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Voltage Reduction

Discussion in 'Power Electronics' started by Electromotive, Oct 3, 2018.

  1. Electromotive

    Electromotive

    13
    0
    Feb 14, 2018
    Hi:
    Can anyone advise how to obtain 12VDC from a Sola Power supply rated at 24VDC?
    Thank you... Tom
     
  2. Bluejets

    Bluejets

    3,517
    713
    Oct 5, 2014
    What loading?
    Are batteries involved?
    What is the solar output capacity?
     
    Electromotive likes this.
  3. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The most effective solution is a step down converter, ideally with MPP tracking to optimize output from the solar array. To find the right one @Bluejets questions need to be answered.
     
    Electromotive likes this.
  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Sola is the brand name for a popular, line-operated, modular power supply. AFAIK the company has nothing to do with solar power. @Electromotive just needs to add a DC-to-DC buck converter to the Sola output to efficiently reduce the output from 24 VDC to 12 VDC.

    Tom, your selection depends on your load-current requirements, which you didn't specify.
     
    Electromotive likes this.
  5. Bluejets

    Bluejets

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    713
    Oct 5, 2014
    Well, he could have said so.....o_O
     
    Electromotive likes this.
  6. Electromotive

    Electromotive

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    Feb 14, 2018
    Sorry Guy's:

    I have read enough of these Forum conversations to realize my information was sorely lacking.

    I will be using the output to feed Model Railroad panel LED's, 17 Tortoise switch machines that have stall motors and misc. structure lighting, also LED's. The switch machines are operated one at a time and draw very low current when at rest and not activated.

    I am presently using an (12VDC) ancient power supply of unknown origin (possibly home-brew) fused and rated at 3 Amps. Worked fine for over a year but has developed a buzz.

    Its planned replacement is a SOLA Model SLS-24-024. Output is stated as 24VDC for 2,4 Amps.

    Wouldn't the output Amps at 12V be somewhat higher than the 2.4 Amps?
     
  7. Electromotive

    Electromotive

    13
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    Feb 14, 2018
    Again:

    FYI

    Each TORTOISE will draw 15-16 ma. at stall, so 30 switch machines can be powered by a single 9 or 12 volt, 500 ma. wall plug adapter.

    Tom
     
  8. duke37

    duke37

    5,252
    725
    Jan 9, 2011
    If the old power supply is 12V and you replace it with 24V, then things could go bang.

    The buzz in the old supply may be reduced if you tightened up the transformer laminations and made sure it is bolted tightly to the chassis.
    You could try heating the transformer gently in an oven and then filling in spaces between laminations with hot melt glue.
     
    Electromotive likes this.
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    9,367
    1,903
    Nov 17, 2011
    It will when you use a switch mode step-down converter rated at higher output current. You'll get rouhgly 2.4 A *2 *0.8 ~3.8 A from that power supply (factor 2 for step-down conversion with equal power at input and output of the converter, factor 0.8 for losses within the converter).
    Cheap modules can be had for as little as 2,5 $.
    Converters with higher current ratings are available for use in trucks, e.g. this one.

    What is your reason for using a 24 V power supply in the first place? If you're going to replace an existing power supply, why not buy a 12 V one right ahead?
     
    Electromotive likes this.
  10. Electromotive

    Electromotive

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    Feb 14, 2018
    OK, Let's start over...

    Clearly, messing around with the 24V Sola is just not a good idea. Before spending $'s, I like to utilize what I have.
    I can open up the existing power supply and see if there is anything I can do to stop the buzzing upon long term "ON" time.

    Possible better idea?
    1 - I have an ASTEC (Model MP4-1E-1L-1Q-1W-0M) 12V switching 400W power supply (3X the size of the existing). It is:

    V1: 5.00V @ 35.0A
    V2: 12.00V @ 17.0A
    V3: 12.00V @ 17.0A

    V4: 24.00V @ 8.5A
    V5: 48.00V @ 4.0A

    2 - I also have a 2nd bigger one that is 12V @ 30 and 17 Amps.

    Would the Switching power supply be a better choice? I understand it has to be under load to function. Will the relatively low power LED's and 16ma times 17 Tortoises be enough to turn it on?

    I can donate the Sola to my local Antique Radio Club (Schenectady, NY) I'll add it to my non-working Techtronics scope.

    Thanks to all who will and have responded. This is one fine forum.
     
  11. hevans1944

    hevans1944 Hop - AC8NS

    4,250
    2,001
    Jun 21, 2012
    Well good for you! These monster power supplies were quite popular about the middle of the previous century when digital electronics equipment required a multiplicity of voltages at moderately high currents. In Dayton, OH, the National Cash Register Corporation surplussed dozens of similar models, which were immediately snapped up by a local salvage and surplus dealer. I was working for the University of Dayton Research Institute as an electronics technician at the time when NCR (which occupied vast areas of soon-to-be-abandoned property next door) invited us over to inspect and take whatever we wanted. I noticed the power supplies mounted in relay rack cabinets, dozens of them in this one building, but what I also noticed was a large, chest-high, steel cabinet with a static Hollerith card reader mounted on top. So, I took that puppy and left the power supplies for someone else.

    On a somewhat hysterical (historical?) note, the building, before its exterior was extensively remodeled, was originally used by a cadre of women "code breakers" who were boarded in strict isolation at nearby Sugar Camp during WWII. When word got out that the building was to be razed, along with most of the other NCR buildings, a protest movement to preserve this "historical" edifice sprung up. But money talks and bullsh!t walks, so after a brief flurry of activity one day the building simply disappeared! Today, the University of Dayton owns most (if not all) of the former NCR property, including the former NCR headquarters building which the Research Institute now occupies.

    Obviously the Astec is waaay overkill for your model railroad application.

    I suggest that you consider using a sealed lead-acid (SLA) 12 VDC battery of the type used in emergency lighting and UPS units. Connect it to a "float" or "trickle charger" as your power source. It should provide plenty of power for a few hours of model railroading activity and then it will replenish the charge overnight.

    Or try to remove the lamination buzz from your existing power supply. I know how annoying that can be, but maybe you could just put the power supply, maybe suspension spring mounted, inside a sound-proof box, maybe with a quiet, low-speed, muffin fan added to the box for ventilation... Happy Railroading!
     
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