Using PHOENIX CONTACT relays (2961105) 24V DC with contact 6 A rating with socket (2966016)at output of siemens PLC. Very unfortunately we are facing problem of the relay getting stuck up many times. I would like your expert opinion to know the reason behind it.I read , it could be because of leakage current.Othere reasons? Any other phoenix relay to kill either leakage current if any?
Phoenix relay sticking
- Thread starter panthripu
- Start date
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ptonsparky
Tom
- Occupation
- EC - retired
While not dealing directly with your DC problem, I have added an additional relay in parallel with the first. There may be enough leakage current to hold in one coil, but not two. You could up the size of the first, but that is too easy.
ptonsparky
Tom
- Occupation
- EC - retired
I did have an armature on a Bell Ringing system that developed residual magnetism over the years. It would hold in just long enough to burn up the coil the on the hammer. Late 60s to early 70s control.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
170407-0925 EDT
panthripu:
You need more information.
1. What is the Siemens output? Solid state or relay contact. A relay contact output should have no appreciable leakage.
2. What is the voltage across the Phoenix coil when the PLC output is off?
3. At what voltage does the Phoenix relay pull-in, and what voltage does it drop-out? If you need to reduce leakage current to the Phoenix coil, then adding a shunt resistor across the Phoenix coil may be adequate. You need to consider margins relative to drop-out.
Suppose your Phoenix relay pulls-in at 16 V and drops-out at 2 V, and has a coil resistance of 500 ohms, then current at pull-in is 32 mA, and at drop-out 4 mA. If your leakage is about 4 mA, then you are in trouble. Adding a 500 ohm shunt resistor in parallel with the relay coil will reduce coil voltage to 1 V with 4 mA leakage. I don't consider this a good margin, but it might work.
If the PLC output voltage is a solid 24 V when on, and is regulated so it does not vary with AC supply voltage changes, then you might consider a 3 V Zener diode in series with the Phoenix relay coil, this makes drop-out 5 V, but you would still want the added 500 ohm shunt resistor outside of the Zener and Phoenix coil, then off state voltage across the 500 ohm resistor would be 2 V at 4 mA leakage ( with the Zener and only 2 V input there is no current to the relay coil), based on above assumed leakage current, providing a pretty good drop-out margin.
A Zener has a much more stable operating point than does a mechanical relay and thus its use adds to the value of the margin.
Leakage current would need to be 4 + 5*1000/500 = 14 mA for the relay to be at its drop-out point. This is a margin of 14/4 = 3.5 compared to 2/1 = 2 for just the shunt resistor. However, some margin for pull-in was lost.
4. Another option is to change the PLC output from solid-state to a mechanical contact relay output.
The above is on the assumption that the problem is from PLC leakage current.
5. If your problem is not the leakage current to the Phoenix, but rather on the Phoenix output contacts causing contact welding, then you need a larger output relay.
Do some measurements,
.
panthripu:
You need more information.
1. What is the Siemens output? Solid state or relay contact. A relay contact output should have no appreciable leakage.
2. What is the voltage across the Phoenix coil when the PLC output is off?
3. At what voltage does the Phoenix relay pull-in, and what voltage does it drop-out? If you need to reduce leakage current to the Phoenix coil, then adding a shunt resistor across the Phoenix coil may be adequate. You need to consider margins relative to drop-out.
Suppose your Phoenix relay pulls-in at 16 V and drops-out at 2 V, and has a coil resistance of 500 ohms, then current at pull-in is 32 mA, and at drop-out 4 mA. If your leakage is about 4 mA, then you are in trouble. Adding a 500 ohm shunt resistor in parallel with the relay coil will reduce coil voltage to 1 V with 4 mA leakage. I don't consider this a good margin, but it might work.
