led, surface mount resistors.

I have a small LED project in the works for my HVAC controls. Just had a few questions and wanted to run them by you guys here first. Make sure I am on the right track.

Here is a picture of the circuit board I will be working with:





I am looking to change all the White 5mm LEDs to Blue. The 5mm LED I will be putting in are rated at 3.2v-3.4v and 20mA. So, I will use a 560 ohm resistor at .25 Watts. Correct so far?

If you notice the current LEDs have surface mount resistors. They are currently rated at 147 ohms. It has a label of 1470 on it.

Would it be easier in a sense to remove the 147 ohm resistor and solder in a new 560 ohm surface mount resistor? Or to add an additional 430 ohm resistor to the led itself.

If using the surface mount LED's rated at 560 ohm will the ones linked below work for what I need?

[url]https://cgi./Resistor-560-Ohm-Surface-Mount-SMD-1206-pack-of-100_W0QQitemZ250380857065QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a4bdcaee9[/url]

TIA

Sall

Buy a couple extra LEdDs and try one with the 147 ohm resistor.  Power it up and check voltae across the LED.  The resistor value is not as critical s most people think. 

i am an idiot wrote:

---

The resistor value is not as critical as most people think. 

---

G'dam - you must be an idiot like me! I agree - resistor values are not that critical.

(Alas I made a similar statement on another site (an MPEG-1 layer) only to get a reply "begging to differ". It ended with the begging smartR begging me to leave.... after I had posted my last reply (of course!). The funniest thing - we were discussing PWM to dim LEDs - the switching FET etc can act as a resistor if it were that critical! At least I killed smartR's "thermal runaway" argument. (He was the type that claimed one parallel "string" would rob current from another parallel string.
Apols - I'm FIGJAMming again.)

My concern is that this is an integral part of the automatic climate control system. These boards are valued above $200 and cost over a $1000 at the dealer.

I don't want to be making a dumb mistake.

You need to do your research on the LED BEFORE putting it in the circuit.

What is the voltage driving the LED?  Most likely it's battery voltage, putting you up around 14.4vdc.  Your 560 ohm resistor would put out ~26mA.  Over the max value but the LED will probably still work for a long time.

However, at this current the LED is going to be VERY bright, possibly too bright for your application. 

I would recomend running the LED through a pot and hook it to your battery.  Dial the pot in until you like the brightness, then measure the resistance of the pot and go with that resistance.  I wouldn't be surprised if you ended up going with over 2,000 ohms of resistance to get them to a level they arn't painful to look at!

I would remove the surface mount LED and replace it with the resistor you want.

-------------
Kevin Pierson

Well, my charging system usually runs right about 14.9 volts which is optimal for my vehicle.

I see where you are coming from though. Just because that is the optimal range, that does not mean I want them that bright. I will just go down to radio shack and buy some resistors and test them out once I get the leds.

And when you said replace surface mount leds, I am thinking you meant surface mount resisitors, correct.

Yes, I meant resistors, sorry!

-------------
Kevin Pierson

That's okay,I appreciate the help!

I finally under stood what you meant by "pot". I always just referred to it as a variable resistor. So, instead of switching resistors in and out, it much easier to use a "pot" and dial in the resistance/brightness to my liking as you said. Then use the desired value for the surface mount resistors.

I will keep you updated on the progress. China drop shipment will take a few days...

DOD - more mpeg1L3 suggestions (constant current devices).

The main risk with this operation (other than driving a short or low resistance) is probably the soldering.
Rather than "replacing" the SMD resistors, you may want to add leaded resistors to the new LEDs. These may include the SMD value, else with a shorting link across the SMD/SMR.

