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Thread: Power draw of amplifiers

  1. #1
    Low Bitrate Linus's Avatar
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    Power draw of amplifiers

    How much power does an amplifier draw? I'm trying to do some calculations on how long my system will run on a deep-cycle battery. If anyone out there has hooked up a multimeter to the power input on their amp (or is willing to do so), I'd be curious to know the result!

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    Variable Bitrate StrataG's Avatar
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    Why not let us know what kind of power your amps are putting out. More importantly the RMS rating vs. peak rating. Someone who has 1000+ watts from their amps is going to draw a lot more power than someone with 200 watts. It's usually pretty easy to tell that max your amps will pull by looking at your fuses on the amps. If you are ever pulling more than that, your fuses will pop.

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    Low Bitrate Linus's Avatar
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    I actually don't have an amp yet. I want to know how much the amperages vary from, say, a 40x2 RMS amp to a 100x2 RMS amp. It will probably be dependent on output volume too, so if people could subjectively specify how loud the music is that would be helpful.

    For load and battery life calculations, I think the average numbers will be much more important than peak, so fuse size and such shouldn't factor in. I'm much more interested in real-world measurements (which shouldn't be difficult) than theoretical calculations.

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    Variable Bitrate StrataG's Avatar
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    Again, your questions are very vague. You'd be better off reading a little more into car audio and electronics to find out what you are really looking for.

    As far as the load, outside of comparing apples to oranges as you would like, the only way to even approximate the load is with formulas for power.

    Amperage = Watts/Volts

    Then you need to factor in efficiency. So if the amperage were say 40 amps, and the efficiency was 80%, you'd get 40 *1.25 (100%/80%) = 50 amps. Your voltage with the car off will start in the 12.x range.

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    Low Bitrate Linus's Avatar
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    Quote Originally Posted by StrataG
    Again, your questions are very vague. You'd be better off reading a little more into car audio and electronics to find out what you are really looking for.
    Actually, much of the car audio stuff I've read pretty much ignores average power draw numbers because there's plenty of power when a car is running. What I'm interested in is figuring out run times when the car is off. I have a pretty good understanding of batteries and DC electronics from my interest in solar power systems.

    Quote Originally Posted by StrataG
    As far as the load, outside of comparing apples to oranges as you would like, the only way to even approximate the load is with formulas for power.
    It's actually rather simple to measure the DC load with something like a clip-on ammeter. I have a Kill-A-Watt power meter that I can use to measure the AC draw of my PC; I'm interested in getting some numbers on the DC draw of various amps. Like I said - I'm interested in real-world measurements, not calculations.

    The power supply on my PC is rated to 285W. Does that mean it draws 285W? Heck no. If I know that it's 75% efficient, does that mean that I can say that it's putting out 214W DC all the time? No. The 285W is a rating of maximum peak power output, which frankly isn't all that important when you're doing runtime calculations (can I battery handle a 300W, 100ms spike? sure.) Carrying this over to amps, I doubt the actual power draw of a 100x2 RMS amp is a constant 200W - maybe it peaks to that amount during a bass thump or something, but I would be surprised if the actual power draw averaged over 30 seconds of music was more than 25% of the rated output.

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    Variable Bitrate StrataG's Avatar
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    You are dealing with too many variables to even attempt to help you. I was basing my statements on you having your volume at 100%. Now you want to throw in with the volume at some arbitrary number? As far as your PSU, if the PSU handles 285 Watts and it is 75% efficient, it does not mean 75% of 285, it is 285 watts is 75% of what the PSU is pulling. Of course your PSU is only going to draw what it needs. Just like your amps will only draw what you need. Bottom line is you are asking a question with so few details that it would be impossible to answer you. I could tell you that I draw 50 amps from my sound system, but what does that do for you? Unless you duplicate my setup, keep the volume at precisely the level that I have mine, and duplicate my electrical system, the answer is completely pointless. This reply is pretty pointless as well I guess, so it will be my last. Maybe someone else can play guessing games with you.

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    FLAC sdashiki's Avatar
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    if you want to run your stuff while the car is off, get a second battery/isolator combo and you are good to go. no more long posts of electrical mumbo jumbo, just some $ spent.

    But in the end, if you are running under 1000 watts, and you arent POUNDING the windows on the blockm it should last a good hour or more without needing a jump. but why the hell would you do this anyway, it cant be good for the battery.
    (All done)
    iPad Mini 128GB, RF 600.5 amp, JL12W0V2, 8 Infinity Components

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    Quote Originally Posted by Linus
    How much power does an amplifier draw? I'm trying to do some calculations on how long my system will run on a deep-cycle battery. If anyone out there has hooked up a multimeter to the power input on their amp (or is willing to do so), I'd be curious to know the result!
    How long is a piece of string?

    This may sound like a silly question, but it is no different than the one you asked.

    The amount of power an amp will draw depends entirely on the amp and how loud you crank it up. And at any given volume level, there will still be a huge difference in power usage depending on the design of the amp.

    That said, I have a portable PA rig driven by a 115 AH deep cycle battery which I can play through a crappy Dual (Chinese) amp (rated at 70 watts RMS/channel) all day and not fully discharge the battery. This is my "daytime" chillout PA rig I take out to Burningman. During the night I run a generator to power a real PA system, and feed the excees A/C into charging the battery back up for the following day.

    -p.

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    Low Bitrate Linus's Avatar
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    Okay, let me try this again. I'm looking for information. I realize that power draw will vary depending on volume level, amp efficiency, max amp output, input voltage, etc., but I'd like to get a few data points so I can see how much these things vary. For example, StrataG, if that 50A is a real number, I'd like to know how much it varies from minimum volume to high volume. I'd like to know what the watt rating of the amp is, and what class (A/B or D) electronics it uses. Then if other people have remotely similar setups with a different amp, I can get an idea of how power draw varies from amp to amp.

    My computer speakers draw 20-22W AC continuously no matter how high or low the volume is - I found this curious considering they're rated at 130W for the sub and 35W for each satellite.

    [Edit]Sorry Gnomad, I hadn't seen your post when I wrote this. Thanks for passing on what you know, even though it's hard to get too much out of it without knowing exactly how much your battery drains in how much time. Assuming the Chinese amp is the only power load, that equates to something less than 172W - not surprising given the max rated output is 140W[/Edit]

  10. #10
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    Quote Originally Posted by StrataG
    Bottom line is you are asking a question with so few details that it would be impossible to answer you.
    Not really. He's asking someone to go out to their vehicle with an ammeter, and measure the current. Then come back, and post what their system consists of, and their current draw.

    Unless i'm misunderstanding him? Either way, i can't help ya out..i dont have a system..yet

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