Byte-sized Topic: Industrial Power Supplies

March 30, 2017

industrial power supply

In the automation industry, a power supply is one of basic components that form the production automated process in that it allows for a stable source of power for process applications.

Technical key aspects of Industrial Power Supplies

  • EMC emission;
  • EMC immunity

Why should we use 5/12/24Vdc instead of classic 220-240Vac? For different reasons:

  • User safety: touch 220Vac and you will risk serious, if not lethal, consequences (unless there is good residual current protection in the circuit);
  • RCDs (Residual Current Devices) tend to generate unexpected power shut downs (due to lightning, high humidity, RF disturbance, etc.)

When installed in homes, it does not represent a problem at 220Vac + RCD. Power can stop from time to time, but that is not a big issue (except during MUnited / Liverpool games).

But many areas cannot be protected effectively with RCDs.
  • Whenever you need electrically unqualified people to play around your technical installation / equipment, then you should choose ELV (Extra Low Voltage);
  • Many equipment to be used in industry is used by non-electrical specialist people who, however, are specialized on something (e.g. automation, setting up an inverter/drive/soft-starter, testing whether the production process is working fine, etc.);
  • So it is common ground to most manufacturers of equipment for such people to make it supplied with 24Vdc (the most common) and also sometimes 12Vdc or even 5Vdc. In such case, you would need a PSU (Power Supply Unit).

industrial power supply

Ratings in & out

  • Input voltage range: what is the minimum and maximum input voltage the power supply can use to do its job?;
  • Output current rating -> maximum current it can run (e.g. 10A), whether on a permanent basis or for a short time (in-rush current consumption);
  • Output power (e.g. 100W);
  • Output voltage (e.g. 24Vdc);

Micro cuts / Hold time

How long can the PSU keep supplying its output, without input power (due to a short / micro-cut on the input side) -> this is critical to ensure process continuity (PLCs cannot stand power supply shortage… even for the smallest time period).

Quality of regulation

  • How stable the output voltage can be, independently from how current is drawn from the PSU?;
  • Ripple: how clean / straight is the waveform going out of the PSU? If there is too much ripple, the supplied device may under-perform / over heat (due to harmonics, etc.);

Type of EMC emissions / immunity

Environments where PSUs operate contain a lot emitted RF disturbance from various devices (UPS, Inverters, Drives, etc.) A PSU needs to be immune to these disturbances, to keep performing despite those.

Conversely, a PSU needs to have an as small as possible RF emission, to avoid disturbing neighboring devices too much.

In-built protections

The system supplied by the PSU can have its own faults (e.g. short circuits, overload, earth faults). The PSU shall be able to detect those and stop supplying if the fault is considered critical.

Standards Compliance

Every country and/or company has to abide to local regulation, which often require compliance with international standards in relation to electrical safety (IEC), people safety (OHSAS), etc.

Useful Info

Major manufacturers of power supplies are:
  • Schneider Electric
  • Meanwell
  • Siemens
  • Phoenix Contact
  • Murr