What I have:
I currently have a RPi connected to a 4-channel bluetooth relay (via bt). At present only 1 of the 4 channels of the relay is used to control a series circuit of 4 LED exterior lights.

What I want:
I want to add 2 things; (1) a 12V-car-battery-powered-LED street lamp and (2) two 24-V 5/2 solenoid valves finally (3) I would leave the compressor on its own for channel to have it turn on only when the pi requires it.

My Issue:
I know I can simply wire in the circuit for the 120VAC compressor. What I don't know is how to wire in the other 2 12 & 24VDC components into my existing relay. My existing relay is a 30A 12VDC relay. From what I understand, it doesn't matter what voltage (up to a point) but what matters is that it can deliver up to 30A? I ASSume this because there is no specification as to the voltage it can manage, just its operating voltage. Here is the spec sheet: (https://www.tinyosshop.com/datasheet/G8P.pdf). It states a max switching voltage of 250VAC and 28VDC. So as long as I don't wire anything more than those 'max switching voltages' or pull more than 30A at the same time, the relay works fine?

This would mean that as long as I feed in a 12V-line for the street-lamp and a 24V-line for the solenoids into the separate channels, I should be ok?

Thanks

Ch1 Incoming 120VAC (5 LED series exterior lights) - EXISTING
Ch2 Incoming 12VDC (street lamp) -
Ch3 Incoming 24VDC (solenoids) -
Ch4 Incoming 120VAC (compressor-check amp rating) -

 

Can you post a picture of your relay board?
I'm assuming you have 4 separate relays. But do not know what the relay is as the data sheet shows 3 variations.
If the version of the relays are "quick connect and PCB", then the outputs are fully isolated from each other so it does not matter what you are switching. But if the board has PCB only, it is worth a good to see if the relay outputs are isolated enough to mix mains and low volts on the one board.

 

This is where I bought the relay:

http://www.tinyosshop.com/index.php?route=product/product&product_id=684&filter_name=Tsrb430

Can you post a picture of your relay board?
I'm assuming you have 4 separate relays. But do not know what the relay is as the data sheet shows 3 variations.
If the version of the relays are "quick connect and PCB", then the outputs are fully isolated from each other so it does not matter what you are switching. But if the board has PCB only, it is worth a good to see if the relay outputs are isolated enough to mix mains and low volts on the one board.

 

The datasheet clearly states that the max switched current is 30 A for AC loads and 20 A for DC loads. And the board appears to have all four sets of relay contacts fully isolated from each other. So far, ok.

BUT

It also says that those ratings are for *resistive* loads only. Solenoids are close to a pure inductance. So are compressor motors. And so are high voltage LED strings if they have a switching power supply as a regulated current limiter, unless that supply has power factor correction. So, it is important to know the peak operating current of each of your loads.

ak

 

I wouldn't hesitate to run right up to max rating with that board. It looks like it has nice beefy terminal blocks and thick PCB tracks that can handle 30A/250VAC same as the relay.

The downer is the DC rating. It's only rated 20A/28VDC. DC is much harder on contacts than AC. As long as you aren't exceeding those values you should be fine. Use snubbers on your solenoid to prolong relay life

 

So the board has the SPST-NO types.
I would be happier if there was some isolation slots between the tracks, but it should be ok. It is 120V and hopefully it will not track over to the lower DC voltage. I would encourage you to cover the part that has the mains on it with a plastic strip to help prevent accidental bridging or touching when you are fiddling with the board. That could really spoil your day
On my mains switching boards there are slots cut to increase the voltage isolation, but I use 240V.

 

Could you explain the inductor vs resistance difference please?

 

Could you explain the inductor vs resistance difference please?

Think of an inductive load like pushing a heavy weight on a trailer, and think of a resistive load like pushing the same heavy weight across concrete with no wheels.

If you're pushing a heavy weight across concrete and you stop pushing, the load stops moving, immediately. With a resistive load, you turn off the supply voltage, and current stops flowing, immediately.

