when enclosing low
voltage wires and
with high voltage
connections in the
insulated with heat
shrink tubing and
electrical tape. Be
sure all high
voltage and low
voltage wires are
each other as
much as possible.
Being cautious cannot be over-emphasized when dealing
with these higher voltages and currents.
Another great device for controlling higher voltage
and current AC and DC loads is the EM relay; see Photos
9, 10, and 11. This particular relay is available from
www.jamco.com for about $6 and the relay socket for
another $5. The EM relay can really be broken into two
parts: the coil used to control the relay, and the contacts
that are controlled by that coil. Relay coils are usually
constructed to be energized by either DC or AC voltages
(usually not both), and can be designed to operate at
voltages such as: 6V, 12V, 24V, and 120V. As you can see
in Photo 12, this relay has a 12V DC coil.
This coil has a DC resistance of 156 ohms and would
therefore draw 12V / 156 ohms = 77 mA. This, of course,
cannot be driven directly by the 3.3V LVTTL 4 mA outputs
of the MyRIO unit. Probably the easiest way to solve this
problem is to drive the coil with a DC SSR. This may seem
like duplication until you look at the contact ratings and
configuration of the relay; refer to Photos 9 and 10.
This relay’s contacts are configured as a DPDT
(double pole double throw; six terminals)
switch; probably the most common type of
relay contact configuration you will find.
The SSRs can only operate as SPST (single
PHOTO 10. PHOTO 11.
48 February 2017