Home Theater Power Protection

Oct 28 2006

Recently, we had a user ask about the effectiveness of AC power conditioners in regards to their HT experience.  Are they "all that" or are they just the latest mumbo-jumbo fad to try and extract cash from your wallet?  Here's where I put on my day job hat (Electrical Engineer/Hardware Designer) and comment.  The opportunity for smoke and mirror marketing in this area is tremendous.  In fact, it is matched only by the wire and cable interconnect industry.  Due to the stringent regulations by which the power companies have to adhere, you can depend on the AC entering your home to be 120VAC @ 60Hz in the US.  The only conditions where this won't be true are:

1.  If you are experiencing a power outage
2.  If you have a heavily loaded circuit in your home and the voltage sags.
3.  If there is an electrical storm in the area and you get a spike.

Item 1 can be temporarily avoided with a battery backed UPS, but who has enough capacity to last through a movie?  Item 2 can be solved by taking an inventory of what is on the circuit and either upgrading the wiring or moving some of the load to another circuit.  An on-line UPS can also help with this, but more on that below.  Item 3 is always a gotcha.  The best surge strip in the world can still be foiled by a bolt of lightning.  You don't honestly think that a lightning bolt which arcs across the sky can be stopped by a 10 cent MOV?  That's right.  Surge suppression is primarily accomplished with a 10 cent part.  Kind of makes you wonder what the rest of the money is going toward doesn't it.

The power conditioning company's marketing department would have you believe that it is important to highly regulate the AC to ensure that it is a pure 120VAC sine wave.  Any sags or distortions will cause imperfections in the performance of your high tech A/V gear.  It is my opinion that all this filtering and correction are not necessary.

Lets start by talking about how a typical A/V component converts the incoming AC power.  Most media players and PCs require 12VDC or less to operate.  This is typically accomplished by a switching power supply.  The power conversion steps involve rectifying, filtering, chopping and regulating to a lower voltage, followed by more filtering.  In the end, variations on the original 120VAC line are easily adsorbed and dealt with leaving no traces of these variations on the output side of the power supply.  Some of these switching power supplies are designed to be "universal" or able to use anything from 90 - 265 VAC without issue.  Some high quality A/V devices use a linear power supply.  These can be identified by the large & heavy transformers that they require.  Even these have filtering and regulation stages that easily compensate for input voltage variations.
In short, unless you have a large sum of cash that you don't know what to do with (I accept donations Smiley ), I would recommend that you purchase a surge strip that you feel comfortable with and use the money elsewhere in your system.  Yes, these devices may do a really good job of regulating everything to 120 VAC, but I submit that it is not necessary with today's electronics.

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