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Filtering output of buck converter

Discussion in 'd.i.y.' started by cubastreet, Aug 10, 2018.

  1. cubastreet

    cubastreet Espresso Fiend

    I'm living off grid with a 24V battery system (actually 25-29V).

    My music comes from a raspberry pi fed from a buck converter.

    The system works great, but all the buck converters I've tried have been a bit noisy. It's the same sort of noise you get if you plug your phone into three aux in of a car stereo, while charging via the cigarette lighter.

    I don't have a lot of battery storage so I'm trying to make everything as efficient as possible, else I'd probably throw a couple of 317s at it. What would filter the noise?

    I think current draw is normally under 500mA but peak current could exceed 2A.

    I was thinking of CLCLC or a VBE but don't really know about the effectiveness in this setup.
  2. snowman_al

    snowman_al pfm Member

    The noise might be on the 'supply' lines and filtering could reduce it. Or it might be RF being radiated from the converter.
    You could try putting the converter in a metal box and slipping a couple of ferrite clamps round the in and out leads?

    Or what about running the Rpi from a mobile phone battery pack? You can get get ones that charge from 240 volt mains or 12v dc for cars. You might even get a lorry one with 24 volts charging?
  3. cubastreet

    cubastreet Espresso Fiend

    Good idea I'll try isolating the converter .I can't really be fussed with a separate battery system.
  4. martin clark

    martin clark pinko bodger

    Buck converters are noisy - as seen from the raw input side. If it is running off raw (battery) supply shared with other boxes in -system, that might be the route in for the noise. If you care to bodge, perhaps try a decent-size/low-esr cap right across the buck-converter 'raw supply in' pins.

    The USB powerbank idea suggested above is def worth a try if you have something suitable to hand. If such is a useful fix, this input-side noise route is a a large part of the problem. If you subsequently want to try a bit of CLC, consider trying it on the converter input first rather than the output. And that'll be easier/cheaper, with lower currents to handle (i.e. smaller current-capacity inductors reqd)

    (Interesting problem context :) - and since this is DIY, care to tell us more about your move off-grid, perhaps another thread..?)
  5. cubastreet

    cubastreet Espresso Fiend

    I didn't think about that, but it makes sense that the noise is on the converter's input. The amp is a TK2050 which sounds surprisingly good but may not have very high PSRR.

    Mrs cubastreet and I bought a few acres here in New Zealand. It's pasture and bush with a cute stream that occasionally becomes a raging torrent and traps us for a few days.

    It was too expensive to get power connected so we decided to go off grid. We also don't have much money left after buying the land so we decided to build ourselves.

    I've got more of an engineering than a building background but I like learning new things, so why not?

    A lot of time has is gone into the land - getting rid of gorse, broom, barberry and brambles. Starting a firewood lot to become self sufficient etc.

    We spent 4 months in a tent which was awesome ,except for when we got 140+km/h winds. We put it in a relatively sheltered spot but we still didn't get much sleep those nights.

    We spent the winter in a small tin hut I built with a logburner, sleeping in a little caravan. The winter wasn't that cold but it was pretty wet and mud has been an issue.

    Now spring is coming, which is a very nice feeling!
    Dowser and martin clark like this.
  6. martin clark

    martin clark pinko bodger

    Wonderful! ATB for the whole adventure.
    cubastreet likes this.
  7. Dowser

    Dowser Learning to bodge again..

    I assume South Island? :)
  8. cubastreet

    cubastreet Espresso Fiend

    Wairarapa, North Island.
    Dowser likes this.
  9. Dowser

    Dowser Learning to bodge again..

    Sounds nice, have fun!
    cubastreet likes this.

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