Forming DC bus capacitors

I have some power supplies that have been sitting on the shelf, de-energized, as spares for far too long, and prior to using them the manuals describe a preconditioning process of stepping the supply voltage up over time (see page 13 of DataSheet OPS3200.1). This process is common to many supplies that use electrolytic capacitors.
The challenge is where do I get a 3phase supply that I can step from 25%, 50%, 75% of nominal supply from?
An old electrical engineer I worked with used to refer to VSDs (Variable Speed Drive) as VVVF (Variable Voltage Variable Frequency) drives.
In looking through the ACOPOS P76 Inverter Manual there is reference to a UnS parameter allowing the setting of the rated motor volt.

At the risk of being declared “completely out of his tree”: Has anyone tried to use an inverter to precondition a power supply before? I’d guess the trick is to monitor the current draw to make sure it’s within limits (of power dissipation at with no load), else declaring the capacitors as “shot”?

Hi @jwapstra,

i did not find any infos about that.

but there is information on how the electrolytic capacitors in VFDs should be formed which is a similar requirement:

so the idea is to slowly increase mains voltage with no load connected to the output.
it should be sufficient to use a simple regulating transformer on just one phase.

Has anyone tried to use an inverter to precondition a power supply before

the output of a VFD is not a sinus. Instead it is a PWM with ± peak mains voltage. That does not sound as a good idea.

To ensure compatibility with the manual you need dedicated electronic hardware to do it. It musst be a DC Voltage and Controllable over the required Voltage range.

The only Component in the B&R Portfolio which comes close is the 80PS080X3.10-01. It can go up to 80 V DC.

I once did it this way with an ACOPOS1016 … 24 V DC , 80 V DC full AC Voltage
But this is not conform to the manual!

Back in the days … I got the Information that the Repair of B&R can do this for older Hardware, but it will cost some amount of money. They have the Equipment in the factory. – But this information should be checked via local Sales to ensure this is still valid, if you want to go this way.


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