RMX-4121 750 W 80 V 28 A Programmable DC Power Supply
The RMX-4121 is a single-channel, 750 W programmable DC power supply for automated validation, production testing, power-electronics development and laboratory research. Its flexible autoranging output supports a wide combination of voltage and current operating points, with rated capabilities up to 80 VDC or 28 A.
The RMX-4121 occupies one full-width 1U rack space. Engineers can operate it locally with the front-panel display, buttons and rotary controls or integrate it into automated systems using LAN, USB, RS232 and analog control interfaces. Remote sensing, programmable protection and multidevice operation make it suitable for demanding rack-mounted test applications.
Key Features of the RMX-4121
- 750 W maximum output power
- 80 V rated output voltage
- 28 A rated output current
- Flexible autoranging output architecture
- 0 V to 84 V programmable voltage range
- 0 A to 29.4 A programmable current range
- Single programmable DC output channel
- Constant-voltage and constant-current operation
- Four-wire remote sensing
- Up to 4 V remote-sense compensation per line
- 1 ms or less voltage transient response
- Programmable overvoltage protection
- Programmable overcurrent protection
- Programmable undervoltage limit
- Three front-panel preset memories
- LAN, USB and RS232 communication
- External analog programming and monitoring
- Parallel operation with up to four identical units
- Series operation with up to two identical units
- Compact 1U full-width rack-mount enclosure
RMX-4121 Technical Specifications
| Product Model | RMX-4121 |
|---|---|
| Part Number | 784762-01 |
| Product Type | Programmable rack-mount DC power supply |
| Number of Output Channels | 1 |
| Rated Output Power | 750 W |
| Rated Output Voltage | 80 VDC |
| Rated Output Current | 28 A |
| Voltage Setting Range | 0 V to 84 V |
| Current Setting Range | 0 A to 29.4 A |
| Voltage Setting Accuracy | ±(0.05% of setting + 0.05% of rated voltage) |
| Current Setting Accuracy | ±(0.5% of setting + 0.1% of rated current) |
| Voltage Line Regulation | ±10 mV |
| Voltage Load Regulation | ±10 mV |
| Current Line Regulation | ±4.8 mA |
| Current Load Regulation | ±10.6 mA |
| Voltage Transient Response | 1 ms or less under specified load-change conditions |
| Voltage Ripple and Noise | 80 mV peak-to-peak; 8 mV RMS |
| Current Ripple and Noise | 65 mA RMS under specified conditions |
| Voltage Rise Time | 100 ms |
| Voltage Fall Time | 100 ms at rated load; 550 ms at no load with bleeder enabled |
| Remote-Sense Compensation | Up to 4 V per output line |
| Overvoltage Protection Range | 8 V to 89.6 V |
| Fixed Secondary Overvoltage Protection | 96 V |
| Overcurrent Protection Range | 2.8 A to 31.36 A |
| Undervoltage Limit Range | 0 V to 84 V |
| AC Input Rating | 100 VAC to 240 VAC, 50 Hz to 60 Hz, single phase |
| AC Input Voltage Range | 85 VAC to 265 VAC |
| AC Input Frequency Range | 47 Hz to 63 Hz |
| Maximum AC Input Power | 1,100 VA at 100 VAC |
| Maximum Inrush Current | 70 A peak or less under specified conditions |
| LAN Interface | 10Base-T or 100Base-TX Ethernet, IPv4 |
| Other Interfaces | USB, RS232 and analog control |
| Parallel Operation | Up to four identical units including the master |
| Series Operation | Up to two identical units |
| Preset Memory | Three settings |
| Output-to-Ground Isolation | ±250 V maximum |
| Rack Size | 1U, full rack width |
| Weight | Approximately 8 kg |
| Cooling Method | Forced-air fan cooling |
| Operating Temperature | 0°C to 50°C |
| Operating Humidity | 20% to 85% RH, noncondensing |
| Maximum Altitude | 2,000 m |
RMX-4121 Part Number and Accessories
| Item | Part Number | Description |
|---|---|---|
| RMX-4121 | 784762-01 | 750 W, 80 V, 28 A single-channel programmable DC power supply |
| U.S. IEC Power Cord | 763830-01 | 125 VAC, 15 A AC power cord |
| China IEC Power Cord | 784686-01 | 250 V, 10 A AC power cord |
| Korea IEC Power Cord | 784685-01 | 240 V, 10 A right-angle power cord |
| Japan IEC Power Cord | 786377-01 | 125 VAC, 12 A AC power cord |
| Taiwan IEC Power Cord | 787642-01 | 125 VAC, 15 A AC power cord |
| European IEC Power Cord | 763067-01 | 240 V, 10 A right-angle power cord |
| India IEC Power Cord | 763072-01 | 250 V, 10 A AC power cord |
Select the AC power cord according to the destination country, facility voltage and connector standard. Output cables, crimp terminals, fuses and fixture wiring must be rated for the maximum voltage and expected continuous current.
