Friday, June 18, 2021

USB-C PD "Magic Cable" version II

Jim Fisher AJ3DI from the Phil-Mont Mobile Radio Club asked me back in May if I'd do a presentation on my USB-C Power Delivery system for QRP radios, since my original article (posted here and published in QRP-ARCI's QRP Quarterly, July, 2020) was published in a recent issue of The Blurb, the PMRC monthly newsletter. How could I say no to the Jedi Master? The presentation went extremely well a week ago on June 9th. 

You can see the slide deck I used here:

And you can watch the Zoom/2m Repeater meeting, complete with the presentation, at:

While preparing for the presentation, found out that the original PD Buddy Sink board by Clara Hobbs I bought from was no longer available, so I did some shopping on Amazon to find some replacements. I'd used some other PD sink boards, that I detailed in another article on this blog about the subject, but didn't really find anything I liked well enough to make a cable using one. 

What I mostly found earlier this year were sink boards that would cycle through a series of configuration settings when you pressed a small tactile button on the PC board, a method I did NOT particularly like. It was far too easy to wind up sending too much power to the radio, since there was no actual feedback to tell you what setting the board was on. You'd have to test it with a DVM every time, which is very impractical. I have a tiny PokitMeter brand micro-DVM/single-channel oscilloscope the size of a keychain fob, that works in tandem with an app on my phone that I could use to easily test the voltage selected, but it really wasn't what I wanted to do. So I waited. My patience would be rewarded.

It was, and a little more so! I found that the PD sink (or trigger) boards had gone through a major evolution during that time, resulting in two major shifts in the boards now available: They're now extremely tiny, and they no longer rely on a button-press or serial terminal programming to select the output. Under most circumstances, you'll want a static voltage/amperage setting, and in my circumstance, that's precisely true. I want to set my sink boards to 12 volts at the maximum current available. So I was very pleased when I discovered that there were now PD sink boards barely larger than the USB-C jack it bore! 

There are two main varieties: 

A) Boards that can be solidly set for a particular voltage by jumpering PCB pads with a solder blob, and... (

B) Boards pre-set for a specific voltage at the factory and sold as an option at purchase. Such as 12 volts... (

I bought some of each type. Some of the jumper-controlled boards provided the whole gamut of supported PD voltages. I got some of the universal boards that can be jumpered for 5,9,12,15, and 20 volts (the red ones, above), a couple that provided 9v and 12v, and I got a 5-pack of the blue board above, that could be ordered for any single voltage desired. I chose 12v, obviously. ALL of the above boards will provide up to 5A of current, even though the maximum current for Power Delivery is 3A. That's fine with me!

I made a "proof of concept" cable using a  5.5 x 2.4 mm coaxial plug with screw terminals, attaching the contacts to a wire pigtail that I soldered to one of the 12v/5A sink boards. It worked, but the quick-connect coaxial plug I used had too large a central pin size, so it would drop out when nudged. 

This was unacceptable, so I attached the pigtail to a longer piece of the same thin zip cord with a proper 5.5 x 2.1mm right-angle DC coaxial plug. I was still experimenting, so I just used solder-seal butt splices to replace the mismatched plug with the screw terminals. It looked awful, with electrical tape still insulating the board and covering the solder seal splice job. But this one worked reliably and solidly, not losing contact if jostled. 

Now it was time to make the actual Magic Cable II. I removed the electrical tape from the sink board, desoldered the wires I'd attached, and cleaned the pads with solder wick. Some isopropyl alcohol made short work of any remaining flux. Then I shortened the wires coming from the good plug to about 10" long, stripped and tinned the ends, and soldered them to the pads on the PD sink board. I gave it a single wrap with electrical tape as a precaution, then I slipped on a piece of marine-grade, glue-lined heat shrink tubing and used my hot air rework pencil to shrink it and seal it around the board and the wire. I tested the result, and it works perfectly.

I also found a short but very heavy-duty USB-C/USB-C jumper cable. This cable is stubby, only about 6" long, but is flat with thick conductors under a reinforced "FlexCore" outer cover. It'll take maximum PD power and data, rated for 100W (20V @ 5A) and 10 GBPS of data transfer. I only intend it for power, so I chose a cable that'll take the 12V for a QRP radio without any question.

The radio I used for the test is my HobbyPCB IQ32, an all-band, all-mode 5W SDR transceiver. I have a small steel plate on the lower left corner of the faceplate, where my tiny Supmotor paddles reside. The base of these paddles is a very strong neodymium magnet. It's the smallest set of paddles I own, the body being only an inch on a side, and the fingerpieces sticking out another inch. The only paddle I have that rivals it would be my NOARC "Te-Ne-Ke" (Teeny Key), that's about the size of a pack of gum. This paddle comes in a little steel can, embedded in foam, including the paddle (with magnet base), a stick-on steel plate, a hex wrench to adjust the tension, and a 3.5mm jumper wire. It's a very comfortable paddle to use, despite the size, and it is easy to adjust for as light or as heavy a touch as you want.

I tested the setup with 3 different PD USB-C power banks: A 10Ah Monoprice "Obsidian" PD power bank and two 20 Ah RavPower "Pioneer" PD power banks, one an older model with a digital readout showing power level, and a newer model with fewer ports that uses LEDs to indicate remaining power. I will be testing with other radios and some other PD power banks later. I've also ordered more of the 12V sink boards and some 5.5 x 2.1mm DC coaxial power pigtails, since I'm lazy and don't like soldering small connectors. This will let me make a few spare Magic Cable II's in case I ruin or lose one, and leave me some sink boards to install in radios I'll build in the future. I'm looking forward to being able to just plug a USB-C cable directly into a QRP rig!

A note on the availability of the power banks I typically use: This month, all of the RavPower power banks are unavailable from Amazon, as Amazon has stopped carrying several brands, of which RavPower is one. Others they stopped carrying were Aukey, TaoTronics, Vava, and Mpow, all subsidiaries of Chinese company Guangdong SACA Precision Manufacturing. The reason cited was that these brands have been allegedly engaging in a practice of giving gifts in exchange for good reviews, which is against Amazon's sellers' agreement. The Monoprice Obsidian bank I used is no longer available, but it was discontinued. (Monoprice is owned by Amazon, in case you didn't know that.) You may still be able to buy the RavPower devices from other sources, including the RavPower website -- though some of them were simply linked to Amazon pages for sale. I expect RavPower, and the other sites removed, will be changing their ordering so they no longer point to Amazon.

For more information on the delisted brands, visit:

No comments:

Post a Comment