Battery power for the QDX? #power


Brent WT4U
 

My home and portable operating is all battery powered, either 3S Li-ion or lead-acid. That means a supply voltage maybe hitting 13V all the way down to 9V and usually hovering in the 11-12.5V range. The nominal 12V, 3:2 winding, option for the QDX wants 13V to put out 5 watts. At 12V, it's down to 4 watts, at 9V, about 2.1! I'll stick with the 3:3 winding.

The quiet option for bringing that down to 9 volts looks to be an LDO regulator, maybe a 2A, 
BA90DD0T. That's throwing away ~2–4 watts on transmit most of the time. A buck, or buck boost DC -DC converter will be a lot more efficient, but the noise could negate a bunch of Hans's excellent work. Shop for a clean one? Build one with shielding and a 100µH inductor or some more sophisticated filter? There's a trick in mobile phone gear of setting a switching regulator at the drop out voltage ahead of an LDO and using it as a filter. A trade-off in efficiency, and I couldn't find any info about how clean that will be at HF. 

Are there preferred switching frequencies for the buck converter to avoid in-band harmonics? Has someone already figured out a way easier solution to this? 

Thanks, –Brent WT4U


Bill Cromwell
 

Hi,

Are you terribly averse to using NiMH cells? Ten of those in series will be pretty close to 12 volts - at full charge maybe a little more. Not thirteen volts plus. Those are available in D size with several Ampere-hours capacity. I sometimes use those. For a five watt radio the AA sizes will probably give you a nice outing.

73,

Bill KU8H

bark less - wag more

On 10/13/21 7:45 PM, Brent Minchey wrote:

My home and portable operating is all battery powered, either 3S Li-ion or lead-acid. That means a supply voltage maybe hitting 13V all the way down to 9V and usually hovering in the 11-12.5V range. The nominal 12V, 3:2 winding, option for the QDX wants 13V to put out 5 watts. At 12V, it's down to 4 watts, at 9V, about 2.1! I'll stick with the 3:3 winding.

The quiet option for bringing that down to 9 volts looks to be an LDO regulator, maybe a 2A, BA90DD0T. That's throwing away ~2–4 watts on transmit most of the time. A buck, or buck boost DC -DC converter will be a lot more efficient, but the noise could negate a bunch of Hans's excellent work. Shop for a clean one? Build one with shielding and a 100µH inductor or some more sophisticated filter? There's a trick in mobile phone gear of setting a switching regulator at the drop out voltage ahead of an LDO and using it as a filter. A trade-off in efficiency, and I couldn't find any info about how clean that will be at HF.

Are there preferred switching frequencies for the buck converter to avoid in-band harmonics? Has someone already figured out a way easier solution to this?

Thanks, –Brent WT4U


Fred Spinner
 

I have several different types of switcher boards, and I will try to figure out the best one by trying them. Putting a LDO after a switcher cleans up low frequency noise better than LC filters, but not the higher frequencies. Unfortunately the feedback loop in most LDOs is pretty low frequency. 

Hans' earlier comment of you have to try it with switching regulators is pretty spot on.  You sometimes can move the frequency of whatever interference you get from a module to somewhere in frequency you don't care about.   You can can "dither" the switching clock to spread out noise peaks. You can LC filter and LDO filter together.  You can Faraday shield the supply.

Newer higher frequency devices are getting pretty good, but still this would be a great problem to solve. 

The 9V voltage range is good to protect the AMS1117 LDO regulators, as that is a safer input voltage range for them.  But this also means that the 3.3v and 5v lines already have a LDO on them.  So one on 9V might not make as much sense.

The 9V range is bad for the Lithium chemistries directly but it's a compatible voltage for NiMH or even alkaline. 

I am going to try a 9v buck converter with my 13.6V nominal output LiFePO4 first and if its meh I am thinking a pack of NiMHs next.  Cheap enough, small enough, and in a decent mAh range for the QDX.  It's pretty miserly on receive current for what it is... 

One wonders if tapping off of the laptop battery with a buck converter is doable too... But that could get ugly... 

Fred W0FMS 

On Wed, Oct 13, 2021, 4:46 PM Brent Minchey <brentm@...> wrote:

My home and portable operating is all battery powered, either 3S Li-ion or lead-acid. That means a supply voltage maybe hitting 13V all the way down to 9V and usually hovering in the 11-12.5V range. The nominal 12V, 3:2 winding, option for the QDX wants 13V to put out 5 watts. At 12V, it's down to 4 watts, at 9V, about 2.1! I'll stick with the 3:3 winding.

