using a solid state relay to bypass OEM relay

hey guys, I’m planning on using a solid state relay to bypass a mechanical relay when its open.

however if my system fails I would like for the OEM relay to function normally.
if my system looses power or if the program sees something not normal then it will restore OEM operation.
here is a drawing of my schematic for the logic level control of the solid state relay

I’m looking for suggestions on what I can add or remove and possible resistor values
that would be super

sorry I posted this in the wrong category. it was supposed to be in "Project Guidance"

Hi,
OPs pic

Tom... :o

Hi,
What SSR will you be using?

Why all the transistors for an Arduino output to control the 5V input of the SSR.

You haven't even identified the type of transistor NPN or PNP, or the emitter, base and collector pins.

I think this is what you are looking for;


Tom... :slight_smile:

I'm using a D2D07. I'm sorry the one prior to the load (ssr) is PNP and post load is NPN.

the ssr should always be active unless loss of power of power at the 5vdc system or if code says other wise

if code says to shut down ssr, then digitalWrite to N of PNP and if power is lost then 0vdc to the P of the NPN.

I put two transistors for the two different reasons stated above. it's super important that if my system fails then the OEM system is restored

Hi,
If the 5V drops due to power failure, then the SSR input will be turn off anyway.
Current to drive the SSR input is not coming from the Arduino output, but from the 5V supply.
The Arduino is only switching the current ON and OFF.
So no supply current, then SSR is OFF.

PNP not needed, also you have not identified Emitter, Collector and Base.


Tom... :slight_smile:

so you're saying to just use and NPN and have a constant digitalWrite HIGH on it. I was thinking on using the PNP so that I don't have to constantly have a HIGH on the designated pin and reduce power consumption. yes? what are you're thoughts on that? and just remove the NPN

LandonW: so you're saying to just use and NPN and have a constant digitalWrite HIGH on it. I was thinking on using the PNP so that I don't have to constantly have a HIGH on the designated pin and reduce power consumption. yes? what are you're thoughts on that? and just remove the NPN

Unless your project is battery powered, I wouldn't worry about power dissipation due to the constant-on output. Go with the circuit from @TomGeorge. Remember: KISS.

Hi, What do you want the Arduino controller do? What is its application?

Tom... :)

It's not battery powered. The circuit is bypassing a locomotive wheel slip contact when the contact goes open. It is bypassed so it has a closed path.