Increasing voltage on 12V server power supplies

Discussion in 'Radio Circuits, Repair & Performance' started by K8AI, Apr 25, 2018.

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  1. K8AI

    K8AI Ham Member QRZ Page

    I'm in the process of writing up a procedure to modify surplus high-current HP server power supplies.

    In the meantime, I can describe how to do it. First, you'll need to solder a couple 1K resistors across a couple pairs of contacts on the edge connector in order to turn the supply on. There should be a few posts on the web describing which pins need to be connected. Once, you have it outputting 12V, you'll need to make the following mod to increase the output voltage up to around 13.6.

    On many HP power supplies, there is a daughter board that's mounted perpendicular to the main board. It will be connected to the main board by a large number of header pins. Connect the lead of your ohmmeter to the positive output contact on the output edge connector. With the other lead, probe each header pin that connects to the daughter card until you measure zero ohms on one of the pins. This is the pin that sends the output voltage (12V) feedback to the PWM controller. The trick is to lower this voltage so the controller will raise the PWM duty cycle to the switching devices so that the output of the supply will increase.

    How you do this is to cut that pin, solder a couple wires, one to the pin on the main board and another to the pin on the daughter board. Then solder two silicon (.6 to.7 barrier potential) diodes in series, anode to cathode. Connect the wire from the main board to the anode and the wire from the daughter board to the cathode. This will "fool" the controller into thinking that the output voltage is 1.2 to 1.4V too low and increase it accordingly.
    Put some heat shrink or tape over the diode assembly and tuck it inside the supply.

    I modified two different supplies today and I plan to add RF hash filtering and more EMI filtering on the input, maybe a overvoltage crowbar circuit and stuff the whole works in another metal box and I should have a very cheap, 13.6V @ 40-50A, efficient power supply.

    I hope to post pix soon.

    Curt, K8AI


    "Radio Amateurs have earned a license to modify, design, build, and operate their own transmitting equipment and antennas. That is unique in the radio services. You have a license to experiment on the air." - Rick Campbell, KK7B
     
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  2. CX3CP

    CX3CP Ham Member QRZ Page

    Hi Curt how are you ?
    very good and convenient post, I have modified some PS of computer servers and / or cell station equipment. In the case of PS servers, I am using in my laboratory, the DPS-800GB model that is capable of delivering 1K watt at 13.8 volts DC. In this case it was only necessary to make a few connections to ensure the PS on condition and place a resistance to raise the voltage to 13.8. all this mod was done only in the output edge connector.
    20180424_233711.jpg 20180424_233726.jpg
     
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  3. AD5HR

    AD5HR Ham Member QRZ Page

    Everyone needs a "Bender" on the workbench!
     
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  4. KJ4ADN

    KJ4ADN Ham Member QRZ Page

    Curt,
    We have several of the HP DPS-600 PB type server supplies, all modded and deliver 13.6vdc.
    Pop the cover off the case, and go directly to the large studs for the output.
    All the connections are easily made inside the case, including adding the resistor, or POT for adjustment.

    They do like to trip easily, when current capacity is exceeded, even for a second - like inrush from connecting a battery.
    I've also added a small bank of 4 caps to give me s little buffer for those instantaneous loads from keying the TX, but placing a battery inline also works.
    Going directly to a radio, and keying up often... like working a contest, trips them. One of my daughters was working the VAQP and kept getting knocked off, till we put a pair of 40ah batteries inline. She was also getting complaints her IC-7300 was putting out scratchy audio & clipping (brand new radio). The batteries took care of that too.

    The major drawback of them has been their inability to adapt to varying loads caused by the radio when you transmit, we've had the same problem with sudden voltage drops while transmitting, even though we're pulling less than 25amps. This has been our experience with 2 IC-7300s, and IC-7610 and K3 - batteries in parallel or Capacitors somewhere near the rig took care of it in each case. The voltage drops really screw up the radio's transmit - beware, it's not a filtering problem, it's a PS load problem.

    On the bright side, they are virtually noise free across the bands, and absolutely will not run over 13.8vdc.
    They work great for supplementing an existing supply, have a really high efficiency conversion rate and handle a *steady* load nicely, like charging.
    But, for radio use, with output amperage bouncing up and down - nope, just hook up a VOM & watch the voltage, and you'll see what I mean.

    I have lots of pictures how I modded mine a couple of years ago, if you're interested.
    13.6vdc was the highest I could get, before they became too unreliable to hold & keep running.

    Oh, BTW, the DELL supplies of similar size and slightly greater capacity - worked for just a short time, and failed, I got about half a dozen of them, all went bad.
     
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  5. CX3CP

    CX3CP Ham Member QRZ Page

    LOL ... this is my luck bender
     
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  6. AFACEFORRADIO

    AFACEFORRADIO QRZ Member

    Greetings,
    I keep coming back here everytime I google "modifying an hp server psu" so I thought I'd field my question here;
    My goal is a simple mod that'll effectively convert these psus into adjustable benchtop power supplies, however dc-dc buck and boost converters rated much higher than 20a are either rare or expensive industrial solutions that don't really suit my needs.
    Then I came across this page and it gave me the idea; why not install a small $20 combination buck/boost voltage converter in place of the above-mentioned diodes that the author writes of? If it works, it'll open up a world of possibilities for me. Does this pin tasked with monitoring voltage also keep an eye on current in the same manner?
     
  7. AI6KX

    AI6KX Ham Member QRZ Page

    I can't see where you installed a resistor on the edge connector. Can you explain please. 73,
    Steve
     
  8. CX3CP

    CX3CP Ham Member QRZ Page

    Hi, for this type of PSU DPS-800GB you just add one 1k8 resistor like the picture show and simply put a wire between the connector pad for the PS ON status.
    with this modification you can get a voltage close to 13.8 vdc

    upload_2019-7-4_20-8-22.jpeg

    upload_2019-7-4_20-8-36.jpeg

    upload_2019-7-4_20-8-47.jpeg

    upload_2019-7-4_20-8-58.jpeg
     
  9. AI6KX

    AI6KX Ham Member QRZ Page

    Thank you, Alberto.
    73,
    Steve JS6TMW
     
    CX3CP likes this.

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