DAM-2 Outputs with Small AC Load Current

Background:

The DAM-2 relay channels have snubber circuits for controlling the voltage of any spikes that may occur due to switching inductive loads (e.g., solenoid valves). During a voltage transient, the snubber circuit begins conducting to equalize the voltage between the lines.  However, this also happens during normal voltage transients, such as the voltage variation for AC power or when a DC power source is turned on.  For large loads, this is typically not an issue because the amount of leakage current is small (on the order of 5 mA), so there is no change in behavior.  But for some small loads (digital input circuits, LEDs, or an audible alarm), this leakage current when the relay is open can cause the device to respond.

This picture shows a summary of what is going on in the snubber circuit:
Note that in the picture above, everything except the relay is located on the wiring hub.
The DAM-2 outputs have a snubber from the common, COM, to the normally closed, NC, and normally opened, NO contact. In the situation where AC is being switched, the snubber can permit up to 5 milliamps AC to flow to the load. If only a neon light, LED, or other load that draws current is attached, the device may be energized.

Cap / Resistor Solution:

A relatively small solution to switching small loads (i.e. you don’t need a big power resistors) would be to place a 2.2uF, such as the one below, across the inputs to the LED. In previous testing this knocked down the input voltage caused by the leakage from 80 VAC to about 8 VAC and solved the issue.   There should be a 10 ohm 1/2 watt wire wound resistor in series with the cap to limit peak surge current when the relay actually does turn on.

Here is a suitable capacitor taken from the Digikey Catalog.

A source for the resistor will need to be selected.

The visual indicator affected by the leakage current should have the series capacitor and resistor added as shown here:

Another option would be to use the DAM-3 solid state relay module, which has much smaller leakage current:

DAM-3 (module) DC leakage at 180VDC < 1 uA

DAM-3 wiring hub AC leakage at 134VAC is 12 uA rms and for the module is 22 uA rms.