10W LED Car Fog Lights... Help

[bustinmi]

Ive brought 2x 10W LEDs recently and I would like to place them into some fog lights for my car. I've brought the desired size halogen fog lights and removed the bulbs to just have the housing remaining. Can someone tell me if the power source will be 12VDC or 13.4VDC? (I've seen both values on certain websites for automotive applications and I'm brand new at LEDs and project electronics so I know only the basics , so thanks)

10W LEDs Specs:
Color: white
Forward voltage: 10V - 11V
Forward current: 1000mA
Power: 10W
Viewing angle: 60 degrees
Luminous intensity: 750 Lumens
Color temperature: 6500K - 7000K

I'm trying to calculate what resistors I should be using and if i should make a simple series or parallel circuit. The calculations for the circuit are below.

Solution 0: 1 x 2 array uses 2 LEDs exactly
+----|>|---/\/\/----+ R = 2.2 ohms
+----|>|---/\/\/----+ R = 2.2 ohms

In solution 0:
each 2.2 ohm resistor dissipates 2200 mW
the color code for 2.2 is red red gold
??? think the power dissipated in the resistors is a concern ???
together, all resistors dissipate 4400 mW
together, the diodes dissipate 20000 mW
total power dissipated by the array is 24400 mW
the array draws current of 2000 mA from the source.

I think that I need a heat-sink for the LEDs as well. I will be looking into that after I form the circuit. I would also like to place a switch in as well obviously. Does anyone have any favourites or preferences regarding switches??

Help would be greatly appreciated

Thanks, Bustinmi [AUS]

 

[poor mystic]

Hi Bustinmi
So what you want is to know is how to use some big led's for headlamps?
Could we have some specifics about the led's please? Manufacturer and part number would be a good start.
(I did see that you posted a value for forward voltage of 10-11V. I'm wondering about that among other things.)

 

[bustinmi]

lack of information... thanks Ebay

Hi Poor Mystic

Thanks for your quick reply

All the information that I posted in the initial thread is unfortunately all the information I have due to the LEDs being cheapies from EBAY because I thought I'd give it a go without spending much money initially and then replicating the working circuit with quality LEDs.

Can [SAFE] default or average values be substituted for suspicious/bogus values?? I'll email the EBAY supplier and see what further information I can obtain.


Thanks again.

Bustinmi [AUS]

 

[poor mystic]

I'd want to try one on a variable voltage power supply and graph what current it takes at what voltage. I'd make measurements of current every 0.1V between 2V and whatever voltage it takes to get the leds consuming the 10VA promised by the supplier.
when you have this curve you'll know the operating voltage and current of the device, and you'll be able to decide the resistance needed to feed each led the proper current.

I do have misgivings though. I would never remove my car's headlights completely in favour of a homemade design. I'd keep them standard, and add led's as supplements only. I'd be scared of losing my vision right when I needed it!

 

[bustinmi]

Ill give it a go

Thanks Poor Mystic

Ill take the information you provided into consideration and see what I can achieve. The aim is to add additional fog/driving lights not replacing my main headlamps.. hahaha I'm not that reckless

Regards

Bustinmi [AUS]

 

[poor mystic]

Hey Bustinmi
It's not that I think you're reckless, just that I need to cover myself - I don't want any liability in case of failure.
There are ways of using active components to do jobs like yours. Generally I like using the best possible components rated at least 10x what I'm going to expect from them. If I could afford and obtain milspec components I'd use them. I'd protect the circuit with capacitors, inductors and zener diodes going both ways. I find cars very easy to underdesign for. All that said, do you want to see some ideas for active systems?

 

[bustinmi]

Hey Poor Mystic

yeah seeing some ideas for active systems would be great! I've started working on my breadboard with 2 x 3.6v 5mm LEDs using a 12v input to start looking into reducing current and voltage to work on my basic understanding behind the process..

Regards

Bustinmi [AUS]

 

[nbw]

Hi Poor Mystic, if it's one of the "sites" I'm thinking about, they have chains of 3 x white LEDs so that with their 3.7V (approx) drop, the remaining drop across the resistor from an auto's 12V is quite small. If it's 10W, they might have something like 1W Cree-type LEDs x 10, in 3 banks of 3. Or similar

 

[poor mystic]

Hi nbw and Bustinmi
Putting 3 led's in series is a good simple high-reliablity approach, but there are ways which are more fun and might make for brighter led's and better control.
For instance you could charge a capacitor from some stable source. Then, every millisecond (say) you could dump the charge into a transformer primary, with the secondary to supply the led load. If the operating frequency of the power supply is twice as high, the transformer can be half as large. There are practical limits, this is electronics not astronomy. The amount of energy in each pulse of current to the led's is easy to calculate ~ E=(1/2)*Q*V^2.
I like the simple switch-mode design of the last paragraph because if it's a nicely-made transformer and you switch current into it with a MOSFET you can get high efficiency.
Moulded ferrite transformer cores are fitted with bobbins which can easily be wound, even by hand.
There's one idea, but don't look for a good, quick result with this (or any) approach.