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Wall warts can be fatal to QMX :-(

 

I am not an engineer and I would never think of powering the QMX or QMX+ with a wall wart. I would think a clean well regulated power supply would be a must.
I for one do not consider this a serious design flaw and would hope Hans does not spend time on this issue. I consider wall warts to be dirty poorly regulated power supplies.

Mike Krieger WA8UOC


On Fri, Nov 15, 2024 at 4:03?PM Reginald Beardsley via <pulaskite=[email protected]> wrote:
OK, I finally got around to addressing this.? The SMPSes in both QMXs were destroyed.? In addition, the main board on one was also damaged and does not boot.? Thankfully, one appears to have survived with SMPS replacements from the unbuilt kits I had on hand.

I used two different wall warts.? A 9 VDC and a 12 VDC.? Both put out ~17 VDC open circuit.? I "knew" this in a general sense, but in my haste didn't realize that 12 V was the damage limit.? ?

From an engineering viewpoint I have to call this a serious design FAIL by Hans in what is otherwise the best design on the market.? Connection of a common wall wart of specified or lower voltage,? sufficient current? and correct polarity should NOT destroy the radio.

I personally can't understand why the SMPSes in the QMX shouldn't withstand? at least 24 V input.? I'd prefer that any voltage and current above minimums and below 24 VDC would operate the radio.? That said, it has a cost.? A Zener, LED and MOSFET to cut off power if the input is over voltage is cheaper.? It just precludes recycling wall warts to power the QMX.? It does prevent damage.

And yes, Hans, I know you're swamped by the QMX+ ;-)? So, I quite understand this might take a while to address.? But destroying the radio by wall wart is not acceptable.

Have Fun!
Reg
 

With several warnings in both the assembly and operations manual to not operate QMX/QMX+ at more than 12V, I am very surprised you think this is a design failure.? It is a design point, well described and advertised.? I would never expect it to survive 17V.
If you want to use simple wall-warts to power it, then build a simple adapter with one of these or the many similar ones:
with the output set to 12V (or 9V if you did a 9V build).? They are very inexpensive, work well, and make it so you don't need to worry about the input voltage.
 

On Fri, Nov 15, 2024 at 09:03 PM, Reginald Beardsley wrote:
I "knew" this in a general sense, but in my haste didn't realize that 12 V was the damage limit.
Reginald! This sums up the situation. You chose to use unregulated power supplies without checking the limits of the device you were connecting to them. Then you blame the device designer for your error. ??
?
In this instance it's probably better to just admit pilot error and move on.?
 

Seeing as you are the only person AFAICS who has attempted to use an unregulated supply on their transceiver, I'd suggest reviewing power supply design and application. You'd explode your 100 watt transceiver if you hooked up a "12 volt 20 amp" unregulated supply to it, as well.
?
I'd call this an application error rather than a design error.
 

Apropos of all this, have a look at the thread Wall Wart Tests. ?Just last week, the first of the three examples I posted to start that thread failed after powering a couple of LED garden lights at about 2/3 of its rated load for a few hours each day for several months. ?These lights started flashing about once a second, and the 'scope revealed a scary failure mode: each flash corresponded to a burst of spikes up to ~60 v. ?The lights survived, but pretty sure a radio wouldn't have!
 

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I have followed email responses like this for years and have learned by observation. ?I do not use wall warts in ham radio, at least any wall warts made after about 1990 as most are junk. There is a reason linear wall warts like those that Yaesu and Icom sell are heavy. ?They have a transformer and other controlling circuits in them. ?

Batteries are low cost in comparison to repairing a blown radio and the Drok battery controllers are cheap and work well. ?

I have built many of Hans radios over the years ever since he started selling his kits and have never blown a single one. Be careful, use your voltmeter, and avoid any wall warts. ?Also beware of the voltage plugs. They may look good and feel good when you plug them in to your favorite radio but poor contacts have blown many a radio. ?Read and learn.

Also remember my story about the battery purchased at a swap¡­. with the RED price tag still fastened to the NEGATIVE battery post¡­. late at night, tired, and testing a radio just once more before going to bed. ?Mislabelled battery smoke smells just as bad as any other electronic smoke. ?The only good smoke is made by heating rosin while kit building.

Be the REASON someone smiles today.

Dave K8WPE

On Nov 16, 2024, at 9:57?AM, spaine via groups.io <spaine@...> wrote:

?
Apropos of all this, have a look at the thread Wall Wart Tests. ?Just last week, the first of the three examples I posted to start that thread failed after powering a couple of LED garden lights at about 2/3 of its rated load for a few hours each day for several months. ?These lights started flashing about once a second, and the 'scope revealed a scary failure mode: each flash corresponded to a burst of spikes up to ~60 v. ?The lights survived, but pretty sure a radio wouldn't have!
 

