Basic Relay Wiring Question

[ScottyB]

Hi Forum,

Sorry for the simple (probably stupid question).  I am trying to use a relay board see here https://amzn.eu/d/04daEqeV to simply switch on/off this actuator found here https://amzn.eu/d/02Avq22T

What I am trying to work out, how do I wire in the actuator to the board - I would assume one to common and the other to NC? Is that correct if not can anyone tell me the correct way?

[themadhippy]

I would assume one to common and the other to NC?

one what? its just a switch ,it don't provide any power you need to shovel that in if you want some out.

[ScottyB]

Does that not come via the 12v Input on the board?

[themadhippy]

Does that not come via the 12v Input on the board?

Normally no,that 12v is just for the circuit controlling the  relay coils.If you look at the PCB pictures the relay switch contacts  appear to go to the terminal blocks only.

Further looking gives an even bigger clue

Relay load voltage: DC 1-100v or AC85-265v

[aliarifat794]

You have to have a suitable power supply for your actuator (12V DC). Connect the relay board to its power supply (usually 5V or 12V depending on the relay board specification). Connect one wire of the actuator to the COM terminal on the relay.
Connect the other wire of the actuator to the NO terminal on the relay.

[NE666]

Connect one wire of the actuator to the COM terminal on the relay.
Connect the other wire of the actuator to the NO terminal on the relay.

Sorry but NO. 

As you and the previous responder have already said, there needs to be an external power supply (seems to be 12V in this case) in the actuator circuit. The relay's contacts are "dry" i.e. no inherent power available from them, just as with a normal mechanical switch.

So:

 - Positive terminal of the external 12V supply to positive input terminal of the actuator
 - actuator negative terminal to relay NO terminal
 - relay COM terminal to negative of the external 12V supply

The whole point of using a relay being that, within insulation limits, the relay contacts and the whole load side of the system are galvanically isolated from the circuitry driving the relay coil.

[ScottyB]

Thanks - I will give this a go and report my findings.

Thanks as always - this community is fantastic.

[NE666]

Have fun with it!

I don't know what your intended application for this is, and you may well know this already so forgive me if I'm teaching you to suck eggs, but bear in mind that this actuator has a stated duty cycle of 10% with maximum power-on time of 2 minutes.  It may well take a lot more in practice, or it might burnt out and/or fail prematurely if you exceed that.

[ScottyB]

I am controlling "something" over a VPN via serial port - so I thought I would make something move as a demo and a relay to switch on a actuator is visually quite pleasing.

Reading you advice below (and I really don't see it as teaching me to suck eggs - its gratefully received) are you saying that I need to "power off" within 2 mins of activating it to prevent burn out?

[ScottyB]

Connect one wire of the actuator to the COM terminal on the relay.
Connect the other wire of the actuator to the NO terminal on the relay.

Sorry but NO. 

As you and the previous responder have already said, there needs to be an external power supply (seems to be 12V in this case) in the actuator circuit. The relay's contacts are "dry" i.e. no inherent power available from them, just as with a normal mechanical switch.

So:

 - Positive terminal of the external 12V supply to positive input terminal of the actuator
 - actuator negative terminal to relay NO terminal
 - relay COM terminal to negative of the external 12V supply

The whole point of using a relay being that, within insulation limits, the relay contacts and the whole load side of the system are galvanically isolated from the circuitry driving the relay coil.

Just to be clear, by keeping the 12V+ supply connect to the positive of the actuator, are we not keeping the actuator always "live"? 

[ScottyB]

I found these two images which are basically the same if I have understood them correct just using two different power supply sources, but they use the negative to the actuator and the positive to NC (I assume I should/could take it to NO).

So is one way better than the other (safer perhaps?) or does it not matter?  I am thinking having a permeant 12V could mean someone touches it is "live".

[Ian.M]

It looks like that is a motor + geared screw drive actuator.  If so, you need to apply power with one polarity to push the ram out and reverse the connections to retract it.  It will not retract on its own when you remove the power nor will the weight of the load force it back in (unless severely overloaded - it would probably break first).   It claims to have internal limit switches which would disconnect the power at the ends of its stroke.  The usual arrangement has a diode in parallel to each limit switch so it can be reversed away from the limit.  However, don't trust them - if something jams it and it doesn't reach the end of its stroke, it will burn out if you don't cut the power to it in under two minutes, so its best to time how long it needs end to end moving your load, then turn the relays off after double that time.

