|Smart Cable connected to PD supply and QCX transceiver
We're coming up on a confluence of two things: Nice weather, and relaxing of the Covid-19 lockdowns in much of the United States. This means more hams leaving their home shacks and taking their operating to the field. For some, this means climbing mountains and doing SOTA activations. For others, this means hiking on trails, and doing POTA activations. For yet others, this means gearing up for Field Day, or doing HF Pack operating, with a manpack station on their back. But no matter what they actually choose to do in the field and why, all of them have a similar need.
They need to power their gear.
This can be a really complex issue. It has a lot of factors, like what radio the person plans to use, what its power requirements are, how many watts do they want to transmit with, how much does the radio draw during receive, will they have access to mains current at any point, if not, will they have gear to recharge their power source, will they be on foot, are they operating from a vehicle...the list goes on and on. But again, there's a need that intersects all of these issues.
They need the power source to be as flexible as possible, and to provide the maximum in available power for as long as possible, but as small and lightweight as practical.
When you're getting to your operating position by backpacking, every ounce and every cubic inch counts. So you want your power source to be small and light, yet you need it to provide enough power to fulfill your goal.
The default position seems to be: figure out how much juice you'll need for the duty cycle you expect, the power consumption your equipment will require, how much weight you can carry for the requisite distance, and what you can do to replenish that power in the field if you have to. It pretty much falls to: carry a lead-acid gel-cell, or a lithium-ion source with similar storage capability. If possible, carry some means of charging it, which usually means "solar panel".
A lead-acid gel-cell with 5-10 amp-hours (Ah) of available juice is fairly inexpensive, between $2.00-$3.50 per Ah (Amazon prices) depending on brand and what the seller says it's for. Some use cases have higher price points, because it's a more or less "elite" use case. You can get a lead-acid 12V 9Ah gel-cell for around $25. But lead-acid batteries are heavy and bulky. If you plan to charge one in the field, it requires a special charger, or your charging device needs to have an output suitable for charging lead-acid batteries. They have a limited lifespan, and can be damaged or destroyed by drawing their voltage down too far before recharging, requiring replacement. Then you have a hazardous material to clean up, as your typical trash service won't take them. They're cheap, but can be a hassle. If you're willing to accept the hassle, though, you can get them very inexpensively.
Some radios, such as the Elecraft KX3, can be upgraded with an internal battery tray. The recommended battery for it is a set of Nickel-Metal Hydride AA cells. The rig will charge them, but ONLY NiMH batteries, the charging process is slow, and if you draw the batteries down too far, may damage the batteries so they no longer take a charge. They're lighter than lead-acid, but provide less power, and have special charging needs.
Lithium-Ion batteries tend to be lightweight, have a fairly high efficiency, and while more expensive, have a longer lifespan, requiring replacement less often. But they require a special charger, can take a long time to charge, and are considered to be a very hazardous material. Lithium-ion batteries have been known to explode or catch fire while charging, while in use, or following some kind of damage from incidental accidents, such as dropping. There are heavy restrictions on shipping them, and over a certain size cannot be taken on an airplane in carry-on baggage. The best chemistry for lithium batteries are the relatively recent Lithium Iron Phosphate (LiFePO4) variety. They're lighter, have an even longer useful lifespan, can be drawn down further without damage, and the chemistry isn't as explosive or prone to fire as other lithium-based cells. But they're expensive, running $8-12 per amp-hour.
The least expensive brand I know of are Talentcell brand. They even have small battery packs, at minimum 12v at around 3A, but some models having 9v and even 5v USB outputs. The 12v and 9v are coaxial jacks, and the units have power switches, power level indicators, and can be charged while in operation. My only complaint about these devices is that they're single-taskers -- they are designed for a limited set of tasks, such as running LED lighting, or IP cameras.
What I had in mind was something of a multi-tasker. Something you could use for powering ham radios, or perhaps other gear as well. I've been looking at the little USB power banks for years, wishing there was a way to operate ham radios from them, but the power and voltage available on them was too low. But now...there's USB-C, and a new protocol for output power on USB-C, the Power Delivery standard.
PD is a handshaking protocol, whereby a device will communicate with a power delivery device and tell it how much power it needs to operate. PD can provide a whole host of values, from 5v at 50mA, to 20v at 5A, with reasonable steps between. It can specify a range of acceptable values, in case the supply device doesn't support the precise value required, but DOES provide something close. The key to the whole thing is a small circuit called a "sink". There are a number of them becoming popular online.
The "PD Buddy Sink" by Clara Hobbs is the first I encountered, on the maker site Tindie. It's a board a little smaller than an inch on a side, with a USB-C socket on one side, and either bare solder pads or screw terminals on the other. To specify the power setting, you connect to the board via a terminal program such as PuTTY over the USB-C connection, and issue the appropriate commands. Then you can write the result to the internal memory of the board and reboot it. The board will retain the setting until you change it. Another board, the ZY12PDN "Type-C USB-C PD2.0 3.0 to DC USB decoy fast charge trigger Poll detector 100W MA", as named on Amazon, is very similar, but instead will cycle between available values when a button is pressed. It's a slightly smaller and less expensive board than the PD Buddy Sink. The Buddy Sink costs $30 on Tindie, while the ZY12PDN costs between $13-18 on Amazon, depending on configuration.
|PD Buddy Sink by Clara Hobbs
|ZY12PDN Board - Amazon
But why go with a cable? Why not put the Buddy Sink board inside the radio itself, with a slot for the USB-C plug? Because a Buddy Sink board is $30, that's why! With a smart Power Delivery cable, I can support a whole collection of 12v QRP radios with the same board setting (12v, 2.5A). With a Y-adapter, I can even supply power to both my KX3 and PX3, though I really wish it had more current. To use a sink in each radio would be a very expensive solution, though it would of course work. It also wouldn't be necessary to leave a way to reprogram the board, since it would only need to supply one range of values, the one necessary to power that radio, and no other. But this is a far more flexible solution, and a far cheaper one!
