-48vdc data power plant

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Bjorn Larsen said:
What is the conversion to properly size the AC side of a -48vdc system that needs 250 Amps?
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Transformer rectifier system?
If you are rectifying 3-phase ac to get 48Vdc, the current at the ac input of (a conventional 3-phase rectifier) is 0.816 times the dc output current or greater depending on what kind of smoothing is o the dc. So, at least 20A rms.
The current input to the transformer, assuming there is one, obviously depends on the step down ratio.
 
Bjorn Larsen said:
What is the conversion to properly size the AC side of a -48vdc system that needs 250 Amps?
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I design/build a lot of these plants but do not understand what you are asking.

On the AC side to the rectifier depends on the supply voltage, single or 3-phase, and the size of the rectifier in amps. At any rate the manufacture specs will tell you what size wire/breaker you need. DC side is not based on NEC OCPD, it is based on voltage drop at a specified current.
 
Bjorn Larsen said:
I have been asked supply a 250A DC load with AC. I will be using 120/208 3-phase as the input.
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All depends on the size of the rectifier you select. For example if you select a 300-amp @ 48 volt with 110% current limit at 208 3 phase input you are looking at a 50 amp circuit.

You first select the rectifier, then look at the specs and see what it requires.
 
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