Your proposed connections wont work - or at least will only work once.  You need a (relay) H-bridge to reverse the power to it as required.  Connect 0V to the NC terminals of two of the relays and 12V to their NO terminals.  Don't forget a fuse in the 12V feed, 1A should be suitable.  Connect the actuator between the COM contacts of the two relays.  With both relays off there is no power to it.  Turn either relay on and it will go in or out depending on which relay and which way round you wired it.  If you turn both relays on, it will put 12V on both of its wires, no current will flow and nothing will happen, so you don't have to worry if that happens by mistake.

[NE666]

Good catch Ian.M, I missed that. I'd not really looked at the mechanical aspects and just assumed a spring-based return. Definitely an H-bridge arrangement required here.

are you saying that I need to "power off" within 2 mins of activating it to prevent burn out?

Yes. Looking at the spec. label in the Amazon listing, 2 mins is the maximum time that power should be applied continuously to the motor AND if you do, you need to rest it for 18 mins before re-powering it (i.e. 10% duty cycle).  However, that assumes its loaded anywhere near the 750N rating and that you don't extend all the way during that time, so that the limit switch doesn't kick in.

As has been said already, you shouldn't only trust the limit-switches so if controlling via software, I'd build-in a maximum power-on failsafe into the control program too.

[ScottyB]

OK I think I am with you both. 

If I use the method suggested by NE666 that would work, but only one way - triggers the actuator. Turning it back to off wont bring the actuator to its "off" state as such,   I would need a second relay to bring it back to "off" effectively.  Is that correct?

Question around the fuse suggestion, I was going to use a 12v supply (rat with a tail) which in itself is fused 13 amp plug  - is that sufficient or would I need to do something else - e.g. - inline fuse holder or similar?

[NE666]

If I use the method suggested by NE666 that would work, but only one way - triggers the actuator. Turning it back to off wont bring the actuator to its "off" state as such,   I would need a second relay to bring it back to "off" effectively.  Is that correct?

Yes, you've got it. Sorry, I missed the nature of the drive previously. You will need to be able to reverse the polarity of the motor current in order to be able to move the actuator rod in both directions.  Look at "H-bridge" on Wikipedia for a good diagram and the theory.

Question around the fuse suggestion, I was going to use a 12v supply (rat with a tail) which in itself is fused 13 amp plug  - is that sufficient or would I need to do something else - e.g. - inline fuse holder or similar?

Way too high a fuse rating.  You should go with an inline holder and start off with a 2A fuse - the rated current for the motor is 0.8A. That should be a reasonable starting point.

[ScottyB]

Our posts crossed at the same time.  I am with you - it is for demo - so on and back off again, so I think I can do this via software safely enough.  It will show the "movement" and then I will bring it back to its off state straight away.

As for the fuse, would you use put something like this - https://amzn.eu/d/0a2NTguC in line on the 12V supply? Rather than using a AC-DC power supply (rat with tail).?  So put this before the relay or after the relay to the actuator?

[NE666]

Yes, something like that would be fine, and you've the bonus of having some spare fuses and a selection of higher ratings if you should need them.

For simplicity's sake, I'd put the fuse in the positive output lead of the "rat" tail, before feeding it to relays forming the H-bridge.

[kevin.gibbs]

It looks like this actuator extends with one polarity and retracts with the other. So, to control it, you will need 2 relays out of the 4 available.

[calzap]

Our posts crossed at the same time.  I am with you - it is for demo - so on and back off again, so I think I can do this via software safely enough.  It will show the "movement" and then I will bring it back to its off state straight away.

As for the fuse, would you use put something like this - https://amzn.eu/d/0a2NTguC in line on the 12V supply? Rather than using a AC-DC power supply (rat with tail).?  So put this before the relay or after the relay to the actuator?

BOJACK fuses?  There are a lot of no-name or made-up fuse brands that don't meet their specs.  Maybe someone has experience with BOJACK (i.e. actually tested them).  Suggest established brand name fuses or testing some BOJACKs.  If you go to the DigiKey or Mouser websites, you can see a list of brand name fuses.  Don't need to buy from DigiKey or Mouser.

Mike

[watchmaker]

Agreed.  For anything even slightly critical, I use only name brand stuff.  For my purposes, resistors, heat shrink, solderable protoboards, speakers, stuff like come from Ali.

Other things are name brands.  Especially fuses.

[calzap]

I recently went through my collection of automotive fuses and tested the no-brand and off-brand fuses.  And tested a few brand-names (Bussman, Littelfuse, PEC).  Brand names did fine.  Many of the no-/off-brands failed.  Some required 10 times the rating to blow.  No-/off-brands got tossed and replaced.

I should do the same with my cartridge fuse collection.  Easy to put off; it’s a huge collection.

Mike