Or just add a dimmer ... (LOL)

PS - I wonder what the patent pending "self-biased transistor technology" is - constant current devices are often made with a pair of transistors, a 3-terminal LM317 voltage regulator, or other nifty combinations.

oldspark wrote:

---

The main risk with this operation (other than driving a short or low resistance) is probably the soldering. Rather than "replacing" the SMD resistors, you may want to add leaded resistors to the new LEDs. These may include the SMD value, else with a shorting link across the SMD/SMR.

Or just add a dimmer ... (LOL)

---

Yes, this was part of my original question. To remove the current surface mount resistor or add another leaded resistor to the LED. Definitely quite a bit of soldering and solder removal. 20 LEDs and 20 resistors equals 80 solders/removals.

Using the pot/dimmer inside the vehicle is not an option. The board is actually powered through a UART B serial data line.

Granted, I do have the extra circuit board and I am really in no way worried about ruining the board, I would still like to the see the project be a success. I could also use the little silicon cap condom things to change the color, but what is the fun in that?

I was thinking about what the first two posters had claimed that the resistors do not matter that would be okay using the current 147 ohm surface mount resistor.So, I did the math...

I came out with I = (14.4v-3.4v)/147ohms which gave me .07 or 70 mA. Is this not way too much compared to the suggested 20mA. Will this dramatically reduce the life of the LEDs?

I am new to this so, if the math is wrong or theory, please improve the learning curve.

TIA

sallc5 wrote:

---

I came out with I = (14.4v-3.4v)/147ohms which gave me .07 or 70 mA.

---

EXCELLENT! That is done correctly - at least "by the book". But I'll say more on that later....

But look at this the other way....
You are saying the 147R (R means Ohm - it's used instead of the Omega symbol) resistors mean 70mA through a 3.4V LED. (That is correct).
Therefore your existing LEDs are also taking 70mA unless they are (say) 1.7V LEDs hence (14.4v-1.7v)/147R = 12.7/147 = 86mA.

Do you see the issue - LEDs do not take that much (except for v.high intensity etc).
So there is some "circuit issue" - it may be multiplexed, use series LEDs, or use a lower supply voltage (maybe 5V regulated - 5V/147R means 34mA MAXIMUM - less if you add LEDS - eg 22mA & 10mA for 1.7 & 3.4V LEDS).

But yet again - is it important? Let's consider it this way....
Your new LEDs are higher voltage than the originals - or so I presume. They are unlikely to be higher voltage.
If your new LEDs are the same voltage (as the original), they will draw/take the same current. If they are higher, they will take LESS current.
Hence it should be safe simply to substitute the new LEDs.
This assumes each LED replaces each original LED. (Otherwise you will need to figure out how the LEDS are connected - is it one resister per LED etc. If each LED is an indicator (bar graph etc) then yes - probably. If it's for illumination, then some LEDs are probably in series with a single resistor.)

Oh geez! Too much?
In summary - the circuit is probably more complex than you think, but it shouldn't matter. The new LEDs may not work or be bright enough, but since they shouldn't take MORE current than the old LEDs, the circuit should not blow up.

The blues may not be bright enough because they may need the higher voltage and higher current. Besides - we are less sensitive to blue than green & red (& hence white). (Yes - aren't those blue headlights so much brighter than white - rotflmfho!!)
The filters may work if the originals are white LEDs. For colored LEDs they usually don't (ie, red, green, yellow etc LEDs generally put out ONLY those colors so any "other color" filter blocks their light output.


Regarding the 14.4V LED supply - that is unlikely - unless they dim & brighten with vehicle RPM.
For various reasons - including the need for circuits to operate from (say) an 8V-10V to 16V vehicle supply - their supply will be protected and regulated.
5V is a common voltage for LED indicators/meters etc for historical reasons, plus reliable regulation at 5V even if the vehicle dips to 8V (eg, during cranking). Not that this voltage variation applies to all systems, but since equipment tends to be made to suit "all" applications....

Anyhow, there are various ways of checking the above, but it can get complicated. Especially if the LEDs are muliplexed (hence very high currents - maybe 70mA - but only for 10% to 30% of the time etc).