The quiet option for bringing that down to 9 volts looks to be an LDO regulator, maybe a 2A, 
BA90DD0T. That's throwing away ~2–4 watts on transmit most of the time. A buck, or buck boost DC -DC converter will be a lot more efficient, but the noise could negate a bunch of Hans's excellent work. Shop for a clean one? Build one with shielding and a 100µH inductor or some more sophisticated filter? There's a trick in mobile phone gear of setting a switching regulator at the drop out voltage ahead of an LDO and using it as a filter. A trade-off in efficiency, and I couldn't find any info about how clean that will be at HF. 

Are there preferred switching frequencies for the buck converter to avoid in-band harmonics? Has someone already figured out a way easier solution to this? 

Thanks, –Brent WT4U


Curt wb8yyy
 

Brent

As you must have a PC to use a qdx I imagine some batteries to make 9 volts is a minimal burden. 

The switchers not only have spurs they can add noise also. Stay alert and perhaps ideas will emerge to power a small PC and qdx in the field. Another challenge is timekeeping on the PC otherwise ft8 will not work. 

Curt


John AE5X
 

>Another challenge is timekeeping on the PC otherwise ft8 will not work.

GPS dongle and software for timekeeping:
https://www.youtube.com/watch?v=XWUjtII1UTw
--
John AE5X
https://ae5x.blogspot.com


Brent WT4U
 

On Wed, Oct 13, 2021 at 05:00 PM, Bill Cromwell wrote:
Are you terribly averse to using NiMH cells? Ten of those in series will be pretty close to 12 volts
Bill, my problem with a 12 volt battery is that I'm terribly averse to running my 5w radio at 4w! That may be terrible of me. As a QRP die-hard, I wouldn't run 6 watts on a bet, but somehow losing that watt in the other direction—when I'm not making a choice to dip down to QRPp—irks me beyond the rational.

There's also the issue Hans mentions of reduced (but unquantified) efficiency with the 3:2 windings. I'm guessing that's because the non-PA parts of the rig are going to regulate the excess away.

73, –Brent WT4U


Gregg Myers
 

Hi Brent,

I have this buck/boost that I got from Amazon and have used with my QCX last weekend for 24 QSO's. I could not hear any noise that I noticed on my QCX with either 20m or 40m. I'll do some more checking but as far as I can tell, it's quiet. I ran it off a 13.8v battery. I did note a 1v or so overshoot on turn-on but so far it appears to be good for my purposes.

73,
Gregg
W7GRM


On Wed, Oct 13, 2021 at 6:51 PM Brent Minchey <brentm@...> wrote:
On Wed, Oct 13, 2021 at 05:00 PM, Bill Cromwell wrote:
Are you terribly averse to using NiMH cells? Ten of those in series will be pretty close to 12 volts
Bill, my problem with a 12 volt battery is that I'm terribly averse to running my 5w radio at 4w! That may be terrible of me. As a QRP die-hard, I wouldn't run 6 watts on a bet, but somehow losing that watt in the other direction—when I'm not making a choice to dip down to QRPp—irks me beyond the rational.

There's also the issue Hans mentions of reduced (but unquantified) efficiency with the 3:2 windings. I'm guessing that's because the non-PA parts of the rig are going to regulate the excess away.

73, –Brent WT4U


Tony McUmber
 

I would be interested to hear from anyone about the feasibility of winding a 3-turn secondary and a 2-turn secondary and then switching between them depending on the available input voltage.  Surely this never could work, especially with a plain-old mechanical switch.  Yes?  No? Take a hike?

Tony N0BPA


Gregg Myers
 

Hi Tony,

For me, adding a 9v regulator inline to the power feed is way simpler that trying to switch a tap on the transformer. A 9v linear regulator or an LDO regulator costs less than 1$ after all. This is the simplest way, IMO.

73,
Gregg
W7GRM

On Wed, Oct 13, 2021 at 8:09 PM Tony McUmber <1tonymc@...> wrote:
I would be interested to hear from anyone about the feasibility of winding a 3-turn secondary and a 2-turn secondary and then switching between them depending on the available input voltage.  Surely this never could work, especially with a plain-old mechanical switch.  Yes?  No? Take a hike?

