What prevents intermixing old 92% power supplies with new 94% efficient power supplies?

[chuckk281]

Rick had a customer question on mixing old and new power supplies:

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My customer is considering moving to the new 94% efficient c7000 PS in their new G7 standards.  They are a self maintainer and asked if any damage was done if they accidently replaced a failed 92% with a 94%?  They know they cannot be intermixed, but what prevents that?  Does the OA just refuse to turn it on?  Does it look different than the 92%?

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Monty and Kurt responded:

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Monty said: 

Each c7000 power supply has a label indicating the part number and electrical characteristics.

If you mix power supplies – the enclosure Insight Display will indicate the fewer number of mixed power supplies as degraded and which bay they are installed

The OA will always try to use all installed power supplies.

However, mixing power supply models will result in the following behavior:

1.      The OA will mark each of the fewer number of mixed power supplies as degraded.

2.      Load sharing in the enclosure is impaired as different power supply models are not designed to share the load with other models

3.      Maximum power capacity of the power supplies is not guaranteed when mixed power supplies are present – due to the inability to accurately share the enclosure load

4.      The OA report of enclosure Power Capacity, Present Power and Available Power is not accurate as this is based on reading the load share signal which is no longer accurate, and using the maximum power output value of the first power supply which might not be the same across a mix of power supplies

5.      Power Limit or Power Capping will no longer be accurate since the OA is no longer able to accurately calculate enclosure power

Please do not leave mixed power supplies in the enclosure.

Kurt added: 

The base reason that we don’t support intermixing of power supplies for normal operation is that they have different architectures and different current sharing algorithms and behaviors.  Proper regulation of the outputs of the supplies cannot be guaranteed when they are mixed.

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Does this answer your quesitons? Comments?