And I was dumb enough to say above "But I'll say more on that later... (referring to your calcs "by the book"). So solely due to commitment (and not my need to ramble)....
You will probably find that - especially for LEDs - near enough is close enough.
I used to do my (12-1.7)V/20mA for cars etc. That became (12-2)V/mA = 10V/mA etc.
Then like others I ignored the LEDs ~2V drop (for 12V).
Why? Because:
: 2V in 12V is under 20% error - not much (for LEDs).
: 12V is really 13.8V typically; often 14.4V or more (ie, ~20% error!)
: resistors came in "preferred values" bands of ~20% gap - ie, 10, 12, 15, 18, 22, 27 ec Ohms. Your 147R would have been 150R (else 120R or 180R)
: resistors has a tolerance of 10% (so 150R could be 135-165R)
etc etc etc.
Although much has changed - like although "preferred values" may still be the E10 scale as above, their (manufacturing) tolerance is now 1% (not 10% or 5% etc), the approximations haven't.
Why? Because LEDs tolerate and operate under a wide voltage variation. [This is what that other-site's "discussion" was about - someone claiming a "non-tolerance" (at the risk of thermal runaway) but the supplying all the evidence to prove me correct - though they tried to provide a "temperature measuring" document as a "proof of thermal runaway" for "LEDs without resistors".]      

Anyhow, because LEDs can now be 3.4V, maybe their voltage can't be ignored. (Though you see the relative similarity between 10, 20 & 30mA when ignoring 1.7V & 3.4V in a mere 5V supply!).
But I'd do your 14.4v-3.4v)/147ohms as (15-3)/150 = 15/150 = 100mA (else maybe 12/150 = 80mA).

A better example may be calculating the resistor assuming 14.4V etc:
R = (14.4-3.4)V/20mA = 550R => 560R (preferred E10 value); or
R = ~10/0.2 = 500 => 470R or 560R (preferred E10 values).
Rats - that last shows a typical problem. One might normally chose the 479R cos it's closer. Or would one chose the 560R anyhow because it's "safer" (less current), or because we know we rounded the voltage down hence getting a lower resistance than reality, or we allow for higher than 14.4V, etc etc.

It is an experience thing....
If in doubt, do it by the book. But do "rough checks" with simple figures as I have shown. You may find you are out by orders of magnitude (ie, 56R instead of 560R), or that rough is good enough.

Damn I hate commitments.   
Maybe I should have breakfast eh?
The I'll re-read by ramble. (Why can't we post-edit after later replies....).

If it makes sense, maybe you can confirm the power (wattage) rating of the resistors?
If the original LEDs are 1.7V from a 14.4V supply, those 147R resistors must be 1W (if not multiplexed) - and I doubt that they are!
But you said it was powered from a UART serial line.... Do you mean the board is signalled via the UART (or the LEDs are controlled via the UART... nah) - because AFAIK UARTs are not for powering - only signalling (and using a serial signal for multiplexing or powering ... )
Got it! The UART may have a regulated output - eg - a 5V supply (ie serial-in to digital-logic out - eg, RS232 to CPU etc).
Is that what is done? That makes sense with the existing "low" 147R.
If the 5V is only powering the LEDs, a dimmer is possible (though probably undesirable).

I read through all of that and yes i do understand most of it. Thanks! Now I do think you are onto something with UART. Maybe it is regulated. Would a snippet from the FSM help you help me, haha?

Here is a description of the hvac controls/driver info center:

The instrument cluster converts the trip computer information to the driver information center (DIC) on the universal asynchronous receiving/transmitting (UART) B serial data line. A discrete input sends the information to the instrument cluster for calculation. The instrument cluster processes the raw data. The instrument cluster uses an internal time keeping function in order to determine the selected information.

Schematics: (but not for the board itself...)



