Low signal 5vdc relay non pcb

leeomurchu · 22-02-2013 5:41pm #1

Hey lads as the title suggests I'm looking for a 5V dc relay.

It has to be a standalone version as it won't be mounted on a board.

Something similar to this (flat type)but it needs to have a low switching current something around 40mA these have a min of 100mA.

Anybody got any ideas.

Thanks

Bruthal · 22-02-2013 6:58pm

leeomurchu wrote: »

Hey lads as the title suggests I'm looking for a 5V dc relay.

It has to be a standalone version as it won't be mounted on a board.

Something similar to this (flat type)but it needs to have a low switching current something around 40mA these have a min of 100mA.

Anybody got any ideas.

Thanks

What are you using it for?

Switching current? Are you talking about the current the 5v coil takes? If so, why is that a problem? If the device switching the relay cant switch the required current, a transistor switched from it, can easily be used to switch the relay.

22-02-2013 6:59pm

leeomurchu wrote: »

Hey lads as the title suggests I'm looking for a 5V dc relay.

Do you mean that the control voltage (the voltage applied across the coil) is 5V?
Is the control voltage AC or DC?
What voltage do you want to switch, 5VDC at 100mA?

It has to be a standalone version as it won't be mounted on a board.

If the control voltage is 5VDC you could use one of these and solder wires to the pins.

Out of interest why can you not use a PCB?
This can switch up to 15VDC.

leeomurchu · 22-02-2013 7:02pm

Bruthal wrote: »

What are you using it for?

Switching current? Are you talking about the current the 5v coil takes? If so, why is that a problem? If the device switching the relay cant switch the required current, a transistor switched from it, can easily be used to switch the relay.

Hi,

I'm using the relay to switch a 20A nc contactor but I'm having issues with the contactor not switching sometimes as the load is not high enough for the relay to energise the coil on the contactor.

leeomurchu · 22-02-2013 7:05pm

I'm using a pcb with a switchable 5vdc supply so I'll be using this to energise the coil on the relay but I want to energise a coil on a 20a contactor from the relay.

I forgot to mention what I'll be switching with the relay. oops.

I probably could use a single channel pcb relay but I may not have room so I was looking for one that I could mount elsewhere if needed.

Bruthal · 22-02-2013 7:05pm

leeomurchu wrote: »

Hi,

I'm using the relay to switch a 20A nc contactor but I'm having issues with the contactor not switching sometimes as the load is not high enough for the relay to energise the coil on the contactor.

Some sort of interlock setup similar to a shower priority setup?

leeomurchu · 22-02-2013 7:09pm

Bruthal wrote: »

Some sort of interlock setup similar to a shower priority setup?

It would be something like that not neccesarily a shower the contactor load may not be 20A sometimes only a few amps.

So I'm having an issue with the relay not energising the contactor coil.

It works fine when there's a high load on the contactor.

Bruthal · 22-02-2013 7:09pm

leeomurchu wrote: »

I'm using a pcb with a switchable 5vdc supply so I'll be using this to energise the coil on the relay but I want to energise a coil on a 20a contactor from the relay.

I forgot to mention what I'll be switching with the relay. oops.

I probably could use a single channel pcb relay but I may not have room so I was looking for one that I could mount elsewhere if needed.

Ok so the contactor is energised by the relay. What is controlling the 5v relay, as in what conditions cause it to become energised?

Bruthal · 22-02-2013 7:10pm

leeomurchu wrote: »

It would be something like that not neccesarily a shower the contactor load may not be 20A sometimes only a few amps.

So I'm having an issue with the relay not energising the contactor coil.

It works fine when there's a high load on the contactor.

So the 5v relay is controlled by a current sensing coil?

leeomurchu · 22-02-2013 7:32pm

Bruthal wrote: »

Ok so the contactor is energised by the relay. What is controlling the 5v relay, as in what conditions cause it to become energised?

