Quote:
Originally Posted by RacerX
First of all, I don't recommend you try any modifications like this unless you're experienced with electric circuits. So my advice is to forget it, unless you can get personal help with the design and installation.
Having said that, I can at least answer a couple of questions. This idea you have is very similar to the aftermarket angel eyes available for Bimmers. I know because I've installed some on my 328i. You can use a normal relay to trigger whatever you want, assuming what you're turning on is its own isolated circuit which has a fuse. I don't see the need for a optoisolator. Many LED strips are 12v with built in current limiting. You must calculate the total power consumption and install the appropriate fuse.
As for the headlights, your idea to measure the filament resistance is flawed. As soon as the lights turn on the impedance of red hot filament drastically increases. If you placed a resistor with the same impedance impedance as a cool filament in parallel with your headlights you'd blow the fuse immediately.
"High frequency transients can be smoothed out with decoupling capacitors and you'll need to account for inductive kickback with a reverse bias rectifier diode. "
If you want a 5w load on a 12v rail then you need a current of about 420mA (5W/12V). Using Ohms law to find the appropriate resistance (12V/420mA) yields about 29 Ohms. I am not confirming that a 29 Ohm 5W resistor is what you need to avoid frying the ECU or avoid any error codes, I'm simply answering your proposed electronics question. In reality you'd also have to account for the power consumption of the LED headlights and be aware of the rated current capacity of that 12V rail. There may certainly be other elements to consider. But typically to run aftermarket LED lights on headlights designed for resistive loads you need a parallel load resistor to satisfy the minimum load requirement.
Again, I don't recommend you attempt any electrical modifications unless you get help personally from someone with experience in wiring electrical circuitry. You don't want to go and fry your new car for a couple lights man. It's not worth the risk if you make a mistake.
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Hey thanks so much for such a complete answer. I know I shouldn't be messing around with this, but If I had zero knowledge on electronics and it's not my case, not that I have a profound experience with cars modding even though with 20xx onwards. I don't know if subarus BRZ are similar to Toyo's 86 in electrical schematics and so on.
But say I want to replace the parking position lights which are normal T10 5 watts (filament bulbs) with LED ones T10 5watts, will that damage the control unit ? I'm not talking about removing these bulbs and placing led strips here.
I'm positive and share your logical sense here about the filament it will get hot and the impedance will change drastically. So It's useless. A friend of mine told me to use a photocell to light up the led strips with an isolated circuit you know the photocells used in streets to avoid removing the bulb and generating a change to the circuit I could place the bulb next to the photocell and when it triggers the photocell I could send the signal to a relay but that would be way to crazy and messy.
Can you again explain to me with more detail what you said about
High frequency transients can be smoothed out with decoupling capacitors and you'll need to account for inductive kickback with a reverse bias rectifier diode.
So not to extend myself that much, in either of these situations :
1) If I want to replace the stock parking lights or position lights whatever they're called which are T10 5watts with T10 LED's 5 watts am I safe?
2) If I want to remove these T10 stock bulbs and place a led strip driving around 600milliamps or less ( I can measure with my DMM in amps how much they're driving) than the stock 5 watts would I blow anything? and I will have to add a load resistor to compensate the resistive load?
Say the led strip drives 600mah , Using ohm's law that would be
Voltage = Intensity (amps ) x Resistance (ohms)
12 = 600mah x R ====> 12/0.6amps = 20 ohms resistor 5watts? in parallel or series?
We know in cars 12volt's it's not fixed 12 volts it always fluctuates who do you account on that?
Thanks ! Again you seem to have some in depth knowledge in diference to other members. I do have electronics background as well but I never did any mods to new cars. that's why I'm asking everywhere here and eevblog , any place I can. The guy who told me about the solid state relay solution is project developer on electronics as well, but I found it to in depth .