Make side markers work with turn signals

[Jerry_K]

Using SSR as a car flasher for LED side markers

I need help with my circuit design.
I want to convert my cars single function LED side markers which are OFF in daylight and ON at night, to blink when the turn signal flashes. That means in the daylight they are blinking ON; at night they are blinking OFF.
The enclosed diagram represents the limits of my electric circuit design ability. I believe what I have is logically correct but I do not know how to proceed.
I am good with a soldering iron and understand how to attach components to each other but not much more. I do not have any test equipment.
Here is a list of my outstanding issues.

1-What SSR part number should I use?
2-Does the SSR have a ground or is the diagram correct?
3-Is the [SCR] designation correct for the SSR?
4-This SSR will get hot because of a high usage rate. It is activated when the turn signal or hazard flashers are active.
Do I need a heat sink on the SSR because of its flasher function?
5-How big a heat sink what does it look like?
6-How does the heat sink attach to the SSR?
7-What are the designations for the SCR terminals and which is which?
8-When I look at the SSR, will I be able to identify the terminals?
9-Will I need any protective circuits?
10-Each of the front and rear LED side markers draws 35mA: 8-14VDC.
11-Does the IGN line into relay terminal 30 need reduction circuit?
12-If so, besides the parts identification I will also need a description of which terminal identifier and how to find it goes where?
13-What gauge of wires and what size circuit board and case will I need?
14-These two units, for left and right blinkers will be located in a trunk but still require some protection.
15-What kind of case can I use and what about heat?


I believe I can do this with detailed instructions.

Need your considerate assistance.

Jerry

 

[crutschow]

1. SSR's provide input to output galvanic isolation through an opto isolator which makes them expensive. All you need is a high-side switch rated for automobile applications such as this.
2. The high-side switch needs connections as shown in it's data sheet.
3. SCR stands for Silicon Controlled Rectifier and is not the same as an SSR (Solid State Relay)
4. The switch won't get hot if you current is only 35mA per marker.
5, 6. Don't need a heat sink
7, 8. See data sheet
9. No. The switch is internally protected from shorts and overheating
11, 12. No.
13. 20AWG wire will be fine.
15. Any type of hobby electronic case would be fine. Heat is not a concern.

Note that you do need some additional logic circuitry to perform the functions you want. To have the markers blink both day and night you need an Exclusive-OR logic function. That would cause the Markers to blink in-phase with the turn-signals when the Marker lights are off but out-of-phase when the Marker lights are on. Would you consider that a problem?

 

[dr pepper]

You might be better with a standard relay.
If you have a relay energised by the sidelights, another by the indicators you should be able to accomplish that.
How come you want to use solid state relays, for the isolation?

 

[EinarA]

An SSR that uses an SCR will latch on if used with DC. Where is the day night decision coming from? An EXOR gate that crutschow mentions would seem to be required. One can be made from a transistor and a few parts.

 

[alec_t]

We don't know which country you're in, but make sure that the vehicle mod you are proposing is legal and won't invalidate your insurance.

 

[crutschow]

Below is the sim of an XOR gate using a diode bridge and a transistor to control whatever bulb driver/relay you use. As you can see the Marker illuminates (Out signal is high) with either the Marker On or Turn Signal is active, and blinks when both are active at the same time.

Edit: The bridge is shown as 4 discrete diodes but it can be a standard bridge rectifier module if desired.

Note that you can do the same thing with a standard relay by driving one side of the coil from the Marker On signal and the other side from the Turn Signal. This works with a standard relay since its coil operates with voltage of either polarity. The only requirement is that there is enough of an incandescent lamp load otherwise to provide a return path for the relay coil current for the coil signal that is off.

 

[EinarA]

Crutschows circuit is almost the same as the one I had in mind, except I use two diodes and two resistors. Each input has a forward biased diode to the emitter and a resistor to the base, I would suggest 4.7K for a 70 mA load at 12V. If there aren't other loads on the inputs then a pull down resistance is needed. You will need one circuit per side.

 

[crutschow]

Crutschows circuit is almost the same as the one I had in mind, except I use two diodes and two resistors. Each input has a forward biased diode to the emitter and a resistor to the base, I would suggest 4.7K for a 70 mA load at 12V. If there aren't other loads on the inputs then a pull down resistance is needed. You will need one circuit per side.

Below is a sim of your circuit. It has the slight advantage of the high output voltage being only 1 diode drop below the supply voltage rather than 2 diode drops.

 

[EinarA]

Thank you Cr ( my spell check doesn't like your name.) I had tested it with actual components. With Ge or schotky diodes voltage loss can be less than .5 V. You are also not limited to two inputs, but don't know when that would be useful. It has the disadvantage that some of the base current flows into the other resistor, making design a little more complicated . I had envisioned driving the LED lamps directly.
( Besides, I never think that getting better performance with fewer parts is merely a slight advantage.)