timer relay woes

[diat150]

I feel stupid having to ask something like this... but I am running into an issue using timer relays to temporarily turn on a red lion g07c000 touchscreen. Its a solar application and I dont want to keep the touchscreen on unless someone pushes a pushbutton to let it run 5-10 minutes. The issue I am having is the timer relays keep getting stuck with the touchscreen on.



I have used 2 different timer relays:


https://www.alliedelec.com/product/schneider-electric-legacy-relays/tdrpro-5101/70185221/


https://www.grainger.com/product/23...ucid=N:N:PS:Paid:GGL:CSM-2294:PSN7SY:20500731


I dont understand. It will work fine for a while, then then relay gets stuck. any ideas? This is really making me pull my hair out. I have dome this sort of thing with a plc output many times with no issue.

 

[drbitboy]

How is it wired?

Which delay function is being used?

 

[drbitboy]

Assuming the INTERVAL timer function is used e.g. from the Allied datasheet:





I would think summat like this (i.e. as physical wiring, not ladder) would work, with U as a momentary contact:

    U                                    Display_On
---] [---+----[Timer  R]---+---/\/\/\/------( )----
         ^                 |
         |                 v
         +<----------------+

Update I: added resistor to apply @Drew's idea about leakage current.


Update II: moved resistor to the right place .




P.S. For that matter, couldn't this be done with a few appropriately-sized capacitors, resistors and transistors? It would cost more in time to build than one of these generic timers, but it should work, no?

 

[Drew Ethridge]

Could it be leakage current on your output. Back in olden days using AC outputs we would run into problems turning off relays. There wasn't enough leakage current to turn on the relay but there was enough to hold it on once it was turned on.

 

[I_Automation]

I would have the timer control an interposing electro-mechanical relay and that relay turn on the power to the HMI. And not a ice-cube relay, but an octal base relay.

I have seen solenoids and relays stay on with a trickle current that only provided 3.5 volts after dropping the 24V.

 

[diat150]

How is it wired?

Which delay function is being used?

it is using one shot mode. constant power to to the timer coil, and then power to the hmi is wired thru the relay common and relay NO contact. When the external control switch contacts are closed, then the timer starts and the relay closes, and then times out based on the preset of 5 minutes.

 

[diat150]

Could it be leakage current on your output. Back in olden days using AC outputs we would run into problems turning off relays. There wasn't enough leakage current to turn on the relay but there was enough to hold it on once it was turned on.

yeah ive seen that but that is usally on PLC outputs. If this timer relay is leaking current and keeping the timer contacts closed when they shouldnt be then it defeats the purpose of having the timer relay.

 

[diat150]

I would have the timer control an interposing electro-mechanical relay and that relay turn on the power to the HMI. And not a ice-cube relay, but an octal base relay.

I have seen solenoids and relays stay on with a trickle current that only provided 3.5 volts after dropping the 24V.

Im thinking about trying that but the schneider has a mechanical relay inside. The timer relay is showing that it timed out and the mechanical relay inside of the timer is staying closed. I guess my thought process is would it be worse to put an interposing relay because that relay would pull virtually nothing across the contact of the timer relay vs the hmi?

 

[OkiePC]

The HMI only takes 7-8 watts, so at 24vdc that's 1/3A. Even though it is DC, the 12A relay rating of the timer contact should not weld trying to break 300mA of DC power. If it is 12vdc that is still only around 600mA. Maybe a flyback diode across the relay contact can help?

 

[drbitboy]

The timer relay is showing that it timed out and the mechanical relay inside of the timer is staying closed.

wow, I'd contact Schneider, if it is not behaving as advertised then it is broken or there is some subtle configuration out of whack; either way they should be willing to help.

 

[diat150]

wow, I'd contact Schneider, if it is not behaving as advertised then it is broken or there is some subtle configuration out of whack; either way they should be willing to help.

its done it with 2 different relays from different manufacturers

 

[drbitboy]

Try taking as much as possible of your circuit out of the mix e.g. check the relay with an Ohm-meter And the timing with a much shorter timeout?

 

[chelton]

The HMI only takes 7-8 watts, so at 24vdc that's 1/3A.

7-8 watts with the display on. Would it be possible if the display turns "off" that power consumption drops below 100mA ?

The specs for the timing relay require minimum switching requirement of 100mA

 

[diat150]

7-8 watts with the display on. Would it be possible if the display turns "off" that power consumption drops below 100mA ?

The specs for the timing relay require minimum switching requirement of 100mA

if you mean the display going into a rest or sleeping state, that isnt setup so the display always stays lit.

 

[osmanmom]

use non continues power to timer