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  • looking for a power supply

    I need 1.8 volts DC at 6 to 7 amps.

    Any ideas on getting this, I only need one so continuity of supply isn't a problem.

    I was wondering about an ATX computer power supply but have no idea what they put out.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  • #2
    Not sure if this one is DC or AC output.

    http://cgi.ebay.com/PT5404N-POWER-SU...item19b854bd62

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    • #3
      John,

      If you can handle a small surface mounted package, Linear Tech has their micro-module series. A chip/module like the LTM4616 puts out dual 8A supplies at 0.6 to 5 volts. Only problem is that the input is 2.7 to 5.5v.

      You can purchase the eval kit online. #DC1245A is $65 and is basically a mounted device (proper thermal design, etc.) with all I/O and control lines brought out to human sized connectors. www.linear.com

      1.8v is a common core voltage on various processors but I haven't seen any power supply modules at that voltage. It is usually generated locally as needed.

      Spoke too soon ... here you go but not cheap: http://www.acopian.com/store/9-%287%...?min=1.5&max=5

      MTNGUN put up a nice TI PT5404 module that is thru hole, similar to the Linear Tech but definitely easier to handle for a one up use. Same issue in that the input is low voltage dc.

      Den
      Last edited by nheng; 12-12-2009, 08:27 PM.

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      • #4
        Originally posted by John Stevenson
        I need 1.8 volts DC at 6 to 7 amps.

        Any ideas on getting this, I only need one so continuity of supply isn't a problem.

        I was wondering about an ATX computer power supply but have no idea what they put out.

        .
        What for? .
        Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
        ~Practitioner of the Electromechanical Arts~

        Comment


        • #5
          ATX won't cut it, closest you could get is 1.7V and that is using 3.3V as a reference and 5V as a supply.

          +3.3 Volts
          +5 Volts
          -5 Volts
          +5 Volts
          +12 Volts
          -12 Volts

          http://www.helpwithpcs.com/courses/p...nc-pinouts.htm

          1.8V can be found on motherboards for memory controllers, etc, but that is probably a DC-DC bridge that runs on 3.3V or 5V. [email protected] is going to see quite a drop over any distance. What kind of efficiency do you need? It would be easy to kludge something together that would feed from an ATX supply if you don't mind some heat loss and know more about what you are powering.

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          • #6
            My first concern is regulation? How close to 1.8 volts? Does the load vary? Is the load reactive or have characteritics that interfer with a regulated or a digital power supply? Will an analog supply do?

            How about a variable dropping resistor from a computer 5 V supply? 3.2 volts drop at 8 Amps is 2.5 ohms @ 25 watts and at 6 amps the volts will drift up to 2.4 volts. Will that hurt?

            Plating supplies are variable, low volts, and frequently reference from the tank busses. They might be a good first choice.

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            • #7
              The forward voltage drop of diodes is reliably 0.7vdc. The collector/emitter voltage of a transistor in saturation is 0.3vdc, depending on the transistor. So if you wire two power diodes and an NPN power transistor in series with the base of the transistor connected to the collector you will have a voltage of 1.8vdc that is highly regulated. You then put a current limiting resistor between the collector and vcc, put your load across the active componnents, and turn it on.

              The limiting resistor has to pass the full current of the load plus some waste current through the diode/transistor devices. This is a simplified circuit - a current limiting resistor is also needed in the base-collector connection.

              Last edited by dp; 12-12-2009, 10:58 PM.

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              • #8
                Originally posted by Weston Bye
                What for? .

                I suspect he is in a pickle ...
                --
                Tom C
                ... nice weather eh?

                Comment


                • #9
                  Id recommend this 100lb supply I just got at auction. Its rated for 0~150v and 0~12A. that fits your needs doesnt it? j/k.
                  For some more useful information...
                  www.allelectronics.com has verious supplys you could start off with an add a simple 1 chip SMPS.
                  Linear regulators keep amps the same, ie you'd need to start off with a 5v+ supply at 8amps.
                  SMPS incress amps at the expense of volts, ie they maintain wattage, more or less (70~90% is rather typical)
                  So, a 1.8V 8A SMPS would only need 5v at 4A~, and also get a lot less hot and need less heatsinks.

                  dp: Shunt regulators are not a great solution at high power. Try considering a series PNP whose base is controlled by the 1.2v.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                  • #10
                    Originally posted by Black_Moons
                    Id recommend this 100lb supply I just got at auction. Its rated for 0~150v and 0~12A. that fits your needs doesnt it? j/k.
                    For some more useful information...
                    www.allelectronics.com has verious supplys you could start off with an add a simple 1 chip SMPS.
                    Linear regulators keep amps the same, ie you'd need to start off with a 5v+ supply at 8amps.
                    SMPS incress amps at the expense of volts, ie they maintain wattage, more or less (70~90% is rather typical)
                    So, a 1.8V 8A SMPS would only need 5v at 4A~, and also get a lot less hot and need less heatsinks.

                    dp: Shunt regulators are not a great solution at high power. Try considering a series PNP whose base is controlled by the 1.2v.
                    He's British - he's even worked around Lucas electrics - he's got to be used to this . He's probably swapped out a few zener diodes on Triumph charging circuits, in fact.

                    And if the limiting resistor is chosen well there will be little shunt current needed. If 5v is the supply then the voltage across the resistor is 3.2v. 3.2v @ 8 amps is 0.4 Ohms which is just a few turns of wire wrapped around a beer can for a heat sink. Leave room for .25A through the semiconductors and you have 0.45W waste heat and the current limiting resistance is now 0.39 Ohms.

                    I presume the load is always attached so there is no need for the semiconductors to suck up the full 8 amps. Total power is now 40 watts or about as much as a refrigerator light. About 14 of those watts is in the attached device leaving 26 watts to heat up the beer can.

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                    • #11
                      Look for a Vicor module. Quite expensive new, but they turn up surplus on ebay (usually in the US). Very reliable and with a wide output trim range, so a 3.3v or 5v module could be trimmed back.
                      Paul Compton
                      www.morini-mania.co.uk
                      http://www.youtube.com/user/EVguru

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                      • #12
                        What for?

                        One cell of a lead acid battery is about 1.8 volts under load.
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                        • #13
                          Originally posted by Evan
                          What for?

                          One cell of a lead acid battery is about 1.8 volts under load.
                          Not any of the lead acid batteries in my workshop!

                          They'll all hold 2+ volt well into the discharge.

                          Of course, they are all AGM lead acids (Optimas or Hawkers).
                          Paul Compton
                          www.morini-mania.co.uk
                          http://www.youtube.com/user/EVguru

                          Comment


                          • #14
                            I guess that depends on the load...

                            Ever seen Gates lead/acid D format gel cells? I wish I could find some of those at a reasonable price. Nothing beats lead acid for monster amps under short term load.

                            I currently () have 2 18 amp hr VRLA batteries and 3 55ah VRLAs in my collection for EV experimentation. The 18ah batteries are rated for 248 amps max!!
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              How much regulation is needed? A variac feeding a 6 or 12 volt center-tapped transformer with a current rating greater than 7 amps, then feeding a full-wave rectifier and large capacitor would do it. Adjust the output voltage by adjusting the variac.

                              A non-center tapped transformer could also be used with a bridge rectifier and capacitor for less ripple.

                              A high current, low voltage transformer could be had from a battery charger.
                              Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                              ~Practitioner of the Electromechanical Arts~

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