.
sallc5 
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Joined: November 27, 2009
Location: West Virginia, United States
Posted: January 28, 2010 at 7:24 PM / IP Logged  
I could do something like this:
led, surface mount resistors. - Page 5 -- posted image.
led, surface mount resistors. - Page 5 -- posted image.
Although this looks haggard. I also do not know how this will work with dimming. Not use the filament bulb base at all.
Just an idea I came across.
sallc5 
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Joined: November 27, 2009
Location: West Virginia, United States
Posted: January 28, 2010 at 7:49 PM / IP Logged  
..or alternatively, something like this with use of the base.
led, surface mount resistors. - Page 5 -- posted image.
led, surface mount resistors. - Page 5 -- posted image.
I would be happier with that than not using the base. This way it is reversible and could go back to the filaments easily if i wanted to.
I can also easily shorten the leads and then cover with heat shrink to fold them down closer to circuit board for clearance. This way the leads will not be in contact with any other solder or circuit on the board.
Now, that I have two method of getting the led to work in the twist-lock holes. I now need to figure out what resistor value to use. Also, how is this going to work with the dimmer switch and resistor? The dimmer control diagram states its range is from 150R-5kR.
oldspark 
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Posted: January 28, 2010 at 8:45 PM / IP Logged  
Now I get it - DIY twistlocks.... (Good - the 5V & 147R is closed.)
A main issue is how they dim compared to original and other bulbs. But you can do a sample - maybe any LED just to get an idea of any variance.
The question is how the voltage varies with the dimmer.
Ordinary bulbs are much like a resistor - current proportional to voltage.
LEDs are more like a zenor with a series resistor - ie, about 3V plus the iR voltage across is "equivalent" resistor.
Whilst LEDs may still glow with an external 5k resistor, it may still have 3V or 2V across it. Whereas bulbs with 5kR will be low-i = low current and hence a low voltage (not the LEDs 2V or 3V "zenor" plus a similar small voltage).
You might find that current-wise, the LEDs "dim" faster and then suddenly extinguish whereas the bulbs still glow.
But that depends on the LED/bulb balance.....
And I say dimming "current-wise" because bulb and LED intensity may vary with current, but to differing curves etc. (Alas all I remember is that a tungsten bulb is brighter than halogen at lower voltages - the halogen's illumination is a bit like zenor offset - ie, nearly 0 at say 6V, but full brightness at 13.8V etc.)
The gist of the above is - suck it and see. It's too complex to model... (At least with my models - not that I have them - but they often tend to include more than others...)
As to the resistor - still the same - ie, (Vs - Vled) for the LED current.
EG (pedantic):
3.2v - 3.6v, 20mA
Assume max 20mA @ 3.6V
Assume Vs=14.4V (typ alternator; no fuse drops etc)....
Make it 14.6V => 14.6-3.6 = 11V @ 20mA (11 x .02 = .22W = 1/4W)
R = v/i = 11/.02 = 550R = 560 Ohms 1/4W (standard preferred value).
Since .22W is close to .25W (we normally try for say 30% margins in design), a 1/2W resistor would be nicer. (They are probably the same price - maybe cheaper - and 1/2W resistors were traditionally beter quality, and are a bit more robust (physically strong).)
The resistor leads should be as short as possible - or rather, NOT long - to prevent breakage through vibration etc.
[Digression - GoTo next para: I remember when they used to recommend looping resistor leads to act as a spring to absorb vibration and prevent breakage. That was another classic case of some expert's "logic" being wrong (again!). Silly people like me ignored the advice. We didn't have the increased failure rate that others had. Nor did we have to replace all those resistors once the experts experienced how wrong they were.]
But the resistor may need clearance around the for heat dissipation (less so if using 1/2W due to greater surface area).
(Also short leads usually means more heat loss through PCB track than from longer lead heat dissipation - ie metal tracks beat air)   
FYI - 560R @ 20mA = 11.2V. Hence if Vs exceeds (3.6+11.2=) 14.8V, the 20mA is exceeded.
Some manufacturers refer to non-warranty or failure above 20mA. Whether this means it blows at 21mA or merely has a much shorter lifespan....
Welcome to the joys of design!
sallc5 
Member - Posts: 45
Member spacespace
Joined: November 27, 2009
Location: West Virginia, United States
Posted: January 28, 2010 at 9:02 PM / IP Logged  
Appreciate the time and explanations.
So, you think I am able to use 560 ohm resistor with LEDs and it will be fine. Keep in mind I either have the dimmer set to full brightness or not at all. So having no actual dimming function is okay with me.
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