Uber beginner question, apologies in advance. I have a project that will control three 120v devices with three 5v relays, 240 max voltage (TE ORWH-SH-105D1F.) The relays will not fire at the same time, but the random code may make two of them fire at the same time. I see most projects using a relay module. I've seen this thread which suggests a transistor and diode to absorb the "large reverse voltage spike" when relay is turned off. How dangerous would it be to just use the raw relay? My (fuzzy) plan is to power the relays with the Arduino 5V/Gnd and control the switch with digital pins, will this blow up an R3 or a Nano? I have no sketches or schematic yet as I'm just starting to think this part through, so completely open to suggestions. Edit: Forgot to mention, I "sorta" get that "what" is on the 120v side matters, especially with motors. The relays are a substitute for a standard fog machine switch. Basically when closed, the switch closes the "on" circuit for the fog machine which activates the pump which is inherently a motor. The heater is always on.

[image] rocknbil: Yes I did, it is designed to only drive two motors AFAIK. The data sheet I looked at showed three motors. One that could be reversed.. Did you know there is NO electrical difference between a relay and a motor? So, the IC could certainly operate two relays and perhaps the part of the IC that can reverse could also operate the third relay.

[image] Paul_KD7HB: The data sheet I looked at showed three motors. One that could be reversed.. Did you know there is NO electrical difference between a relay and a motor? Well, I know they both have a coil hahaha . . . never made the connection. in the Super Starter tute it says "the left side of the chip is for the first motor, the right is for a second motor," I took that as fact - it indeed looks like this chip can handle four outputs, correct? I'm going to try it and hope nothing blows up! (wouldn't be the first time. :smiley: ) The only question remaining is if this is the "best" way to do what I'm trying to do. [image] Edit: the above is the schematic from the Elegoo Super Starter for the L293D, data sheet here.

Mind the diodes on each motor/relay. Also be aware the temperature ratings for the relay and the IC ALL assume the device is mounted and soldered to a printed circuit board so the copper traces. solder and even the board material can act as heat sinks.

Thanks again, not seeing temp ratings on the data sheets for these https://www.te.com/usa-en/product-1-1721150-0.datasheet.pdf and https://www.mouser.com/datasheet/2/418/NG_CD_1721150_D-687178.pdf And wouldn't you know it, I only have two 2n2222A's in my box (to go the module route LOL) I'm beginning to doubt my relay idea now, reading a lot about arcing in these relays, maybe a mechanical relay isn't the way to go and if I'm going to have to wait for parts, maybe a solid state relay is the ticket.

I see the relay rating of 360mW. So if you keep below that number, even for continuous service, you will be ok.

Sorry to switch gears on you Paul, but I think the below may be a better idea, especially based on a lot of the posts here in the Arduino forum (many of which @Paul_KD7HB participated in! :smiley: ) Omron G3MB-202PL Solid State Relay Being mechanical, mechanical relays will fail sooner. There is the potential for arcing which can be reduced with a snubber circuit which = more stuff to learn when my head already hurts. :stuck_out_tongue: SS relays are faster. -Pictured in the DS is 24V, but below it specifies they come in 5V, 12V, and 24 with the input resistor. -257F max does need ventilation Peak 30A (I won't even get close) 600V Digikey says they're no longer made (red flag?) Mouser and eBay as below have them Will these work? The reason I'm looking at these is there are people on eBay who have built 1/2/4 channel 5v versions using this exact chip. This would make a lot of problems go away (among which, finishing this project LOL) Thanks again Paul maybe I just needed to think it through. I've worked on cars and their relays for over 40 years but first time in small electronics.

[image] rocknbil: Being mechanical, mechanical relays will fail sooner. I don't know what you have been listening to or reading, but mechanical relays can last way beyond your and my lifetimes. And mechanical relays will not fail before SSR. But all up to you and how you will eventuall begin to test you assumptions.

[image] Paul_KD7HB: I don't know what you have been listening to or reading, but mechanical relays can last way beyond your and my lifetimes. Haha was going to say almost that exactly. :smiley: Most of the posts I've read are here on the Arduino forum, SS vs mechanical sounds like a Ford vs. Chevy discussion. I really don't know "what is best." I'm going to try the SS relays, will probably refer to this thread often and come back to mechanical relays for a different project (after I have module components.)

For anyone reading, the solid state relay modules, although cool beyond my dreams, will not work for this project (at least the ones I got.) They work GREAT if you actually have 120 V on the switch side, but as confirmed by @DvDdoug in this thread, they're not just a "switch." In my initial test I tested a 120V light unit, worked great, as expected. Since the fog machine switch is just a switch, [image] rocknbil: The relays are a substitute for a standard fog machine switch. There is (apparently) no actual current between the two switch leads. The Relays cycle along fine, sometimes it will fire on the first signal, but none after. I experimented with bursts from 500ms to a full second. To test I disconnected the relay leads and shorted them out manually, fired every time. :expressionless: So I guess it's back to mechanical relays but I don't have protective modules, investigating circuit protection as mentioned by Paul above.

You missed the part on AC SSR that they turn on when the internal LED lights, but only turn OFF when the AC current goes to the zero crossing of the sine wave.

Using Raw Relays vs. Relay Modules

Other Hardware Motors, Mechanics, Power and CNC

rocknbil March 31, 2024, 9:16pm 22

Yup. It's in two parts - this is the last sub part of synchronizing the cannons, I have the LED's and sound all worked out.

This is one of the Craigslist foggers, I have like six of them all together but only using 3 for this project.

The second part is animating the skeletons on the ship.

Topic		Replies	Views
Solid State Relay interference General Electronics	72	629	November 11, 2026
Help with relay board project General Guidance	40	587	September 18, 2026
DC power switching General Electronics	31	789	October 20, 2024
How to properly connecting a 12v relay with arduino - solenoid control General Guidance	59	1786	August 22, 2025
Simple Lora on/of communication General Guidance	106	1586	June 17, 2026

Using Raw Relays vs. Relay Modules

Related topics