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I recently found out there are very cheap (down to under a dollar) adapters that convert the 5 Volts from a USB port to 12 Volts. Manny small QRP stations draw very little power. For instance, the Venus SW-3B (which I have) draws 0.8 A at 12 V during transmission. A little less than 10 W. Many power banks can deliver 2 A at 5 V, or even 3 A.

Edit: Several portable QRP transceivers will work with a span of voltages, e.g. the SW-3B accepts 8-15 V. If the converter can deliver exactly 12 V that's good, but it's not critical.

This begs the question: Is it a good idea to use one of these to power a portable QRP station with a USB power bank?

Just looking at the numbers suggests this might be possible!

Problems I could imagine are that the DC is not pure enough, or that the converters might not be able to handle effects as high as 10 W. This is just speculation though. It could also be the case that some converters are suitable for this usage while some are not, but it's hard to tell as I haven't found good specs on any of them.

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    $\begingroup$ If you need both 5V for USB and 12V+ for a QRP operations, it might be better to use a small 12V battery (LiFePo4, etc.) plus a 5V down-converter to run the USB peripherals. That way the power to the radio is a bit quieter, and most of the RFI gets passed to the USB port side. $\endgroup$
    – hotpaw2
    Commented Oct 5, 2021 at 2:20
  • $\begingroup$ @hotpaw2 Of course a 12 V battery would be the better choice, but the ubiquity of USB powerbanks still makes this question interesting I think. If it works it would mean that everyone and their grandmother sits on several hours of extra portable qrv time in the form of really compact batteries. This fact would be useful to know about if that's the case. $\endgroup$
    – EdvinW
    Commented Oct 5, 2021 at 6:43

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Your 10W output from the power bank will not be 10W after the upconverter has changed the voltage -- if you're lucky, it'll be seven or eight watts, but it might be as little as four. The first one you lined is rated for a real 0.8 A output, but I'm certain it will need more than 2 A from your power bank.

Because of that, while you could (inefficiently) use the power bank and converter to charge a 12V battery, your 10W QRP radio would, at best, be operating below its rated output due to voltage drop from the converter when you try to draw 0.8 A. More likely, the converter will shut down or the radio will just not transmit (though it will most likely receive just fine, since that's significantly less power draw).

From a power bank that can output 3 A or more, it's getting close to possible, but then you need to have a converter that can handle the power. The first one you linked might do the job, if your 5 V supply is up to it. Don't forget that radios usually draw more power than they radiate -- for intance, my 50 W mobile wants about 95 W of input power during transmit...

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  • $\begingroup$ Some USB ports can deliver more than 2 A, would that make a difference? I've edited my question to acount for this. $\endgroup$
    – EdvinW
    Commented Oct 4, 2021 at 18:49
  • $\begingroup$ It would make a difference only if the converter can output more current on the 12 V side. The one that's entirely incorporated in the USB cable end likely can't take the heat of conversion losses above even 1 A. The smaller the components, the less power they can handle, generally. $\endgroup$
    – Zeiss Ikon
    Commented Oct 4, 2021 at 19:02
  • $\begingroup$ As @ZeissIkon says, it really depends on how the conversion is done. Many use a buck-boost converter, which will be limited amps. Also, remember that if you are taking one current at 5 volts and shifting it to 12 volts, the current will decrease. $\endgroup$
    – David Hoelzer
    Commented Oct 4, 2021 at 19:12
  • $\begingroup$ Thanks for your update! The 0.8 A is what the stations DRAWS, according to its specification, while output is 5 W. $\endgroup$
    – EdvinW
    Commented Oct 4, 2021 at 19:24
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I haven't experimented myself, but the USB-to-12VDC adapters surely use a boost converter, and those make RF noise. I have no idea what frequencies they make noise on (tens or hundreds of kilohertz?), but I wouldn't be surprised if noise (harmonics of the original frequencies most likely) makes it up to the ham bands.

Such noise may or may not be a deal-breaker, but it would be something to experiment with before setting out on a multi-day wilderness backpacking trip with the QRP radio as the official link to civilization. (Such a trip may not be your plan, I realize.) I would consider also trying a battery pack made of three or four Li-ion cells in series, which would develop something between 11 and 15 VDC, for the sake of comparison. Just the cells themselves with no boost or buck converter wouldn't radiate any noise at all.

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Look for a USB-PD power bank rated 27W or higher (which should guarantee it supports 15V output), and a 12V and/or 15V trigger (a small device or cable with a USB connector on one side, a chip that does the PD negotiation, and DC output on the other, often on a 5.5x2.1 mm barrel connector).

That way you will have the power bank regulating up the battery power directly to 12V or 15V, instead of cascading a 5V regulator with a 12V or 15V regulator. Then you just have to find one that's relatively RF-clean... which is a matter of some trial and error, because there's no real way to get reliable information about that.

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  • $\begingroup$ Not a product recommendation, Just an example: amazon.com/dp/B08NRM6X2Y $\endgroup$ Commented Oct 7, 2021 at 0:31
  • $\begingroup$ @SolomonSlow yup, exactly that kind of thing, thank you. $\endgroup$ Commented Oct 7, 2021 at 0:33
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If you have access to QST there was an article on this subject with circuits you can build yourself. September 2018: "Power Gadgets from USB Sources with Simple Switching Boost Supply". The device used was an MC33063A https://www.onsemi.com/pdf/datasheet/mc34063a-d.pdf. In general buck and boost power converters are quite easy to build these days, basically you need the right IC, an inductor, a high-speed diode and a few capacitors. I built a 12V to 20V 5 Amp booster with a LT1270A https://www.analog.com/media/en/technical-documentation/data-sheets/lt1270afc.pdf once.

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