How to size a high-power DC power supply: voltage class, autoranging, energy flow and parallel systems

Short answer. List the highest voltage, the highest current and the highest power your device under test will need, and whether it ever returns energy. Then check each point against a specific model's voltage class and autoranging envelope, not just its kW rating. Allow headroom for inrush and transients and, if the programme may grow, choose a range that can be paralleled.

Start with operating points, not the nameplate

A supply's nameplate gives three maximums: voltage, current and power. They are not available all at once. A 30 kW supply rated to 500 V and 180 A, for example, can't deliver 30 kW at every voltage. Power is voltage times current, so at 100 V its 180 A current limit holds it to 18 kW.

So begin with the device under test, not the catalogue. For each mode of operation, write down:

the highest voltage it needs, including any overvoltage or open-circuit tests
the highest current, and the voltage at which it's needed
the highest power
whether current ever flows from the device back into the supply

An illustrative example. Say a DC-DC converter under test needs an input of up to 400 V at 60 A (24 kW) at the top of its range, and 100 V at 250 A (25 kW) at the bottom. Neither point is above 30 kW, so a 30 kW unit looks big enough. But the voltage class has to cover 400 V. In the EA Tektronix PU 10000 4U range that means the PU 10500-180 (0 to 500 V, 0 to 180 A), which can't reach 250 A. The 60 kW PU 10500-360 in 6U (0 to 500 V, 0 to 360 A) covers both points, as would two 30 kW, 500 V units in parallel. The deciding figure was current at low voltage, not power.

What autoranging gives you

A fixed-range supply delivers its full power at only one point: maximum voltage and maximum current together. An autoranging supply has a power limit as well as voltage and current limits. It trades voltage against current, so it can hold its full rating across part of its range.

Take the PU 10060-1000 (0 to 60 V, 0 to 1,000 A, 30 kW). Its current limit and its power limit meet at 30 V, so it can deliver its full 30 kW anywhere from 30 V to 60 V: 1,000 A at 30 V, or 500 A at 60 V. A fixed-range supply that reached both 60 V and 1,000 A would need a 60 kW rating.

[Chart: output envelope of the PU 10060-1000 (30 kW, 60 V, 1,000 A) against a fixed-range 30 kW supply rated 60 V and 500 A.] Illustrative, based on published ratings.

Autoranging works within a voltage class, not across classes. Each 30 kW PU 10000 4U model covers one class, from the PU 10060-1000 (0 to 60 V) to the PU 12000-40 (0 to 2,000 V, 0 to 40 A). Choose the class that covers your highest voltage, then check that your highest current, at the lowest voltage you'll need it, sits inside that model's envelope. The Pacific Power Source AZX Series takes a similar approach, with dual voltage ranges and constant power profiles.

Does energy flow back from the device under test?

If the device under test only draws power, a unidirectional supply such as the PU 10000 is enough. If it ever returns energy, the supply has to sink current as well as source it. Batteries, bidirectional converters and motor drives under regenerative braking all do this. There are three ways to handle it:

A bidirectional supply. The EA Tektronix PUB 10000 sources and sinks through the same output. In sink mode it's regenerative, feeding energy back into the grid at up to 96% efficiency rather than turning it into heat. For battery simulation, EA lists its Battery Simulator software for the PUB 10000.
A four-quadrant source. The Pacific Power Source AZX Series sources and sinks in AC or DC, with regenerative operation, from 30 to 55 kW per unit.
A separate supply and load. A PU 10000 paired with a regenerative electronic load such as the PUL 10000. This suits a test station that needs to source one device while loading another at the same time.

For low-voltage work such as cell testing, check the sink side at low voltage too. EA's datasheets give the minimum voltage at which each PUB model can sink its full current, from 0.62 V on the 60 V and 80 V 30 kW models. Our bidirectional power supplies category lists the bidirectional range.

Inrush, transients and dynamic response

Steady-state figures aren't the whole picture. A device with a large input capacitance can draw a high inrush current when it's first powered, and a load that steps between operating points may need a supply that responds within milliseconds. Allow headroom on current for those peaks, and check the supply's rise and fall times and how it recovers from a load step.

Where response is the priority, a fast-response supply can help. The Zenone AL series is designed for applications that need rapid response and precise control, with rise and fall times down to 500 µs and efficiency over 95%, from 5 kW to 500 kW.

Scaling up: parallel operation, space, power and heat

If the programme may grow, check how a range parallels before you buy the first unit.

EA Tektronix 10000 series: up to 64 units connect through a master-slave bus and behave as a single supply. Units of different power classes can be combined, but the voltage class must be the same. With 60 kW units that's up to 3,840 kW. EA's own example is a 150 kW system built from two 60 kW 6U units and one 30 kW 4U unit.
Pacific Power Source AZX Series: 30, 45 and 55 kW units, up to 440 kW in parallel.
Zenone AL series: from 5 kW to 500 kW.

Then plan the site:

Supply. These are three-phase units. The PU 10000 4U accepts 208 to 480 V three-phase, but EA derates it to 18 kW on a 208 to 240 V supply, so check what your site provides.
Heat. A regenerative unit returns most of the energy it sinks to the grid instead of turning it into heat, but every unit still has losses to remove. The EA 10000 series is available with water cooling as an option.
Space. EA quotes a 300 kW system in a single 42U cabinet.

Our article on the EA 10000 Industrial series in 6U covers the 60 kW supplies and loads in more detail.

Automation and interfaces

Most high-power supplies run inside an automated test system rather than from the front panel. Ethernet and USB are standard on the EA Tektronix 10000 series, which supports SCPI and Modbus, with plug-in modules for CAN, CANopen, EtherCAT, Profinet, Profibus and others. The AZX Series has USB, LAN, RS232 and GPIB as standard. The Zenone AL has RS485 as standard, with USB, LAN or optical fibre as options. If your controller speaks a particular protocol, check it at the start, not after delivery.

Short-term needs and custom systems

A test campaign or a short programme may not justify a purchase. If you need a supply for a short period, talk to us about rental: we can often find a way to help. Where a single instrument isn't enough, we also supply custom AC and DC power test systems built around your requirements.

Our industrial power supplies page brings the EA Tektronix, Pacific Power Source and Zenone ranges together, from 5 kW to 500 kW.

Not sure how much power you need?

Send us your operating points (the voltage, current and power, and whether energy flows back) and we'll support you in choosing an appropriate configuration.