2. Product Introduction

2.1. Key Features

The WRx Series MagnaLOAD DC electronic load is available in power levels of 12.5 kW, 25 kW, 50 kW, 75 kW, and 100 kW. The 12.5 kW models come in a 4U rack-mount package, while the 25 kW to 100 kW models come in various stand-alone cabinets. Each power level has three models, with a wide voltage-current operating profile where full power can be achieved. The key features of the MagnaLOAD electronic load are as follows:

Product Features

  • MagnaLINK™ distributed DSP architecture
  • 16-bit programming and monitoring resolution
  • Voltage, current, power, resistance, rheostat, and shunt regulator control modes
  • Various diagnostics and protection features, including: over voltage trip, under voltage trip, over current trip, over power trip and over resistance trip.
  • Front and rear panel USB (host), RS485, MagnaLINK™ IN and OUT ports
  • Configurable 25-pin analog-digital External User I/O port
  • Designed and manufactured in the USA

2.2. Models

The following tables list the available models in the WRx Series MagnaLOAD DC electronic load.

2.2.1. Model Ordering Guide

The following ordering guide defines how an WRx Series MagnaLOAD DC electronic load is defined:


Fig. 2.1 WRx Series MagnaLOAD DC electronic load Model Ordering Guide

2.2.2. WRx Series Models

Model Maximum Power Maximum Voltage Maximum Current Package Type Minimum Voltage
WRx12.5-200-130 12.5 kW 200 Vdc 130 Adc Rack-mount 2.5 Vdc
WRx12.5-500-52 12.5 kW 500 Vdc 52 Adc Rack-mount 3.0 Vdc
WRx12.5-1000-26 12.5 kW 1000 Vdc 26 Adc Rack-mount 5.0 Vdc
WRx25-200-260 25 kW 200 Vdc 260 Adc Floor-standing 2.5 Vdc
WRx25-500-104 25 kW 500 Vdc 104 Adc Floor-standing 3.0 Vdc
WRx25-1000-52 25 kW 1000 Vdc 52 Adc Floor-standing 5.0 Vdc
WRx50-200-520 50 kW 200 Vdc 520 Adc Floor-standing 2.5 Vdc
WRx50-500-208 50 kW 500 Vdc 208 Adc Floor-standing 3.0 Vdc
WRx50-1000-104 50 kW 1000 Vdc 104 Adc Floor-standing 5.0 Vdc
WRx75-200-780 75 kW 200 Vdc 780 Adc Floor-standing 2.5 Vdc
WRx75-500-312 75 kW 500 Vdc 312 Adc Floor-standing 3.0 Vdc
WRx75-1000-156 75 kW 1000 Vdc 156 Adc Floor-standing 5.0 Vdc
WRx100-200-1040 100 kW 200 Vdc 1040 Adc Floor-standing 2.5 Vdc
WRx100-500-416 100 kW 500 Vdc 416 Adc Floor-standing 3.0 Vdc
WRx100-1000-208 100 kW 1000 Vdc 208 Adc Floor-standing 5.0 Vdc

2.3. Specifications

2.3.1. Power Specifications

AC Input Voltage
1Φ, 2-wire + ground
85 to 265 Vac (UI: Universal Input); Available on 12.5 kW Models
120 Vac (120SP: operating range 108 to 132 Vac); Available on 25 kW to 100 kW Models
208 Vac (208SP: operating range 187 to 229 Vac); Available on 25 kW to 100 kW Models
240 Vac (240SP: operating range 216 to 264 Vac); Available on 25 kW to 100 kW Models
AC Input Frequency 45-66 Hz
AC Input Isolation ±1500 Vac, maximum AC input voltage to ground
DC Input Isolation ±1500 Vdc, maximum DC input voltage to ground

2.3.2. Programming Specifications

Resolution (All Modes) 16-bit, 0.0015%
Voltage: ±0.1% of full scale voltage rating
Current: ±0.2% of full scale current rating
Power: ±0.3% of full scale power rating
Resistance: ±0.3% of full scale resistance rating
Rise/Fall Time, Maximum
Voltage Mode: 100 ms, 10% to 90% max voltage
Current Mode: 2 ms, 10% to 90% max current
Power Mode: 100 ms, 10% to 90% max power
Resistance Mode: 40 ms, 10% to 90% max resistance
Trip Settings Range
Over Voltage: 10% to 110% of max voltage rating
Under Voltage: 0% to 110% of max voltage rating
Over Current: 10% to 110% of max current rating
Over Power: 10% to 110% of max power rating

