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Entry type: FAQ Entry ID: 41036, Entry date: 04/01/2004

Power supply unit 6ES5 955-3..4.; LED "RB low" lights

  • Entry
  • Associated product(s)

Why does the "RB low" LED (voltage of rechargeable battery has dropped below limit) light after starting up the power supply unit?

This applies to the following power supply units:

  • 6ES5 955-3LC4.
  • 6ES5 955-3LF4.
  • 6ES5 955-3NC4.
  • 6ES5 955-3NF4.

The built-in rechargeable battery is not connected. To connect it you must remove the right fan and connect the red connecting cable to the rechargeable battery. Please note that the RB low LED lights during the initial charging period of the battery when first installed.

Information on this is available in the system manual "SIMATIC S5-135U/155U" in Entry ID: 1085837:

  • Section 4.3.1 Product Overview - list of the latest power supply units 11/99
  • Section 4.3.2 Setting and Connecting the Power Supply Unit - Brief Instructions for Startup - Stage 3 in the associated table

Error indicator, Error LED

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