Losing Relays

[califflash]

Just a follow up on this problem. I changed to omoron 10 amp relays with snubbers for the motorized valves. Everything has been working like a top for the last several days. It appears to have been a duty cycle issue as many relays could be removed for about 30 minutes then replaced and start working again, at least until the coils gave out. It was unusual that some would stick closed though. Although I suppose there could have been some mild arc welding although I saw no evidence of that.

I'm glad I got this figured out this system is saving my plant 20k-80k gallons of water per run day. Other than this nagging issue I thrilled how well it works

 

[sbaum]

You mentioned the LED indicator on the isolating relays was dimly light.

It sounds to me like there is leakage current from the transistor outputs of the Micro830.

Next time go for the 700-HLT1L24 instead of the 700-HLT1U24. The relay is double the price but has a built-in leakage suppression circuit. I use these often for 2-wire prox switches.

I also agree with the rest a larger relay is better for an inductive load, but given the coils are burning, I believe this is the issue.

 

[califflash]

the leakage current was an issue with my installation of the PLC. The plc utilizes both +com and -com. I did not have the -com connected therefore the output could not bleed off current and caused a leakage issue with the relays. I believed originally that this leakage merely damaged the coil so I replaced the relays. After that point, I realized there was another issue since they kept going out.

 

[Genman]

You need to install a mov across each coil to hold the voltage spike to a minimum when the coil is turned off... simple as that. That spike voltage is not only damaging to the contacts on the relays but just about any other kind of electronics it can get to.

 

[JesperMP]

I realise it is an old thread, but I wont to state that I disagree with that it is sufficient to use a transient suppressor over the motor coil.
Better than not having it, but not a genuine solution.
For any inductive load, dont fiddle about with relays and transient supressors etc. go for a real contactor sized for the load.
If you are worried about the space needed for the contactors, then take a look at this one. Schneider LC1SK0600P7 2-pole contactor w. 230V coil, integral transient suppressor over the coil and rated for 6A AC1/AC3. Only 27 mm wide :

In my old job we used to have never-ending problems with small motorised actuators. We fiddled with relays, transient snubbers, "heavy-duty" relays, with no improvement. We finally decided to go for real contactors, and I found these small ones that could be in the same space as the relays, and the problems went away.

 

[Lancie1]

For any inductive load, dont fiddle about with relays and transient supressors etc. go for a real contactor sized for the load.

Right, relays are made to relay signals, and contactors are made to contact power conductors.