2.3.3. Connectivity Specifications

Communication Interfaces (Standard)
USB Host (Front): Type B
USB Host (Rear): Type B
RS485 (Rear): RJ-45
MagnaLINK™: RJ-25 x 2
External User I/O: 25-pin D-Sub female
Communication Interfaces (Optional)
LXI TCP/IP Ethernet (Rear): RJ-45
GPIB (Rear): IEEE-488

2.3.4. External User I/O Specifications

Digital Inputs 5 V, 10 kΩ impedance
Digital Monitoring Signals 5 V, 32 mA capacity
Digital Reference Signals 5 V output, 20 mA capacity
Analog Sampling Rate 2 kHz
Analog Programming Input 0-10 V
Analog Programming Impedance 10 kΩ
Analog Programming Resolution 12-bit, 0.025%
Analog Monitoring Signals 0-10 V, 3 mA capacity
Analog Monitoring Impedance 0.005 Ω
Analog Monitoring Accuracy 0.05% of max rating
Analog Reference Signal 10 V, 20 mA capacity

2.3.5. Physical Specifications

Power Level Rack Units Size Weight
12.5 kW 4U
7” H x 24” W x 19” D
(17.8 x 60.9 x 48.2 cm)
165 lbs (74.8 kg)
25 kW 12U Cabinet
30.7” H x 24” W x 31.5” D
(78.0 x 61.0 x 80.0 cm)
455 lbs (206.4 kg)
50 kW 24U Cabinet
58.25” H x 24” W x 31.5” D
(148.0 x 61.0 x 80.0 cm)
785 lbs (356.1 kg)
75 kW 24U Cabinet
58.25” H x 24” W x 31.5” D
(148.0 x 61.0 x 80.0 cm)
1115 lbs (505.8 kg)
100 kW 36U Cabinet
74” H x 24” W x 31.5” D
(188.0 x 61.0 x 80.0 cm)
1445 lbs (655.4 kg)

2.3.6. Environmental Specifications

Ambient Operating Temperature 0°C to 50°C
Storage Temperature -25°C to +85°C
Humidity Relative humidity up to 95% non-condensing
Air Flow Front air inlet, rear exhaust

2.3.7. Water Cooling Specifications

Water Connection Provided
12.5 kW Models: 1/2” NPT male inlet and outlet
25 kW to 100 kW Models: 1” NPT male inlet and outlet
Maximum Inlet Temperature 25°C
Maximum Inlet Pressure 80 PSI
Minimum Flow Rate
12.5 kW Models: 1.5 GPM
25 kW Models: 3.0 GPM
50 kW Models: 6.0 GPM
75 kW Models: 9.0 GPM
100 kW Models: 12.0 GPM

2.3.8. Regulatory Compliance

EMC Complies with European EMC Directive for test and measurement products, 2014/30/EU
Safety Complies with EN61010-1:2010-02
CE Mark Yes
RoHS Compliant Yes

2.4. Dimensional Diagrams

2.4.1. WRx Series - 12.5 kW Models


Fig. 2.2 WRx Series 12.5 kW rack-mount models front panel, rear panel, and side panel (top to bottom).

2.4.2. WRx Series - 25 kW to 100 kW Models


Fig. 2.3 Front panel dimensions for WRx Series 25 kW to 100 kW floor standing models.


Fig. 2.4 Rear panel dimensions for WRx Series 25 kW to 100 kW floor standing models.


Fig. 2.5 DC output bus dimensions for WRx Series 25 kW to 100 kW floor standing models.