The Relay would be controlled via a pcb board with a switchable 5vdc output.

It is switched remotely.

Bruthal · 22-02-2013 7:35pm

leeomurchu wrote: »

It would be something like that not neccesarily a shower the contactor load may not be 20A sometimes only a few amps.

So I'm having an issue with the relay not energising the contactor coil.

It works fine when there's a high load on the contactor.

A high load on which contactor though? A 2 contactor setup, so when one is loaded, it energises the relay to energise the other contactor, opening its contacts to switch off its load?

Its probably just me, but im not very clear what you are trying to do.

DublinDilbert · 22-02-2013 7:35pm

What voltage is the contactor coil you are trying to energise?

If the contactor is coil is running off 12 or 24V DC, I would just use a "low-side" N Channel mosfet to turn it on. The gate of the FET would easily turn on with 5V and will easily be able to sink the current required to pull in the contactor.

22-02-2013 7:37pm

It may be best to post a diagram.

22-02-2013 7:39pm

DublinDilbert wrote: »

What voltage is the contactor coil you are trying to energise?

If the contactor is coil is running off 12 or 24V DC, I would just use a "low-side" N Channel mosfet to turn it on. The gate of the FET would easily turn on with 5V and will easily be able to sink the current required to pull in the contactor.

Yes, I have heard that mosfets are now being used for switching heat tracing circuits (230VAC at 25A).

leeomurchu · 22-02-2013 7:39pm

DublinDilbert wrote: »

What voltage is the contactor coil you are trying to energise?

If the contactor is coil is running off 12 or 24V DC, I would just use a "low-side" N Channel mosfet to turn it on. The gate of the FET would easily turn on with 5V and will easily be able to sink the current required to pull in the contactor.

Sorry I'm not being very clear about this it's a 20A nc 230v coil contactor.

basically I need a 5dc relay that'll switch a 230V load (which will be the coil of the contactor)

the issue I'm having is that if the 230V contactor is switching a high load the relaay I have works fine 100mA but if the contactor load is low say 5-10A the relay will not switch.

leeomurchu · 22-02-2013 7:40pm

DublinDilbert wrote: »

What voltage is the contactor coil you are trying to energise?

If the contactor is coil is running off 12 or 24V DC, I would just use a "low-side" N Channel mosfet to turn it on. The gate of the FET would easily turn on with 5V and will easily be able to sink the current required to pull in the contactor.

any links to one of these. Is it a pcb mounted relay?

leeomurchu · 22-02-2013 7:42pm

2011 wrote: »

It may be best to post a diagram.

I'll try post one later. Drawing wouldn't be my strength

Bruthal · 22-02-2013 7:42pm

2011 wrote: »

Yes, I have heard that mosfets are now being used for switching heat tracing circuits (230VAC at 25A).

Are they not triac`s they are using?

22-02-2013 7:43pm

leeomurchu wrote: »

basically I need a 5dc relay that'll switch a 230V load (which will be the coil of the contactor)

As Dilbert said, a mosfet will do this. Apply 5V to the gate and switch 230VAC through the mosfet.

Bruthal · 22-02-2013 7:43pm

leeomurchu wrote: »

any links to one of these. Is it a pcb mounted relay?

He was taking about using a mosfet (type of transistor) to switch the relay, a logic level one will fully switch from 5 v. But its not suitable for an AC contactor.

22-02-2013 7:47pm

Bruthal wrote: »

He was taking about using a mosfet (type of transistor) to switch the relay, a logic level one will fully switch from 5 v. But its not suitable for an AC contactor.

Sorry, I was thinking of an IGBT.

Bruthal · 22-02-2013 7:48pm

2011 wrote: »

As Dilbert said, a mosfet will do this. Apply 5V to the gate and switch 230VAC through the mosfet.

Id imagine 2 mosfets would be needed to do that.

If the problem is very low switching current available to switch the 5v relay, then a transistor to switch the relay would be the method.

