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TB206 Rev4 How to use QuenchArcs aka Snubbers for Noise Suppression
Overview
Snubbers aka Quench Arcs prevent Noise problems created by coils CNC control cabinet building basics
QuenchArcs should be installed across ANY inductive load that includes relay coils fans transformers solenoid valves and
anything with a coil of wire in it This document describes where to properly install snubbers to suppress electrical noise being
generated by an inductive load which can produce false inputs and errors in a CNC control
Installing Snubbers is required on the following components
β’ all contactor coils
β’ 3 phase motors and pumps that are operated by a contactor i e carousel & swing arm motors flood & lube pumps and chip
conveyors
β’ single phase lube pumps
β’ holding brake coils for motors
β’ air solenoid valves
Installing Arc Suppressor/Snubber Network
Snubbers are essentially an insurance against electrical noise Snubbers are typically a circuit containing a resistor in series with a
capacitor Centroid recommends using the 0 1uF 100 ohm 600V rated Quencharc snubber
https //shopcentroidcnc com/shop/cnc accessories/quencharc aka snubbers/
Picture 1 Pakron Quencharc Suppressor Centroid PN 1819
Use one snubber for each and every contactor coils single phase motors and ALL solenoid coils air or hydraulic Item Description SNUBBER CAP 1 UFD WITH BUILT IN 100 OHM RES
QUENCharc
Centroid PN 1819
Manufacturer Part Number 104M06QC100
Seen on all Centroid Hookup schematics this symbol is the Snubber
Typical Estop contactor with snubber
Typical Flood contactor with snubber any contactor!
Examples
Examples
When using DC voltages an alternative to a QuenhArc is a βFlyBackβ diode Either will work with DC Voltages do
not use flyback diode when AC voltages
Example of a Solenoid valve coil that has a built in snubber check your part number spec sheet to make sure the solenoid has a
snubber built in if not install an external snubber
Quencharc assembly for 3 Phase motor Centroid PN 12610
Use three snubbers for three phase motors
WARNING not for AC or DC servo motors! nor inverter driven motors
There are alternative manufacture of QuenchArc below is an example of a Fotek unit that contains three snubbers in one for AC
motor coils
Fotek Suppressor a 0 12uF 47 ohm 550V Fotek snubber will also work fine
Note Any motor that is commanded by a VFD drive rather than a contactor IS NOT REQUIRED to have a snubber installed on its
phases
Snubbers can be installed on the contactor terminals but are NOT as effective
Picture 4 Snubber installed on swing arm ATC drive motor
Tool changer carousel motors have been found to be especially noisy! So be sure to get some snubbers on them
Every contactor MUST have its own snubber installed across its relay coil as shown in Picture 5 Just because there is a snubber
installed across the contactor's coil DOES NOT give a valid reason to not install a snubber across the motor
Picture 5 Snubber installed on contactor coil
Picture 6 Wire diagrams of snubber installation
Picture 7 Diagram showing snubber installed across air valve/solenoid/coil
Discussion Flyback vs QuenchArc for DC use
When using DC circuits typical on air and hydraulics you can use a quench arc OR a fly back diode
QuenchArc
Advantages Works in both AC and DC circuits
Reduces high frequency ringing and EMI electromagnetic interference
Allows faster solenoid release compared to a flyback diode
Disadvantages More expensive than a flyback diode
Requires careful selection of RC values to match the solenoid and circuit characteristics
May dissipate more power during operation especially in high frequency applications
Example components Typical snubber values 100Ξ© resistor in series with a 0 1Β΅F capacitor adjust based on solenoid inductance
and switching frequency
Use non polarized capacitors for AC circuits
Key Considerations for ChoosingCircuit Type DC Use a flyback diode unless fast release or high frequency switching is needed
AC Use a snubber as diodes are not suitable
Flyback Diode A flyback diode also called a freewheeling diode is a single diode placed in parallel with the solenoid oriented to
conduct in the opposite direction of the solenoid's normal current flow ONLY WORKS WITH DC It provides a low resistance path for
the inductive kickback current when the solenoid is de energized dissipating the energy stored in the solenoidβs magnetic field
When to use a flyback diode DC circuits Flyback diodes are typically used in DC circuits where a solenoid is controlled by a switch
or transistor e g in relays solenoids or motors driven by DC
Simple and low cost protection If you need a straightforward inexpensive solution to suppress voltage spikes a flyback diode is
ideal
Low frequency switching Flyback diodes work well when the solenoid is switched on and off at low frequencies e g <1 kHz as
they donβt significantly affect switching speed
Minimal impact on solenoid release time If the solenoidβs release time how quickly it de energizes is not critical a flyback diode is
suitable though it may slightly slow the release due to the current decay through the diode
Flyback Diode for DC Advantages Simple and cheap
Effective at clamping voltage spikes to a low level typically the diodeβs forward voltage ~0 7V for a silicon diode
Easy to implement in DC circuits
Disadvantages Slows solenoid release time slightly due to the diode maintaining current flow
Not suitable for AC circuits diodes conduct only in one direction
Example components 1N4007 or 1N5408 for general purpose solenoids
Schottky diodes e g 1N5819 for faster response and lower voltage drop
Cost and Complexity Flyback diode Cheaper and simpler
Snubber More expensive and requires tuning R and C values depend on solenoid inductance and switching characteristics
Practical ExampleDC solenoid in a relay circuit e g 12V DC low frequency switching Use a flyback diode like a 1N4007 across
the solenoid to protect the driving transistor
AC solenoid in an industrial valve e g 120V AC 60 Hz Use an RC snubber e g 100Ξ© + 0 1Β΅F to suppress voltage spikes and
reduce EMI
PWM controlled solenoid e g 24V DC 10 kHz switching Use a snubber to manage high frequency transients and ensure fast
response or combine a diode with a snubber for optimal protection
Design NotesFlyback diode Place the diode as close as possible to the solenoid terminals with the cathode connected to the
positive side of the solenoid and the anode to the negative side
Snubber Calculate RC values based on solenoid inductance L and switching frequency A rough starting point is R=L/CR = \
sqrt{L/C}R = \sqrt{L/C}
and C=0 1β1Β΅FC = 0 1β1Β΅FC = 0 1β1Β΅F
but simulation or testing is recommended
Combination In some cases e g high frequency DC circuits you can use both a flyback diode to clamp the initial spike and a
snubber to dampen ringing
Document History
Rev4 Created by 387 10 3 25
Rev3 Created on 2016 08 11 by #391
Rev2 Created on 2011 11 16 by #240
Rev1 Created on 2011 11 16 by #240