Powering a 5V circuit from 400VDC

Discussion in 'General Electronics Chat' started by Crispin, Jul 4, 2011.

  1. Crispin

    Thread Starter Member

    Jul 4, 2011
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    hi Folks,

    First post so be kind :eek:


    I have a solar array which I want to monitor remotely. I want to measure the voltage and current of the array using a voltage divider and a hall-effect current sensor using a netduino / arduino.
    The latter two, plus a couple of other active components, require a supply. Luckly for me, I have that to hand. Unlucky for me, it is 400VDC.
    What is the best option for me to "reuse" the available supply and not need something else? A simple voltage divider would not work, be quite wasteful, unstable and I think just dangerous.

    To add to that, the Vin ranges from zero at night to around the 400 mark during the day.

    I've had a loot at some high voltage DC-DC convertors which will work (400 -> 12 etc) but they are rated at 10A so are bulky, expensive etc etc. All in all, I doubt I would every need more thant 250ma. Not done the maths yet.

    The junction where I want to monitor all this is in PVC box which has no sun (I thought of sticking a tiny solar panel to it)


    TIA


    Cheers,
    Crispin
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Just a loose thought: Always a 555 or C555 & a high V P- ch FET, large cap, current limiting resistor; comparator with 5 V ref to reset 555.
     
    Last edited: Jul 4, 2011
  3. tom66

    Senior Member

    May 9, 2009
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    Many computer power supplies will work from straight 400V but they are quite big.
     
  4. Crispin

    Thread Starter Member

    Jul 4, 2011
    88
    2
    Thanks folks,

    As for the array, each panel has a nominal voltage of 37V. I currently have 8, 10 is the plan.

    Any clues on the 555 jobbie? I've only ever used a 555 for, well, a flashing LED timer:cool:

    Cheers,
    Crispin
     
  5. #12

    Expert

    Nov 30, 2010
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    Being able to snag a connection for 37 volts is way better than trying to manage 300 to 400 volts down to logic level! Now that we've changed the requirements from incredible to managable, there are regulator chips that can handle 37 volts directly. I'm thinking 317H, but I just made that up. The H suffix means "higher than the normal voltage input".

    The single panel voltage can be used to estimate the total voltage, or you can do a voltage divider from the 400V line. I'll go look up regulators with an H suffix.

    edit: can I bet your chips' life that it won't see more than 40 volts?
     
    Last edited: Jul 4, 2011
  6. tom66

    Senior Member

    May 9, 2009
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    Actually, an LM317 can tolerate 37V in a floating condition. As long as the output is not shorted, up to 42V inputs are possible with 5V out. Chaining them is also a possibility.

    Some high voltage linear regulators are also available. TI make one that goes to 120V, I forget it right now though.

    A better solution though for such a large input voltage would be a switching converter. LM2576 comes to mind, it can tolerate up to 60V for the HV version (40V for the normal version.)
     
  7. Crispin

    Thread Starter Member

    Jul 4, 2011
    88
    2
    An issue that I have is the junction where I want to measure all this is quite far (and "complex" through the house) from the actual array so if I wanted to measure a single panel, I would have to put a splitter on the panel and run another cable (if I used the first panel I could get away with only a single run) down to the box. Not really ideal but not impossible.

    Having a look at the spec sheet for the ACS714 which I am to use, it uses 10ma so batteries might be an option (some hi capacity NMh or LiPo).

    Also just seen this: "Maximum working voltage according to UL60950-1 354V" means I'll be slightly over - bummer. Did not think (doh!) there would be a limit on this...


    Having another look at where I plan to put it and I don't think it'll be _that bad_ running a 4-core alarm cable there for power and bits...

    :( Not what I had hoped :(
     
  8. #12

    Expert

    Nov 30, 2010
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    I think the "better solution" is for high wattage, which includes both voltage and current. If you can figure out the actual current your brains need, it can be calculated whether a more complicated (switching) regulator is needed.
     
    Last edited: Jul 4, 2011
  9. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Perhaps a rechargeable battery would be easiest. uC's do not consume much power.
     
  10. #12

    Expert

    Nov 30, 2010
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    Yes. A third of a watt (32V x .01 amps) is not worth building a fast switcher circuit. Three or four AA NiMh batteries could last a week under those conditions.
     
  11. iONic

    AAC Fanatic!

    Nov 16, 2007
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    A solar alternative would be to buy a small PV to power the uC only.
     
  12. Crispin

    Thread Starter Member

    Jul 4, 2011
    88
    2
    All the gubbins are in the loft :|
    If I could find an incandescent bulb that runs off 300-400V we might be styling ;)

    I'll look at running it off batteries or running a 4 core cable to it and do away with the RF stuff) Not the end of the world...
     
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