Now that the smart cable is out of the way, what about the OTHER end?
There are a number of Power Delivery options for power banks and chargers. I bought a 45W GaN (Gallium Nitride) PD wall charger as a backup for my USB-C Chromebook, but found that it also charged PD power banks quite adequately and quickly. Since it is a PD device, it can also provide mains power to the PD smart cable, and is smaller than a deck of cards. The battery banks I purchased are a 10000mAH model and a 26,800mAH model, both by RAVPower. Both will supply around 30W of power, and will power any of my QRP radios at full output, including the KX3 at 10W.
They may not be able to supply as much juice at 12v/2.5A as a dedicated 12v battery, but they also don't weigh nearly as much or take up nearly as much space as a 12v battery. I have a Talentcell 12Ah LiFePO4 battery that weighs about 2 1/2 pounds. The RAVPower 10000mAh PD bank weighs about 6 ounces. The 26,800mAh PD bank weighs about 15 ounces. They also cost much less. The 10Ah model cost about $20, the 26.8Ah, about $50. The 12Ah battery cost around $100, and appears to be no longer available from Talentcell. By my calculations, the 26,800mAh bank should provide around 8,250mAh at 12v, and the 10,000mAh bank, around 3,000mAh.
|RAVPower PD 26,800mAh Power Bank, Buddy Sink Cable,
and QRP-Labs QCX 40m Xcvr - 7 hour test
It's also a multi-tasker. It can charge my phone via the USB-A port while operating the QCX. It can charge my USB-C Chromebook. It can charge other USB devices, such as my watch, or the flashlight I wear on a chain around my neck. It can charge my Baofeng BF-T1 Mini 70cm handy-talkie. It can charge my electrolytic water purifier, which equates to 150 liters of purified water. It can run a USB LED lamp, or my TS100 soldering iron. Except for the soldering iron, I'd need an adapter to use the 12v battery on any of those other devices.
I also have more options to charge it back up. I have a solar panel set, also by RAVPower, which can charge either of the PD power banks. I also have two different thermoelectric generators, that provide USB level power from a strong heat source. I can make hot water for drinks or freeze-dried food while charging the power banks. If my car is available, I can recharge the banks from my lighter socket, a source that isn't clean or stable enough to power the radios directly. I can use the GaN charger to recharge the banks, or I can run the radios from that charger with the smart cable while I have access to mains power. It's all very compact and lightweight, making it easier to transport into the field, such as when hiking on a trail or climbing a mountain. (I'm disabled, so my hiking and climbing days are over, but I still go to parks to operate, on picnic tables convenient to nearby parking!) Talentcell put a battery management board inside the case for the large battery, so it can be charged from a charger for a lead-acid battery, but that would still require AC mains power to use!
Power Delivery is still a very new power bank technology, but it appears to be getting more popular. I think it'll be easier in the long run to use such multi-tasking power bank options to run portable ham radio gear than to lug about heavier and less convenient power sources as the technology improves over time. I have a new PD power bank on order, also by RAVPower, a 20,000mAh model with a digital power meter, so I can better gauge how much of the power bank's capacity is being consumed during use.
From some questions I've received since posting this, I have a couple of points to add.
- If your power bank has a low-drain timeout feature (it shuts off if the device you connect doesn't draw enough current), it will NOT turn off if your radio doesn't draw a lot in receive mode. The power bank is not seeing the RADIO'S consumption level, it's seeing the handshake from the sink board, which does not automatically turn off if the draw is "too low".
- There is no oscillator noise from the sink board because it is not boosting 5v from the power bank to 12v. The board is requesting 12v from the power bank, and the power bank is supplying it under the USB-C PD standard. So there's no oscillator boosting the voltage, hence, no noise from the sink board.
- You need to use a USB-C Power Delivery power bank for this. Qualcomm fast-charge is a different standard, and will not work. There will be a "PD" logo on the power bank if it is supported, and should say it is Power Delivery in the documentation. Here is a document explaining the PD standard: http://www.ti.com/interface/usb/type-c-and-power-delivery/getting-started.html
Gwen Patton, NG3P
Links to items:
PD Buddy Sink: https://www.tindie.com/products/clarahobbs/pd-buddy-sink/
ZY12PDN Sink: https://www.amazon.com/gp/product/B07T2858G6
RAVPower 10Ah: https://www.amazon.com/gp/product/B07Y9QYCDC
RAVPower 20Ah: https://www.amazon.com/gp/product/B07TF73QZS
RAVPower 26.8Ah: https://www.amazon.com/gp/product/B01LRQDAEI
Inateck 45W GaN Charger: https://www.amazon.com/gp/product/B0719KV9PH
3d Printed PD Buddy Sink Case: https://www.thingiverse.com/thing:2847318
This article Copyright © 2020, by Gwendolyn S. Patton. This article may be reprinted in Amateur Radio publications without prior permission, so long as it is reproduced in its entirety, with author credit preserved, and a link back to this page. Derivative works and edited versions require express written permission from Gwendolyn S. Patton. Send inquiries to NG3P@arrl.net.