But im still lost as to the actual exact question.

leeomurchu · 22-02-2013 7:49pm

I'm thinking a little more heavy duty something along the lines of these. Flat type.

http://pewa.panasonic.com/assets/pcsd/catalog/jm-catalog.pdf

Bruthal · 22-02-2013 7:50pm

leeomurchu wrote: »

I'll try post one later. Drawing wouldn't be my strength

ms paint is actually good for that type of thing

DublinDilbert · 22-02-2013 7:52pm

leeomurchu wrote: »

any links to one of these. Is it a pcb mounted relay?

They are some times called a "solid state relay", which use opto couplers & mosfets to basically form a simple relay. Many soild state relays are designed to switch AC loads only, but ones are made to switch DC.

I had to do something similar, i needed to control a 24V contactor from a national instruments digital output (eg 5V out). I got a din rail mount solid state relay from RS.

Something like this would probably be the job for you:-
http://radionics.rs-online.com/web/p/solid-state-relays/7401321/

But RS literally have 100's of them

22-02-2013 7:52pm

Bruthal wrote: »

Id imagine 2 mosfets would be needed to do that.

If the problem is very low switching current available to switch the 5v relay, then a transistor to switch the relay would be the method.

But im still lost as to the actual exact question.

I was getting me terminology mixed up, I meant to say IGBT (which contain mosfets). Good article here:

http://www.ixys.com/Documents/AppNotes/IXYS_IGBT_Basic_I.pdf

Bruthal · 22-02-2013 7:53pm

leeomurchu wrote: »

Sorry I'm not being very clear about this it's a 20A nc 230v coil contactor.

basically I need a 5dc relay that'll switch a 230V load (which will be the coil of the contactor)

the issue I'm having is that if the 230V contactor is switching a high load the relaay I have works fine 100mA but if the contactor load is low say 5-10A the relay will not switch.

The load being switched by the contactor wont have any bearing on the current its coil takes to switch it on.

So where is the contactor load level coming into it?

DublinDilbert · 22-02-2013 7:56pm

Here's one that looks good too

http://radionics.rs-online.com/web/p/solid-state-relays/7360873/

Also make sure you have a suppressed contactor coil, or fit a reversed biased diode across the coil contacts...

Bruthal · 22-02-2013 8:00pm

Its a 230v ac contactor being switched though.

The problem is the 5v relay is not switching the contactor with the contactor is at certain loads.

So the problem is finding out what is the setup exactly.

I think finding out exactly what is switching the 5v relay coil itself is the main question.

The contactor coil current will be the same no matter what load the contactor is switching through its contacts, therefor the 5v relay contacts will have the same loading on them.

DublinDilbert · 22-02-2013 8:06pm

Bruthal wrote: »

Its a 230v ac contactor being switched though.

I don't know the full set up, but if its a 230V contactor, I'd just use an AC SSR to control it from 5Vdc control signal.

Bruthal · 22-02-2013 8:09pm

DublinDilbert wrote: »

They are some times called a "solid state relay", which use opto couplers & mosfets to basically form a simple relay. Many soild state relays are designed to switch AC loads only, but ones are made to switch DC.

I had to do something similar, i needed to control a 24V contactor from a national instruments digital output (eg 5V out). I got a din rail mount solid state relay from RS.

Something like this would probably be the job for you:-
http://radionics.rs-online.com/web/p/solid-state-relays/7401321/

But RS literally have 100's of them

Doing a bit of transistor-relay switching stuff myself lately. Another tractor project before christmas there, all microcontroller setup this time, switching the car relays via transistors to drive it.