750 W Autoranging Output
The RMX-4121 provides many voltage and current combinations within its 750 W output-power envelope. This autoranging architecture gives engineers more operating flexibility than a conventional fixed-range supply with the same total power.
The rated 80 V and 28 A limits cannot be delivered simultaneously because that would require 2,240 W. When operating at 80 V, the available current is limited to approximately 9.375 A. At 28 A, the available voltage is limited to approximately 26.8 V.
Always confirm that the DUT’s required voltage and current operating point fits inside the RMX-4121 power envelope.
80 V Rated Output Voltage
The RMX-4121 has a rated output voltage of 80 V and a programmable setting range extending to 84 V. This range supports 48 V and 60 V systems while providing adjustment headroom for power conversion and margin testing.
Typical DUTs include telecommunications equipment, industrial power electronics, battery-powered systems, DC-DC converters, motor-control electronics and electronic assemblies operating above conventional 24 V supply levels.
28 A Rated Output Current
The supply provides a rated maximum current of 28 A, with a programmable current setting range extending to 29.4 A. This current capacity supports medium-voltage equipment requiring several hundred watts of continuous power.
At high current, cable resistance and connector resistance contribute to voltage drop and heat. Correctly sized conductors and secure terminal connections are essential for safe and repeatable operation.
Constant-Voltage Operation
In constant-voltage mode, the RMX-4121 regulates the programmed voltage while allowing the connected load to draw current up to the configured current setting. The CV front-panel indicator shows when voltage regulation is active.
If the DUT attempts to draw more current than the configured setting, the supply transitions to constant-current operation. This behavior helps prevent excessive current during startup, overload or fault conditions.
Constant-Current Operation
In constant-current mode, the RMX-4121 regulates the programmed current while allowing the voltage to change according to the connected load. The voltage setting establishes the maximum output voltage.
This mode can be used for component conditioning, LED assemblies, controlled charging experiments and other applications requiring regulated current.
Four-Wire Remote Sensing
The RMX-4121 supports four-wire remote sensing to reduce voltage-regulation errors caused by resistance in the load cables. Separate sense conductors measure voltage directly at the DUT terminals.
The supply can compensate for as much as 4 V of drop on each output line. This is especially useful when the supply is installed at a distance from the DUT or when high current produces significant cable voltage drop.
The output remains subject to the 84 V maximum programmable setting and 750 W power limit. Remote sensing cannot extend the supply beyond its maximum terminal ratings.
Remote-Sense Wiring
Use twisted-pair or two-core shielded wiring for the sense connections. Route the sense wires separately from high-current cables and electrically noisy conductors whenever possible.
Connect positive sense to the positive DUT terminal and negative sense to the negative DUT terminal. Incorrect polarity or disconnected sense wiring can cause unstable or unexpected output behavior.
1 ms Transient Response
The RMX-4121 provides a voltage transient-response time of 1 ms or less under the specified load-change conditions. This helps the output recover quickly when the DUT changes between low-power and high-power operating states.
Actual dynamic performance depends on the load, output-cable inductance, remote-sense wiring and external capacitance. Evaluate performance with the intended fixture and DUT before finalizing an automated test.
Voltage Regulation and Ripple
The RMX-4121 specifies voltage line regulation and load regulation of ±10 mV. Voltage ripple and noise are specified at 80 mV peak-to-peak and 8 mV RMS under the applicable measurement conditions.
