Echelon SmartServer 2.2 Hardware User Manual
Page 26
You can connect the dry contact relay outputs on the SmartServer to a voltage source and a load.
When an ON value is asserted, the circuit will be closed and the voltage source will drive the load.
The following figure demonstrates this configuration.
5
6
7
8
Resistive Load
Switched DC +
Switched AC Line
DC -
AC Neutral
Voltage
Source
DC +
AC Line
Inductive loads such as motors, relays, or contactors present a special case for the SmartServer relay
contacts. A high voltage known as a back or counter EMF is created across an inductive load when
interrupting the current flow through it due to the change in electromagnetic field. This voltage can often
be in the range of several kV. In the case of inductive DC loads such as relays, use a protection diode
across the load to eliminate the back EMF. In the case of inductive AC loads, use series resistor, capacitor
(RC) snubbers across either the load or contacts to limit the rate of change of voltage and peak voltage
apparent across the contacts. You can also use metal oxide varistors in parallel with RC snubbers to further
limit the peak voltage. The peak voltage across the SmartServer relay contacts must be kept within the
440VAC switching limit.
In addition, switching AC inductive loads can also create further issues due to the radiated differential and
common mode noise created, even when snubbers are used. This noise can potentially cause damage and
interference to adjacent electronics, such as modems. To avoid this effect, use a solid state relay (SSR) to
switch the load where the control voltage for the SSR is supplied through the SmartServer relay. An SSR
still requires a load or contact snubber and overvoltage protection; Crydom
can
supply SSRs with these features integrated into a single package. SSR control currents tend to be quite
small and if necessary to keep within the minimum switching current of the relay contacts, a parallel
resistive load must be used if the control load for the SmartServer output is less than 5V at 100mA .
The following figure demonstrates this configuration.
14
Assembling the SmartServer Hardware