开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. QRPLabs
  2. Topics

QCX Recommended Supply Voltage

 

I’ve just completed building the QCX 20 meter kit and it’s working fine with a wall wart power supply. I would like to use a Milwaukee 18 volt rechargeable battery but the recommended power for the kit is 7 - 16 volts. I could use a dropping resister but that’s a problem with the difference between 123 mA on receive and 514 mA on xmit. ?Example: 10 ohm resister would give drops of 1.12 & 5 volts. Any other ideas out there? Thanks
 

Why not a regulator?? REsistor give excesss voltage on RX and maybe enough on tx.
Or better yet a 12V battery.
?
--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.
 

PD capable power bank with decoy adapter for 12v is silent, good and lightweight solution.
?
For your battery you can drop voltage with series diodes, or use buck convertor which add a bit of noise to reception.
 

I've been using a couple of 25000mah power bank batteries from INIU (bought them from Amazon) with a few different 12v PD adapters with zero problems for about a year now.
Work well with my QMX HB and my QMX+.?
?
GREG KI4NVX?
 

Use a 12v linear regulator, should be able to supply at least one Amp.
With 18 Volts in, the regulator will be dissipating (18v-12v)*1Amp = 6 Watts, so you want a fairly big heat sink on it.
Modern 12v linear regulators have reverse polarity protection (in case you reverse the leads from the battery)
and a very low dropout voltage (so 12.5v from the battery still gets 12.0v to the radio).
Needs caps nearby at input and output as specified in the datasheet.
Shuts down with an internal current limit if rig has a short, also shuts down if regulator gets too hot.
?
An LM2940CT-12 should work
I'd bolt the tab to the aluminum case as a heatsink after first buffing off the anodized finish, use heatsink compound.
Costs about $1, heatsink tab can be grounded, maximum recommended current of 1 Amp
A wimpy regulator like that is a good thing, provides an inherent current limit.
If you need more current, the more expensive MIC29150, MIC29300, and MIC29500 are capable of 1.5A, 3A, and 5A respectively.
?
A switch mode power supply sync'd to a 2.5 MHz oscillator would be more efficient
and have no harmonics in the ham bands except at 50.0 MHz.
But that would be a small project.
?
Jerry, KE7ER
?
?
On Fri, Nov 1, 2024 at 04:03 AM, Roy Vickers wrote:

I’ve just completed building the QCX 20 meter kit and it’s working fine with a wall wart power supply. I would like to use a Milwaukee 18 volt rechargeable battery but the recommended power for the kit is 7 - 16 volts. I could use a dropping resister but that’s a problem with the difference between 123 mA on receive and 514 mA on xmit. ?Example: 10 ohm resister would give drops of 1.12 & 5 volts. Any other ideas out there? Thanks
 

One of these should work perfectly for your 18V battery.? Just set its output somewhere between 12V and 15V.
[email protected]
 

The voltage drop accross silicon diodes is typically .5 to .7 volts and pretty stable so i use them in series for cheap voltage droppers and spike arrestors. 6 of them in series would bring it down to about 13 to 16 volts. At 514ma thats about 1.5 watts dissipated in heat. Not the most efficient but easy.
 

Some here think 13v is too much.? 16v certainly is, better buy a bunch of BS170's along with them diodes.? The LM2940CT-12 can be had for a dollar.
?
On Fri, Nov 1, 2024 at 09:42 AM, <dhorner@...> wrote:

The voltage drop accross silicon diodes is typically .5 to .7 volts and pretty stable so i use them in series for cheap voltage droppers and spike arrestors. 6 of them in series would bring it down to about 13 to 16 volts. At 514ma thats about 1.5 watts dissipated in heat. Not the most efficient but easy.
 

I use the LM2940SX-12 - very low drop-out and built-in reverse polarity protection.
[email protected]
 

Yes until you tweaked it in and wanted the little scary extra output at 16v , i would go with more diodes, a 9v power supply or maybe a 12v regulator or supply. I find some of the switching voltage droppers to be really noisy as they run at about 49khz and make lots of noise. The old 7809 and 7812's are still a nice way to go with appropriate heat sink.
 

The 7812 has been around for nearly 50 years now.? If you happen to have some collecting dust in a drawer, go ahead and use them.? But the dropout voltage at 1 Amp is 2 Volts, meaning you need at least a 14 Volt battery to get 12 Volts into the rig.? Newer parts such as the LM2940CT-12 and MIC29150-12WT have a dropout voltage of only 0.3 or 0.5 Volts, and offer reverse polarity protection.??
?
Jerry, KE7ER
?
?
?
On Fri, Nov 1, 2024 at 12:53 PM, <dhorner@...> wrote:

Yes until you tweaked it in and wanted the little scary extra output at 16v , i would go with more diodes, a 9v power supply or maybe a 12v regulator or supply. I find some of the switching voltage droppers to be really noisy as they run at about 49khz and make lots of noise. The old 7809 and 7812's are still a nice way to go with appropriate heat sink.
 

I have Milwaukee batteries and equipment too, and I would love the option to use them.? My charger charges both 18V and 12V (actually 12.6V) batteries and that would be the path I would like to go.
 