These characteristics support stable device powering and repeatable functional testing. For sensitive measurements, use appropriate grounding, shielding, remote sensing and separation between power wiring and low-level measurement signals.
Programmable Overvoltage Protection
The primary overvoltage protection threshold can be programmed from 8 V to 89.6 V. If an overvoltage condition occurs, the supply turns off the output, displays the OVP message and activates the alarm indicator.
A secondary fixed overvoltage protection threshold is set at 96 V, equal to 120% of the rated output voltage. Configure the primary OVP threshold according to the DUT’s maximum safe voltage.
Programmable Overcurrent Protection
The OCP threshold can be set between 2.8 A and 31.36 A. When the detected current exceeds the configured protection threshold, the RMX-4121 turns off its output and reports an overcurrent alarm.
OCP is different from the normal constant-current setting. The current setting regulates normal operation, while OCP provides a shutdown response for an abnormal current condition.
Undervoltage Limit
The undervoltage limit prevents the output voltage from being set below a configured value. Its setting range extends from 0 V to 84 V.
This protection can help prevent incorrect operation of devices that must remain above a minimum supply voltage or that may draw excessive current when operated at an unsuitable voltage.
Three Preset Memories
The RMX-4121 can store up to three groups of frequently used settings. Each preset can include voltage, current, OVP, OCP and undervoltage-limit values.
Preset memory simplifies repetitive bench testing and reduces manual configuration errors when operators regularly switch between known DUT profiles.
Front-Panel Operation
The front-panel display, buttons and rotary controls allow engineers to configure voltage, current and protection values without creating a software application. Indicators display constant-voltage, constant-current, output, alarm and remote-control states.
Local control is useful during system development, maintenance and troubleshooting. The key-lock function can prevent accidental front-panel changes during an automated test.
LAN Remote Control
The RMX-4121 supports 10Base-T and 100Base-TX Ethernet communication using IPv4. LAN control is useful when the supply is installed in a production rack, shared laboratory or remote equipment area.
Configure the IP address and network parameters before opening the software connection. The control computer and instrument must be located on compatible networks, and security settings must permit the required communication.
USB Connectivity
The USB interface provides a direct connection to a nearby computer. It is suitable for benchtop development and rack systems in which the controller is located close to the power supply.
Install the required driver and VISA communication components before connecting the supply. A direct computer connection can simplify initial identification and troubleshooting.
RS232 Serial Communication
RS232 support allows the RMX-4121 to be integrated into industrial controllers and existing test stations that use serial communication.
Verify the COM port, baud rate, data format and command termination settings. The controller and power supply must use matching serial parameters.
External Analog Control
The external analog interface can be used to program and monitor the RMX-4121 through analog voltage or resistance signals. It is useful for real-time controllers and systems that do not rely exclusively on message-based commands.
Review the interface scaling, grounding and maximum signal ratings before applying external analog control signals.
Parallel Operation
Up to four identical RMX-4121 supplies, including the master unit, can be configured for supported master-slave parallel operation. This increases the total current and power available to the DUT.
Only identical models should be combined. The output cables, current-sharing connections, AC circuits and protective devices must be rated for the combined system capacity.
Series Operation
Up to two identical RMX-4121 supplies can be operated in series to increase the available output voltage. Series operation must remain within the output-to-ground isolation rating.
Review grounding, remote sensing and protection requirements before connecting supplies in series. The total system voltage may create additional electrical-safety and fixture-insulation requirements.
Typical RMX-4121 Applications
- DC-DC converter testing
- Power-electronics development
- 48 V telecommunications equipment testing
- Industrial controller validation
- Automotive and commercial-vehicle electronics
- Battery-powered equipment simulation
- Motor-drive and actuator testing
- Server and network equipment testing
- Electronic device validation
- Production functional testing
- Burn-in and reliability testing
- Research and laboratory automation
- Rack-mounted automated test systems
- Multiple-supply power sequencing
48 V Telecommunications Testing
The 80 V range makes the RMX-4121 suitable for powering nominal 48 V telecommunications and networking equipment. Engineers can evaluate device behavior across normal operating voltage, startup and controlled margin conditions.
