Increasing voltage on 12V server power supplies

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

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  1. YOSUA

    YOSUA QRZ Member

    Hi,
    What I have do with a Dell DM/N Z670P-00 power supply is trying to connect each pin of the daughter board to either the +12V output or the ground output, through a high value resistor (above 120kΩ) while the power supply was ON, and read the voltage output, where was also connected a 12V 50W lamp. Until I found a pin that when connected to the + 12V the voltage drops to about 11V, so I tried to connect that pin to the ground instead, and the voltage increased to about 12.7V. I immediately saw the lamp becoming brighter. I then replaced the resistor with resistors of lesser values until I obtained about 13.7V with a resistor of 43kΩ. So I am now able to modify the voltage output from about 10.8V to 13.7V with a 50kΩ potentiometer connected to both +12V and ground outputs with two adjustable resistors in serial each sides. The problem with that method is that when I try to increase the output voltage above 13.7V (or lower it below 11.8V) then a protection circuit stops the power supply. (That's why I put adjustable resistors to limit the voltage change). If I now I add your two silicon diodes trick, I will be able to vary the output voltage from about 12V to 14.9V instead of 10.8V to 13.7V. If I put a switch to bypass the diodes then I can have both. It may be even possible to add more diodes and more switches.
     
    Last edited: Sep 17, 2020
  2. YOSUA

    YOSUA QRZ Member

    Hi,
    I have the same power supply, and it becomes very hot. There is a sign on a yellow sticker that warns about that. Anything inside becomes hot even with the cover removed and nothing connected at the ouput. I think that the holes on both side of the power supply is to let pass the air from a fan located elsewhere. I would not let that power supply running without a fan...
     
  3. KD0CAC

    KD0CAC Ham Member QRZ Page

    There were a couple different versions , some had fans in the removeable / hot-swap container , and others required using the fans inside the server box .
    Already have several setup to be used , took the connector off the motherboard and use it for coverting from multiple connectors to 2 large for fur current and have the plug .
     
  4. YOSUA

    YOSUA QRZ Member

    That's why one of the IC on the daughter board is a fan speed controller...
     
  5. YOSUA

    YOSUA QRZ Member

    Update 17 Sept 2020:
    I tried the trick to add the two silicon diodes (I used 1N4007 diodes) and got about 13V at the output instead of 12V. That's one more volt, the trick works well. Howewer I am still restricted to adjust the output voltage to the same values as when I don't use the diodes trick. With or without the diodes, the power supply stops when I try to adjust the voltage above 13.7V. Either the protection cicuit doesn't care of the daughter board supply voltage, or that protection circuit is located elsewhere; there are a lot of other components on the main board. Anyway with 10.8V to 13.7V and more than 50A, I have a nice power supply, or a light but powerful car battery charger...
     
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    That is one problem with using them and other open frame / Computer switching supplies.

    They are designed to be mounted in another metal housing, With forced air cooling. If not they can overheat and produce RFI above normal limits.
     
  7. YOSUA

    YOSUA QRZ Member

    Hi,
    I have successfully modified that same DM/N 7670P-00 Dell server power supply to about 14.7V.

    The daughter board is powered by TWO 12V supply, one connected to the main +12V output, and another that is NOT connected to that output. The first one, that is connected to the main +12V output is for the supply of the UC28025DW pulse width modulation IC that regulates the output voltage. The other 12V, that is NOT connected to the main +2v output powers the other ICs, two 339 and one 324 operational amplifiers / comparators that set the over / under voltage protections. It,s this last 12V supply that have to be inserted the two silicon diodes, so that the over / under voltage protection level is increased. Then a small resistor (try between about 30kΩ and 120kΩ) have to be added between the output ground and either the pin #1 of the UC28025DW or the emitter of the small transistor near the right top corner of that UC28025DW. The good thing is that with this modification,the voltage is increased AND we still have a functioning over-voltage protection.

    Dell DM N Z670P-00 modification.jpg Dell DM N Z670P-00 modification 2.jpg

    Hope that helps.
     
    KD0CAC likes this.
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    Thanks , I go look at mine .
     
  9. AH7I

    AH7I Ham Member QRZ Page

    I picked up a couple of the HP HSTNS-PL11 supplies. They are surprisingly small for 100 A 12 V.

    Looking over the schematic I see the stuff that needs voltage higher than 12 V is at 16 V. I also see that the 12 V control circuitry is referenced to the 12 V output tab on the board edge P100C-10 (plug 100 pin 10). Not being an engineer, I'd like a little verify before I trust that shifting this reference will change the output voltage. If one of y'all engineers could help out here. FWIW, this supply is in the $20 ballpark and appears to be easily available.

    I'm contemplating 3 x 1n914 in series to drop reference by 1.8V from the output tab.

    Find P100C-10 with <ctrl F> or look just above box "MB2" which is on the right side of the pdf page 5 (the page with the 12 V transformer output and filter caps)

    Schematic: https://sector.biz.ua/docs/power_supply_schemes_10/HP_HSTNS-PL11_PS-2122-1C.pdf

    What say engineers?

    73, -bob ah7i
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    It looks like there is a voltage adjust pot.

    Have you tested the range of the adjustment ?
     

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