David,

Amen.

Let me summarize, in UNpolitically correct terms:

wart warts and ham radio LICENSES should be considered mutually exclusive terms.

Giuseppe Marullo
IW2JWW - JN45RQ
 

I would not make any blanket statements about wall warts vs any other form factor,
it's what's inside that counts.? We used thousands of fairly inexpensive
wall warts at work some 20 yrs ago with good results.
?
Old style wall warts with a transformer (kind of heavy, get warm even when not supplying power)
probably have just a diode rectifier and a cap after the transformer, those are not well regulated.
Modern wall warts have switching power supplies, if it's made to the lowest possible standards
so it's $0.05 cheaper than the competition, then it might not be suitable.
?
Form factor doesn't matter, crappy switching power supplies can come in other styles of housing too.
Buy from a reputable supplier.
Make sure it is rated for somewhat more than you expect your rig to use, perhaps twice as much.
Evaluate carefully before using with your rig.
?
Jerry, KE7ER
?
 

One data point.
?
I have one of those 30v 10a CVCC bench power supplies from Amazon similar to this:
?
It's been very useful, but is much too noisy to power an HF receiver.
I have 12v wall warts that do better on the QMX.
A brick desktop style of power supply does have more room for parts,
and therefore more likely to work well for the QMX.
Asking for 12v at an Amp or more from something as small as the typical wall wart
is asking a bit much.
?
Jerry, KE7ER
 

If you're not worried yet, I'll bet this traveler's tale will do it. I had a business trip to Fiji last year so bought a power plug adaptor on Amazon to use my JA/US devices with the Australian large 3-pin outlet. No electronics, transformer, etc. With nothing plugged into it, I plugged it into an outlet and there was a quick pop, flash, and the whole room went dark. After the room breaker was located and reset, i gathered up nerve and tried it again, and two out of the three output sockets worked fine. ?Later on I opened the bomb but found no evidence of a short.?
 

I normally use one of my many, very good linear lab supplies. I was readying a 2nd QMX I bought to lend to an old USAF diddybopper living in a memory care facility. An adjustable lab supply was not a practical PSU in his situation, particularly as I'd have no way of preventing the voltage from being changed by accident.

So I thought a wall wart would do as all I needed was 100 mA for Rcvr operation. Bill was not going to get on the air. Sadly, I never got a radio to Bill he could use before he passed away. The FRG-7 was too complicated and he didn't stay up late enough. I found a 12 V 1 A wall wart, so I thought it made sense. I'm generally used to them being *below* rated output. I'm also used to seeing 176 V on the ground lead on 2 wire mains powered T&M kit from China e.g. the F***Tech FY6800.

There is an old proverb among the Unix greybeards. "Be tolerant of what you accept and strict about what you produce." I see no reason that should not apply to power inputs for QRP kit.

Have Fun!
Reg
 

Did a quick search, seems the spelling is best made a little different:
A ¡°ditty bopper¡± was a slang term for a Morse code intercept operator, MOS 05H in the Army. Most were assigned to the ASA (Army Security Agency)?...
?
Good of you to try to help your friend like that, give him something to do other than stare at the wall all day.
?
I agree that power requirements into our gear should not be so fussy.? Next board rev of the QMX
should be laid out for an LM2940CT-12. or LM2940CT-9.0 (have a dropout voltage of 0.5v at 1a).
For now, easy enough to add one as a lump in your power supply cable,
include the caps suggested in the datasheet.
?
Jerry, KE7ER
?
?
On Wed, Nov 20, 2024 at 05:49 AM, Reginald Beardsley wrote:

I normally use one of my many, very good linear lab supplies. I was readying a 2nd QMX I bought to lend to an old USAF diddybopper living in a memory care facility. An adjustable lab supply was not a practical PSU in his situation, particularly as I'd have no way of preventing the voltage from being changed by accident.? There is an old proverb among the Unix greybeards. "Be tolerant of what you accept and strict about what you produce." I see no reason that should not apply to power inputs for QRP kit.
 

The LM2940CT-12 seems to work fine on my 12v rig.
Could be some QMX's built for 9v may want more than 1 Amp.
The LM2940CT-12 is around a dollar for one piece, higher currents cost more.
?
Here's a selection of 9 and 12 Volt low dropout linear regulators in the TO220 package
that are good for 1.5 and 2 Amps.? If Hans wishes to keep cost of a kit to a minimum,
he could lay the board out for a TO220 and have cheapskate builders jump it with a wire.
?
?
Jerry, KE7ER
?
?
On Wed, Nov 20, 2024 at 07:05 AM, Jerry Gaffke wrote:

Next board rev of the QMX
should be laid out for an LM2940CT-12. or LM2940CT-9.0 (have a dropout voltage of 0.5v at 1a).

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