“Lunch box” power banks or stations have become very popular for portable and emergency power. Potentially they offer a lot of capacity and versatility as power sources for small transceivers, but there are problems to be solved if they are to be viable.
The Rockpals 300W version that I initially purchased for emergency and camping is an example. It allows for multiple charging methods, including solar (it has a built-in controller), and can be charged while being used. Ports are provided for standard USB, USB-C, nominal 12v DC, and there is a cigarette lighter jack. It also has a built-in pure sine inverter for 120v output. An LCD display reads out charging wattage and status as well as wattage being drawn. Why not use this to power my KX3 for extended portable operation, I wondered?
I ran into two problems. Most of these power packs have unregulated DC, and the voltage is actually lower than 12V. That would not allow me to use the KX3 at its full 15W power when I wanted to. Also, the start-up sequence in the KX3 seemed to trigger the protection circuit in the power bank, so it wouldn’t start. When I tried to use a DC boost converter from that output, that also triggered the protection circuit.
The start-up problem is easily solved by having internal batteries in the rig (see my previous blog). With those batteries in place, the protection circuits are not triggered and the power bank does work with the KX3 from a 12v DC jack. A DC boost converter does not work, however.
To get higher DC output the AC inverter output could be used to power a small DC power supply, of course, but that added bulk and didn’t seem very elegant.
Once again my engineer friend and retired “solutions architect” Jim Richards had a solution: USB-C. USB-C ports contain a power delivery system that can deliver a variety of voltages from 5-20V, including 15v, at power levels up to 100W. What is required is a small Power Delivery (PD) board or dongle that will call up the right voltage from the USB-C port. One or two diodes in series with the output drop the voltage a bit below 15v so that it is within the KX3’s parameters. A ZY12PD board from Amazon (e.g. B07T2858G6 bare board version with voltage selection button) is the kind of board in mine. The Amazon B08NFKT1YM is a fixed voltage version that would probably be more convenient. My arrangement uses two 5A Schottky silicone diodes with a typical forward drop of 0.2-0.5v in the output line.
The board and diodes could simply be encased in shrink tubing. I mounted mine in a small Altoids box and added a small digital voltmeter for reasons I will explain shortly.
The Rockport’s USB-C port is rated at 30W, below what I needed for the KX3 at 15W out, so I also needed a cigarette lighter charger with a higher-wattage USB-C port. The one I used isn’t currently available but something like the WOTOBEUS USB C Car Charger 83W (ASIN Number B089SJFN5Q) should work.
You will also need a USB-C to USB-C cable; I recommend the 100W variety.
Once you have put the unit together, if you have used a board with voltage selection, the next step is to select the correct voltage. To do this, plug the PD unit into the USB-C connection and push the button on the PD board several times until 15v is selected (net output through the diodes will be 14v+). If you have used a PD board with fixed voltage you of course can skip this step.
Sometimes the PD doesn’t call up the right voltage the first time I turn it on but instead defaults to 5v. Turning the power bank switch off and back on brings the right voltage. If I didn’t have internal batteries in the KX3 the radio would not come on and it would be obvious that I wasn’t getting the right voltage. With batteries internally, however, the radio will come on but not at the full voltage that I want. I added the voltmeter to provide a visual alert if I am not getting full power from the power bank.
I had thought I would use this for extended portable operation, and it will work nicely for that. However, it is primarily the basis for a solar power system in my shack. I run my KX3 setup – KX3, PX3 panadapter and power speakers – purely on solar. Solar panels on my carport keep the power bank charged and the LCD reads out the status of the charge and current draw. I have not found an RFI problem on the bands I use (mostly 80M-20M) but have not tested it on others.
In addition to powering my KX3 station, I also charge all of my devices – phone, tablet, etc. - with this. It’s a small measure, but the principle of reducing reliance on the power grid seems a good one.
This setup also makes a good way to get adequate voltage from a vehicle cigarette lighter plug to power a KX3 at full output.
If you don’t want to bother putting together your own, Jim is open to building a custom one for you. Email him for more information: mediadogg@mediadogg.com
UPDATE: Jim is now selling a very slick, compact version of this adapter. See https://www.mediadogg.com/shopping/usb-pd-power-dongle-for-elecraft-kx3.html
Solar-charged Rockpals power station powering my KX3 gear.
The Renogy controller on the right is the solar setup that the Rockpals setup has replaced.
Power supply on the left powers my TS-590sg.
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