Tony N0BPA


Fred Spinner
 

So one know-it-all comment on syncing the clock in the field.  You can get a GPS USB dongle for about $13 from the evil A to Z empire.  A quite decent one.  Now for that price and physical case, you are missing the PPS output, so I would not run my network's NTP server off of it.  But, even so, running a clock sync over a consumer grade GPS without PPS will still get you a very small fraction of a second accuracy sync.   Way better than the 2 second accuracy needed for FT8.

If you rig up one with PPS you will likely be better than network derived NTP sync.  But that is a whole another project.  

You can then stop the program or daemon in Linux, remove the dongle and you will be accurate enough for the WSJT-X modes for the outing and maybe for a week with a normal PC RTC.   And that is a cheap solution for a Raspberry Pi not having a built in RTC too.

The dongles also emulate a serial port on USB and tend to just work. 

Fred W0FMS 


On Wed, Oct 13, 2021, 7:16 PM Gregg Myers <gregg.w7grm@...> wrote:
Hi Tony,

For me, adding a 9v regulator inline to the power feed is way simpler that trying to switch a tap on the transformer. A 9v linear regulator or an LDO regulator costs less than 1$ after all. This is the simplest way, IMO.

73,
Gregg
W7GRM

On Wed, Oct 13, 2021 at 8:09 PM Tony McUmber <1tonymc@...> wrote:
I would be interested to hear from anyone about the feasibility of winding a 3-turn secondary and a 2-turn secondary and then switching between them depending on the available input voltage.  Surely this never could work, especially with a plain-old mechanical switch.  Yes?  No? Take a hike?

Tony N0BPA


Daniel Holmes
 

My thought was to use a USB C PD battery pack with a negotiator to put out 12V. The other port will run the rPi. 

(Now to figure out if my order ever went through—got a confirm from the cart, but no email. Gonna wait a few days to make sure the charge goes through before I worry about it’s)

Dan

--
. Please pardon any mispelings or errors.


On Oct 13, 2021, at 6:06 PM, Fred Spinner <fred.spinner@...> wrote:


I have several different types of switcher boards, and I will try to figure out the best one by trying them. Putting a LDO after a switcher cleans up low frequency noise better than LC filters, but not the higher frequencies. Unfortunately the feedback loop in most LDOs is pretty low frequency. 

Hans' earlier comment of you have to try it with switching regulators is pretty spot on.  You sometimes can move the frequency of whatever interference you get from a module to somewhere in frequency you don't care about.   You can can "dither" the switching clock to spread out noise peaks. You can LC filter and LDO filter together.  You can Faraday shield the supply.

Newer higher frequency devices are getting pretty good, but still this would be a great problem to solve. 

The 9V voltage range is good to protect the AMS1117 LDO regulators, as that is a safer input voltage range for them.  But this also means that the 3.3v and 5v lines already have a LDO on them.  So one on 9V might not make as much sense.

The 9V range is bad for the Lithium chemistries directly but it's a compatible voltage for NiMH or even alkaline. 

I am going to try a 9v buck converter with my 13.6V nominal output LiFePO4 first and if its meh I am thinking a pack of NiMHs next.  Cheap enough, small enough, and in a decent mAh range for the QDX.  It's pretty miserly on receive current for what it is... 

One wonders if tapping off of the laptop battery with a buck converter is doable too... But that could get ugly... 

Fred W0FMS 

On Wed, Oct 13, 2021, 4:46 PM Brent Minchey <brentm@...> wrote:

My home and portable operating is all battery powered, either 3S Li-ion or lead-acid. That means a supply voltage maybe hitting 13V all the way down to 9V and usually hovering in the 11-12.5V range. The nominal 12V, 3:2 winding, option for the QDX wants 13V to put out 5 watts. At 12V, it's down to 4 watts, at 9V, about 2.1! I'll stick with the 3:3 winding.

The quiet option for bringing that down to 9 volts looks to be an LDO regulator, maybe a 2A, 
BA90DD0T. That's throwing away ~2–4 watts on transmit most of the time. A buck, or buck boost DC -DC converter will be a lot more efficient, but the noise could negate a bunch of Hans's excellent work. Shop for a clean one? Build one with shielding and a 100µH inductor or some more sophisticated filter? There's a trick in mobile phone gear of setting a switching regulator at the drop out voltage ahead of an LDO and using it as a filter. A trade-off in efficiency, and I couldn't find any info about how clean that will be at HF. 

Are there preferred switching frequencies for the buck converter to avoid in-band harmonics? Has someone already figured out a way easier solution to this? 

