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Thread: Keypower ATX DC-DC Suppy

  1. #11
    Dustin Haug
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    No there shouldn't be any noise from the DC/DC even at high levels. If there is noise present it's likely from something else.

  2. #12
    Newbie
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    I was thinking about getting an MSI also and i was a little worried about the PSU fitting inside, but, if you wanted, it's techncally posible to leave the PSU outside the box and just drill some holes or something. It's kind of ugly and jury-rigged, but if you absolutely NEED a way to do it, then that's a possibility. Maybe you could do some fancy wire-work and mount connectors to the outside of the case to plug the PSU into from there so that there aren't any gaping holes in the side, and also to keep the cords from straining the connectors on the mobo and H.D and misc parts. This is what I'm thinking about doing.

    Also, I talked to Keypower recently (last week) and they quoted me $130.

    Why the hell are they so expensive when you can buy a regular atx PSU for $40? Is it doing something special or is it just because these are a sepcialty item?

  3. #13
    Constant Bitrate
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    Yes, it is doing something special. Well...not special...just not something that you see everyday...therefore they can charge big bucks and get away with it It converts 12v DC Current from your car's alt/bat. to the proper voltages needed to drive a computer motherboard/devices, whereas a standard atx power supply converts AC current into the proper voltages (DC). I do not know a lot about electronics...

    Are DC-DC supplies anymore complicated than a AC-DC? I always suspected that the higher price of DC-DC supplies was just due to the low demand for them.
    Athlon 500, 128 MB, ATI Xpert 4MB AGP TV-Out, Sound Blaster Live! Value, 8.4 GB, 2x20 Backlit LCD, Keypower 250 Watt ATX DC-DC, DSchmitd Startup/Shutdown Controller, IRMan + Backlit IR Remote, Custom Keypad, 5.6" NTSC LCD, In-Dash Slot Loading DVD, all installed in an '87 Honda Accord LX-i

  4. #14
    Maximum Bitrate
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    I would be willing to bet that if millions and millions of AC input ATX supplies had not already sold, the price of one would be higher than the price of the DC ATX supplies we are seeing...

    AC supply is basically a transformer and a rectifier (I think)

    DC supply is capacitors & regulators (i think)

    mike
    1999 voyager pontoon boat
    (soon to be computerized)

  5. #15
    Variable Bitrate
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    Most DC-DC power supplies are just AC power supplies that work at a lower voltage and have an extra step to convert the incoming DC power to AC. AC is usually easier to work with in a more efficient manner.

    The price difference is most definitely a volume issue. If they sold more, it'd be cheaper. IF you'll notice, out of the DC-DC supplies, the 42-52V ones tend to be cheaper than the 12V ones. That's because the telecom industry makes heavy use of the 42-52V ones. But relative to the computer industry in general, the telecom industry is still small.
    Player: Celeron II 633MHz, 256MB RAM, 20GB IBM 9mm 2.5" Laptop HD (180G/2ms), onboard ethernet/sound/video/tvout, 10"11"x3" case, MPBS1 70W DC-DC PS w/auto-shutdown controller, in-dash lighted switches, 7" NTSC TFT widescreen in-dash LCD, touchscreen, rear-window brake light installed Garmin GPS35 GPS, credit card sized IR remote w/IRMan, mini-wireless keyboard/mouse (sits under seat), PowerMate black knob, MP3s and GPS Navigation (Winamp, CoPilot, SA8.0).
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  6. #16
    FLAC
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    Originally posted by mikeinsanmarcos:
    <STRONG>
    AC supply is basically a transformer and a rectifier (I think)

    DC supply is capacitors & regulators (i think)

    mike</STRONG>
    A linear AC-DC supply is a transformer, rectifier, capacitor, regulator and then another capacitor.

    The way an ATX power supply works is like this:
    120 AC comes in. It goes through a rectifier to become 170 volts (Its either root 2 or root 3 times 120, I can't remember..) The 170 volts is then switched on and off into a transformer at a high frequency (100 KhZ) This means you can use a smaller transformer with thicker wire and less windings (because of the frequency). The transformer then provides several secondary windings and the controller that is switching the power on and off into the transformer looks at the 5 volt line and acts accordingly. (This is why you have mins on the 5 volt line sometimes.) DC-DC supplies work under the same principal. If our cars all ran on 200 volts DC, we could eaisly hack an AC-DC ATX power supply into a DC-DC power supply. If we want to use them at 12 volts, we have to design a transformer that can deal with the lower voltages as well as change a bunch of other componentes to go that route. That is typically called flyback transformer based Switching. One choice is to go the route of inductor based designs that generate 1 voltage per coil. (buck and boost) Since there are a bunch of components made by national and maxim, it is very easy to go this route with out having to deal with transformer.

    Jeff_
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

  7. #17
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    Sorry for the late reply, guys. Here's the URL for the Keypower Dc/Dc unit: http://www.keypower.com/DC_power/DX-250H.htm

    The $130 they quoted you was for a dealer price. I'm sure if you only wanted to buy one from them they'd give you the price I got, if not a little cheaper by now. No, the $180 was w/o shipping. The unit's pretty small, too. Off the top of my head I'd say the unit's about 4.5"Hx5.5"Wx5.75"D. Obviously if you take the case cover off there's a sticker they put on it that'll get broken, thereby voiding your warranty.

    So far I've had my unit and it's working great. Yes, the price is steep but....
    P4 2.4GHz, Intel mobo w/onboard sound & video, 128MB memory, 100GB Seagate Momentus laptop drive, Xenarc 700TSV 7" touchscreen, IRman using Girder, 150W Opus dc/dc psu, Alpine CDA-9835 h/u, MBQuart speakers, Infinity 15" sub, MTX amps.

  8. #18
    Newbie
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    Just for you guys info. I had one for about a month. It works great. I did all kinds of things to it. I took apart the case and mounted upside down to fit it in my homemade case for my mobo. I put some silicone on all the heavier parts so they down fall off. I even extended the wires about 3feet. I comes with about 1ft1/2 of wire. longer and thicker than normal. I used 10gauge wire for all the 5volts and 12gauge wire for 12volt. The rest same gauge wire as powersupply. I turn the fan speed down with a 10ohm power resistor (pretty quiet). Can't save too much space by taking it apart, maybe 1/2in of the top and 1in of the side. When I measure the off mode with 12volt to the ps, it was only 32mA. I guess you could put constant 12volts at that amperage and leave it hook up to the battery. Oh, another thing, My machine is using 800MHz, ATI 32mB rage pro, TV wonder and the power supply doesn't even get hot. Works very well.

    hope this was informative.
    66 Mustang

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