Solid State Relay to avoid blowing ECU on our cars? anything led

[dssence]

Hi guys , I have a Toyota 86 FT (same as Scion or Subaru BRZ) so to be short I wanted to add a led strip to my position lights (ones which light up when you turn on backlight on instrument panel) or a T10 led bulb to replace the ugly stock original bulb. I know you can easily screw up "Body System Integrated" units when diminishing the amperage going through that circuit, as most circuits are designed for resistive loads.
So,if I take out the led bulb for instance which is a T10 format 5watts , and replace it with a led strip which draws 600mah I could easily blow up the driver of that circuit on my car.

So take 2 scenarios

-First Scenario (Adding led strips for position lights to each headlight, removing the original 5 Watts T10 bulbs )

In this scenario a friend of mine came up with a solution to use a solid state relay opto coupled (IXYS part number LC717) to avoid damagin the driver. This is in theory how it would be connected. But I have many doubts

As you see the output + of the SSR to switch both ledstrips go to the cars battery, and the Control line of the solid state relay goes to one of the positive lines of the position light harness, so when I turn on the knob on the instruments panel it lights up
Now these are all my doubts

1) We are lighting up an IR led diode with the positive line form the position lights which in turn is coming from a driver. I know it's not the same as plugging a resitive load there. But we're lighting up a led diode. So this could, well blow/damage the driver?

2) Shouldn't we be emulating the original resistive load instead? rather than lighting up a Solid state relay IR led. By emulating the original load I mean, if the original position light was a 5watts bulb and if I measure it with a dmm and it's filament measure 150ohms, shouldn't I replace a 5watts resistor 150ohms in series with the led strip I want to place there?. All this instead of using a solid state relay?



- Second Scenario (replacing the original 5 watts incandescent bulbs with LED bulbs T10 same wattage)

Say I want to replace the original incandescent bulbs 5watts with led bulbs T10 same wattage , would this damage the Control unit. ? My friend said it could. Cause the circuit it's not designed to handle this kind of load which is not resistive.

This is the kind of bulb I'm talking about . The T10 5watts I bought I got it from ebay, what my friend said I could only replace these led bulbs if the manufacturer actually tested it with my car




Should I have to use this load resistor instead? Or precisely on which case should I add a load resistor like this one


http://www.vleds.com/resistors/parki...s/lr-park.html

[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.

[dssence]

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.

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 .

[RacerX]

I understand you're confident in your knowledge to wire up your own custom circuit, but your asking questions that require a thorough understanding of the electrical system in your car, which I do not have. I don't know for certain what you need in order to "emulate" an incandescent bulb. I could give you my best guess, but there is no guarantee. it's not worth the risk. I'm currently going to school for electrical engineering so I am by no means an expert with years of experience. I don't want to give you false advice. Your best bet would be to call Diode Dynamics or any other custom shop and ask them if they have any products designed and tested for the FRS.