Make relays hold position during UPS Switch-over.

[JohnLoves2Ski]

I have a UPS providing 120Vac to a transformer which converts it to 24VAC. This 24Vac circuit powers several Idec relays (50-80mA coil current each).
I expected them to stay in position when power goes out since it's on UPS, but I failed to recognize that the UPS I am using has a .004 second switchover time.
Is there a simple circuit method of holding this 24V AC voltage for a fraction of a second, so it will ride through a minor power interruption while the UPS switches?

I do HVAC PLC work primarily, and my electronics knowledge level is low.
I would really like to find an inexpensive solution that doesn't require me to purchase (7) new dual conversion UPS's @ $550 each... Can you help?
Thank in advance!
John

 

[Skogsgurra]

Dave, I think that you need to experiment a great deal yourself before you suggest unrealistic solutions to others.

The problem has been addressed more than seventy years ago. It then involved a diode, a capacitor, a resistor and an NC auxiliary contact with late breaking.

The NC Contact allowed enough current for the coil to pull in the core. When the NC contact opened, the resistor was connected in series with the coil to prevent it to overheat and at the same time provide enough current to seal the core in.

I think that the arrangement was Siemens K915 with a special suffix.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[LionelHutz]

The second paper briefly discusses the myth of needing zero switchover time.

I have had issues with a switching UPS like the OP is using causing chatter on a 600A vacuum contactor. The contactor uses rectified AC to power the DC coils and is supposed to have a 90mS average opening time.

I always insist on a UPS that has seamless transfer for AC control circuit backup.

 

[ScottyUK]

4ms isn't bad for a static switch, but a proper double-conversion UPS shouldn't need one unless the inverter fails. APC's bottom-end designs give a false sense of security and take advantage of their typical pc load to cover the weakness in their own performance.