TIme Delay Switch

[ShaneA]

Hello, I have a 12VDC battery bus where I charge with solar PV and a wind turbine. The system is controlled using a Siemens PLC. When there is a system fault, the PLC will open all relays, but this included relays that power the PLC itself (example an emergency pushbutton). When restarting the system (Black start), I need a way to temporarily connect the batter bus to the Inverter that powers the PLC. the current upon start up I believe will be as high as 30A, so I am looking for a solution that will allow about 50A to pass for about 5mons, and then automatically switch it self off. I am currently achieving this using a manual breaker, but the risk is someone forgets to switch off the breaker. Can anyone recommend a time delay switch that can work here (max 150VDC, 50Amps)? I am trying google but not really getting anywhere. I suspect there are existing electrical systems that have a similar black start requiement.

 

[marconi]

https://www.albrightinternational.com/product_family/low-voltage-stud/

Push-Button Switches | Rapid Online - https://www.rapidonline.com/Push-Button-Switches

The first link is to a maker supplier of heavy duty dc contactors. I leave it to you to select a suitable SPST device with appropriate coil voltage.

I assume '5 mons' is 5 minutes. This timer-relay can be set to provide a 5 minutes on pulse after receiving a control pulse from a normally open push button:

RS PRO Off Pulse, ON Pulse with Control Switch, ON Pulse without Control Switch, On-Off Pulse Multi Function Time Delay | RS Components - https://uk.rs-online.com/web/p/timer-relays/1617612/

This timer-relay (see above) will repeat the sequence every time the control push button is pressed.

If you do not want that to happen once the PLC has powered up then you will have to arrange for this circuitry (ie the push, timer-relay and dc contactor) to be inhibited until another shut-down has occurred. This could be done by another simple relay sensing the state of the system (viz operational or shut down/fault - an output from the PLC or inverter?) whose NC contacts are used in the inhibition role I mentioned earlier - in series with the dc supply to the contactor coil and push button for example. Or we could look at another timer-relay which has a one-shot mode.

If you want I will look over what you propose as a solution.

 

[snowhead]

A couple of observations,

The PLC is loosing power when there is a fault.
What's the cause of the fault(s) and how often are they?
It might be simpler to overcome the faults than to have to keep restarting (regularly?)

Second, it seems unusual that the PLC is powered from the circuit(s) it controls.
Is this a standard system supplied by a manufacturer or a one off put together just for this system?

Are there any circuit diagrams for it?

Additional thought, this must be off grid and the only 240ac is from the inverter?
If so maybe the PLC needs it's own control cct inverter.

 

[Lucien Nunes]

If the PLC can turn the inverter off, surely it already has a power contactor or logic control input, and the black start override only needs to operate that, not carry the whole inverter current?

And yes, it would seem better to power the PLC separately so that ordinary fault scenarios don't shut it down.

 

[marconi]

ShaneA: it would be nice to see a sketch/pictures/diagram of the system 'to tickle our fancy' and understand better your problem. Perhaps you might elaborate?



Marconi