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Unknown Farnell Power Supply Questions

Discussion in 'Power Electronics' started by hoiler, Apr 4, 2013.

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  1. hoiler


    Apr 4, 2013
    hello everyone,

    I have a Farnell GS600-048 power supply, im just asking about if any one has a manual for it or something, or if anyone knows of it. It is a ex-BT power supply from a cabinet that was being thrown out and i though it would be a shame to let it be thrown so i asked for it.
    It puts out 48V DC, 12.5 A max, around 600w.

    at the far back near the heat sink there are 2 massive transmitters,- bux98a if any one know about what is does, I'd be grateful.

    I'd love to be able to convert it to output 12V, that would be so useful. i have heard somewhere that it can be done but there was no explanation as to how.

    I'm including some photos just in case someone recognizes it.

    and here one was sold on ebay a while ago, the seller suggests that it is possible to change the voltage

    Thanks a bunch.

    Attached Files:

    Last edited: Apr 4, 2013
  2. Electrobrains


    Jan 2, 2012
    Well, first I would not recommend any changes being made without fully knowing the consequences. It's a dangerous thing to manipulate an existing, well dimensioned power supply and no responsibility or warranty may be included in advising on this topic!

    One thing must be made very clear: if you change the output voltage, you should never drive it higher than the specified data, i.e. never higher voltage than 58VDC and never load it with more than 12.5A (it's not written if the supply has over current protection).

    This is how I would try to make a quick (down-) modification of a power supply:
    The advantage here is that the PS has a voltage adjustment.
    I would concentrate on the adjusting potentiometer and the components around it.

    A very simple test would be to exactly measure the voltages at the end positions of the potentiometer. Then desolder the potentiometer (ALL CHANGES MADE IN POWERLESS STATE). Measure it!
    If it for instance is a 10k potentiometer, I would exchange it towards a similarly sized, next larger value (eg. 15k).

    Then I put the slider exactly in the middle position, step away from the supply and plug it in with a DMM connected measuring the output voltage.
    If it's out of range (>58V), then the cable must be quickly pulled (and an electronic specialist contacted).

    If the output voltage is within range, then I turn the potentiometer in different directions to see if the voltage span has changed (never go over 58V!). If I now can go lower than before, I am on the right way*.

    To "push down" the voltage span, I would now put the potentiometer in the lowest position and note the output voltage. Then (unplugged) add a small resistor (eg. 1/10 of the poti value) in series with one of the end position pins of the potentiometer and start-up the PS. If the output voltage raises, it's the wrong side of the potentiometer!

    If the voltage decreases, I am on the right way! By increasing that resistor, the potentiometer span can be pushed down in a secure area (<58V).

    If the lowest voltage is still too high, the procedure can be repeated with next size larger potentiometer value (resistor left in place and the new potentiometer in the middle).

    * If the minimum output voltage would raise at the first potentiometer change, I would have to decrease the potentiometer value instead of increasing it!

    Important: The Power Supply may NEVER be switched on without the potentiometer installed. That could cause a rapid raise of the output voltage with exploded capacitors and other components!
  3. hoiler


    Apr 4, 2013
    Dont' worry, i have no intention of messing about inside it without thinking it through first.

    On the voltage adjustment side of things, i see what you suggest, it sounds like a good idea and i might try it later today. I just checked and the blue caps are rated at 200V and the black ones on the output side are rated 63V. i will take care, don't worry. i just hoped that seeming that there are other supplies with the same design it might not be so difficult to change the output voltages
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Leave the original PS as it is.Get a 48V to 12V DC/DC converter. Or a few if you want to make use of the full 600W.
  5. GreenGiant


    Feb 9, 2012
    I would go with what Harald said, either a 48 to 12V converter, or you could build yourself a divider box with multiple outputs (a 24V, 12V, and 2 x 5V, or 5V and a 3.3V) then you would have all the most common amounts.
  6. hoiler


    Apr 4, 2013
    thanks, thinking about it, getting some 48V to 12V converters does sound like a good idea, and there would be space in the case for them too. i do plan on using the full 600 watts ( or trying to anyway - i know that i will lose some efficiency anyways ) .
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Yes, only you don't need the waterproof feature and could save a few cents using a simpler cosntruction.

    For using the full 60W: note that you cannot simply put 5 of these converters in parallel. You can use them as 5*120W outputs, but if you want 1*600W, you need to add some kind of load sharing. Or you need a (more expensive) 600W converter.
  8. william chasney

    william chasney

    Jun 16, 2015
    Hi, guess this is very late in the day, but a simpler solution would be to 'program' the psu to give you the required voltage by connecting a resistance between the '+S', and 'EXT' connection on the 8-way terminal block, after removing the link between 'INT' and 'EXT'. The relationship is one kilohm per volt, so for 12 volt output a 12k resistor would be required. You would only be able to use the power supply up to its maximum output current of 12.5 amps.
    Arouse1973 likes this.
  9. AnalogKid


    Jun 10, 2015
    This is a switching power supply, which means that the power transformer is designed for a specific range of current, frequency, and pulse width values. Changing the output adjust components or manipulating the remote sense input both will work up to a point, but that point is nowhere near a 4:1 reduction in output amplitude. Also, the power transformer secondary is designed for a specific output current range. Even if you could get the output adjusted down to 12 V, the max output power would be limited to 150 W before either the transformer started to overheat or the output current limiting protection maxed out. Sometimes a great front-end power supply is just that and nothing more. Lotsa cheap bare-board dc/dc buck regulators out there. Get some.

  10. william chasney

    william chasney

    Jun 16, 2015
    I know this information is freely available to all, but the response was to assist hoiler, (or anyone else in his situation), it struck me he was a novice and he wanted to use his unit to provide 12 volts for whatever he needed to power. I assumed he was keen to experiment and use the unit without compromising safety issues, or attempting to alter it in anyway.
    Lets just get a few things clear,
    1. the switching frequency is in not altered.
    2. yes,this may not be an efficient use of the unit, and in this case it would provide a maximum output of 150W.
    3. as already quoted, the unit will limit at its stated current, 12.5A.
    4. this unit will work at 12 volts, external voltage programming is provided on this model and is designed as an end user facility.
    Hope this clarifies things
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