2.5. Options and Accessories

The following is a list of integrated options available for the WRx Series MagnaLOAD DC electronic load:

Name Option Code Description
LXI TCP/IP Ethernet +LXI Integrated TCP/IP Ethernet communications port
IEEE-488 GPIB +GPIB Integrated IEEE-488 GPIB communications port
Blank Front Panel +BP Front panel providing only control power, status LED, and USB port

The following is a list of accessories available for the WRx Series MagnaLOAD DC electronic load:

Name Description
MagnaLINK-6 6-ft MagnaLINK Cable
MagnaLINK-12 12-ft MagnaLINK Cable
MID-M MagnaLINK Interface Device - Master
MID-S MagnaLINK Interface Device - Slave
CAB1 12U Cabinet, 32” H x 24” W x 31.5” D
CAB2 24U Cabinet, 51.5” H x 24” W x 31.5” D
CAB3 30U Cabinet, 67” H x 24” W x 31.5” D
CAB4 36U Cabinet, 75” H x 24” W x 31.5” D
CAB3x2 60U Double Cabinet, 67” H x 48” W x 31.5” D
CAB4x2 72U Double Cabinet, 75” H x 48” W x 31.5” D


Cabinets are only available for rack-mount MagnaLOAD electronic loads. Floor-standing MagnaLOAD electronic loads come standard integrated into cabinets.

2.6. Principle of Operation

Magna-Power Electronics MagnaLOAD DC electronic loads are offered in three variations: the ARx Series, the WRx Series, and the ALx Series. The ARx Series and WRx Series is comprised of a bank of MOSFETs and a series connected array of power resistors configured in a binary format. The ALx Series, which utilizes a more conventional electronic load circuit topology, is comprised simply as a bank of MOSFETs. Both models use three MOSFETs arranged in modular subassemblies called linear modules. These modules contain the necessary drive, feedback, and protection circuitry.

Fig. 2.6 shows a simplified version of the ARx Series and WRx Series, which includes two basic series connected elements: resistor R1 and current source Q1. The current source consists of MOSFET Q1, shunt resistor R2, and operational amplifier U1. Load current, IL, is set with voltage V1 applied to the positive input of operational amplifier U1. V1 drives the gate of Q1 high until the voltage across the shunt resistor, VR2, equals that of V1. The load current, IL, will be equal to V1/R2.


Fig. 2.6 Basic ARx Series and WRx Series MagnaLOAD dissipative component

Assuming the power across the shunt resistor is insignificant, the power dissipated in load resistor R1 is IL x VR1 and the power dissipated in MOSFET Q1 is IL x VQ1. The resistors can be operated at higher temperatures than the MOSFETs, simplifying cooling requirements of the passive elements. Keeping VQ1 small and VR1 large lowers system costs in comparison with purely semiconductor electronic loads. Adjusting the value of resistor R1 is accomplished with a binary switching matrix.

Keeping the resistor switching increments small and over a wide range maintains the smallest voltages across the linear modules and over the widest operating range. The ARx Series and WRx Series has 31 resistor switching states to accomplish this goal. In parallel with the resistors is a shorting switch which provide a very low impedance to bypass the resistor matrix. With the shorting switch enabled, the ARx Series and WRx Series operates like a conventional electronic load and is capable of providing a near zero impedance. The power limit in this mode is that of the linear modules.

With the linear modules fully conducting, the ARx Series and WRx Series can operate solely with the resistor matrix providing 31 resistor states. This mode, called rheostat mode, has no feedback controls for automatic adjustment. Rheostat mode eliminates any possible instabilities between the source and load and is basically a programmable power resistor.

The linear modules have protection circuitry to protect itself from abusive conditions. Each linear module is protected against over current and over voltage conditions. These fault conditions are independent of normal feedback operation. Over current conditions causes shutdown of the system. Over voltage conditions operate in two states. If the voltage applied to the load exceeds it rating, the linear module first acts as a power Zener diode to clamp any transient voltage such as that produced by Ldi/dt. After short instant in time, the ARx series shuts down like over current protection.

The ALx Series uses the same linear modules as the ARx Series. The ALx series has no resistor matrix and no shorting switch. The ALx Series uses 12 linear modules for 2,500 Watt operation, while the ARx Series and WRx Series uses 4 linear modules for 6,750 Watt and 12,500 Watt operation, respectively. The ALx Series has a wider constant power range since there is no restriction with application of the resistor matrix.

The control system has multiple digital signal processors (DSPs), a minimum of 4 are used with others depending on external communications. The combination gives both the ARx and ALx Series powerful control in regulating current, voltage, power, resistance, and rheostat mode. Both the ARx Series and ALx Series use the same control scheme. Like all Magna-Power products, all control circuitry is referenced to earth ground eliminating ground loops between communications equipment.