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12 volt regulated power supply and compaq dc/dc converter

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  • 12 volt regulated power supply and compaq dc/dc converter

    hey guys, i've been a lurker around here for a while but i figured id start on my own first project. so im a poor university student so im trying to roll my own power supply. this is what i've found so far. i've succesfully used this http://cgi.ebay.com/HP-COMPAQ-DC-POW...item4a9daf987c

    power supply to power my intel d845hv motherboard. its going pretty well, but it doesnt look like the 12 volt rail is regulated, still, not bad for the price. i've been looking around for a regulated 12volt supply capable of 10 or more amps, but it looks like these are pretty hard to find for a reasonable price (i have no job ). the next step im going to take is to roll my own boost converter followed by a buck converter to get a regulated 12 volts. why not a boost/buck? because im lazy and its just easier for me to do this. should give it a wide operating supply while still being relatively simple. ill post some more info as the parts come in, possibly schematics. wish me luck!

  • #2
    Good luck! I think you'll find that while it may be less expensive than buying a proven power supply, it may be more risky for your costly electronics to be connected to them, costing you more than you save.

    If you know exactly what you're doing, no problem. If you're pretty sure you know what you're doing, it might be a problem.

    Carnetix P1900's are for sale in the classified section for around $80. I'm going to guess that you'll spend half of that in parts and more in effort. But, this hobby is about doing it your way. If you come up with a solution, be sure to post it here. There will be plenty of people interested in it!
    Originally posted by ghettocruzer
    I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
    Want to:
    -Find out about the new iBug iPad install?
    -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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    • #3
      well, im pretty sure im going to spend 5 times the money and get 1/3 the performance. but i have like 30 sticks of ram several motherboards and a pile of power supplies lying around. Worst case i break something i reach into the pile and get out another p3 board. Im mostly doing this for the fun of it but hopefully ill learn some usefull things that i can give back to the community.

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      • #4
        alright, so heres a few things i've learned so far. on the dc/dc converter, all you need to do is splice your 12 volt wires into the 2 16 volt capacitors on the board closest to the slot connectors. the atx looking connector has 3 5 and 12 volt connectors. 5 volts is red, 3 volts is brown, and orange is 12 volts. it has a voltage range of 11.52-12.6 volts, and its rated to 340 watts. it has a -12 volt line but i was unable to find it, so i used an isolated 15 volt dc/dc converter http://www.bgmicro.com/PWR1293.aspx ($2) and a lm79m12 regulator. i hooked the positive output to ground and the negative to the atx -12 volt line. for power on, i used a relay on the positive line of the board and connected the coil to a pnp transistor. when the board pulls the pwr_on line low this activates the relays and turns the power supply on. standby power is supplied by a lm7805 regulator that is powered before the relay. the intel d845hg board has been super picky about power. sometimes it works perfectly, sometimes it refuses to boot and drives have to be disconnected or ram has to be changed. my old dell p3 board boots perfectly every time on it. so far its running windows xp like a champ. the power supply is going to be a dc laptop power supply (that has 12 volt out!). if this works ill have a cheap supply for about $30 . ill try and get some pictures later.

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        • #5
          quick tip. if you use this converter, don't touch the little thin wire connector. i tried to power a small (1 watt) amp from this. apparently it has a connection that connect to the feedback of the voltage regulator. Im out a 120GB sata drive now (smoke and fire) i feel really dumb for using that as it was my last sata drive i had. so long story short, old dell boards are built like champs and DO NOT TOUCH THE THIN WIRES!!!

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          • #6
            well, i just destroyed two motherboards today. my GF hit the power cable and the mobo didnt like it :/.... shortly after replacing it my hand hit the pci riser and it knocked it out, shorting some pins in the process :/.... motherboard didnt like that either. so some advice, do your testing somewhere other than your bed. anyway, just got in a 12 volt to 15 amp 5 volt switching regulator and a 5 volt to 9 amp 3.3 volt regulator. once the laptop power supply comes in ill test both of them. if those little switching regulators work ill be able to make a super tiny power supply. heres what they look like



            http://www.mouser.com/images/emerson...C%20Series.jpg

            edit: Those 5 volt switching regulators suck. so far i've burned out three of them. connected the vin, paid attention to the trimming resistors, watched the amperage. but nope. suddenly huge amp draw and smoke.

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            • #7
              well, some progress. found that those cheapo walmart phone chargers make an excellent 5v standby power source, got rid of the lm7805 (pretty warm). i took a look at the switching circuit inside, its based on an ap34063 switching regulator. it looks like it barely needs any external parts. im going to take the inductors off those other 5 volt supplies, use some high power fets and gate drivers (lying around) and try to make the a 5 volt buck and a 12 volt buck/boost. should have some results and pictures by monday.

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              • #8
                That's what I've been doing - buying cig-plug chargers for $2 each for their PCB & MC34063 (else TL496 or LM2576 etc) chips with the intent of changing the feedback resistor divider for 5V and boosting the inductor size (with optional FET/transistor) to boost current.

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                • #9
                  well, the mc24063 thing has been interesting. their output waveform sucks and my fets dont like it, but they seem to work for a while, going to experiment more with that. boost converters are hard to make :/. going to bust out the 200kilowatt igbt because im getting tired of these little fets dying out. might as well have fun with this. next attempt involves a 48VDC server power supply and a cheapo ebay boost converter. one of these combinations is bound to work.

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                  • #10
                    How can you blow FETs - not using 60A to 80A units?

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                    • #11
                      30 amps units, running them in linear mode. the output waveform was pretty much a triangle with a peak of 2 volts (shivers)

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                      • #12
                        You had me confused - a 34063 in linear mode?

                        But you mean the FETs. Why?
                        Surely they should be full on-off for SMPS...?
                        They'll be blowing due to overheating (over 200W peak?)

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                        • #13
                          the 34063 was not outputting a proper waveform. the ideal fet gate drive is a square wave wheras this was a triangle. triangle waves keep the fet in linear mode for far too long causing extreme resistance losses and cause the fet to heat up alot. the heat and current draw cause the fet to fail.

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                          • #14
                            A-ha!
                            And rats!

                            You'd expect square, though I haven't looked in detail... Well I have, but across a dozen or so chips.
                            I do recall a triangular wave but I thought that was related to the rC charging...
                            If it's a low slew rate at high frequency, maybe lower frequency hence a lower "linear" duty-cycle....

                            And the last time I looked at these was for a CDI (Capacitive Discharge Ignition) when I realised there were great PSUs that drove (MOS)FETs directly for the 350-500V DC CDI supply. All of a sudden my ideal CDI became a cheap item - $10 to $20 for the PSU, and then $2 for every splug (IgCoil) output and a $few for whatever triggering....
                            Then I got a common standard reluctor ignition system that cold-started below 6V and I lost interest....

                            My only resurgence was to build my own supply(s) rather than spend many $tens on 5A and higher outputs.... (Have I mentioned suckers that spend $300 - $500 for 20A or 40A dc-dc converters so they can "charge auxiliary batteries properly(sic)"?) (Yes - that mob that buys one or 2 rehoused 5c diodes for $42.)


                            I'll keep my eyes open....
                            Maybe could integrate or Schmidt the outputs, but surely that isn't needed....?

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                            • #15
                              tried 2 schmitt triggered not gates in series, that didnt really work out so well. i think i destroyed that chip anyway......... which is why i bought 3! i think i need to clean up my circuit layout and really double check things, im sure with some love i could get this circuit working.

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