All of the LEDs have an individual surface mount resistor. The LEDs themselves also never dim. There are other twist-lock style bulbs which are NOT leds. I am able to dim these bulbs in conjunction with the gauge cluster. This really has nothing to do with this though I guess.

How would you suggest I test to see how many volts the factory LEDs are getting. So that I can confirm the voltage. I am guessing multi-meter with the car on...

The LED must be lit when testing the voltage.  Simply place one lead on one connection and the other lead on the other connection.  What is the DC voltage reading.  Also check the voltag drop across the resistor.  One lead on one end of the resistor, and the other lead on the other end of the resistor.  The LED must be lit up.

Your assumption is SPOT ON. I found the correct diagram.



This definitely changes the game. So, I need to redo some math. Let me know what you think in the mean time.

My apologies this one is correct diagram. I need to postmoreto be able to edit, darn rookie. :(



5V as expected. So Would I also be right in assuming I can just pop in some twist-lock leds? Let's not go there quite yet though...

So, with this diagram clearing stating that the circuit board receives 5v, it is basically a waste of time to remove the 147R resistors.

https://i45.tinypic.com/2lawv0k.png

R = (5v-3.4)/.02

R = 82

So, I would "by the book" need an 82R 1/8W resistor. If anything the LEDS will not be as bright as they could be but more than likely bright enough for this application and not hard to look at. Is this a good assumption?

Don't ya hate "Rookies" that aren't rookies?!

You are spot on (IMO!).

I get 80R (not 82R), but big deal. 80/82 means 82R in preferred values.
P = iiR = .02 x .02 x 82 = .0328W (check VI = 2.6x.02 =0.052 wth? P-vv/R = 2.6x2.6/82=.082 wth#2?) Oh well, seems under 1/10thWatt etc.

Maybe a good way to change the SMD 147R to 82R is to parallel a 180R (185R) resistor with the 147R. Just an option.
Otherwise I'd either short the 147Rs with a link, else take a flying lead from the "start" of the 147R to the 82R & LED.

But just substitute the new LEDs for now.
They might be bright enough (though probably not???).
If not, a temp "parallel" 180R or "bypassing" 82R can be used to see the difference. (Maybe blue is too dark?)

But I'm happy....
You seem to agree that you "can't blow the PCB" etc by merely substituting the LEDs. And it seems the new LEDs are NOT higher current than the originals.


As to bluddy MLAs, FSM is Full Service Manual? No - Field...? (I knew my TLAs once upon a time - until I cross-technology'd)
HVAC is not HiVoltage AC - it's Heinous Voltage Air-Con etc.
It's important to know exactly what they mean..... LOL!

(Save the FSM until AFTER we blow it up. That's what engineers & real blokes do!)

Thanks for confirming my thoughts/suggestions. If it now blows up, it means YOU didn't confirm enough! LOL!
(BTW - most boards can be repaired assuming non-proprietry etc. I assume to UARTs are still available. Only older stuff can be a problem - like trying to decode EFI/ECUs from the 1980s - you can't get the chip information!)

Yes, I just rounded up to the next value.

My theory is to test it with a 6v battery with pot set to 150R.This should give me the same output of light as if using the 5v source at 82R. Then I can see whether or not it is as bright as I would like. These LEDs are pretty much staring me in the face while driving. Peripherally but that is your best night vision source.

Even though the circuit boards are dealer expensive 1.5k range they can be had on ebay for fairly cheap. I already have a tested working board just for this project in case anything goes awry,I have the original to put back in. So,no worries there.

Thanks for the help thus far. Let me know if pot theory is correct.

Oh yeah - FSM as in Factory Service Manual. You were close!

Yep - the pot theory is good noting that 150R is yet another preferred value, and at 20mA = .02 x .02 x 150 = 1/16 Watt - most resistors & pots should handle it.