If the PLC output voltage is a solid 24 V when on, and is regulated so it does not vary with AC supply voltage changes, then you might consider a 3 V Zener diode in series with the Phoenix relay coil, this makes drop-out 5 V, but you would still want the added 500 ohm shunt resistor outside of the Zener and Phoenix coil, then off state voltage across the 500 ohm resistor would be 2 V at 4 mA leakage ( with the Zener and only 2 V input there is no current to the relay coil), based on above assumed leakage current, providing a pretty good drop-out margin.
A Zener has a much more stable operating point than does a mechanical relay and thus its use adds to the value of the margin.
Leakage current would need to be 4 + 5*1000/500 = 14 mA for the relay to be at its drop-out point. This is a margin of 14/4 = 3.5 compared to 2/1 = 2 for just the shunt resistor. However, some margin for pull-in was lost.
4. Another option is to change the PLC output from solid-state to a mechanical contact relay output.
The above is on the assumption that the problem is from PLC leakage current.
5. If your problem is not the leakage current to the Phoenix, but rather on the Phoenix output contacts causing contact welding, then you need a larger output relay.
Do some measurements,
.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
Gar gave you some great troubleshooting info ... I put the relay part number into Google and see it is 7mA nominal at 24V, 3390 ohm coil nominal.
__IF__ removing the coil power allows it to drop out, it is likely leakage. I'd try a half-watt 2200 or 2700 ohm resistor in parallel with the coil.
__IF__ removing the coil power __DOES NOT__ allow it to open, I'd evaluate the relay selection; it is not appropriate for the load.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
It is hard to give you much in the way of good advice w/o better information. However, I can make these general comments.
I have had some of this style of relay fail on me in the past. Sometimes they fail open, sometimes the contacts weld closed. I don't like to use them for that reason. Sometimes brand new they come in non-functional.
The contacts themselves do not seem to be very robust.
I am not sure what you mean by leakage current or by "stuck up". Is the leakage current coming from the Siemens output module and keeping the relay on when it should shut off? If so, a simple resistor in parallel with the relay coil should fix that.
I have had some of this style of relay fail on me in the past. Sometimes they fail open, sometimes the contacts weld closed. I don't like to use them for that reason. Sometimes brand new they come in non-functional.
The contacts themselves do not seem to be very robust.
I am not sure what you mean by leakage current or by "stuck up". Is the leakage current coming from the Siemens output module and keeping the relay on when it should shut off? If so, a simple resistor in parallel with the relay coil should fix that.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
170407-1917 EDT
GeorgeB:
Good find on the relay. After seeing your post I went looking for the Phoenix datasheet. The Phoenix website is very poor as is the datasheet. I did not find the coil resistance. I just found 24 V input and 6 A 250 V on output.
For all:
GeorgeB using your coil resistance coil power input at 24 V is 0.17 W, that is going to be an extremely wimpy relay, and I would never consider such a relay for a 6 A output load capability.
A P&B KUP relay has a coil resistance of 450 ohms at 24 V DC, or 1.3 W. However, the KUP can be up to 3 poles. Its current rating is ether 5 or 10 A depending upon the contact material. If the KUP was redesigned for only 1 pole, then it might have a coil power of about 0.43 W. Can you build a comparably reliable relay to the KUP with 1 pole at 0.4 the KUP coil power. My guess is no. Thus, I don't trust the Phoenix specifications.
On leakage current the OPTO 22 0AC5 DC output solid state relay has a spec of 1 mA max at I believe 70 C. Seems low, but might be similar for the Siemens output.
1 mA at 3390 ohms is 3.4 V. But under this operation I doubt 70 C for the Siemens output would be likely. I don't have an easily found 0DC5 to test at room temperature.
panthripu:
Measure the DC resistance of your Phoenix relay coil. Then connect to a Siemens output in the off state. What is the voltage drop across the Phoenix coil. Separately measure the pull-in and drop-out voltages for your Phoenix relay.
.
GeorgeB:
Good find on the relay. After seeing your post I went looking for the Phoenix datasheet. The Phoenix website is very poor as is the datasheet. I did not find the coil resistance. I just found 24 V input and 6 A 250 V on output.
