help with voltage spike suppression for my circuit

[johntee65]

Hi folks. The attached schematic shows my Room Access Control system. The RFID reader determines if access to the room should be granted, and if so, completes the circuit to the 782XBX relay for 5-seconds; the relay turns on power to an AC transformer to power the electric door strike (unlocking the door) for 5-seconds, and also to a Timer Relay that lights up the room for a 10-minute period after the relay signal ends.

My question is about the need for spike suppression on the 120VAC parts of the system, including the AC Transformer and a mix of fluorescent and incandescent light fixtures. When the power is cut by the Access Control unit, how do I protect the system from transient voltage spikes, wherever they might occur?

(I confess, I have no real clue on these spikes or how to protect against them, so specific part numbers that I could locate for purchase would be great! And where would they be located in the 120VAC line?)

Thanks for your help/thoughts!
John


Relays:
--- 782XBXM4L-12D Magnecraft Electromechanical Relay, "Ice-Cube" Style, 16A DPDT, 12VDC Coil (added a 1N4004 diode)
--- Time-Delay Relay to feed 120VAC lighting circuit: 822TD10H-UNI Magnecraft 10 Function Programmable Time Delay Relay, 15A DPDT, Universal Coil Voltage 12 - 240 VAC/VDC (Solid-state, so no need for an external diode.)
--- Transformer: Primary is a 120VAC line, secondary is 24VAC, 20 Watts).
--- Lights: Mix of incandescent (2x60W) and fluorescent (probably 1-2 banks of four T12 48" bulbs)

 

[itsmoked]

Look up MOV.

Metal Oxide Varistor

You can put them across the relay contacts.

You could also put an 'X' cap across the power or a standard HV rated cap across the contacts.

Keith Cress
kcress -

http://www.flaminsystems.com