Bruthal · 22-02-2013 8:10pm

2011 wrote: »

Good article here:

http://www.ixys.com/Documents/AppNotes/IXYS_IGBT_Basic_I.pdf

Looks interesting alright,

22-02-2013 8:14pm

This puppy will do everything that you want:

http://www.lightobject.com/25A-Solid-State-Relay-SSR-DC-In-AC-Out-P61.aspx

Bruthal · 22-02-2013 8:15pm

DublinDilbert wrote: »

I don't know the full set up, but if its a 230V contactor, I'd just use an AC SSR to control it from 5Vdc control signal.

Yea its not clear so far, but definitely a 230v ac contactor.

There is no obvious reason why the 5v relay is not working. It sounded at first like the 5v relay coil was taking too much current, which would be sorted by a simple transistor.

But probably need to see a clearer description, as to exactly what energises the 5v relay and why different loadings on the contactor chage its behavior.

Its like as if the relay is a current sensing one, or has a current sensing circuit controlling it.

22-02-2013 8:16pm

Solid State Relay

Input: 3 to 32VDC
However it can switch up to 380 VAC up to 25A

Bruthal · 22-02-2013 8:16pm

2011 wrote: »

This puppy will do everything that ou want:

http://www.lightobject.com/25A-Solid-State-Relay-SSR-DC-In-AC-Out-P61.aspx

But why is the 5v dc relay not working?

DublinDilbert · 22-02-2013 8:18pm

Bruthal wrote: »

Yea its not clear so far, but definitely a 230v ac contactor.

There is no obvious reason why the 5v relay is not working. It sounded at first like the 5v relay coil was taking too much current, which would be sorted by a simple transistor.

But probably need to see a clearer description, as to exactly what energises the 5v relay and why different loadings on the contactor chage its behavior.

Its like as if the relay is a current sensing one, or has a current sensing circuit controlling it.

Yea many systems with 5V outputs will have some sort of current limiting resistor in series with them. I've seen some recently with 1K in series with the output, so had to use a low side n channel mosfet to turn on the load.

22-02-2013 8:19pm

Bruthal wrote: »

But why is the 5v dc relay not working?

Don't know to be honest. Perhaps it is faulty. Try changing it out for same.
I like my solution though as it provides everything required in a single device.

Bruthal · 22-02-2013 8:20pm

2011 wrote: »

Input: 3 to 32VDC
However it can switch up to 380 VAC up to 25A

You can make them up as well, triac controlled by an opto coupler. Opto coupler has an LED in it, so dc in, and low level triac output, to switch a power triac.

Just as a matter of interest I mean.

22-02-2013 8:21pm

Bruthal wrote: »

You can make them up as well, triac controlled by an opto coupler. Opto coupler has an LED in it, so dc in, and low level triac output, to switch a power triac.

Just as a matter of interest I mean.

Nice one

Radionics ?

Bruthal · 22-02-2013 8:24pm

2011 wrote: »

Don't know to be honest. Perhaps it is faulty. Try changing it out for same.
I like my solution though as it provides everything required Ian single device.

Yea but it would be nice to know the exact problem first. Why is the load on the contactor altering the working of the relay? Is it a current sensor in the circuit?

If that is the case, and it simply wont switch on the 5v relay at low current level, there may be zero output to the 5v relay until a certain current level is reached on the contactor load, in which case replacing the relay wont be the solution.

22-02-2013 8:30pm

Bruthal wrote: »

Yea but it would be nice to know the exact problem first.

Yes, but you really need a diagram to see the "big picture" and diagnose properly.
Without it we are just speculating.

leeomurchu · 22-02-2013 8:31pm

Hey sorry.

Bath night for the rug rats. right so clearly you guys know your relay so go easy on me

I was using the solid state relays but they seemed to work intermittently depending on the load being switched through the contactor.

I've no idea of the reasoning for this.

I'm just gonna have a read back through the posts I see a couple of solutions thrown out there.

Thanks everyone for their input.

Bruthal · 22-02-2013 8:43pm

2011 wrote: »

Nice one
Radionics ?

They can be got on ebay as components as well.