Thanks, –Brent WT4U


Tony McUmber
 

Well, Gregg, I absolutely had not thought of that.  I will look for such an item.  
<$1.00, he says (plus shipping, of course).
Still, for me, the thought of a tiny double-throw retro knife switch on the back panel has its appeal.

...and some troll earlier was complaining about all the stupid questions!  Hah!

Thanks!

Tony N0BPA


Tony McUmber
 

I'm not replying to myself to be seeming to generate traffic -- I just couldn't think of another way to add to my previous remarks.

Anyway, Gregg got me to thinking about this power dilemma, and thinking always seem to confuse me in many ways.

I understand about using a 9V in-line regulator to provide 9V from a 12V source.  It seems, though, that it may still be necessary to find a way to switch between a 3-turn secondary and a 2-turn secondary because the 3- is optimized for 9V feed and the 2- is optimized for 12V feed to get the best performance.  Is this not so?  If so, then is it practical (and practicable) to find a way to shoehorn in an extra couple of turns of wire and a switch?  Am I losing my way here?  It seems to me that one must decide at the outset (because it is the first component to be installed!) how to wire the secondary, thus committing forever to an unchangeable input voltage.  I'm pretty sure that this would not make an untenable difference in one's life, whichever potential is chosen, but it seems like it would be neat to be able to adjust the power supply and then make a counter-adjustment to the rig for optimum performance under a wider range of conditions.

Maybe such a mechanical beast would be incompatible in any practical way with today's sub-atomic circuitry.  A kid can dream, no?


Curt wb8yyy
 

Consider how and where one will use this qdx. In the shack the dissipation of an adequate 9 volt linear regulator is just a little more heat, on battery well not so nice. One could install the regulator network in an adapter unit for in shack use, retaining 9v operation for field use. Or an excuse to build some kind of low noise 9v supply. 

Curt


Daniel Conklin
 

I've been experimenting with the Power Delivery power packs and chargers with trigger devices to change the voltage outputs. I recently picked up a newish Dell 65w laptop charger with PD compatible USB-C and it outputs 5v, 9v, 12v and 20v selectable. My lower wattage PD power pack puts out 5v 9v or 12v depending on the triggering device. I have one triggering device with a LED readout that makes a beep in the receiver of the QCX when it samples the voltage and another without a readout that is quiet. Anyway, Power Delivery devices are good options for QRP power sources. 
--
73, Dan - W2DLC


Mike Perry, WA4MP
 

Here is an option some might consider for powering the QDX with its expectation of 9 volts. It’s 8.4 volts, but might do until you have something better.

A little background. I just ordered a QCX mini for 40. Looking for a way to power it from 18650 batteries, I was going to cobble together a three-battery holder, when I came on various 18650 waterproof case outputting USB plus either 8.4 v. or 12 v. from either three or four 18650s. They were only a little bit more and offered waterproofing, so I ordered one. They’re intended for bikers and apparently 8.4 and 12 volts are the standards for high-end bike lighting.

They are cheaply made. I’d already purchased a 12 v/three-battery version whose switch for the USB output didn’t work. This time I ordered a 8.4 v version for a bit under $12. It runs off four 18650 batteries (not included). If it knows how to use them wisely, might mean a bit more battery life. It is also a bit more compact.

The eBay prices are all over the place, even for products that look identical, so I won’t recommend a specific vendor. If you’re interested, search eBay for "8.4V 4x 18650 Waterproof Battery Pack Case Box House Cover For Bicycle”. You’ll get dozens of results, many using the same pictures.

Just keep in mind that I don’t yet have a QRP-Lab products to test them with. They must do something to get 8.4 volts from four 3.7 volt batteries, so that might mean noisy RF. If alll else fails, you can use that USB output to recharge a smartphone for days.

—Mike Perry, WA4MP

On Oct 14, 2021, at 7:48 am, Curt wb8yyy via groups.io <wb8yyy=yahoo.com@groups.io> wrote:

Consider how and where one will use this qdx. In the shack the dissipation of an adequate 9 volt linear regulator is just a little more heat, on battery well not so nice. One could install the regulator network in an adapter unit for in shack use, retaining 9v operation for field use. Or an excuse to build some kind of low noise 9v supply.


Brent WT4U
 

Mike,
4.2v is the fully-charged voltage of an 18650, so 8.4 from four of them would be a 2x2 series/parallel arrangement. It won't stay at 8.4v for long. At an average working output of 7.2v, that's only ~3.2w out of the QDX. I wonder at what minimum voltage other parts of the radio quit working.

Likewise, three in series is '12.6v' but will spend more time between 11 & 12v. 

