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Thread: 200 Watt DC-DC PSU

  1. #51
    Maximum Bitrate Rundell's Avatar
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    Wow Thanks! That's a great idea! Took me a little bit of thinking of what exactly you were saying but I get it. I drew a diagram just to be sure. If you don't mind let me know if I have everything right and that I'm not missing anything. I'm using a regular automotive 12V relay I got at Napa.
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  2. #52
    FLAC Mastero's Avatar
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    Quote Originally Posted by mobileh1
    There is only *one*sure fire way to survive a crank with a load like a computer draws, and that is an auxillary isolated battery. Especially in a diesel where the glow plugs cycling draw a huge current. My vehicle has two (in parallel) batteries for cranking, and one for the electronics, the alternator charges all three, but the 3rd battery is isolated from the others. The cranking batteries are deep cycle Optima yellow tops, and the electronics battery is an Optima red top.

    I dont agree My homebuilt Sproggy Mk-3.5 Survives the Diesel Start of my Mercedes C250 D with no problem..

    Mastero

  3. #53
    Raw Wave Rob Withey's Avatar
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    Quote Originally Posted by Mastero
    I dont agree
    Ditto. My homebuilt ISR supply survives the diesel start of my car too. The power supply is rated right down to 9v.
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  4. #54
    Constant Bitrate STI_FFY's Avatar
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    Quote Originally Posted by Rundell
    Wow Thanks! That's a great idea! Took me a little bit of thinking of what exactly you were saying but I get it. I drew a diagram just to be sure. If you don't mind let me know if I have everything right and that I'm not missing anything. I'm using a regular automotive 12V relay I got at Napa.

    That was the gist of it. The ITPS in your drawing shows "acc power" through a 30A fuse. Actually there should be two inputs - the car's battery to the ITPS "+12V battery" terminal as well as the ACC power through something much smaller like a 1/4A fuse to the ITPS "switched +12V" terminal. The ITPS has a built-in polyfuse to protect the battery line, and current draw on the ACC input should be less than a milliamp.
    SeeYa! -Jim-

  5. #55
    Constant Bitrate STI_FFY's Avatar
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    Oh, two other nits, Rundell -

    The power out from the ITPS to drive the relay and the power out from the ITPS to the fans/LCD is actually the same wire. Your diagram implies they are separate.

    It would also be a good idea to put a "snubber" diode across that relay's armature winding to prevent inductive kick from zapping something in the fans or LCD when the ITPS output is deactivated. You can use a 1N4001 for this, they are cheap and available at local radio shack.
    SeeYa! -Jim-

  6. #56
    Maximum Bitrate eCarô's Avatar
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    STI_FFY, if the PSU shuts down properly, you wouldn't need the relay at all, would you? Once the PC shuts down, there is relatively no current draw from the PSU, because it shuts down everything except the 5VSB rail.

    If you did add the relay, you may need a mobo that supports "Restart after power failure", or a delay on the power on signal from the ITPS (so the PSU has time to power up first).

  7. #57
    Constant Bitrate STI_FFY's Avatar
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    Quote Originally Posted by eCarô
    STI_FFY, if the PSU shuts down properly, you wouldn't need the relay at all, would you? Once the PC shuts down, there is relatively no current draw from the PSU, because it shuts down everything except the 5VSB rail.

    If you did add the relay, you may need a mobo that supports "Restart after power failure", or a delay on the power on signal from the ITPS (so the PSU has time to power up first).
    You could be right about the current draw, I suppose it depends on the PSU being used whether or not the residual current drain is negligible.

    I also assumed one is not using "standby", and is using the ITPS power switch pulse to cause shutdown or hibernation (the latter is my choice) when the ACC voltage disappears, so the concern for restart after power failure is irrelevant.

    The idea was based on the behavior of the ITPS itself when used as a regulator for the DCPS input. It totally removes power from the DCPS' input via an FET after the shutdown delay has elapsed.
    SeeYa! -Jim-

  8. #58
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by STI_FFY
    You could be right about the current draw, I suppose it depends on the PSU being used whether or not the residual current drain is negligible.

    I also assumed one is not using "standby", and is using the ITPS power switch pulse to cause shutdown or hibernation (the latter is my choice) when the ACC voltage disappears, so the concern for restart after power failure is irrelevant.

    The idea was based on the behavior of the ITPS itself when used as a regulator for the DCPS input. It totally removes power from the DCPS' input via an FET after the shutdown delay has elapsed.
    My concern was that the PSU and mobo won't have good power on 5VSB for several milliseconds after the ITPS is triggered, and it may not be ready for the power on signal.

    Setting "Restart after power fail" would get around this, because the mobo will start after power returns to 5VSB rgardless of whether or not it sees the start signal from ITPS.

    If "Restart after power fail" is not available, you may need to delay the power on signal from the ITPS until the mobo is ready.

  9. #59
    Maximum Bitrate eCarô's Avatar
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    Quote Originally Posted by eCarô
    ...you may need to delay the power on signal from the ITPS until the mobo is ready.
    Or maybe the ITPS does that already. I don't have any experience wth one.

  10. #60
    Constant Bitrate STI_FFY's Avatar
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    Quote Originally Posted by eCarô
    Or maybe the ITPS does that already. I don't have any experience wth one.
    Yes, the ITPS senses ACC going active, gates it's output, then delays about 4-5 seconds before pulsing the power switch of the mobo. The input power to the DCPS (and its 5VSB output) will be stable before this occurs.

    Sorry I misunderstood your concern.
    SeeYa! -Jim-

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