SCR Contactors for Resistance Welding

Undoubtedly the most popular resistance welding contactor for the past twenty years are Darrah's direct water cooled SCR Contactors. The selections shown are in stock in welding current ratings to 3996 Amps RMS at 50% duty cycle. Choose between single or double sided cooled, and in SCR voltages to 2600 Volts. These are the workhorse in medium to heavy KVA welding controllers. Mounting bases and bus bar connections are identical throughout the series therefore offering flexibility and conformity from 15 KVA through 600 KVA designs.

Darrah Part Number	Welding Rating Amps RMS at 50% duty cycle	Welding Rating Amps RMS at 100% duty cycle	SCR voltage rating (PIV) (VRRM)	Water Cooled SGL DBL
D09ST15 D09ST18	900 900	400 400	1500 1800	X X	- -
D13DT15 D13DT18	1300 1300	695 695	1500 1800	- -	X X
D13SE18 D13SE20	1300 1300	695 695	1800 2000	X X	- -
D18DE18 D18DE20	1800 1800	970 970	1800 2000	- -	X X
D21DM18 D21DM20 D21DM26	2100 2100 2100	1225 1225 1225	1800 2000 2600	- - -	X X X
D26DN18 D26DN20	2600 2600	1710 1710	1800 2000	- -	X X
D32DN18 D32DN20 D32DN26	3200 3200 3200	2075 2075 2075	1800 2000 2100	- - -	X X X
D40DD18 D40DD26	3996 2230	2188 1946	1800 2600	- -	X X

Water Requirements: Amps RMS is achieved with a cooling flow rate of 1.2 gallons (4.5 liters) per minute at 40°C water temperature

Water Connections: Fits 3/8 inch hoses

Thermostat: If required add suffix J to part number

MOV: For MOV add suffix M to part number

Example: 13DT15JM, 1300 Amps RMS, 1500 Volt, with thermostat and MOV.

Click to enlarge diagrams


D09ST & D13SE SERIES SINGLE SIDED DIRECT WATER COOLED	D21DM & D26DN SERIES DOUBLE SIDED DIRECT WATER COOLED
D13DT & D18DE SERIES DOUBLE SIDED DIRECT WATER COOLED	D32DN20J SERIES DOUBLE SIDED DIRECT WATER COOLED

Darrah HS-6 design direct double sided cooled SCR Contactors have proven to be dependable for years in resistance welding controllers.
Choose between two popular current ratings with SCR voltages to 1800 Volts.
Darrah's HS-6 design switches are available with either 3/8 " or 1/2" water hose connections. As always, thermostats, MOV's and R/C snubbers are easily added.

Darrah Part Number	Welding Rating Amps RMS at 50% Duty Cycle	Welding Rating Amps RMS at 100% Duty Cycle	SGL. Cycle Surge Current (ITSM)	SCR Voltage Rating (PIV) (VRRM)
DO8HS6-16	1200	800	5500	1600
D12HS6-18	1800	1200	7500	1800

DO8HS6 & D12HS6 TYPES
DOUBLE SIDED
DIRECT WATER COOLED

This series is also popular for frequency converters, seam, and flash butt welding duty cycles.

Bus tang connections are standardized to fit all applications.

Four holes plus center slot. Holes are on 1.06" centers. The center slot is .5" x .75"

Darrah Part Number	Welding Rating Amps RMS at 100% Duty Cycle	SGL. Cycle Surge Current (ITSM)	SCR Voltage Rating (PIV) (VRRM)
DPH7825-468	1200	10000	2600
DPH7844-468	1700	10000	2600
DPH7845-468	1750	18000	2600
DPH7824-468	2500	18000	2600

DPH7824 SERIES
DIRECT WATER COOLED
AUTOMOTIVE STYLE

Darrah's Heavy Duty Contactor ranks as the largest found in the resistance welding industry. Capable of welding current ratings of 8972 Amps at 10% duty cycle, the DPH7847-470 delivers 5144 Amps continuously. This contactor is in Darrah's inventory with 2200 Volt rated SCR's. This is truly the choice for heavy seam and flash butt welder controls.

Darrah offers the resistance welding industry our line of indirect water cooled Contactors. Indirect water cooling refers to SCR Contactors that isolate the welding voltage from the water cooling.

