Circuit building - Need someone really electrically savvy
 

Trying to design a circuit make a brighter cargo light using high power COB LEDs. Specifically, these. Really just wanna see if this is feasible before I bite the bullet and order these LEDs
Before you ask, yeah, it'd be easier to buy a $20 LED, but the fabrication itch is getting to me again. lol

My only real experience with LEDs are the cheapo 3 or 5mm dome LEDs and some SMD, all of which have a forward voltage of like 3V and 20mA current. These have a drop voltage of 9.35V and max current rating of 1.4A (15W rated).

12VDC input, 3 LEDs wired in parallel (because that's how many will fit in the cargo light housing), and obviously some sort of resistor. One calculator told me that these would take 2ohm resistors. Also, some wiring diagrams I found for high power LEDs involved transistors that, to be honest, I had no idea their purpose in the circuit without diving too hard into what transistors were being used.

Anyone know if high power LEDs will work in a simple setup like this, and if so, what resistors am I supposed to use? This is what I got, hoping it'll work. LEDs will be mounted on the shown side, wiring running on the backside, T10 bulb base pigtail to connect to OEM socket. Also, yes, I realize the diagram looks backwards from how the board is laid out, but if you flip the board upside down to show where the wiring is going, it's oriented correctly.
https://cimg0.ibsrv.net/gimg/www.civ...c6a926de67.jpg
https://cimg2.ibsrv.net/gimg/www.civ...15313f2970.jpg

edit: the realization that I may actually flip the negative and positive sides because of how the source voltage pins are laid out. The top pin/bulb connector is most definitely positive side bc of how the diode is oriented. Nevertheless, diagram is for functionality purposes.

edit 2: more on the feasibility.. knowing full well that high power LEDs can get hot.. anyone know if these LEDs would get too hot for the plastic piece? They'd be sitting literally right on the plastic, maybe a few mm off of it

Re: Circuit building - Need someone really electrically savvy
 

Nevermind. Not really feasible. Did more research and more math.

Each 15W LED would be drawing around 1.07-1.25A. Amps in parallel is additive, so this makes this circuit 3.75A. Total power draw for this one apparatus would be 44.625-53.25W based on the car's assumed variable-ish operating voltage of 11.9-14.2V. A standard 168 bulb draws .35A and 4.9W power.

That, and a recommended resistor would, in fact, be 2ohm, but it'd have to be one of those big ass, ceramic-encased 5W suckers

Time to look at lower powered LEDs that'll be bright enough with a high enough CRI to make me happy. lol

Re: Circuit building - Need someone really electrically savvy
 

So, what's the point of the resistor? Are you trying to match the OEM bulb resistance so the dimming still functions?

Each one putting out roughly the equivalent amount of light as a 60W bulb that would be really bright :rolleyes:

Re: Circuit building - Need someone really electrically savvy
 

Applying 12VDC to a 9VDC LED. Needs a resistor to keep it from burning out

Re: Circuit building - Need someone really electrically savvy
 

Data sheet gives current ratings at 9V, 18V, and 36V. I was assuming that meant input voltage was 9-36V.

Re: Circuit building - Need someone really electrically savvy
 

Different models have different forward voltages. Same luminous flux for the 9V 90CRI 4000k and the 18V90CRI 4000k LEDs. If I underpower the 18V LED, theoretically, it'd light up at 66.67% power, assuming voltage vs. luminous flux is a linear relationship. About 450lm. Bright as shit, still. But, will sending 66.67% rated voltage light it up?

Re: Circuit building - Need someone really electrically savvy
 

You are correct, I read through the datasheet too quickly.

A quick Google search I'm coming up with needing about 60-65% of the rated voltage before the LED will light. Using the 18V LEDs would be awfully close to that limit. Sometimes they will show this in the datasheet but I'm not seeing it. There is no harm in under-powering an LED though.

For a price of under $3 you could always buy one and play around with it. There were some temperature diagrams in the datasheet so keep that in mind.

Re: Circuit building - Need someone really electrically savvy
 

else fails, I can always go with a step down transformer. Found one that steps from 12VDC to 9VDC, and its footprint is .5"x.6"