If you're pushing a heavy weight on wheels and you stop pushing, the load wants to continue moving, and might run away and damage something. Once current gets flowing through an inductive load, it wants to keep flowing, and could damage something. You cut off the supply voltage to an inductive load and the load itself briefly turns into a constant current power supply (output current initially equal to previous supply current). This inductive load, once power is disconnected by relay, acting as a CC power supply, will rapidly increase its voltage to way, way above what the previous supply voltage was, until the voltage is high enough to arc across the relay's contacts and get back to the power supply.

This arcing across the contacts with Inductive loads is what will cause premature failure of a relay. What we typically do to preserve the relay is install a flyback diode ("flyback" is the term for this voltage increase and arcing) or even better, a RC snubber. The capacitor of the snubber captures the energy released by the inductive load upon de-energizing, and dissipates it across the resistor.

Anything like a motor, coil, solenoid, etc. is an inductive load and deserves a flyback diode or preferably a snubber. Resistive loads like heater elements, resistors, light bulbs, etc do not typically need a snubber or diode, but you can still put one on anyway, if you're not sure how much inductance the load has (every load has a tiny amount).

 

I think here you meant inductive:

"This arcing across the contacts with resistive loads is what will cause premature failure of a relay."

Ok so here is the thing, I have this air compressor (powered by a motor its gotta be inductive):

Im thinking of using it with that relay controlled from an Arduino. The connection would be something like:

Where would the flyback-diode or snubber go? It should go in the NO2 line coming from the compressor, right?

 

I think here you meant inductive:

"This arcing across the contacts with resistive loads is what will cause premature failure of a relay."

Ok so here is the thing, I have this air compressor (powered by a motor its gotta be inductive):

Im thinking of using it with that relay controlled from an Arduino. The connection would be something like:

Where would the flyback-diode or snubber go? It should go in the NO2 line coming from the compressor, right?

1. yes, I meant Inductive. thanks for the correction. I've fixed it.
2. Beautiful drawing LOL. I'm not sure I've ever seen that much effort put into one.
3. Do not use a flyback diode with AC circuits. Only use a RC snubber. Diode is only appropriate for DC circuits.

The Snubber should be ideally placed placed in pos.1 below however if you cannot tap into the 2nd wire, then pos.2 would work. Pos.2 would allow a bit of AC current in the motor when not running (safety hazard, if you're working on the motor and expecting it to be "dead") and would waste a tiny bit of power when not powered on. The suggestion below assumes that blue is LN, orange is N, and yellow is GND.

 

Yes sorry I wrote the post quickly without referencing the proper color codes.

Live is blue, should be black.

Neutral is orange, should be white.

Gnd is actually green but yellow is fine.

Ok so I found this schematic on Wikipedia:
https://en.m.wikipedia.org/wiki/File:RC_Snubber_(Model).PNG

But I tried following this:https://www.quora.com/How-do-I-pick...snubber-what-are-the-most-important-equations

Step 1: 120vac over the switch/relay
Step 2: max current rating of relay 10A
Step 3: min R value = 120/10 = 12 Ohms
Step 4: 60 khz
Step 5: (1/(120^2)) * 60 khz =
But I'm not sure about that last step?

Can you help please?

 

bump

 

Also Post #27 here for snubber descriptions, https://forum.allaboutcircuits.com/threads/triac-for-ac-motor-speed-controller.144106/
Also a little observed practice, if using in a clean environment, snap off the venting pips in the corner of the relay, they can prolong the life of the relay when rated current is used.
If not you can experience reduced contact life in some case.
Max.

 

Ok so I take the L and N wires, cut them open, put the R in series with the C across from the L to the N wire and tape everything back up?

 

Essentially, yes.
Max.

 

Essentially, yes.
Max.

Like So?

The resistor is in the black tape wrapped around the other wire. I left the other live line open so as to show the connection to the cap

 

Ideally you should use it at the terminated end and use heat shrink tubing.
Max.

 

What do you mean at the terminated end? I still need to connect the L wire to my relay.

 

Ideally snubbers should be placed at or near the source of any interference, across relay coils or contacts, or at least at the power input to the board.
Max.

 

Ok So i should put It near the the relay board as close as possible?