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USB Powered QDX ?

 


Has anyone tried using a USB to 12v Buck converter to power their QDX??
I would like to plug into my laptop and not have to carry a separate battery for the QDX.?
 

On 23/02/2024 11:58, Dan Hurd W5DMH wrote:
Has anyone tried using a USB to 12v Buck converter to power their QDX?
Dan,

From 5 volts USB you might get ~300mA at 12 volts?
Even if you do not get any QRM from the converter TX would have to be QRP. Maybe feed the PA from 5 volts on another USB socket.
Then why use a converter? 5 Volts could power a QDX directly

What I'm saying is I do not think it would work:-)

73 Alan G4ZFQ.
 

So I tried it and it worked fine, same transmit power as my 12v battery (3.2w on 40m) .?

No issues whatsoever.?
 

The official spec of USB 2 is 5V 500mA max. But probably many modern ports can exceed that.?

Regarding converter noise being an issue, if you power from a USB port. I agree and I prefer linear regulators (of course that limits it to step-down) where possible. The only exception being the QMX buck converter systems ;-)?

However having said that - a lot of people are using power banks and other power systems involving switching converters. Presumably some are better than others regarding switching noise. But I'm not sure why a USB port powered converter application would be worse than what many are using anyway?

73 Hans G0UPL


On Sat, Feb 24, 2024, 2:29?AM Dan Hurd W5DMH <dan@...> wrote:
So I tried it and it worked fine, same transmit power as my 12v battery (3.2w on 40m) .?

No issues whatsoever.?

 

On 24/02/2024 07:27, Hans Summers wrote:
The official spec of USB 2 is 5V 500mA max. But probably many modern ports can exceed that.
I was surprised when Dan said it worked.
A QDX might take up to 700mA at 12 volts transmit.

From 5 volts a buck converter would take more than twice 700mA to produce 700mA at 12 volts.
It does seem that some USB outlets could provide that current.

73 Alan G4ZFQ
 

I am using it on a Panasonic Toughbook, USB 3.0 and probably higher current rating than a standard USB 3.0 port, but I have been unable to find a specification for the current on those ports.?
I see no noise in the waterfall at all and reception appears to be the same as on battery.?

I am wondering if I tried powering directly from the USB 5v (no buck converter at all) could damage the QDX??
 

On 24/02/2024 10:34, Dan Hurd W5DMH wrote:
I am wondering if I tried powering directly from the USB 5v (no buck converter at all) could damage the QDX?
Dan,

There would not be enough voltage to run the QDX if you put 5 volts to the power socket. I see no reason that it would be damaged, just not work.

It is possible that with a slight mod to the QDX it could run at low power from 5 volts directly. Possible but probably not worth the effort.

73 Alan G4ZFQ
 

I have not used a 5V to 12V boost converter, but I have added a couple diodes to my QDX to pull 5V from the QDX USB data port and apply it to the +12V and VCC rails to power the rest of the radio. Since the QDX transmit power is relative to the input voltage, powering it will 5V results in about 100mW of transmit power. I have made contacts at 1000 miles using JS8Call with this modification. Powering the QDX with 5v has been discussed in other posts in the past.

BE AWARE! There is a known "issue" with the QDX switching regulator when rapidly transitioning from a lower voltage to a higher voltage (i.e. connecting 5V from the USB and then 12V) that will destroy components due to over voltage. Always connect power first before the USB cable after making this modification.
 

Forgot to mention that USB current draw on transmit is less than 500mA when running the QDX on 5V from the USB data connector as mentioned. This is a picture of a USB power meter while transmitting with a QDX powered solely by 5V from the USB port on a Raspberry Pi 4.
 

Sorry to hijack this thread, but I built my high band QDX to run off off 12VDC but realize that my gel cells can carry an initial charge of as high as 13.93 VDC. After treading the admonitions, I am hesitant to? power up the QDX with these unless I use a 78L12 or similar. The only problem is that the regulators are inefficient and require 2,5VDC headroom to operate. Similarly, buck converters require 1 VDC of headroom.

How is this situation addressed?

TIA!
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."
 

Please disregard above. Jim, AJ8S, has suggested a product that my resolve my quandary.

A very good way to reduce risk is to limit the current available to the rig, I use a buck converter set to 12 volts out and with current limiting set to 0.7 amps. I use this one: For those of you running on batteries this device will also keep the voltage going to the rig at 12 volts even when the battery droops lower than that.
..if I am all wet of this, advice appreciated.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."
 

Hi Howard

> BE AWARE! There is a known
> "issue" with the QDX switching
> regulator when rapidly
> transitioning from a lower
> voltage to a higher voltage

You're mixing up with QMX. QDX doesn't have switching regulators. There isn't any such issue on QDX...

73 Hans G0UPL


On Sun, Feb 25, 2024, 4:11?AM Howard <howard@...> wrote:
I have not used a 5V to 12V boost converter, but I have added a couple diodes to my QDX to pull 5V from the QDX USB data port and apply it to the +12V and VCC rails to power the rest of the radio. Since the QDX transmit power is relative to the input voltage, powering it will 5V results in about 100mW of transmit power. I have made contacts at 1000 miles using JS8Call with this modification. Powering the QDX with 5v has been discussed in other posts in the past.

BE AWARE! There is a known "issue" with the QDX switching regulator when rapidly transitioning from a lower voltage to a higher voltage (i.e. connecting 5V from the USB and then 12V) that will destroy components due to over voltage. Always connect power first before the USB cable after making this modification.

 

Hi William,

The product that AJ8S suggests is a Buck Boost converter.? ?It converts the input power and current to the set voltage output as long as it is within the range of the device.? It will maintain the 12 volts to the point where the battery can not supply enough power to convert to the higher voltage.

73
Evan
AC9TU
 

Hi Hans,

Thanks again for the great QRP Labs products.

You're right about me getting my wires crossed somewhat. I was thinking about the following QMX issue when I made the comment:?. I was also thinking of the 1.5V SMPS transmit bias circuit in the QDX.

I had an unexpected failure of my QDX during initial testing of the diode modification I described. The failure occurred while powered by 5V from the USB cable and then connecting 12V, and the symptoms were similar to what Gunnar explained in his original post. I believe it was a Rev 4 QDX. It has been a few months since this happened, and it sounds like I need to revisit this scenario.

The initial intent of the diode solution was to allow 5V operation via the existing USB connection, while also allowing 12V operation when desired. This solution seems to work reliably as long as, when your want to run full power, you connect 12V first.
 

I am powering my QDX from USB directly like Howard for almost a year and no problems. The only difference in my power mod is I removed IC2, 78M05 altogether from QDX pcb. This clears any 12V to 5V conflict.
--
?

73, Barb, WB2CBA
 

Although the USB 3.x standard states "any device" may not draw more that 500 mA, there are "charging standards that allow current draw up to 1,500 mA.? Many laptops and other devices have dedicated USB charging ports.? "Most" will allow the high current on the normal USB port

Keep in mind that this works best when you are using a single high current draw device, and any other device on that "hub" is not drawing more than (say) 50 mA.? I do "in vehicle testing".? We have tested devices similar to what Howard showed on a couple of Lenovo and Dell laptops.? In some cases, we had issues with charging the battery during the process and some ground look issues with our other equipment connected to the same laptop.

-------
Rob KB8RCO

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