The 750 W power envelope supports switches, routers, radio equipment and other communications devices with substantial current requirements.
DC-DC Converter Testing
The RMX-4121 can supply a programmable input to DC-DC converters over a broad range of voltage and current combinations. Automated software can sweep input voltage while instruments measure efficiency, ripple and output regulation.
A programmable electronic load can be connected to the converter output to create an automated source-and-load characterization system.
Battery-System Simulation
The supply can reproduce the DC voltage provided by batteries within its unidirectional output capabilities. This supports testing of battery-powered controllers, power converters and charging-related electronics without requiring a physical battery for every test.
The RMX-4121 is a source rather than a regenerative battery emulator. Applications requiring bidirectional power flow may require a source measure unit, bidirectional supply or regenerative system.
Industrial Electronics Testing
The voltage and current ranges support industrial controllers, actuators, motor-drive electronics and power-distribution assemblies. Programmable protection can limit the energy applied to prototype or production devices.
For motors, solenoids and other inductive loads, evaluate reverse voltage and returned energy. External suppression or energy-absorption hardware may be required.
Burn-In and Reliability Testing
The RMX-4121 can continuously power electronic devices during burn-in, environmental and reliability testing. Remote interfaces allow the output and alarm condition to be managed from automated monitoring software.
Maintain adequate rack airflow and verify that facility power, output cables and fixture terminals support continuous operation at the required load.
Calibration and Warm-Up
The RMX-4121 ships with a calibration utility. The official specifications assume a 30-minute warm-up with current flowing and correct calibration in a 23°C ±5°C environment.
Calibration intervals should follow NI recommendations and the user’s quality procedures. Heavily used production instruments may require more frequent verification.
RMX-4121 Troubleshooting
The RMX-4121 cannot output 80 V at 28 A
The two maximum ratings cannot be delivered simultaneously because the supply is limited to 750 W. At 80 V, the available current is approximately 9.375 A. At 28 A, the available voltage is approximately 26.8 V.
The output voltage is lower than programmed
Check whether the supply has entered constant-current mode or reached its 750 W power limit. Inspect output cables for voltage drop and use remote sensing when appropriate.
The power-limit alarm is active
The programmed voltage and load current require more than 750 W. Reduce the voltage, reduce the required current or consider a higher-power supply.
The output cables become hot
Stop the test and inspect conductor size, crimp quality, terminal tightness and cable length. Replace any cable or connector that is not rated for the expected continuous current.
The remote-sense output is unstable
Check sense-wire polarity, shielding and routing. Keep sense wiring away from noisy power conductors and add an appropriate capacitor at the sensing point if permitted by the DUT and NI guidance.
The RMX-4121 reports OVP
Verify that the OVP threshold is above the intended operating voltage and below the DUT’s safe maximum. Check remote-sense wiring and external sources connected to the output.
The RMX-4121 reports OCP
Check for a DUT short circuit, excessive startup current or an incorrectly configured OCP threshold. Remember that OCP shuts down the output and is separate from normal current regulation.
The LAN connection does not work
Confirm the IP address, subnet mask, Ethernet cable and network link status. Verify that the controller can reach the instrument and that firewall rules are not blocking communication.
The USB interface is not detected
Check the USB cable, computer port, driver installation and VISA configuration. Connect directly to the computer while troubleshooting.
The power supply shuts down during continuous operation
Review the front-panel alarm, AC input, rack airflow, fan operation and ambient temperature. Ensure that the ventilation openings remain unobstructed.
RMX-4121 Comparison with Similar Programmable Power Supplies
| Model | Rated Output | Power | Best Suited For |
|---|---|---|---|
| RMX-4120 | 30 V, 75 A | 750 W | Low-voltage, very-high-current testing |
| RMX-4121 | 80 V, 28 A | 750 W | Medium-voltage power electronics and 48 V systems |
| RMX-4122 | 230 V, 10 A | 750 W | High-voltage converters and industrial devices |
| RMX-4123 | 650 V, 3.5 A | 750 W | High-voltage semiconductor and power-system testing |
| RMX-4125 | Medium-voltage, higher-current output | 1,500 W | Applications requiring more power than the RMX-4121 |
| RMX-4104 | Up to 100 V or 40 A, depending on version | Up to 864 W | Fixed-range rack-mount power applications |
RMX-4121 vs RMX-4120
The RMX-4120 supports up to 30 V and 75 A, while the RMX-4121 supports up to 80 V and 28 A. Both supplies provide 750 W and flexible autoranging operation.