I calc currents of 19.5 & 17.3mA for the 5&6V & 82 & 150R combinations.
With the pot you might get a feel for the variation of voltage/current and brightness of the LED. (IMO - the brightness variation is less than the voltage(current) variation (relative to "nominal" voltage) - ie, LEDs are NOT that critical wrt voltage etc.)


Good to hear of cheap eGay alternatives.
I am often amazed at the purchase of $1,000 PCBs when a mere 20c item has failed, but that's just my DIY mentality (resulting from earlier neccessity; and possible use for future inevitabilities...)

I got this spare one at salvage for $15. Haha so, I am golden. Like I mentioned it tested in working condition on my vehicle. Anyways here is the ride I am doing this project on. Olds Aurora!

i dunno of anyone has covered this yet, but usually when surface mount is used that means that there's some high speed switching going on in some ic controller and the surface mount is there so less current is loss. i would personally take the time to redo all the soldering, though it might have just been done to save space, so take my thoughts with a grain of salt

Good tip Knox, but I think that has been covered - the LEDs concerned seem to have voltage & resistor values consistent with non-switched circuits (once the 5V rail was determined).

Though many LED were switched anyhow - long before SMD (a good method of color equalisation, extra brightness, power & circuit saving, etc).


Sall - nice ride! Good to hear of the cheap pickup - beats the $1,000.

I have another question. Can I simply replace the 3 and 5mm twist-lock style filament bulbs with 3 and 5mm component leds as well?

If so, how would I get a resistor on one of these pc sockets? I would be pulling the filament and replacing the bulb with the respective size LED using the same pc socket.

Sorry that is the wrong picture... here it is...

The bases on these are the same except these already have LEDs.

ahh... messed up again.

LINK

Voltage is also 5v. Not sure about resistance but they are hooked into a pot dimmer. Taking it I just need to ohm out the dimmer switch and see if the resistance falls into alright area for the LEDs?

I don't understand....

It sounds like you want to substitute LEDs in place of filament bulbs.
I presume the filament bulbs are 12V (not 5V).
The NeoWedge LEDs at your LINK operate from 9-15V (& 10-19mA depending on type/color).


Substituting LEDs for bulbs is reasonably common. The problem is the method - mount a LED in a base; with internal resistor etc?
(Reduced contact reliability due to less whetting current.... oh no - more gold contacts (to be used with gold plated fuses and battery terminals of course!)...)

I apologize that was way too jumbled for anyone to understand really. I looked up some schematics.

There are about 20 total twist-lock style bulbs on the HVAC Panel as well as about 10 or so other ones throughout the car. These twist-lock style filament bulbs on HVAC, etc. are dimmable (unlike the LEDs we discussed earlier). The link was just to describe what the base of the bulb looks like. I would like to remove the filament bulb and drop in an LED. I was not sure at the time if I needed a resistor or not thus why I was asking how in the world would I solder one onto these. I now do not think I need a resistor.


There is a pot dimmer switch on the dash which dims the instrument cluster and all the other twist-lock style filament bulbs.

Here are the schematics:





There are plenty more if you need to see more. They all pretty much say the same thing.

From these diagrams I can see that dimmer and the interior lights have a 5v reference. The dimmer switch is a pot. It sets resistance on the 5v reference in order to dim the interior lights. The resistance is at minimum 150R and a maximum of 5k R.

I tested this today with a 5k pot on one of the LEDs I got in the mail. Pot set 150R with a 6v reference the LED is nice bright blue, but not too hard to look at. Moving the pot down slowly, I can see the LED dim. At 5k the LED is dim and still visible. A noticeable difference between the 150 and 5k resistance. I usually have the IC and the other lamps on as bright as the go when it is dark. So, I would not be over powering them they basically would see the same resistance and power that the HVAC LEDs we discussed earlier would. Thus both would be at right around 150R when on.

I think I could be happy with results. Otherwise I take it I will need to use a pwm.

Thanks for re-reading this. I definitely jumbled all that last night and made 2 or 3 erroneous posts. Let me know what you all think.