I have a great big 26AH supply with a built-in inverter & usb ports. Nominally 12v, but obviously 3Sx?? configuration, so usually running at 11.x volts. I've taken every screw I can find out of the thing and still haven't figured out how to crack it open. Handy gadget, but I'd really like to replace or supplement the barrel connectors with powerpole ports. Anyway, it will last way longer than I'll care to operate, but not what I want to lug up a hill.

I also have loose 18650s I use for various gadgets in 1 and 3-battery trays and ebay protection/charging boards. Not nearly as tidy as your new setup. Spring connections give up some series resistance to the soldered connections in pre-made packs, but I haven't made the jump to buying/making a spot welder.

73, –Brent WT4U


Mike Perry, WA4MP
 

Thanks for your suggestions. Yes, these packs are intended for bike lights, where the voltage isn’t as critical as with electronics. Since the QCX mini is good down to 7 volts, I guess I am OK. It was either this or pay almost as much for primitive and open battery holders. I searched for about an hour for a sealed case that was just a holder for 3-4 18650s. No luck. The only one I found wasn’t waterproof and only held two.

One of the frustrations with having China dominate electronic parts is that these vendors don’t understand market differentiation. Dozens will sell the same product, differing only in a few pennies on the price. And when I contact them about gaps in the market—such as a replaceable 18650 battery holder for common ham handhelds—I get nowhere. I can’t understand why they want to sell what others sell, particularly when they’re making so little on each sale.

But then again, I’ve never had to live in a one-party dictatorship. Not long ago I met a professor from China and, as he was about to return, got an earful about how little freedom he had there.

—Mike Perry, WA4MP

On Oct 14, 2021, at 11:27 am, Brent Minchey <brentm@zanswer.com> wrote:

4.2v is the fully-charged voltage of an 18650, so 8.4 from four of them would be a 2x2 series/parallel arrangement. It won't stay at 8.4v for long. At an average working output of 7.2v, that's only ~3.2w out of the QDX. I wonder at what minimum voltage other parts of the radio quit working.


R. Tyson
 

>I'm terribly averse to running my 5w radio at 4w!

Interesting....     and what difference do you think the extra watt is going to make ?

I run mine at 3.5 watts and am happy. I could strive for 5 watts but why bother. The rig is comfortable with the lower output and the guy at the other end is never going to notice the difference between 3.5 and 5 watts.

Reg                     G4NFR


Hans Summers
 

Hello all

We had a defective internet cable at the new offices most of the day... So I'm way behind. 

QDX works fine down to 5V and will still produce over a watt. 9r would be possible to power it from a USB power bank at a pinch. 

I really don't think it is feasible switching the T1 secondary between 2 turns and 3. The effect of one unused turn flapping around may not be ignorable. Any wiring to and from a switch is also going to disrupt things. 

I think it's better to accept the output power may vary a bit with supply voltage and whether it's 6 or 5 or 4W doesn't really make a lot of difference. 

73 Hans G0UPL
http://qrp-labs.com


-------- Original message --------
From: "Mike Perry, WA4MP" <editor@...>
Date: Thu, Oct 14, 2021, 7:55 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Battery power for the QDX? #power
Thanks for your suggestions. Yes, these packs are intended for bike lights, where the voltage isn’t as critical as with electronics. Since the QCX mini is good down to 7 volts, I guess I am OK. It was either this or pay almost as much for primitive and open battery holders. I searched for about an hour for a sealed case that was just a holder for 3-4 18650s. No luck. The only one I found wasn’t waterproof and only held two.

One of the frustrations with having China dominate electronic parts is that these vendors don’t understand market differentiation. Dozens will sell the same product, differing only in a few pennies on the price. And when I contact them about gaps in the market—such as a  replaceable 18650 battery holder for common ham handhelds—I get nowhere. I can’t understand why they want to sell what others sell, particularly when they’re making so little on each sale.

But then again, I’ve never had to live in a one-party dictatorship. Not long ago I met a professor from China and, as he was about to return, got an earful about how little freedom he had there.

—Mike Perry, WA4MP


> On Oct 14, 2021, at 11:27 am, Brent Minchey <brentm@...> wrote:
>
> 4.2v is the fully-charged voltage of an 18650, so 8.4 from four of them would be a 2x2 series/parallel arrangement. It won't stay at 8.4v for long. At an average working output of 7.2v, that's only ~3.2w out of the QDX. I wonder at what minimum voltage other parts of the radio quit working.