Latching Circuit Example

[Redskinsdb21]

Attached is a motor control circuit...with latching. I have a question about how it works. If I push the forward button...the M1 auxiliary contact will close...energizing coil M1...but what happens to normally closed M2 contact when I pust forward button? Does it open? If so would this not keep motor from running?

 

[bobadrew]

When the forward button is pressed, the coil M1 pulls in and then contact M1 closes and seals in the circuit. The forward button is momentary and does not stay closed or latched.

The normally closed M2 does not change state because coil M2 has not pulled in.

The normally closed M1 and M2 contacts are in the circuits as interlocks.

 

[Redskinsdb21]

WHAT IS THE PURPOSE OF THE INTERLOCKS? Also, does thie mean, when normally open contact M1 closes that normally closed, contact M1 on the reverse rung opens?

Thanks!

 

[mevans154]

The purpose of the interlocks is that the motor can only be energized either in the forward direction or only energized in the reverse direction at any given time. Actually the schematic shown is not a functional circuit. When the forward button is pressed, the M1 contactor (relay) is energized causing the normally open contact to latch (seal) the circuit. With M1 energized, the normally closed M1 contact opens and inhibits M2 from being energized. What turns off M1?? The way the circuit is drawn, the only way to de-energize M1 is to have the overload (O/L) contact open. Typically there should be a normally closed "Stop Switch" in series with the interlock relay contact. This way the Stop Switch can de-energize M1 so that M2 can be energized.

Normally open contacts close when the contractor (relay) coil is energized

Normally closed contacts open when the contactor (relay) coil is energized.

Hope this helps!

 

[bobadrew]

mevans is correct, there is no way to deenergize the circuit!

All of the contacts associated with a relay will change state when it is energized. A normally open closes; a normally closed opens.

 

[Redskinsdb21]

tHANKS FOR CLEARING IT UP FOR ME gENTLEMAN.