For all:
GeorgeB using your coil resistance coil power input at 24 V is 0.17 W, that is going to be an extremely wimpy relay, and I would never consider such a relay for a 6 A output load capability.
A P&B KUP relay has a coil resistance of 450 ohms at 24 V DC, or 1.3 W. However, the KUP can be up to 3 poles. Its current rating is ether 5 or 10 A depending upon the contact material. If the KUP was redesigned for only 1 pole, then it might have a coil power of about 0.43 W. Can you build a comparably reliable relay to the KUP with 1 pole at 0.4 the KUP coil power. My guess is no. Thus, I don't trust the Phoenix specifications.
On leakage current the OPTO 22 0AC5 DC output solid state relay has a spec of 1 mA max at I believe 70 C. Seems low, but might be similar for the Siemens output.
1 mA at 3390 ohms is 3.4 V. But under this operation I doubt 70 C for the Siemens output would be likely. I don't have an easily found 0DC5 to test at room temperature.
panthripu:
Measure the DC resistance of your Phoenix relay coil. Then connect to a Siemens output in the off state. What is the voltage drop across the Phoenix coil. Separately measure the pull-in and drop-out voltages for your Phoenix relay.
.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
I cheated ... highlighted " PHOENIX CONTACT relays (2961105) ", right clicked and selected search google ... 2nd or 3rd hit was https://www.phoenixcontact.com/online/portal/us?uri=pxc-oc-itemdetail:pid=2961105&library=usen&tab=1
kwired
Electron manager
- Location
- NE Nebraska
First thing is to derermine if you have leakage current keeping the coil energized or if you have a welded contact.
As mentioned additional load in parallel with the coil will lower the leakage current level through the coil. If contact is welding, maybe you need to re-evaluate if this relay is suitable for the load it drives.
ptonsparky
Tom
- Occupation
- EC - retired
I was very surprised with the performance of one relay vs another brand. I checked everything thinking something was wrong with the wiring or a failed component somewhere. Same ratings on the two but brand A just could not handle the load while brand C did fine. The project was done by another EC and his work was good. The choice of relay was not. I now buy other items from that supplier, just not those relays.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
AB makes a similar relay. We use a lot of them. They had a run of them a while back where maybe 1 in 20 was DOA. Have not had much problem with them the last few years. Gave me a bad taste for that style of relay though.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
170409-1324 EDT
panthripu:
Tell us what load the relay is switching --- voltage, current, and nature of the load (resistive, inductive, or capacitive).
.
panthripu:
Tell us what load the relay is switching --- voltage, current, and nature of the load (resistive, inductive, or capacitive).
.
Phoenix relay sticking
So many interesting replies.I googled and came to know that phoenix has some of relay holders which has inbuilt resistance to overcome problem of leakage current. But unfortunately , i am not able to find exact part number. If some one has any idea , please share..
This relay is 24V DC ( coil supply ) and the auxillary contact is feeding to solenoid coil of hydraulic valve. I could find the details on the coil as 24 V/1.2A .
So many interesting replies.I googled and came to know that phoenix has some of relay holders which has inbuilt resistance to overcome problem of leakage current. But unfortunately , i am not able to find exact part number. If some one has any idea , please share..
This relay is 24V DC ( coil supply ) and the auxillary contact is feeding to solenoid coil of hydraulic valve. I could find the details on the coil as 24 V/1.2A .
ptonsparky
Tom
- Occupation
- EC - retired
Try paralleling two or more of your relays or follow gars instructions to diagnose your problem.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
170410-1733 EDT
panthripu:
Do the tests I suggested.
Measure the voltage across the relay coil when only leakage current is present. Report results.
Measure the relay pull-in voltage, and the drop-out voltage. Report back. If you do not know how to do this, then ask and we will describe how.
.
panthripu:
Do the tests I suggested.
Measure the voltage across the relay coil when only leakage current is present. Report results.
Measure the relay pull-in voltage, and the drop-out voltage. Report back. If you do not know how to do this, then ask and we will describe how.
.
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