Here is an moc3062 opto triac

And an moc3042 coupled to a power triac to form a solid state relay.

And a bit more on them here

The 3042 (400v peak to peak) is like a lower peak to peak voltage version of the 3062 (600v peak to peak). They are simply low power triacs in a 6 pin configuration used to optically isolate the dc input from the ac switching output. They can then switch power triacs. That is in effect what a solid state AC relay is.

DublinDilbert · 22-02-2013 8:44pm

leeomurchu wrote: »

I was using the solid state relays but they seemed to work intermittently depending on the load being switched through the contactor.

There's obviously something funny happening there. A SSR should be able to switch a contactor no problem.

If the contactor is switching a large load (or possibly and inductive one), you could end up with big voltage spikes on the 220V supply causing other bits of the circuit to misbehave.

Bruthal · 22-02-2013 8:46pm

2011 wrote: »

Yes, but you really need a diagram to see the "big picture" and diagnose properly.
Without it we are just speculating.

Yes but we know the relay is having problems switching the contactor.

And that the current the contactor is switching seems to affect the relay operation. So there is where to find out whats happening.

Bruthal · 22-02-2013 9:00pm

DublinDilbert wrote: »

Yea many systems with 5V outputs will have some sort of current limiting resistor in series with them. I've seen some recently with 1K in series with the output, so had to use a low side n channel mosfet to turn on the load.

I had a mosfet overheating last week when switching at 1khz. I noticed input capacitance in the mosfet gate in the data sheet. With the 1k resistor, and continuous rapid switching, id say the delay to full on due to the reisitor-capacitor time on the gate was causing it. No problem for switching on and off like a manual switch, but seems significant for high rate switching.

I got a transistor to directly switch the gate with no resistor, and it worked perfect then, and put the 1k resistor between gate and 0v as a pull down. It was all just experimental, but interesting enough.

22-02-2013 9:03pm

Bruthal wrote: »

I had a mosfet overheating last week when switching at 1khz.

What were you doing, PWM ?
What chip was controlling the gate signal?

22-02-2013 9:05pm

Bruthal wrote: »

Yes but we know the relay is having problems switching the contactor.

As I said, it would be nice to change the unit out to see if it is simply a faulty component.

Bruthal · 22-02-2013 9:05pm

DublinDilbert wrote: »

If the contactor is switching a large load (or possibly and inductive one), you could end up with big voltage spikes on the 220V supply causing other bits of the circuit to misbehave.

Yea I was thinking that same thing myself.

But it seems to fail to work when switching smaller currents. Again, its like there is a current sensor in the mix, like a shower priority unit, and leo is just trying to get it to work at lower currents.

A shower priority unit for example, will let both showers operate if they are on cold with no elements on, because the pump and solenoid current draw is below the threshold of the sensor circuit operating the contactors.

Bruthal · 22-02-2013 9:17pm

2011 wrote: »

What were you doing, PWM ?
What chip was controlling the gate signal?

I was actually just testing a mosfet I had, irl540n one to see was it working, or faulty. I just set it dimming a car headlamp up and down with a pic chip 12f675, just counting up and down a pulse width to dim it up and down every few seconds.

A mosfet transistor just needs a voltage on its gate to set it on. The on resistance will be higher for lower gate voltage, and the gate voltage rise is not instant due to inherent gate capacitance. So when it has voltage applied, it is like charging a capacitor, there is a time factor, and during this very tiny time, the mosfet has some resistance.

It is a tiny capacitance, of no significance for normal on and off use, but can be for high speed switching for pwm control, and the time factor will be increased with a gate resistor added in. They can be used without a gate resistor anyway.

A standard transistor needs a base resistor, as it is switched on by current flow into the gate, and without the resistor, would be like a short. Where as the mosfet just has voltage applied to its gate, with no current flow after the initial gate capacitance charge factor is gone, which is in micro seconds or less with no gate resistor.

Low signal 5vdc relay non pcb

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