CT5.121

C-Series

CT5.121 power supplies can be paralleled to increase the output power. This

power supply has no feature included which balances the load current

between the power supplies. Usually the power supply with the higher

adjusted output voltage draws current until it goes into current limitation.

Therefore, the power supply can only be used in parallel as long as the

ambient temperature stays below 45°C. The output voltages of all power

supplies shall be adjusted to the same value (±100mV). A fuse or diode on

the output of each unit is only required if more than three units are

connected in parallel. If a fuse (or circuit breaker) is used, choose one with

approximately 150% of the rated output current of one power supply. Keep

an installation clearance of 15mm (left / right) between two power supplies and avoid installing the power supplies on

top of each other. Do not use power supplies in parallel in mounting orientations other than the standard mounting

orientation (input terminals on the bottom and output terminals on top of the unit) or in any other condition where a

derating of the output current is required (e.g. altitude, above 60°C, …). Pay attention that leakage current, EMI,

inrush current, harmonics will increase when using multiple power supplies.

Unit A

AC

DC

Unit B

AC

DC

-

+

-

+

Load

+

-

Power supplies can be paralleled for redundancy to gain higher system availability. Redundant systems require a

certain amount of extra power to support the load in case one power supply unit fails. The simplest way is to put two

power supplies in parallel. This is called a 1+1 redundancy. In case one power supply unit fails, the other one is

automatically able to support the load current without any interruption. Redundant systems for a higher power

demand are usually built in a N+1 method. E.g. six power supplies, each rated for 8A are paralleled to build a 40A

redundant system. For N+1 redundancy the same restrictions apply as for increasing the output power, see also section

23.6.

Please note: This simple way to build a redundant system does not cover failures such as an internal short circuit in

the secondary side of the power supply. In such a case, the defect unit becomes a load for the other power supplies

and the output voltage can not be maintained any more. This can only be avoided by utilizing decoupling diodes

which are included in the decoupling module YR2.DIODE.

Recommendations for building redundant power systems:

a)

Use separate input fuses for each power supply.

b)

Monitor the individual power supply units.

c)

1+1 Redundancy is allowed up to an ambient temperature of 60°C

N+1 Redundancy is allowed up to an ambient temperature of 45°C

d)

It is desirable to set the output voltages of all units to the same value (± 100mV) or leave it at the factory setting.

Jan. 2010 / Rev. 1.0 DS-CT5.121-EN

All parameters are specified at 12V, 8A, 400Vac, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.

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