The RFC-1 control relays provide a momentary contact when energized. The length of the contact closure is adjustable from 0.3 to 4.8 through a software setting at address 1006. This setting is global--it effects both the raise and lower relays on all channels. There is no built-in provision for latching relays on the RFC-1. The hardware architecture simply does not allow it.
Nevertheless, there are applications that require the use of a maintained contact. In those instances an outboard latching relay is suggested. Relay selection will depend on many factors: the voltage and current of the device that is being controlled, the coil voltage, mounting options, footprint, etc. There are literally hundreds if not thousands of variations. In general, a relay from any reputable manufacturer should work fine as long as the appropriate relay is selected for the task.
It is impossible to suggest a specific relay that is appropriate for every installation. But we can make a few suggestions to assist in the selection process.
A relay with dual coils is easier to connect to the RFC-1 than one with a single coil. Single coil relays often require a polarity reversal to toggle the relay contacts. With a dual coil relay, one coil can be connected to the "raise/on" control relay of the RFC-1 and the other can be connected to the "lower/off" control relay. Connections are straight forward: use the common (COM) and normally open (NO) connections of two control relays on the RP-8 to switch a low voltage control signal--one control relay will operate each coil of the latching relay. Make the connections so that the latching relay operation is consistent with the on/off behavior of other channels so that operation is intuitive.
The choice of control voltage, contact ratings and mounting options can be tailored to the application as long as the control voltage is within the contact ratings of the RFC-1 control relays (typically these contacts are rated for 5A @ 30VDC or 5A @ 125VAC for resistive type loads).
Here are some links to some of the more common latching relay manufacturers and possible sources. Most of the manufacturer web sites have excellent search tools to help narrow the selection. This list is by no means exhaustive.
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