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Thread: PSU question

  1. #1
    Low Bitrate enhanced08's Avatar
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    PSU question

    I'm new here and am having problems picking which PSU to use, AC to DC or DC to DC. I have been building computers for years and am A+ and Net+ certified so as far as the computer itself, I can do it. I took some electronics classes in high school and know that converting DC to AC then back to DC is a waste so DC to DC seems like the best way to go. I have figured out that my computer will use about 275 watts of power (I always add a bit more just to be safe).

    I read on here that DC-DC only works with less that 200 watt systems so AC-DC seems to be my only option. The thread I read was from back in 2005 so has anything changed since then or is the 200 watt rule still apply?

    One other small question I have is, I keep reading about the use of hibernate on the computer rather than shutting it down. Wouldnt it draw power from the battery when its hibernating? Whats wrong with simply shutting the system down?

    Thanks!

  2. #2
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    if you suspend to disk not ram than the computer is completely off when the car is off and not drawing any power but it well act just like you never turned it off when it boots up the next time.

  3. #3
    Neither darque nor pervert DarquePervert's Avatar
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    Quote Originally Posted by enhanced08
    I'm new here and am having problems picking which PSU to use, AC to DC or DC to DC. I have been building computers for years and am A+ and Net+ certified so as far as the computer itself, I can do it. I took some electronics classes in high school and know that converting DC to AC then back to DC is a waste so DC to DC seems like the best way to go. I have figured out that my computer will use about 275 watts of power (I always add a bit more just to be safe).
    There are no DC-DC PSUs currently on the market that will support a 275w power draw.
    You also need to understand the three rails output by the PSU. If you're A+ certified, you should know all about that.

    I read on here that DC-DC only works with less that 200 watt systems so AC-DC seems to be my only option. The thread I read was from back in 2005 so has anything changed since then or is the 200 watt rule still apply?
    How about looking in the store here (link at bottom of page) and seeing what the DC-DC PSU offerings are?
    Better yet, read this thread in the FAQ Emporium. It explains much. I recommend reading every topic in the FAQ Emporium that even remotely relates to your setup ideas.

    One other small question I have is, I keep reading about the use of hibernate on the computer rather than shutting it down. Wouldnt it draw power from the battery when its hibernating? Whats wrong with simply shutting the system down?
    There is no power draw by a PC that is in hibernate mode. The entire contents of RAM are written to the HDD, then restored when the PC resumes from hibernate.
    Nothing is wrong with a complete shutdown, but resuming from hibernation is significantly faster than a cold boot. That means you get to hear your music that much sooner and your media player will be at the same point in the same song it was playing when you hibernated.
    Have you looked in the FAQ yet?
    How about the Wiki?



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  4. #4
    Low Bitrate enhanced08's Avatar
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    Ah... save the image to disk! That makes sense, I was thinking it would be saved in RAM. Does the system start faster after hibernation than it does from a normal start? I dont own a laptop and never use hibernate so its all pretty new to me. It seems it would be about the same booting right into your front-end or using hibernate to "never turn the system off". Know what I mean?

  5. #5
    Low Bitrate enhanced08's Avatar
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    Awesome, thanks for the help! I'll get myself an inverter and go from there.

    Thanks again and I'm sure I'll be back for more help real soon!

  6. #6
    Constant Bitrate RawsonDR's Avatar
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    Suspend to RAM is what's called "Standby." Hibernate will be a bit faster usually, but you can experiment with that stuff on your own and do whatever works best for you. It's also important to remember that, even if your computer is off (from either hibernate or shut down) there might still be some power draw on the +5VSB line on your PSU, and inverters also might draw power even if everything connected to them is turned off. If your power supply doesn't handle this you'll have to be aware of it and solve it yourself - there are many threads about this.

    Don't forget that many system power calculators used inflated values, as do some desktop power supplies. Point is, unless you are positive your system consumes an actual 275 Watts of power during use, you may be able to still use a DC-DC power supply. Many people here are using computers that would normally calculate to over 250 Watts depending on which calculator you use, but are powering them from an Opus 150, M2-ATX, or DSATX power supply. You can either power up your system and measure it's power draw first hand, or search through this forum and look at other's Worklogs to find people with components similar to yours, and seeing what they are doing for power.

  7. #7
    Low Bitrate enhanced08's Avatar
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    I thought about setting up my computer as a desktop first and but a "Kill-a-watt" which would allow me to measure exactally how many watts the system will use. I would prefer using a DC-DC because it makes more sense and will be more efficient.

  8. #8
    Neither darque nor pervert DarquePervert's Avatar
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    Actually, suspend to RAM has the fastest resume time. The problem is that suspend to RAM requires power to the PC to maintain that state. The power draw is minimal compared to what the PC normally draws, but it's still drawing power.

    Some laptops have an option to automatically hibernate after a certain period of time. I think you could suspend-to-RAM and have the laptop hibernate after XX minutes to prevent draining either the laptop battery or the car battery. You might be able to have the same options on a desktop by enabling both S1 & S3 states, but I've never attempted it.
    Have you looked in the FAQ yet?
    How about the Wiki?



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  9. #9
    Constant Bitrate RawsonDR's Avatar
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    Quote Originally Posted by RawsonDR
    Suspend to RAM is what's called "Standby." Hibernate will be a bit faster usually, but you can experiment with that stuff on your own and do whatever works best for you.
    Yeah, I meant to say that hibernate would be a bit faster than normal boot-up. They were separate responses to separate questions. I see how it sounds, now.

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