Power draw question...

Discussion in 'AV Receivers' started by Vader, May 19, 2004.

  1. Vader

    Vader Supporting Actor

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    Hi all,

    I am upgrading my amplifier, and I would like to verify my understanding of power consumption as reported in user documentation. If the power consumption is listed in terms of wattage, I am taking that to mean the RMS value. However, my surround processor lists it in terms of current, and am converting it to the VA value, dividing by 2**(1/2) to get the RMS value. My question is, can I automatically assume that if the power consumption is listed in wattage, it is the RMS value, and if it is in terms of current, I need to perform the above conversion before I can compare "apples to apples"? I am trying to determine the additional load my UPS will have to take on (and avoid exceeding its capacity) TIA!

    Peace... Derek
     
  2. Drew_W

    Drew_W Screenwriter

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    You're running your HT off a UPS?

    And I'm rather confused since I've never seen power consumption listed in Amps. The back of the unit should have an indication on it in Watts...
     
  3. Bob McElfresh

    Bob McElfresh Producer

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    You are going to have trouble doing the math because of the following:

    - Power consumption largely depends on how loud you play
    - Power consumption numbers on a reciever are a bit strange because the reciever really does not 'consume' much power. It changes the power to feed the speakers. So the efficiency of the speakers have a large effect on how much 'power' the reciever handles
    - Different speakers consume different amounts of current based on their 'nominal' impedence. 4 ohm speakers draw roughly twice the current of a 8 ohm speaker.
    - Speakers change their impedence based on the frequencies being played at that moment. Lots of low-frequency draws lots of current.
    - Your reciever provides different amounts of power to each speaker based on the movie. A drama/comedy is dialog heavy with music, but a action/adventure has lots of effects which take more power.

    So your real-world use adds so many variables that it's really hard to read the manual and do the calculations. Its probably better to just hook it up and watch at normal listening volumes to see if the UPS complains.

    Note: typically a UPS is horrible for AV gear. It's like hooking a car battery-charger in-line with your AC power and expecting the left-over power to be 'clean'. It's not. There are some UPS units that now claim to provide 'smooth' power to AV gear, but these are new and I have not had much feedback on them.

    I'd go with a good surge-supressor power strip for the AV gear. If you did want to 'protect' your system, focus on the TV and DVD/source electronics and not the reciever/amplifier. The reciever/amp is a 'high-power' device and tends to draw lots of power/current in bursts so it is designed to handle wider-ranges of AC fluxation than the low-power digital electronics.

    Note: the real damage to electronics is done not when the power drops out, but when it comes back. The first few cycles of the returning power are at a lot higher voltage and current and this frys un-protected digital electronics. This is why surge-supression is so important.
     
  4. Matt_Smi

    Matt_Smi Second Unit

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    Thanks for the info; I was wondering if I should buy a UPS or a decent surge protector for my HT setup, now I know which I am getting. I have always found it strange that a UPS provides you power from a battery anyway, and I did not want to worry about exceeding the wattage rating on it. I may get one for my computer however, as many of them can connect to it via a USB cable and automatically shut down your computer for you in case the power goes out while you are not home. Another thing I was wondering about, would there be anything wrong/bad about buying one of those two outlet surge protectors that plug right into the wall and cover both outlets, and then just plugging a power strip into that surge protector, and then plugging all of you equipment into the power strip?
     
  5. Vader

    Vader Supporting Actor

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    Bob,

    Thanx for the information. I currently protect my system with both a Monster Power Center and 1050VA UPS in series. I checked with the engineers at both Monster and Tripplite and confirmed that how I have stuff set up is OK. In other words, I have the surge protector plugged into the wall, and the UPS plugged into that. All of the equipment is plugged into the UPS. The logic being that the power is "cleaned" by the Monster, and that the battery only engages during a brown or black-out. I know that hooking it up the other way (wall --> UPS --> Surge Protector) is a big no-no due to the specific waveform sent from the UPS during a power loss. I need the UPS because the power is rather unreliable around here, and I need to be able to shut down safely.

    Peace... Derek
     
  6. Drew_W

    Drew_W Screenwriter

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    I'm not sure this is really an issue since your setup probably consists of all solid state electronics. The only thing to worry about is the surge that may follow when power is brought back after an outage.
     
  7. Vader

    Vader Supporting Actor

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    Drew,

    My concern is mainly if the power goes out and stays out for an extended period. In addition to DVDs, I am from the old school, and still watch LDs. I am extremely concerned about warpage, and the discs are warmed in the player. I want to be able to get them out before shutting everything down. Also, I worry about brown-outs: if I am watching a loud movie and the power "blinks", could that not damage the speakers or amp (going from loud --> silence --> loud in rapid succession)?

    Bob,

    What do you mean by "bad"? While there is no power outage, my UPS is a direct pass-through (aside from minimal surge protection and RF filtering), and only switches to battery when necessary. The times it has switched, I have not noticed any degradation in AV quality, and I shut down immediately. Note that I do not attempt to continue watching the movie while on battery power. My research prior to getting the UPS was that the power was, at the worst, not any cleaner (or dirtier) than normal, run-of-the-mill household electricity (the UPS RF filters really don't do that much). Was I misimformed?

    Peace... Derek
     
  8. Bob McElfresh

    Bob McElfresh Producer

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    True. But remember - there is a battery trickle-charger that constantly clicks on/off/on to keep the battery charged in the UPS. This is a high-current device like a washing machine. This causes crackles in the audio and dimming/momentary noise in the video.

    I'm not against a UPS in concept. But early ones made for a PC created a 'sawtooth' waveform in the AC pass-through because of the sensing and charging circuitry. Not a problem for computers, but is was an issue for analog audio and video systems.

    Apparently companies like APC have noticed this and seeing a new market (Home Theater) have their latest models offer a "clean waveform" output. If you were going to buy a UPS - look for one of these.

    If you already have a UPS try this:

    - Let your equipment warm up with the UPS installed
    - Pause a DVD/CD and turn up the volume until you start hearing hiss/background noise (it is always there). Note the sound and the position on the volume dial where it becomes noticible.
    - Turn the volume down and power everything down.
    - Unplug the main power-strip from the UPS and connect it straight to the AC power. UnPlug the UPS.
    - Turn the system back on and go to the PAUSE like you had before.
    - Turn the volume back to where the noise just became audible.

    Is the noise gone? If so, you have removed the noise caused by the UPS. If the noise is the same - the UPS added nothing and it's fine to use for your system.
     
  9. Vader

    Vader Supporting Actor

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    Bob,

    I will try your suggestion tonight and let you know. You mentioned the "Battery Trickle Charger" (new one on me...[​IMG]) ; can this cause any damage (ie. "micro-spikes" or something like that)?

    Thanx... Derek
     
  10. Vader

    Vader Supporting Actor

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    Bob,

    Follow-up on that test you suggested. I was unable to get any type of static out of the mains, or center regardless of the volume on the amp (that's with the UPS in place). Based on your aversion to using older UPS units on HT, I removed it just to be on the safe side. However, I am concerned about your comment in another thread that when engaged, the output is extremely rough. I have been using the UPS since '95 (replacing batteries as needed; once so far) and have never noticed anything wrong. Could any cumulative damage have been done to my equipment (such that would shorten longevity)? This would be somewhat ironic, as I really thought I was protecting them against that very thing... [​IMG]
     

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