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I have a Yaesu VX-8DR radio, and its power input is a barrel connector. In the age of smartphones, where basically every single device I have uses a USB cable to charge at up to 2.4 amps, I'd like to make a USB cable to power this device as well. I have a small case I pack around with a charger and assortment of USB cables, and I'd like to just add one more USB-to-power-barrel cable to it, rather than two additional discreet proprietary car charger and wall charger units.

(Or buy one; I don't know the barrel connector size, though, and I don't have calipers, and I don't see it listed anywhere in the manual. Although this answer to another question I found here seems to indicate exactly what connector I may have, if Yaesu followed this standard. The plug does have the yellow insulating ring as mentioned in that answer.)

The Yaesu car charger output current is 2A, and the included wall charger output current is 1A, both at 5V like all my USB devices. This means I should be able to use my existing USB car charger that outputs 5V/2A and my existing USB charging hub at home, right?

To clarify, I want a full-size USB connector on the end where there is currently an integrated wall-wart or an integrated car power plug. The barrel connector will stay on the radio end of the cable, I just need to feed it from USB instead of feeding it from an integrated plug.

Can I literally just chop off the integrated cord that runs out of the car charger and solder a full-size USB connector to the end and call it good?

Secondarily, the radio treats any connection on this power port as "attached external DC power", and increases the output wattage on the 1.25m band from 1.5W to 5W until the external power is removed. If I connect this new USB connector to a battery (such as one used to recharge a dying cell phone) is there any possible problem with this increased output wattage connected to a battery instead of to an actual continuous DC power source?

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    \$\begingroup\$ Usb male A to barrel connectors are non standard but not uncommon. To find your barrel size take the device to a radioshack and use their ring of connector wires to find the right one. Two common ones are 2.1mmx5mm and 2.5mmx5mm. \$\endgroup\$
    – Passerby
    Oct 26, 2014 at 23:26

3 Answers 3

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This means I should be able to use my existing USB car charger that outputs 5V/2A and my existing USB charging hub at home, right?

No. The VX-8R series radios require 11-14 V DC (Negative Ground, EXT DC jack) input to charge ("Operating with Charging" pg 166 of the Operating Manual). Take note of the PA-48B charger: PA-48B Vertex Standard Co 12V AC adapter for Yaesu Radio

Can I literally just chop off the integrated cord that runs out of the car charger and solder a full-size USB connector to the end and call it good?

No. Not only does your device not support 5V charging, but it is also not a qualified USB device and can neither negotiate power delivery nor respond to different chargers.

If I connect this new USB connector to a battery (such as one used to recharge a dying cell phone) is there any possible problem with this increased output wattage connected to a battery instead of to an actual continuous DC power source?

Since your device **cannot* be charged by 5V from USB, a cheap lithium battery pack for USB phone charging is not appropriate.

However, for continued operation at high power, you could use an external 12V lead-acid battery (car, motorcycle, marine) connected with the correct polarity to a barrel jack to supply external power such that your radio will operate in high-power mode. When using such a battery, be sure to use fuses to reduce the possible damage from the high-current capability of a lead-acid battery.

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You can cut and splice the cords. I do that kind of thing all the time. You do have to take care to connect the correct wires so that you do not end up with a power polarity reversal. Such reversal could spell disaster to the end device.

When you splice low voltage DC power cords it is wise to use a good scheme for insulating all the connections. I always open up the individual wires to be joined so that they are long enough to let me slip heat shrink tubing over the wire on one side before lap splicing the two wires by soldering. A very handy tool for holding the wires in place while soldering the stripped ends together is pictured below. Also before soldering anything slip a somewhat larger diameter heat shrink tubing over the overall cable on one side that will be used to cover the wires and the small insulated joints.

enter image description here

Once you have soldered the individual wires slide the small heat shrink tubing over the solder joints and shrink using a heat gun. After that you slide the larger tubing over the whole works and shrink that into place.

Some notes. Heat shrink covered wire splices are not very flexible and if made too long or tool close to a plug end can make the cable very awkward to use or store so plan the splice point accordingly.

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  • \$\begingroup\$ You have the usb charging idea backwards. The chargers signal their capacity capability, the device then decides how much to pull. 99% of chargers do not implement charger side curent limiting. \$\endgroup\$
    – Passerby
    Oct 26, 2014 at 23:21
  • \$\begingroup\$ OK. I changed my answer some. But some target devices will not accept full (fastest) charge unless the charger device recognizes the device. It is a known issue that certain Apple devices charge slower from a 3rd party charger than they do from an Apple charger. Also I invite you to read about the Power-IQ capability designed into many of the Anker USB chargers. \$\endgroup\$
    – Michael Karas
    Oct 27, 2014 at 1:59
  • \$\begingroup\$ No, even Apple chargers are simple. The Apple chargers keep the Data Pins at certain voltage levels. There is no smart logic or communication on the charger side. All control is done on the Apple Device. \$\endgroup\$
    – Passerby
    Oct 27, 2014 at 2:05
  • \$\begingroup\$ Very well. I just deleted my comment. I guess the comments, wrong or otherwise, were not really relevant in this case. \$\endgroup\$
    – Michael Karas
    Oct 27, 2014 at 2:10
  • \$\begingroup\$ This DOES NOT answer the question. Additionally, the VX-8R CANNOT be charged from 5V. \$\endgroup\$
    – user2943160
    Jun 6, 2016 at 20:26
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Yes. If a usb supply meets your device's needs (5V 1+ Amps) then a physical connector doesn't matter.

As for the usb battery pack, it depends on how your device deals with voltage drop on the input. Some usb battery packs simply cut off when the battery + regulator drops below a predefined point, other cheaper ones simply keep providing a lower voltage.

Keep in mind 5W is 5V 1A. Your battery pack should be able to supply 1A for that to work well.

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  • \$\begingroup\$ What equipment do I need in order to test this aspect of my battery packs? \$\endgroup\$
    – Bryson
    Oct 27, 2014 at 7:34
  • \$\begingroup\$ @bryson the first is easy, use it until your phone says its not charging anymore, then check the voltage with a voltmeter. If it shows a voltage below 4.75 it doesn't cut off, and that could lead to deep discharging of the battery (killing it). For the power capability, you could take the battery pack's stated output limit at its word, but I would look at the ICs on the pack's regulator and then look at datasheets. \$\endgroup\$
    – Passerby
    Oct 27, 2014 at 15:34
  • \$\begingroup\$ @bryson For example, cheaper ""1Amp"" usb car chargers use the mc34905 (sp?) With its builtin mosfet, which limits output to a max of 750mA. And the current sense/limit resistor actually set it at 700mA. Cost cutting lies. \$\endgroup\$
    – Passerby
    Oct 27, 2014 at 15:34
  • \$\begingroup\$ NO. The VX-8R CANNOT be charged from 5V. \$\endgroup\$
    – user2943160
    Jun 6, 2016 at 20:27
  • \$\begingroup\$ @user2943160 then explain why OP said it uses a 5V 1 Amp supply? \$\endgroup\$
    – Passerby
    Jun 6, 2016 at 21:25

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