Ah, second picture is a bust again: Here it is. My apologies again.

One last time, tinypic messing with me...



If it does not work, I suppose take my word for the 5v reference then.

Tee hee! I too hate being unable to edit else delete posts, but it's not my server space. And readers just have to read ahead in anticipation of corrections & addendums.

The last to https://i47.tinypic.com/2lu9wth.jpg has also been deleted.
But I have had no problems uploading pics here provided the filename is not long (say 10 characters).
In fact that's one thing I REALLY like about the 12volt - it hosts my images - I do NOT have to link to images stored elsewhere.


Interesting that for a LED that would nominally have a 150R resistor, it still glows at 5,000R (compare that to a 2W-3W bulb with its equivalent 15R to 500R range).

That shows how sensitive LEDs can be.
It also demonstrates what a pain they can be in circuits with leakage, or why they are unsuitable as charging-lamps for alternators.

As to needing resistors for the LEDs - they should be needed if the supply exceeds their voltage (say 2V or 3.4V etc) unless each LED is current limited (to 20mA etc).

But it may be possible to limit their voltage.
EG - if 5V supply, want 3.4V max: 5-3.4 = 1.6V.
Diodes have a fwd V drop of 0.6 to 0.7V.
2 diodes might hence drop 1.2-1.4V (hence LEDs get max 3.6-3.8V - a bit high?)
3 diodes 1.8-2.1 => LEDs 2.9-3.2V - maybe ok?

Just the 2 or 3 diodes in series with the supply (ie, from the dimmer pot etc). The diodes need to be rated for the full current (number of LEDs x 20mA etc, hence a 1A IN4004 etc should handle 50x20mA LEDs).

Not that I looked at the circuitry too well, and I assume you are correct about the 5V lamp supply (which seems strange unless they use 5V bulbs - sure they ain't 12V - maybe a grounded dimmer?).


BTW - I assume the blue LEDs are not needed for colour discrimination or as a point source?
It was something I meant to say much earlier....
If colour discrimination is required, then "the standards" say it must "subtend an angle of 2 degrees at the eye". In other words, if blue and too small, we can't tell it's blue. Or, we tend to be blue insensitive - blue need much higher power than greens or reds.     
Blue can also be stressful for some - eg, cars with blue LEDs (windscreen washers etc).
And blue with red makes for a 3-D image for the 95% of people with misaligned retinas etc (ie, most people have "faulty" eyes!) - or am I confusing the fault with those 3-D printed pictures.... yes - I am - blue bends different to red - hence the 3-D effect through glasses. The 3D effect through focussing works for the ~95% with misaligned eyes...
Alas my eyes are also misaligned, and MadCow is still apparent....

Everywhere I look says the illumination lamps receive a 5v reference and is tied into the pot/dimmer on the dash.

Let me post some link to some pdf and maybe you can take a look at them for me:

UART.pdf

IP & Console.pdf

IC Illumination Lamps.pdf

HVAC SW Radio IC.pdf

DIC Schematics.pdf

Dimmer Control.pdf

In any case I will pull the dimmer bezel and measure what one of those twist-lock style bulbs are receiving voltage wise. just let me know if you gather the same thing form the diagrams that I did. thank you!

Second pdf did not link correctly.

ICIlluminationLamps.pdf

One last try...

IPConsole.pdf

Grrrr! How I ever told you how much I hate you? LOL!

Other than that, I'm merely saying that I've downloaded the pdfs but won't look till later.
Damned reality calls.....

Cheers.

Haha I'm not forcing you to help, but I do appreciate it man! Not too many knowledgeable folks over at the Aurora forum with this type of stuff.

Take your time. I have plenty of time to figure this out. I won't receive the rest of my items for another ten or so days. Still like to a set game plan though!

I probed out one of the twist-lock filament bulbs. Contrary to my belief it was anywhere from 5v on dim to almost 11v at max. Maybe I am missing something in the diagrams.

