48v LED Festoon retrofit.

[TheGuitarist]

So basically every festoon in our board is dead or dying... so we thought, lets bring this into the future and make LED ones!!

Just wondering if you guys would be able to help me and just confirm that this circuit is good.

basically this will be my led driver.

http://au.mouser.com/ProductDetail/Supertex/CL2N3-G/?qs=sGAEpiMZZMu8%252bGBKj8XSFHtFgo%252blW1jNCjvCXIhjCuU%3d

and i was thinking this for the led.

http://au.mouser.com/ProductDetail/Avago-Technologies/HSMW-A400-U00M2/?qs=sGAEpiMZZMtEjy7lsqBi5V4oFSfwoxtG%2fJUB19uB34w%3d

or

http://au.mouser.com/ProductDetail/Seoul-Semiconductor/MWT801/?qs=sGAEpiMZZMtEjy7lsqBi5R8gqztvUI%2fS6rqQbrqvyp4%3d
.

Now basically all i have to do is put a 100nf cap in parallel to the led driver, and the leds (could i connect them in series?) before the other side of the festoon holder.

probably use the old festoon bulbs as the ends.

 

[shabtek]

this could be a good idea as long as the bulb can be salvaged
seems like a dead simple hook-up
would conventional leds not work? be too big?
never seen a led driver before (purpose build/marketed ccs)
need a way to diffuse the light. glass 'frosting' spraypaint?.
ive backlit a meter with a string of leds; to soften the point-source light I applied the dremel to each led, grinding the lense flat and translucent.

 

[TheGuitarist]

I'm just going off a circuit that was suggested to us. There were a few difused white LED's on there i'll have a look.

I didn't realise there were LED's that ran off say 24v (if in series) but truth be told i'm not 100% sure what to look for... LEDs confuse me....because if i could just use standard led's and just say solder them to the old festoon (dodgey but it would work, even if i still used perf board or whatever) that'd be great!


Just had a look and i couldn't find any white 12 or 24v standard LED's

also how come you say they need to be diffused? any particular reason?

http://coldduckpost.com/home/images/console1024.jpg thats what the design is off.

 

[helterbelter]

I replaced the lamps of both the lcdmeters and VU meters in my console , simply with 2x 3v leds and a resistor in series. For the VU's I sanded the tops of the leds off too, to "spray" the light a bit.

But what's the need of a driver ?

 

[TheGuitarist]

like i said, just working off a circuit that was suggested. Seems like this is an easier way to do it.

This is going to sound so stupid... i'm just drawing a complete blank but what value resistor do i need for 2X 3v leds? Just a 500 ohm one isn't it?

Oh and just checking that your console has 48v meter lights

 

[Gus]

You could use a resistor(s).

Use ohms law

1st find the min and max voltage of the power supply you want to use for the LEDs.

2nd find the voltage drop of the led at the current you want to run them at.  Look in the data sheet or measure it yourself.

Determine how many LEDs you need.  I would use high brightness ones to run them at less than 20ma I have run some at 1ma or so.

Sum up the LED voltages in a series string, is the total more than the supply voltage?  If so you will need to do a series parallel(s) circuit.

(power supply voltage - series voltage sum of the LEDs) / the current you want to run them at gives the resistor needed.

Now you need to find the power rating needed for the resistor.  I^2 x R, E x I etc

Now the only tricky part using a resistor and why the min max voltage measurement.  Figure out the min and max current.  Hint if you drop more voltage across the resistor and use less LEDs in the series string, what happens with the same min max calculations?

The IC is nice but be mind full of the power dissipated in the IC.  You will need to make sure you don't exceed the power dissipation.  20ma could be more current than you want or need.  Also note you need >5VDC drop across the IC to keep it operating correctly.

It is not clear if you want to use 1 LED or a string of LEDs

 

[TheGuitarist]

Regarding the fact that its not clear, thats sort of my question.


My two options are to one, have the LED driver and 2 smd (or standard i guess) leds, or 2 standard 3v LEDs and a resistor.

either way i'll probably build them into mini circuit boards so its more of a question of what is going to be easier. The IC was suggested by a guy who has done his entire ssl with them so they obviously work quite well. He also said to add a 500 ohm resistor to help with power dissipation i think.

The fact that i only want to use two is the issue, as i can't find almost any LED that can handle 24v straight up, thus the driver.

 

[Gus]

If I understand correctly.

You have a simple circuit to build and IMO the IC is a waste to use in your case you are only lighting a LED at about a 17 Volt dc drop the resistor will make an OK quasi constant current device.

24VDC - (page3 of the 1st link data sheet pick a current)  I would pick say 5ma so the LED drop will be about 3.2VDC(the speced current range voltage drop is from about 3VDC to 3.8VDC)  You might want more or less current I would build a test circuit for the current you want to run at IMO.

24VDC - (2x3.2VDC) =17.6VDC

17.6VDC/.005a=3520 ohms.  So use a 3.3K (little higher current)to a 3.9K(little lower current) you don't need to be exact.

Power = voltage x current 17.6VDC across the resistor at .005 or so amps about .09watts.

Or you could use one LED 24VDC -3.2VDC = 20.8VDC
20.8VDC/ LED current = resistor value
Then do the power math.

 

[sodderboy]

Automotive festoon replacements are a good choice, and in quantities they get affordable.  I never had the time to re-design when there are so many choices available.  As far as voltage goes, you can either drop the voltage, wire 4 in series, or feed a different, 12 VDC for automotive, to the bridge.
Mike

 

[TheGuitarist]

FWIW they need 48v lamps, but i like the automotive lamp idea.

 

[QUEEF BAG]

my opinion, but-white LED    eewwww
very bright and cold.  only thing worse would be blue.

i would think about yellow, OR bouncing the light from a white one
off of yellow or orange tape.  it's amazing how much of that nice
VU meter glow is the incandesent bulbs.  and they glow yellow.

the reason for sanding is an unfrosted led is very directional with
it's light, bulbs are not.

one guy spray painted his white leds orange after he turned on the console,
and that was with dark tinted plexi in front!  (Quad 8 Ventura)

 

[TheGuitarist]

i'm just on orders from the boss and he likes the white... i agree with you, i showed him the yellow solution from recycled audio and he didnt like it at all.

 

[sodderboy]

Your boss sounds like. . . . such a boss!  ;D
Compare the costs of replacement bulbs vs. auto replacements vs. T&M to design boards, shatter blown bulbs, solder them to the cards, solder all the LED's.  Some of the auto replacements mix white and yellow to get closer to that drab incandescent look.
Read my post again- there are at least two ways to deal with retrofitting 12V bulbs into a 48V supply.
I personally save my "wow, I made that" $$ and energies for more important things.
Mike

 

[TheGuitarist]

Think i might take your idea and wire 4 in series, shouldn't be too hard to mod.

I know what you mean about the design process though.

And re: the boss, nah he's cool, just has a picture in his head of how he wants everything to be and i'm the one who has to achieve it.