Potential relay
- Thread starter domnic
- Start date
- Status
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
141017-2134 EDT
Most relays have two states, energized and de-energized.
For two state relays pull-in is the input threshold level where the relay changes to its energized state. Drop-out is the input threshold where the relay returns to its de-energized state. Drop-out must be lower than pull-in or the relay would oscillate at certain input values.
.
Most relays have two states, energized and de-energized.
For two state relays pull-in is the input threshold level where the relay changes to its energized state. Drop-out is the input threshold where the relay returns to its de-energized state. Drop-out must be lower than pull-in or the relay would oscillate at certain input values.
.
- Occupation
- Licensed Electrician
Are we talking about motors here or not?
StarCat
Industrial Engineering Tech
- Location
- Moab, UT USA
- Occupation
- Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
Potential relays
Potential relays
Potential relays are used extensively on Single Phase HVACR Compressors and some pumps I have worked with.
They have a " Normally Closed " set of contacts that connect the start capacitor and start winding, which then " Pick Up" or open to remove the start circuit by " Back EMF across the coil." " Drop out " is when the contacts go back to their N.C. state as Back EMF dissipates and the spring tension on the contacts take over at shutdown.
The " Pick Up " and " Drop Out " voltages are critical and must be absolutely correct for the motor in question or the Start Winding will be damaged. One size does not fit all and substitutions in the field are NOT ok unless you have a cross reference and the voltage parameters are the SAME. Its always best if the start capacitor is equipped with a bleed resistor. This will extend the service life of the PR contacts. Common failures are contacts burned and stuck closed leading to a failure to remove the start winding from the circuit.
I am guessing JRAEF may offer us a more eloquent explanation.
All the best
Potential relays
Potential relays are used extensively on Single Phase HVACR Compressors and some pumps I have worked with.
They have a " Normally Closed " set of contacts that connect the start capacitor and start winding, which then " Pick Up" or open to remove the start circuit by " Back EMF across the coil." " Drop out " is when the contacts go back to their N.C. state as Back EMF dissipates and the spring tension on the contacts take over at shutdown.
The " Pick Up " and " Drop Out " voltages are critical and must be absolutely correct for the motor in question or the Start Winding will be damaged. One size does not fit all and substitutions in the field are NOT ok unless you have a cross reference and the voltage parameters are the SAME. Its always best if the start capacitor is equipped with a bleed resistor. This will extend the service life of the PR contacts. Common failures are contacts burned and stuck closed leading to a failure to remove the start winding from the circuit.
I am guessing JRAEF may offer us a more eloquent explanation.
All the best
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Pick up and drop out is referring to the state of the coil and operating armature, not the state of output contacts.
Pick up is when enough voltage is present to operate the armature, drop out is when voltage is too low to remain holding the armature.
Pick up is when enough voltage is present to operate the armature, drop out is when voltage is too low to remain holding the armature.
Hameedulla-Ekhlas
Senior Member
- Location
- AFG
A perfect explanation is given in this link http://www.actechaids.com/#!the-potentual-start-relay/c1r2z
StarCat
Industrial Engineering Tech
- Location
- Moab, UT USA
- Occupation
- Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
Exellent Point
Exellent Point
This is an excellent technical point and the contact state mirrors it.
Exellent Point
This is an excellent technical point and the contact state mirrors it.
JoeStillman
Senior Member
- Location
- West Chester, PA
Some of the old-style NEMA contactors literally "Pick Up" when the coil is energized. The load contacts move upwards to complete the circuit. When the coil is de-energized, gravity pulls them apart - hence the "Drop Out" stage of operation.
- Status