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Thread: Convert DC Power -48v to 12v

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    Default Convert DC Power -48v to 12v

    Dear All,

    I have a rectifier power supply 220VAC to -48VDC

    Any chance to convert the -48V to 12 V?

    Looking for workinf circuits or shecmatic diagrams.

    Thank You



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    What you need is a switch mode type buck converter and just reverse the output cables to change the polarity. Gets a bit more complicated if either side of the DC output is connected to earth though.

    EG 48V to 12V 3A converter

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    thank you for the info.

    is there any circuit diagram.

    That power supply output is -48V 60A.

    I want to convert to 12V because going to use it with my VHF mobile radio

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    That's some industrial scale supply there, is it in a vehicle?
    The mobile radio's demand is the key thing to determining what converter is required IE how much load will be on the 12V supply?

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    sounds to me to be a electric forklift charger ??? what brand ???
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    Back in the day all we would do was use a zener diode and a resistor. However, that was usually just to power a led test lamp, not anything as sensitive as a radio. Given that it already is (relatively) low voltage DC, You might get away with a simple t
    I'm out of my mind, but feel free to leave a message...

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    Quote Originally Posted by drahtlos04 View Post
    thank you for the info.

    is there any circuit diagram.

    That power supply output is -48V 60A.

    I want to convert to 12V because going to use it with my VHF mobile radio
    Holy mackerel that is something you can use for welding and must weigh a ton.
    Alone the standby power of the transformer (you said rectifier so I assume it is a standard transformer with a full wave rectifier, not a switched mode PSU) would exceed the consumption of a mobile VHF com.
    Unless that was a typo and you meant 6A, I would seriously consider using something else alone for safety reasons.

    This step down converter should have enough peak reserve for a VHF :


    Although I have a hunch that you might get it quicker here :


    No schematics here, it would be overkill (just like your 2.88kVA power supply) to actually attempt to build something like that and probably more expensive and risky too.
    Last edited by nomeat; 26-02-19 at 10:30 AM.
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    If this is a vehicle, the onboard DC is almost certainly earthed to the chassis and could be +ve or -ve to 'earth'. As you stated it as -48V I take that to mean that the chassis is +ve and the radio is -ve earth (pretty conventional these days) making it incompatable unless it can be totally insulated from the chassis of the vehicle (all parts including mic, antenna, speakers etc).

    The 48V to 12V supply would need to have complete isolation between the primary and secondary sides which eliminates simple regulator types. Another problem with simple regulators is heat IE say the radio takes 2A on transmit at 12V; that means the regulator will be dissipating (48-12)x2=72 watts! which will be damn hot if not self destructing. A switching supply with a transformer is far more efficient and cooler.

    Need more info on everything to make an informed decision on this

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    its not that hard if you are already at dc volts You might get away with a simple voltage regulator circuit post #6 ???scrounge around the repairers of vsd for a isolated gate bipolar transister they are marvelous devices one will handle 120 amps easily in this circuit with a heat sink of course. there are heaps of these laying around industrial sites as well , big frequency drives .
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    Quote Originally Posted by Skepticist View Post
    That's some industrial scale supply there, is it in a vehicle?
    The mobile radio's demand is the key thing to determining what converter is required IE how much load will be on the 12V supply?
    No. It was in my 42U netwrork rack.

    need 12V aroung 10-20Amp

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    Thanks you for all replies.

    I think, I will look for ready made step down converter.

    Will let you guys know the power supply model later. Its brand is Emerson.

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    That supply looks pretty straight forward so the 20A converter should do the job well.
    The '-48V' had me thinking of all sorts of complications but it's simply what's marked on the power supply label and presumably just the manufacturer's graphical symbol for 'DC'.

    You could get a separate 12V 20A power supply for around the same cost as the converter too
    Last edited by Skepticist; 26-02-19 at 12:31 PM.

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    Quote Originally Posted by drahtlos04 View Post
    Thanks you for all replies.

    I think, I will look for ready made step down converter.

    Will let you guys know the power supply model later. Its brand is Emerson.
    OK, things are a bit clearer now.
    For me this is a -48V(referenced to chassis/earth) switched mode power supply module that the networks guys call a 'rectifier'

    What Skepticist said above about isolation is still valid.
    I am not aware of any low cost step down converters that have an isolated output.
    So your radio's chassis will have a -48V potential against the house earth which is illegal at least here in Australia if you use them. Every time you touch something metallic on the radio and something around you that might be earthed you are going to get an electric shock.
    There might also issues if you install a fixed antenna.

    For less than the cost of that inverter I suggested above, you could get a 12V 200W LED strip light power supply like this:


    ...and you won't have any of these problems.
    Last edited by nomeat; 26-02-19 at 12:47 PM.
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    The power supply model is

    EMERSON NetSure 211 C23

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    grab 4 12v car batterys and series them then put your radio across the last one with neg to ground job done
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    OR you could get something like this for about $25 (12V 20A)

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    60A is a bit much of an ask, but I know exactly what you want. We throw them in the bin.
    Actually I save them for use as power supplies. I runoff grid -48V batteries and 12V lights.
    I'm not sure exactly how much power they convert on the 12V side. I'd guess ~20A, maybe 30A.
    So putting three of them in parallel with isolation diodes is all you'd need. They're small, 1RU 19 inch rack mount and you can remove the racking rails.
    They're also completely isolated. The input is typically -48v but I'm not sure if the positive is tied to ground on the input.
    The output is floating 12V, so you can easily earth the negative. And that's the way I've always run them -48v in and +12Vout.

    I think I have two spare, I always keep one as a backup else I might not have lights in the house if the one being used breaks.
    But I gave a box full of them to a friend. If I remember, I'll ask him if he still has them and if he wants to part with them.

    You can also dumpster dive at your local depot and chances are you'll find one in there every now and then.
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    Trash, can they be regulated up to 55V ?
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    Never mind found the pdf:


    Nice, up to 57.6V, this model only has 40A though not 60A but still more than enough for me.
    Last edited by nomeat; 14-03-19 at 09:16 PM.
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