These switches are manufactured in such a way that once installed in a controller, if servicing is required, the contactor is disassembled with a simple allen wrench. The SCR puck assembly can be removed, leaving the water cooled chill block intact, thus eliminating any need to disconnect or reconnect any water lines. The puck assemblies can be replaced or repaired within minutes of a failure with simple tools. Since the puck assemblies are pre-assembled, there is no need to be concerned about special torquing or mounting techniques.

Darrah currently offers three types of indirect water cooled SCR Contactors. All three types have the same water cooled chill block, but offer different bus tang or power connections.

Another advantage of Darrah's line of indirect water cooled SCR Contactors is that the chill blocks are isolated from the AC line power. Contactors can be mounted directly to the side of the control cabinet, therefore eliminating the need for lengthy hoses in your enclosures.

Darrah Part Number	Welding Rating Amps RMS at 50% duty cycle	Welding Rating Amps RMS at 100% duty cycle	SGL. Cycle surge current (ITSM)	SCR Voltage rating (PIV) (VRRM)	Bus Tang Type
DEC12ISM18-J	1100	600	10000	1800	STRAIGHT
DEC14ISM-18J	1100	600	10000	1800	1 Straight, 1 90° bend
DEC17ISM-18J	1100	600	10000	1800	both 90° bend

DEC14ISM - 18J
INDIRECT WATER COOLED

DEC17SM SERIES SINGLE SIDED
INDIRECT WATER COOLED

For Three Phase controls, dual or three cascade controls, Darrah offers its line of indirect water cooled contactors mounted on a triple chill block. Choose from either of the three bus tang connections and have Darrah mount them on our specially designed triple heat sink. This means one pair of water connections cools three contactors.

Darrah's Tri-pack design is compact, thus eliminating bulky cabinets and excessive water connections.

For lighter KVA systems, Darrah provides Isolated Tri-Pack Module Assemblies. A single water connection provides cooling for three SCR Contactors in a small convenient package.

Choose between 500 Amp or 1000 Amp RMS rated SCR Modules.

Bus bars, thermostat and MOV's are included.

This product line features industry standard dual SCR modules with integral water cooled bases. Our improved design has eliminated thermal barriers associated with separate cooling bases. This has increased current ratings by as much as 15%. In addition, because the water connections are directly tapped to the module base, water leaks are virtually eliminated. To further enhance water integrity, each unit is 100% pressure tested at 150 psi for one minute.

Another significant feature is that the modules are vacuum filled with a high performance, flame retardant silicone -based material at final assembly which eliminates hidden voids inside the package and prevents dust and dirt from penetrating which may cause premature failure.

Darrah's integral water cooled modules are available in three popular packages.

Darrah Part Number Welding Rating
Amps RMS at 10% Duty Cycle Welding Rating
Amps RMS at 50% Duty Cycle Welding Rating
Amps RMS at 100% Duty Cycle SCR Voltage Rating (PIV) (VRRM) Water Connection Location Package Design

Q20001 1592 1278 717 1800V Side
1-1/2' Centers MP03

Q20002 1592 1278 717 1800V Bottom
1-1/2' Centers MP03

Q20003 1592 1278 717 1800V Side 2" Centers MP03

Q20006 1592 1278 717 1800V Side
1-1/2' Centers MP03

Q20008 1068 755 450 1800V Side 2" Centers MP02

Q20009 1068 755 450 1800V Bottom
2' Centers MP02

Q20011 2797 1522 1097 1800V Side
1-1/2' Centers MP04

Q20012 2797 1522 1097 1800V Bottom
1-1/2' Centers MP04

Q20013 2797 1522 1097 1800V Side 2" Centers MP04

Water requirements: Amps RMS is achieved with a cooling flow rate of 1.2 gallons (4.5 liter) per minute at 40° water temperature

Water connections: 1/4-18 NPT tapped holes

Thermostat: All modules are supplied with an accelerated thermostat sensor, 50°C open on rise and isolated to base 2000 Volts. Thermostat leads are 24 inches long.

Options include: R/C Snubber, MOV's and bus bars.

MP02 Package Design
Q20008 Shown
MP03 Package Design
Shown Q20002

MP04 Package Design
Shown Q20011