开云体育

?There are a couple of hams in our radio club that use the Drok buck/boost converters with such power tool batteries. They do CW with their xiegu radios and tell me they work well. ?I use a Drok converter with my QMX and it works fine.?

This is the one I use:


Be the REASON someone smiles today.

Dave K8WPE

On Nov 2, 2024, at 12:08?AM, Paul K7VIQ <de.k7viq@...> wrote:

?
I have Milwaukee batteries and equipment too, and I would love the option to use them.? My charger charges both 18V and 12V (actually 12.6V) batteries and that would be the path I would like to go.

 

Haven't used that particular power supply, but DROK generally does not sell junk.? David's DROK switcher has a current limit feature, which could save your rig.? The $2 switchers might work if you first screen out the dead-on-arrivals and can deal with some receiver hash, but for the QMX I'd spring another 15 bucks for the relatively good one.? Would be interesting to determine the frequency it is switching at, then hunt for harmonics on the receiver.? If they are bothersome, perhaps chokes on the wires to the rig and a metal box for the supply would help.
This one's a bit smaller if that's of interest: ?
?
Jerry, KE7ER
?
?
On Sat, Nov 2, 2024 at 02:40 AM, David Wilcox K8WPE wrote:

There are a couple of hams in our radio club that use the Drok buck/boost converters with such power tool batteries. They do CW with their xiegu radios and tell me they work well. ?I use a Drok converter with my QMX and it works fine.?
?

 

Is anyone successfully using the cheaper switchers?
Have you evaluated it for receiver noise?
?
On Sat, Nov 2, 2024 at 06:52 AM, Jerry Gaffke wrote:

The $2 switchers might work if you first screen out the dead-on-arrivals and can deal with some receiver hash

 

开云体育

Seconded on the one Dave pictured. I have several of them and have never had a problem. I even have one that I use with my Elecraft KX3 when I use external battery power. I keep the KX3 supplied with 14 volts which allows me full power output, even when my LiFePo supply starts to drop. No generated hash.

Jim Bennett / K7TXA
Eagle, ID

On Nov 2, 2024, at 7:56?AM, Jerry Gaffke via groups.io <jgaffke@...> wrote:

?
Is anyone successfully using the cheaper switchers?
Have you evaluated it for receiver noise?
?
On Sat, Nov 2, 2024 at 06:52 AM, Jerry Gaffke wrote:
The $2 switchers might work if you first screen out the dead-on-arrivals and can deal with some receiver hash

--
Jim / K7TXA
Eagle, ID

SKCC 10447T
BUG 301

 

I've used two of these mostly on the bench.?
Easy to set voltage and current limits.
Can handle up to 215 Watts out, though I've never felt the need to test that.?
Has an on off switch which is a nice feature.?

https://www.amazon.com/DROK-Converter-Regulated-Adjustable-Regulator/dp/B0BFCSK2J5/ref=mp_s_a_1_9?crid=PAXI6SU75P0D&dib=eyJ2IjoiMSJ9.fsbuV6Gcpze02SHIchkBBXIs-3sVcQUGGqyk5XYWdFz8thWTC86tdLTtv4FL4RQBtNpi8NRlQhZQQ3a4kmxTGXEbGyIcs5Mhp2nXOnauTPy46Yqho9a1pN-fWzjarNMMRNQrc1JcXRAH5DaW-XC-GPpmqnK6juknSO-ZbmOvni3G_yGXbPkaMq-l6Nxe23bbpYtCBv2FVaalwBrKqM9Kfg.K7tbvJuARvQ4QNfHvNLhyIHI8_86KVdQtIupP6ug4TQ&dib_tag=se&keywords=drok+buck+boost+converter&qid=1730561431&sprefix=DROK+buck+%2Caps%2C135&sr=8-9

Various displays for volts/current, WattHours and others.??

Rock solid for me. Used with both a 7Ah LiFe and a 35Ah AGM battery. No noise noticed.?

Built in fan cuts in at 2 Amps output.

73 GREG KI4NVX?




On Sat, Nov 2, 2024 at 9:53 AM, Jerry Gaffke via groups.io
<jgaffke@...> wrote:
Haven't used that particular power supply, but DROK generally does not sell junk.? David's DROK switcher has a current limit feature, which could save your rig.? The $2 switchers might work if you first screen out the dead-on-arrivals and can deal with some receiver hash, but for the QMX I'd spring another 15 bucks for the relatively good one.? Would be interesting to determine the frequency it is switching at, then hunt for harmonics on the receiver.? If they are bothersome, perhaps chokes on the wires to the rig and a metal box for the supply would help.
This one's a bit smaller if that's of interest: ?
?
Jerry, KE7ER
?
?
On Sat, Nov 2, 2024 at 02:40 AM, David Wilcox K8WPE wrote:
There are a couple of hams in our radio club that use the Drok buck/boost converters with such power tool batteries. They do CW with their xiegu radios and tell me they work well. ?I use a Drok converter with my QMX and it works fine.?
?

 

I found this on Amazon. It works great with my QCX mini 20 meter rig. search for it on Amazon:

?

Talentcell Rechargeable 12V 3000mAh Lithium ion Battery Pack for LED Strip, CCTV Camera and More, DC 12V/5V USB Dual Output External Battery Power Bank with Charger, Black

1 - 18 of 18