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.

[url]https://cgi./ws/eBayISAPI.dll?ViewItem&item=370199470254&ssPageName=STRK:MEWNX:IT[/url]

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.)

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.

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......

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.

I could do something like this:





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.

..or alternatively, something like this with use of the base.





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.

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!

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.

Also, you say the resistors do need clearance. Is using heat shrink tubing not advisable then?

Again, welcome to design....
Does the heatshrink conduct as good or better... etc?

It'll probably be fine.
Or maybe heatshrink isn't needed. I often don't for grounded ends, or resistor junctions, or resistor-LED junctions - but that is based on those junctions not causing damage to other circuitry (ie, low or no current through resistors, LED or gnd) as opposed to OTHER conductors hitting them (and thus doing damage).

But I have learned that it doesn't matter that nothing can ever hit an exposed conductor because eventually something will. (I should have learnt from telcos - even when their DC bussbars go through inaccessible areas, the are still covered with insulation. Not that their bussbars are fused, but often neither are our exposed circuits in terms of NOT damaging surrounding circuitry.)

Of late, I have tended to wrap (heatshrink) whether needed or not, though often this had been to increase joint strength for flying leads etc.

Besides, if your resistors get too hot, you'll probably smell the heatshrink - ie, get a warning.
And if they do overheat, they should go higher resistance. If they do blow, they should blow open - ie, a circuit failure but non-destructive (other than the resistor, and the burning Aurora (Borealis?))


The 560R (1/2W, else 1/4W) should be fine. That should give max intensity and be ok for a supply up to 14.8V shown before.
If your system goes higher than 14.8V (as some do) - but at the LED source - and if those LEDs thus destruct, you can increase the resistor. 680R is the next size, then 820R.

That means lower intensity but it may still be sufficient for your needs. You might find you want bigger resistors anyhow if they are too bright. (And at 680R and above, 1/4W should be fine: P = iiR = i x i x R; or (VxV)/R.)


Post-Edit: Most readers should stop here... The rest has little value-add. Maybe.

Funny how this thread reminds me so much of another.....
The other thread gave the following link for these OSRAM HyperPointLEDs (pdf; 643kB). I liked the datasheet because it showed so many aspects of LED behavior. (It also blew several of the thread's arguments out of the water. I like people that supply their own rope!)
A lot of the info is batch & physical stuff, but some diagrams illustrate color, intensity, current, voltage etc shifts with temperature/current etc.

Its CIE "color" diagram may be a bit confusing. Essentially it is a 3D "color map" drawn in 2 dimensions, but essentially it covers all visible colors and assigns coordinates (u,v or Cx,Cy) so that any color can be defined.
(Manufacturers and Standards use them - eg, one Standard (ISO-whatever part 17?) states that for colour redundancy (discrimination), the different colors used must be separated by (u,v) > 0.2 (or something similar...) - it's all fabulous stuff except when moron managers start specifying those standards for OH&S reasons yet have no idea of the implications nor implementation, but I'm not one to whinge!)

Oops - I digressed.
Anyhow, flick through the pdf and look at some of the graphs.
In many ways it shows why approximations are ok, or aka near enough is close enough (aka some implement extreme pedantics for no reason, but at the expense of reliability and serviceablity).


But again - try/test and see.
If >560R is okay, use that for more margin. (ie, 680R, 820R, 1k etc)
Do they work okay under dimming?
Feel the heat from the resistors.
[Note that a LED-free resistor on 14.4V dissipates nearly 50% more power than at 12V - ie, P in a resistor = VxV/R, so P is proportional to voltage-squared. P@14.4 compared to 12 = (14.4 x 14.4)/(12 x 12) = 1.44 = 44% more heat. That's a principle I've tried to knock into a few local audiophiles with under-rated alternators and poor SMPS (dc-dc converters) in their amps - ie, for normal amps (45-200W per channel), the amp at 14.4V will put out 44% more power than at 12V (usually more, but it all depends...).]


