Wiring an indicator LED to SSRs

Such an easy thing to do, I’m sure, but I’m still struggling with my simple electricity math. I promise I’m working to better understand this and will quit with novice questions is short time.

I’m making an enclosure. There will be a converter that goes 120vAC to 5vDC@3A. I will be powering a small 5v 40mm fan and my Spark and RPi with that. Hopefully that will work. I would like to attach a small LED to the panel that illuminates when the SSR is active. I have several 5v LEDs. Can you connect the +/- of one of the digital outputs to the SSR and then continue on to the LED? I’m really struggling with the additive effect of voltage drop. I’m now starting to worry that my spark and RPi won’t have enough power if I connect the 5v fan too.

Is it possible to connect the LEDs? Will my Spark and RPi even work if I have 5v fan connected to my 5v supply that will also go to my Spark/RPi? Do I sound like a guy who knows nothing about electricity?

If you have any questions about eyeballs, I can repay you for your time.


The Pi needs about 1A max, so it depends on what your fan draws at peak load.

To connect an extra LED, put an LED and resistor in parallel with the SSR, not in series.
A good resistor value would be 330-470 Ohms. This will power the LED with 5-10mA, depending on the color LED you use.

Okay, thanks @elco. There will actually be two fans and each draw at max 65mA and I actually made a sort of thermal voltage switch that really restricts power so I doubt they ever get to the 65mA. So my idea is to power those and then the RPi from the source 5v@3A. I will have the Spark connected to the RPi so it sounds like I should have enough power there.

Thanks. And thanks for the LED info. Really helpful.

Having a similar situation here… I’m trying to run 120v LED’s in a control box that light up when one of the SSR’s are active. The way I have it wired works, but if I don’t have anything plugged into the outlet then the LED’s stay on whether or not the SSR’s are activated. I’m guessing I need a resistor… but I don’t know where or what type. Here’s a diagram of my control box. Any suggestions?

When you say “the way I have it wired works, …”, do you mean that if you have your freezer and heater plugged into that outlet then the lights are on when the SSR is on and then off again when the SSR is off? And then when you don’t have your heater and freezer plugged in, the lights just stay on all the time?

Exactly! I should mention that when uplugged from heater/freezer the LED’s are dimmer than if the Heater/Freezer is plugged in. So, I’m assuming there is a very low level of power going to the LED’s (hence my assumption for a resistor). I have read/heard that the digital SSR’s allow a very small amount of voltage even when they are “off”. I just don’t know exactly how to fix this.

For reference here are the LED’s I’m using: http://www.amazon.com/Alpinetech-NPL-22-Pilot-Indicator-Light/dp/B00FLZ6SQE/ref=sr_1_3?s=industrial&ie=UTF8&qid=1446578378&sr=1-3&keywords=Alpinetech+NPL-22

Yeah, I think you are absolutely correct about a small amount of power going to the LEDs. They take such a small amount of current to light up. A resistor right off the light should work.