Tuesday, December 02, 2014

Why do manufactuers over-specify power requirements for broadcast equipment?

It's actually a rhetorical question and I'm glad they do. Most of the time I have to tell a customers' electrician and air-con contractor how much power (and hence how much heat) the machine room will be pulling/genarating. Most customers refuse to believe that 99.9% of the electrical power entering a server room/TV MCR leaves it as heat! Just think about it; a 1v video signal leaving the room and terminating into 75 ohms represents a tiny amount of energy. Everything winds up as heat and so I've got to the point where I tell the electrician how many amps we'll need and the aircon guy how many BTUs of heat he'll have to move. By turning them into different units the customer stops complaining!
Anyway - why are the numbers always so different? I've been installing Avid shared storage chassis since 1999 when Unity v 1.2 was considered clever - 500 Gigs across three arrays and usable by around ten edit rooms. Fast forward to 2014 and the ISIS range are what you'll buy from Avid and the new ISIS 2500 near-line storage is just the thing for cheaper, non-edit storage.

This is the rear of this monster - two supplies with 20A C19 inlet connectors and you can see from the clamp-meter that the thing is pulling 1.3 - de-powering one of the supplies shows the current draw by the single supply rise to 2.6A (so they are properly balanced). Re-powering the thing shows that the total draw across both PSUs rises to 3.3A for around thirty seconds but settles to the total 2.6A once everything is up and running. 
So, P=IV and (not forgetting the inductive load which has a power-factor of 0.8) means we are seeing a bit less than a kW max. However - on the Avid website;


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