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Parallel Operation of SMPS

Parallel Operation of SMPS

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Why to use SMPS in parallel mode?

Power supplies are the very foundation of all the electronic devices and provide consistent, clean power conditions. Most electronic devices, especially with integrated circuits, need a reliable DC voltage solution that can supply power to the circuit without any hiccups. Switching mode power supplies are known to convert power from AC mains into DC efficiently, and the same goes for DC.

The objective of connecting power supplies in parallel is to gain the maximum total current available for a system or for redundancy. In case of power failure, system will break down, with parallel connection at least some of the important systems may function properly.

Below are the advantages of connecting SMPS in the parallel configuration:

  1. We get the increased power.
  2. Load sharing causes generation low hot points in the panel.
  3. Load can be isolated due to use of independent power supplies.
  4. Can be used as redundancy model.
  5. Enhance the reliability and life of the SMPS.

So let us check how the SMPS are connected parallelly.

How to Use SMPS in Parallel Mode?

Below is the normal connection diagram for connecting SMPS in parallel


Above schematic shows the connection of three SMPS in parallel config, the input received to each SMPS shall remain same and from single source (Single phase/two phase/three phase). In similar fashion we can connect multiple SMPS. Refer the manufacturer’s datasheet to check how many SMPS it can support in parallel configuration.

The following rules should be followed while connecting power supplies in parallel:

  1. Connect power supplies in parallel if the characteristic and rating class are alike.
  2. Install the power supplies in areas with identical (or nearly identical) environmental conditions.
  3. Power supplies must be arranged side by side rather than one on top of the other.
  4.  Align the output voltage of the power supplies for no-load operation (without connecting load) so that the value is identical. With the power supplies at operating temperature and under load, align the voltage value again to compensate for temperature drift.
  5.  All connecting wires should be of the same length and have the same cross-sectional area. The difference in wire sizes will lead to uneven load share to each power supply.
  6. The wire should converge at the load, not at the power supplies.
  7. If load in operation is less than 10% of the total output in parallel configuration it would lead to a situation where only one unit bears the load and there would be absence of load for other units.
  8. The SMPS which supports parallel mode usually comes with sliding switch between normal and parallel operation. Make sure the switch is positioned in parallel configuration before operation.
  9. Normally in parallel connection the load capacity of the SMPS degrades to 90% of the total SMPS rating. So the load rating must be calculated before turning on the system, SMPS may misbehave or is most likely to get damaged due to the higher load current.