DC Motor Reversing Circuit
Description:
A DC motor reversing circuit using non latching push button switches. Relays
control forward, stop and reverse action, and the motor cannot be switched from
forward to reverse unless the stop switch is pressed first.
Notes:
At first glance this may look over-complicated, but this is simply because three
non-latching push button switches are used. When the forward button is pressed
and released the motor will run continuously in one direction. The Stop button
must be used before pressing the reverse button. The reverse button will cause
the motor to run continuously in the opposite direction, or until the stop
button is used. Putting a motor straight into reverse would be quite dangerous,
because when running a motor develops a back emf voltage which would add to
current flow in the opposite direction and probably cause arcing of the relay
contacts. This circuit has a built-in safeguard against that condition.
Circuit Operation:
Assume that the motor is not running and that all relays are unenergized. When
the forward button is pressed, a positive battery is applied via the NC contacts
of B1 to the coil of relay RA/2. This will operate as the return path is via the
NC contacts of D1. Relay RA/2 will operate. Contacts A1 maintain power to the
relay even though the forward button is released. Contacts A2 apply power to the
motor which will now run continuously in one direction. If now the reverse
button is pressed, nothing happens because the positive supply for the switch is
fed via the NC contact A1, which is now open because Relay RA/2 is energized. To
Stop the motor the Stop switch is pressed, Relay D operates and its contact D1
breaks the power to relays A and B, (only Relay A is operated at the moment). If
the reverse switch is now pressed and released. Relay B operates via NC contact
A1 and NC contact D1. Contact B1 closes and maintains power so that the relay is
now latched, even when the reverse switch is opened. Relay RC/2 will also be
energized and latched. Contact B2 applies power to the motor but as contacts C1
and C2 have changed position, the motor will now run continuously in the
opposite direction. Pressing the forward button has no effect as power to this
switch is broken via the now open NC contact B1. If the stop button is now
pressed. Relay D energizes, its contact D1 breaks power to relay B, which in
turn breaks power to relay C via the NO contact of B1 and of course the motor
will stop. All very easy. The capacitor across relay D is there to make sure
that relay D will operate at least longer than the time relays A,B and C take to
release.
Title: DC Motor Reversing Circuit
electronic circuit
Source: www.electronics-lab.com
Published on: 2005-02-03
Reads: 1388
Print version:
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