Robo-Tank DIY Aquarium Controller Forum
Relay - Printable Version

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Relay - aquaalgae - 09-24-2018


What model relay is in the relay boxes?  I wanted to check their life expectancy.


RE: Relay - Rob F - 09-24-2018

Here's the datasheet, they should be good for 20,000 - 100,000 clicks.

RE: Relay - fietsenrex - 10-18-2018

Does the controller work with ssr’s right out of the box?
Iaqua required some modifications to work with ssr’s instead of normal relay’s
Or is there a specific type I need to use?

I plan on swapping the “normal” relay’s for ssr’s since 2 have died in the on position already and since they have a longer life-span

RE: Relay - Rob F - 10-18-2018

They do if you get them on a module like the other relays. If you use just an SSR you might need a circuit, it depends on the SSR, some have this built in.

RE: Relay - fietsenrex - 10-25-2018

I’m going to use some industrial grade ssr’s
All I need is a DC voltage between 3 and 30 volts

Do the relay channels provide a ground or a voltage of some sort?

RE: Relay - Rob F - 10-25-2018

Cool, post a link if you have one, I would like to see.

Those relay outputs are digital pins that put out +3.3v so you should be good to go.

RE: Relay - fietsenrex - 10-25-2018

Hmmm was hoping is was 12v since the relay pins were 12v on the boards..
Got a couple of 7-30v relays So 3.3 isn’t going to cut it..

You Think i can boost the voltage to 12v by using something like a bd135?

Something like this will be used:

RE: Relay - Rob F - 10-26-2018

Sorry I'm a little confused, what boards require 12v? That seem like silly relay you have, most work using low voltages to switch on/off.

Not sure about boosting the voltage but you can use a NPN transistor however you might want a Logic MOSFET instead of BJT, BJT uses current to switch, the MOSFET uses voltage and are a little easier to work with. Not much power is required for the relay so most Logic MOSFET's will work. Make sure it's a logic type though so it works with low voltages.

If you connect the 3.3v from controller to MOSFET it'll switch a GND on/off. On the relay you would connect +12v to input and the GND input would come from the MOSFET. The 3.3v from controller would then turn the MOSFET on/off which turns the relay on/off because the DC GND to it is cut.

RE: Relay - fietsenrex - 10-26-2018

It has been a rough week for me So not everything I’m saying makes perfect sense.

But the robo-tank supplies 12v for the relays (or 5v if you use the spare 5v and use 5v relays) If I’m correct.

I plan on doing the swap during my christmas week so plenty time to figure out how to make this work properly

But using the Logic mosfet I Just everything up as follows:
+12v to the + of the ssr
- from the ssr to the drain of the mosfet
+3.3v from the robo-tank to the gate of the mosfet
And the source from the mosfet to the - of the robo-tank

RE: Relay - Rob F - 10-26-2018

You're correct, I send 12v to the power bar so most relays can be used, if someone has 5v relays a DC-DC is used to drop 12v to 5v. The part your missing is all those assembled relay module boards use MOSFET's for the GND of the relay to switch it on/off. Even though you are sending 12v to your relay board the signal wires from controller only put out 3.3v. This works because the MOSFETS are Logic type and switch on with only 3.3v, a regular MOSFET typically requires 10v to turn on so it must be Logic or also know as "enhancement type". The datasheet will say on the first page typically.

You have it correct on wiring the MOSFET.

Here's a very basic diagram to follow.

Gate = signal pin from controller
Source = common GND
Drain = -GND on SSR input
On the + of SSR input you can use any DC voltage that falls in the correct range.

Just thinking I gave you bad advice a couple posts up, you NEVER want to connect the 3.3v from controller signal wire directly to the SSR even if the SSR can switch with 3v. The +3.3v signal wire from the controller can only handle very low currents and the relay could draw more or just push the pin to it's max. MOSFET's should always be used directly from the source pin as they require very little current to switch.

One other thing, you might want to add a snubber circuit, some have this built in but lots don't so do some searching on this. There's a few types and not to difficult to add, just more components to work with. :(

RE: Relay - fietsenrex - 10-26-2018

But since a SSR doesn’t have a coil there Should be no inductive load, at least that is what I understood..
So with the milliamps used by a SSR there also Should be little ripple on the DC line used for switching.

We use them on USB lines from a pc to switch off desk heaters when the pc is switched off :p

RE: Relay - Rob F - 10-26-2018

I'm not sure but based on what I read a snubber should be added to the output, here's a quote I found. I've also read in some SSR datasheets where they recommend adding one and I've seen a couple with the snubber built in.

Quote:Like the electromechanical relays, a Resistor-Capacitor (RC) snubber network is generally required across the output terminals of the SSR to protect the semiconductor output switching device from noise and voltage transient spikes when used to switch highly inductive or capacitive loads.

RE: Relay - fietsenrex - 10-26-2018

Ah output.. that makes sense :p

But the relay’s are rated for 25A, I’m not exceding 2,5A xD

But I’ll dig up the datasheets to see if they are required or not

RE: Relay - Rob F - 10-27-2018

Yeah its for the output but not sure how necessary it is. I'm guessing if it's low current devices connected it's probably not as important but again it's only a cap and resistor so should be easy to add. Just put them directly on the screws of the SSR, shouldn't need to solder anything.

RE: Relay - fietsenrex - 10-28-2018

Yeah the adding would be easy :p
But the figuring out what I need is a nightmare for me..

RE: Relay - Rob F - 10-28-2018

Yeah I think it's a nightmare for most people including myself, I've seen that page you linked, it's not for the faint of heart. I'm not 100% sure on the snubber and could be wrong if it's actually required, I know those relay modules and other power bars, Angel Reef for example, don't have those so maybe just a nice feature. The only thing used on the relay modules are the flyback diodes so maybe that's all you need. Currently that's all I have on my power bar but thought it would be good to add a snubber on the outputs or at least some of them. I've been stuck on this snubber because I've seen it mentioned in some data sheets.

RE: Relay - fietsenrex - 11-03-2018

Did some asking around at my workplace and multiple electricians but the RC snubber is only reccomended when switching highly inductive or capacitive loads.
But since I’m not switching high-power coils or anything I was advised not to break my head on it :p
So I only need to figure out which Logic mosfet i need

RE: Relay - aquaalgae - 11-03-2018

The Reef Angel outlets don't have it but the ones you make do Rob? The reason I ask is because I was having all kinds of issues with Reef Angel including outlets not coming on/off when they should and weird flickering on the PWM LED channels. If I unplugged most of the stuff from the outlets, things would go back to normal.

RE: Relay - fietsenrex - 11-03-2018

Reef angel has SSR’s without RC snubbers which causes issues?

RE: Relay - aquaalgae - 11-03-2018

Reef Angel doesn't have SSRs, it's mechanical relays. I don't know about the snubber circuits, I think Rob was saying they don't. I was thinking that may explain the issues I was having when I was running my Reef Angel.