Isn't it good that with all the things that can go wrong, you can get a $15 replacement? That's about $985 to spend on other projects - maybe a holographic heads up display (direct projection - not crappy 3D windscreen stuff) - then you scrap all illumination etc except for the projector (and I prefer synaptic injection rather than retinal - electro-mag is still more efficient than optic for modern transducers).
But let's make sure you close this project first.

Yep - I definitely need a cool soak soon!

What can I say other than thanks for the complete and thorough explanation? It all makes sense now.

So, I think I have a set game plan. My charging system in my vehicle operates normally between 14.8 & 15.3 depending on loads (ac, etc). So, I will use that highest value to calculate for the resistor. Overkill?

As you said I may find 560R is too bright and decide to use a higher value resistor.

I will keep you updated once I receive all my shipments. Thanks again!

Your welcome.
Alas I may have overkilled my replies, but it seems to have been worthwhile.

As to your design overkill (using the highest voltage) - that's not overkill but good design practice.
IE - do worst-case calculations & design.
The do "nominal" (expected) design.
Usually thanks to "preferred values" and other variances and margins, they will align fairly well.

It's only when there is a borderline - eg, if 560R is close to 1/4W should I use 1/2W.
Or if 560R may allow >20mA should I use 680R to allow for 15.x volts?
In this case they both suggest 680R as a nice solution - less power and current! But will that drop intensity too much?

When I have borderline issues, I then have to decide what is to give. Stick to 560R 1/4W for luminosity and small size and risk that >14.9V doesn't occur (long enough) etc?
And that reminds me - a 560R resistor will not be 560.0R etc. These days 1% tolerance is common so it's 555R to 565R. But 5% used to be the norm - ie, 532R - 588R. (Remember I calculated 550R, not 560?)
That's what makes a joke of pedantics.
And you may have seen the LED electrical variations? And LEDs from the same die (crystal whatever) have differing Vf (forward voltage drops).

Anyhow, no such thing as overkill in terms of finding out the worst-case scenario.
Better to know that it will or might blow up than not to have considered it.

The overkill instead may come from using "exact" figures when rounding suffices. EG - 3.4 or 3.6V LED? 12.7V or 14.4V supply? Burger it - call it 10V for the resistor - that suits 20mA. Or a 120R resistor - lets make it 12V across it instead of 10V.

That latter seems contradictory to using "worst case" etc, but there's a difference between "getting a feel" for the design (ie, an idea of how much power is needed, how hot, wire thickness etc) and getting the "whole design" with a ballpark size & component value, and then going through with the "real" figures, the real specs & temperatures or voltages etc.
I think I'm stating the obvious to anyone with good experience in any art, I mean, science. Most will have their rough sizing or intuition etc. I once sized concrete costs for a floor: 6x8=~50, thickness of ? means ~1/15th so 50/15 ~60/15 = 4 cubic units at ~$100/unit ~$400 which is no problem: irrelevant. My techHead colleague returned after several minutes having calculated $345.67. They were not happy when I said "fine - it's way under $1,000" (the budget). But they insisted on the accuracy - else were unable to do simple estimates - despite knowing the budget and measurements etc. If I had have estimated closer to $1,000, I too would have run for the calculator - unless I knew that rounding & estimated were generally pessimistic - ie, bad or worst case.
But I still don't know how many bags of sugar we needed though.

Alas, another ramble - so boring for those log standing gifted contributors hereon.
(That's my technique to get away with errors and ludicrous statements. They never catch me.)

Giving an update! The project HVAC project has been completed. I did stick with the factory SMD resistors for the 5mm 3.4v 20mA LEDs I used. Turned out very nice and I am happy with the results! Here is one snapshot.

Thanks for all the help!! The DIY twist-locks turned out really well as well.