Choose the RMX-4120 for low-voltage devices requiring very high current. Choose the RMX-4121 for 48 V, 60 V and other applications requiring voltage above 30 V.
RMX-4121 vs RMX-4122
The RMX-4122 extends the rated voltage to 230 V while reducing the rated current to 10 A. The RMX-4121 provides substantially more current but has a lower maximum voltage.
Select the RMX-4121 for medium-voltage, higher-current electronics. Select the RMX-4122 for high-voltage converters, industrial equipment and devices requiring more than 80 V.
RMX-4121 vs RMX-4104
The RMX-4104 is offered in several fixed voltage and current configurations with output power up to 864 W. The RMX-4121 provides a flexible autoranging operating area within its 750 W limit.
Choose the RMX-4121 when the DUT requires different voltage and current combinations across a broad operating range. Choose the RMX-4104 when one of its fixed configurations closely matches the required load.
Recommended Related Products
- RMX-4120 750 W 30 V 75 A Programmable Power Supply
- RMX-4122 750 W 230 V Programmable Power Supply
- RMX-4123 750 W 650 V Programmable Power Supply
- RMX-4125 1,500 W Programmable Power Supply
- RMX-4104 High-Power Programmable DC Power Supply
- PXIe-4138 Precision System SMU
- View More NI PXI and PXI Express Modules
Selecting the Right RMX Power Supply
Choose the RMX-4121 when the application requires up to 80 V, up to 28 A and a maximum power envelope of 750 W. It is particularly suitable for 48 V telecommunications equipment, medium-voltage converters and industrial power electronics.
Select the RMX-4120 when current above 28 A is required at lower voltage. Choose the RMX-4122 or RMX-4123 for higher-voltage applications, or consider a corresponding 1,500 W model when the operating point exceeds 750 W.
Why Choose the RMX-4121?
- Provides 750 W from one programmable channel
- Supports voltage up to 80 VDC
- Supports current up to 28 A
- Offers flexible autoranging operation
- Compensates cable voltage drop through remote sensing
- Provides fast 1 ms transient response
- Includes programmable OVP, OCP and UVL protection
- Supports LAN, USB, RS232 and analog control
- Supports series and parallel multidevice configurations
- Occupies only 1U of rack height
Frequently Asked Questions
What is the RMX-4121?
The RMX-4121 is a single-channel, 750 W autoranging programmable DC power supply with rated output capability up to 80 V or 28 A.
Can the RMX-4121 output 80 V and 28 A simultaneously?
No. That operating point would require 2,240 W. Voltage and current combinations are limited to a maximum output power of 750 W.
What is the voltage setting range?
The programmable voltage range is 0 V to 84 V. The rated output voltage is 80 V.
What is the current setting range?
The programmable current range is 0 A to 29.4 A. The rated output current is 28 A.
Does the RMX-4121 support remote sensing?
Yes. The remote-sense terminals can compensate for up to 4 V of voltage drop on each output line.
Can multiple RMX-4121 units be connected in parallel?
Yes. Up to four identical RMX-4121 units, including the master, can be used in a supported parallel configuration.
Can RMX-4121 units be connected in series?
Yes. Up to two identical units can be used in a supported series configuration, subject to grounding and isolation requirements.
Which communication interfaces are available?
The RMX-4121 supports LAN, USB, RS232 and external analog control.
Does the RMX-4121 include protection functions?
Yes. It provides programmable overvoltage protection, secondary fixed overvoltage protection, overcurrent protection, undervoltage limiting and thermal protection.
What is the RMX-4121 part number?
The standard NI part number for the RMX-4121 is 784762-01.
Request a Quote for the RMX-4121
Contact us for current availability, lead time and project pricing for the RMX-4121 750 W 80 V 28 A Programmable DC Power Supply. We can also help identify compatible AC power cords, output cables, rack accessories and related RMX power supplies for your automated test system.
