Current Monitoring Relay Confusion

[hotponyshoes]

I have a project that requires the use of a current monitoring relay (basically a box with 2 socket outlets. Both live but the output in one socket needs to be switched off when the load on the other exceeds a couple of amps)

I have got one of these

DIA53S72420A

1-phase AC overcurrent monitoring relay, input range 2-20 A AC, NPN-PNP open collector output, self-powered, 17.5 mm DIN-rail housing

www.gavazziautomation.com

Obviously not suitable for this project as it only has 2 wires to connect. I can not work out what these are actually for?
As in, what does the relay part do if there are no connections for the relay?

 

[m_c]

I'm going to guess it's basically a stripped down version of one with extra connections, just to provide a visual monitor in a control panel, but it does seem to be a bit pointless, as given the costs of designing/manufacturing this version, I doubt it's any cheaper than one with the contacts.

 

[Agroshield]

Reading the data sheet, the wire whose current you are monitoring pokes through the 12mm diameter hole in the item.

It says it is self-powered, and the two connections are switched open circuit by a transistor when the current exceeds the set point.

So it is designed to be used in a low voltage monitoring (control) circuit, not as a direct means of switching something on or off.

It would light a light on a panel or provide an input to a PLC - effectively saying "there's a problem and somebody else needs to deal with it".

 

[hotponyshoes]

Reading the data sheet, the wire whose current you are monitoring pokes through the 12mm diameter hole in the item.

It says it is self-powered, and the two connections are switched open circuit by a transistor when the current exceeds the set point.

So it is designed to be used in a low voltage monitoring (control) circuit, not as a direct means of switching something on or off.

It would light a light on a panel or provide an input to a PLC - effectively saying "there's a problem and somebody else needs to deal with it".

I've read the data sheet 5 times and not managed to understand that.
Makes perfect sense when explained by a real person. Thanks!

I did see the reference to a 12mm hole. This confused me further as neither of the terminals are 12mm. I just presumed this was a mistake and they ment the terminals would accept (the ridiculously strange size) 12mm² cable
I also noticed the 12mm hole on the drawing and the 12mm hole in the unit itself and still didn't twig!

Not only that, but I have previously used several Amp clamps and current monitor devices that go around a cable.

I still don't think it will do what I want as I was planning to mount it on a din rail in a distro board and I don't think I'll have enough room to run a cable through it. If there are enough ways I could fit it with a blank either side. Or, as I'll only need to adjust it once, mount it internally..

 

[daedalusminos]

What you could do is use that device to monitor the current through the load socket and then use it's 'over current' NO open collector output to turn on your second relay from which you have connected the socket to the NC contacts.

So under normal use (<2A) you have both sockets live (one permanently, primary, but being monitored), the other, secondary, via the NC contacts of a relay. >2A the ouput of the sensor energises the relay and cuts power to the secondary socket.

It's not nice as it fails 'unsafe'

 

[hotponyshoes]

What you could do is use that device to monitor the current through the load socket and then use it's 'over current' NO open collector output to turn on your second relay from which you have connected the socket to the NC contacts.

So under normal use (<2A) you have both sockets live (one permanently, primary, but being monitored), the other, secondary, via the NC contacts of a relay. >2A the ouput of the sensor energises the relay and cuts power to the secondary socket.

It's not nice as it fails 'unsafe'

This was my plan,
I've also got a din mount contactor and a din mount psu so I could get the 3 to work together. The issue is the physical amount of space on the din rail / number of ways in the housing. I don't think I've got the 2 extra spaces I will need to run a cable through the body of the current monitor relay.

It's probably easier and neater to change to a different current sensing relay, ideally I'd like one that could switch the 2nd outlet directly but I'm struggling to find one that has 16a terminals.
I have seen some Unbranded ones that claim 16a but I'd prefer a name I have heard of.
Although it's not exactly a critical application and doesn't need to be failsafe

 

[daedalusminos]

You just need a single phase overload relay controlling a contactor.

Edit....this may not be a good idea since the you'll be going beyond the overload cutout!

 

[daleyd]

What contactor are you using? You can get some slim single pole ones if you are struggling for space.

As said, it seems unlikely that a current sensing relay would be big enough to switch more than a few amps, they are usually used in conjunction with contactors or bigger relays - which has some advantages in that the high power stuff is separate from your relatively expensive current sensing device, so in the case of failure in the power side you don’t have to change the whole thing, just a (relatively) cheap contactor.

 

[hotponyshoes]

What contactor are you using? You can get some slim single pole ones if you are struggling for space.

As said, it seems unlikely that a current sensing relay would be big enough to switch more than a few amps, they are usually used in conjunction with contactors or bigger relays - which has some advantages in that the high power stuff is separate from your relatively expensive current sensing device, so in the case of failure in the power side you don’t have to change the whole thing, just a (relatively) cheap contactor.

I've got a selection of random bits here that I was just seeing if they will work together, the contactor I have has a 24v coil and I also have a 24v rail mount psu.

There is not a particularly tight budget for this so I think it's probably easier to get a new current sensing relay that will switch the 230v, forget about using the psu and get a suitable contactor as well.

 

[Agroshield]

So under normal use (<2A) you have both sockets live (one permanently, primary, but being monitored), the other, secondary, via the NC contacts of a relay. >2A the ouput of the sensor energises the relay and cuts power to the secondary socket.

I did wonder if the set up might need to be slightly more sophisitcated.

Draw a time/behaviour graph. The sensor senses >2A and switches off the breaker. It now senses zero on that circuit so it switches the breaker back on. It now senses >2A since nothing has changed in the controlled circuit to reduce the current being drawn. So it switches off. Repeat ad infinitum.

For sure, it should not act as the flasher on your car.

 

[hotponyshoes]

I did wonder if the set up might need to be slightly more sophisitcated.

Draw a time/behaviour graph. The sensor senses >2A and switches off the breaker. It now senses zero on that circuit so it switches the breaker back on. It now senses >2A since nothing has changed in the controlled circuit to reduce the current being drawn. So it switches off. Repeat ad infinitum.

For sure, it should not act as the flasher on your car.

No, socket #2 will have a load connected all the time.
When socket #1 draws more than 2a socket #2 needs to switch off.
When the load on #1 drops back below 2a #2 can switch on again.

 

[daedalusminos]

Something like this..

Normally Closed/Open Current Detection Module Adjustable Current Sensing Switch M3050 M3056 M3060 M3066 M3070 M3076 M3080 M3086 - AliExpress 13

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[hotponyshoes]

Something like this..

Normally Closed/Open Current Detection Module Adjustable Current Sensing Switch M3050 M3056 M3060 M3066 M3070 M3076 M3080 M3086 - AliExpress 13

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Sort of. I'm a bit dubious about £4 electric devices from aliexpress. I reckon a box of matches would be less likely to catch fire on me...

Something like this would suit better, will mount on the din rail through the enclosure so easy to adjust if required.
Doesn't need the cable running through a hole either so only takes up one slot.
Plus it's over twice the price so less than half as likely to go up in flames..

Not sure if it will switch a 16a load though?
Maybe best to play safe with it and use a contactor anyway..

GEYA GRI8 Current Relay Monitoring Range Overcurrent Undercurrent Switch 0.05A-16A AC24-240V OR DC24V - AliExpress 13

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com