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Thread: A 12v dc-dc 12v power supply

  1. #1
    sam
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    Wink A 12v dc-dc 12v power supply

    Havent seen this one mentioned before but after trawling through the Farnell site found this manufacturer and went direct

    www.switchedmode.com product code SM3392. 138w output Apparently it has a pot inside so the output voltage can be adjusted around the 12-14 mark. At less than 9.5v it will grey out.

    My grand plan is to have a split charge relay going into a sealed leadacid battery followed by this DC-DC converter followed by the cupid case with its 12v atx dc-dc converter. This will hopefully let the engine crank and the computer stay alive.

    delivery time was about 2 weeks and cost was about 64 ex vat ex shipping.

  2. #2
    Raw Wave Rob Withey's Avatar
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    SM3392 looks like 13.8V output at 85W afaics.
    SM2430 is the 138W unit, also at 13.8V.

    There is still some contention as to whether it's a good plan to run more than 12V into these power supplies isn't there?


    Rob
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  3. #3
    sam
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    Correct !

    But I rang Switched and they said that it was just a case of adjusting the potentiometer to get the 12v. Time will tell !

    The power output is an upgrade from the old spec - datasheets can be downloaded from the address given previously.

  4. #4
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    hmm..

    why do it the hard way ? :P iwe been using mye car's battery charger as a "power source" for my OPUS psu ... the charger can deliver 6A . ( the carputer uses 2 - 3A ) .. iwe been using this solution for 2 weeks now.. without any issues.. or problems... (ive checked the voltages the charger gives the PSU.. it ranges from 11V - 17V (usually stays at 12 - 13V) ... goes a litt dodgy ... but the carputer stays on ..


    just a thought... could the charger solution be a long time strain on the PSU ? .. so that one day the thing would die on me? or would that happen like, instantly ?
    "If A equals success, then the formula is: A=X+Y+Z. X is work. Y is play. Z is keep your mouth shut."
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  5. #5
    sam
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    Your setup is somewhat different, I am not using an Opus power supply in the computer.

    In the Cubid case there is a small 55W? DC-DC converter that probably would not like 17v and I believe has a common rail on the 12V to the hard disk etc.

    This system is going into a diesel van, Cranking is typically harder on the battery and the system needs to stay up through 40+ stop starts per day.

  6. #6
    FLAC cproaudio's Avatar
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    Originally posted by sam
    This system is going into a diesel van, Cranking is typically harder on the battery and the system needs to stay up through 40+ stop starts per day.
    the input voltage on most those power supplies are 11-15. Cranking a diesel will drop below 10 volts into the 8-9 volts area. If you don't want the power to drop during crank, then get a battery isolator and a small seprate battery for the computer.
    NEW complete and updated My project with 100+ pics on 7-4-03
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  7. #7
    Maximum Bitrate CrazyLittle's Avatar
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    forget a second battery - just build a Tank circuit (Big Cap with diode in line)

  8. #8
    Variable Bitrate
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    Originally posted by sam
    Your setup is somewhat different, I am not using an Opus power supply in the computer.

    In the Cubid case there is a small 55W? DC-DC converter that probably would not like 17v and I believe has a common rail on the 12V to the hard disk etc.

    This system is going into a diesel van, Cranking is typically harder on the battery and the system needs to stay up through 40+ stop starts per day.
    ahh, ok .. im only using the charger when im transferring larger amount of data from my home computer .. (thru WLAN, or regular LAN) ...

    Richard
    "If A equals success, then the formula is: A=X+Y+Z. X is work. Y is play. Z is keep your mouth shut."
    Albert Einstein

  9. #9
    sam
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    Originally going to use a second sealed lead acid battery with a split charging relay. Would be interested in how to wire up the "big cap" and diode.

    Assume that the diode goes on the positive and the diode goes ??? when you say big, what do I look for ?

    Thanks

    There is also the issue of residual drain on the battery over night - guess it will be a switch to cut the power going to the 1st DC DC converter

  10. #10
    FLAC cproaudio's Avatar
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    Originally posted by sam
    My grand plan is to have a split charge relay going into a sealed leadacid battery followed by this DC-DC converter followed by the cupid case with its 12v atx dc-dc converter. This will hopefully let the engine crank and the computer stay alive.
    The cost of Split charge relay (in the states, we call them battery isolators), second leadacid battery, DC-DC converter, cupid case would cost you more than an Opus DC-DC PSU. If you have the knowledge to wire up all that, then im sure you have the knowledge to custom build a plastic case for the mobo, opus, HDD and CD drive.

    Originally posted by CrazyLittle
    forget a second battery - just build a Tank circuit (Big Cap with diode in line)
    The diode's current rating on a tank circuit must be greater than the current rating on the electronic components. This means if all of his DC-DC PSU's maximum current draw is 12 amps then he would need a 15 amp diode. The current that the DC-DC PSU needs during normal operation goes through the diode. The cap just holds the voltage up enough so that the computer won't reboot when he cranks the engine. There's still a risk that the cap might discharge enough for the computer to reboot during crank. To gurantee no reboot during crank, 2nd battery or Opus DC-DC PSU is the way to go.
    NEW complete and updated My project with 100+ pics on 7-4-03
    If you have a Shuttle FV24 motherboard in perfect working condition for sale, please PM me.

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