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KX3 Lipo Battery Mod

My only complaint about the KX3 is the choice of batteries Elecraft chose to use. The only thing they are good for is keeping the time on the clock when the radio is turned off. When the batteries are fully charged you can make a few Q’s, if you are lucky.

Elecraft made a much better choice in battery power with the KX2 but that does not help the KX3. 

The answer to making the KX3 a “Grab and Go” radio, like the KX2, is to trash those junker Nickel Metal Hydride batteries and put a LiPo battery pack in its place. When doing so, remember one thing, “You CAN NOT use the onboard battery charger to charge the LiPo battery pack.” They must be charged with an external charger. I charge mine with the Elecraft charger that is used for my KX2's internal battery packs.

The picture to the left was taken out of the Elecraft assembly manual.

Remove the four phillips screws that hold the battery holders in place. You will also need to unplug the wires from the battery holder to the PC board. 

I decided to purchase an extra battery holder assembly from Elecraft so I can put the radio back to stock if needed. Some people don't like when you modify a radio. The Elecraft part number is E850519 and cost $18. (Not that I plan on selling the KX3, but one never knows?)

To the right is my battery of choice. 3000 mah, 3 cell LiPo battery. I've used this battery, externally, with the KX3 numerous times. I've added the DC plug to the battery pack. You may want to order two each of these batteries. Put the extra battery in your backpack or the case you use for carrying your KX3.. When operating portable and the internal battery gets low, just plug the extra battery into the power jack on the side of the radio. This will give you a total of  6 amp hours of operating time.
The KX2 has an amp hour usage meter, the KX3 does not. Keep an eye on the battery voltage and don't let it drop below 9 volts. You can set the low voltage cutoff in the KX3's menu. It's still a good idea to keep a visual on the battery voltage so you can keep track of your run time.

Here is where you can purchase the Venom Battery for $35.99. (So sorry, this battery is now discontinued. I'll post a replacement if I can find one?)
For charging the battery, you can either use the same charger that Elecraft sells to go with the batteries used in the KX2 or you can purchase a charger from Hobby Parts for $19.95. 

The DC power plug on the battery pack is 5.5 x 2.1mm. Marlin P. Jones has them for $.59 each. The mating plug is also from Marlin P. Jone and they sell for $.99 each. Get extra just incase you melt one when soldering the wires to the plugs. I did an needless to say, " I melted one." Glad I had the spare !

Once you remove the two battery trays the surface mount components will be exposed. It’s not a good idea to lay the LiPo battery directly on the board. You will want to use a piece of plastic to screw to the PC board and hold the battery in place. The plastic must be pretty thin since there is not a lot of space in the KX3. A good place to get plastic is at a welding supply or the Sears Hardware Store. Get a 4-1/2" x 5-1/4" welding hood lens. I got mine at Sears for $2.99. You can actually make two pieces out of one so you can share the second with a friend. 

Cut the plastic to a length of 3-15/16" and a width of 2".  Lay the plastic where the left battery holder use to be, keeping the plastic to the left hand side. You will be drilling two each holes. The holes that I used are the ones that were used to hold the left battery holder in place.

Lay the velcro between the plastic and the PC board and then attach the plastic to the PC board.  

The velcro used above was purchased at Lowes. The velcro is 1/2" wide by 45' long and cost only $2.97. You will want to use this mostly because it is a lot thinner than those 6" long strips most people use. This stuff is very thin. I think a thicker velco strap will cause clearance issues. 

Both power connectors have to be slightly modified. 

Remove the back part of the plastic boot as shown on the right connector.
You will have to do this to both male and female connectors. This is not shown
in the above picture showing the battery and connector.

Before you solder the power cables to each connector, make sure you slide a short length of shrink tubing over the wires attached to the center pin of the connector. Once the wire is soldered to the connector, slide the shrink tubing over the center pin, making sure you completely cover the pin, solder and all of the wire. Keep in mind, there is no fuse used on this assembly and  you want to make sure all wires are completely covered. A short circuit here will have catastrophic results! 
When soldering the wire to the center pin of each connector, mate both connectors. The reason for doing so is one connector will provide a heat sink for the other connector as you solder. Be very careful not to overheat the connection. 

Assembly before re-attaching the back of the radio to the main body

And now the complete package

Slide the two connectors so the ground part of the connector
is covered with the velcro. 

Make sure you wrap the velcro around, not only the battery, but also the power connectors. You do not want the connectors moving around, inside of the radio, when transporting the radio from one site to another.
It is very easy to remove the battery for charging. 

With nickel metal hydride batteries, the voltage window was from 11.2 volts down to 8 volts. With the LiPo battery pack the voltage window is now 12.6 volts down to 9 volts. 
I've used Enloop batteries before and they were rated at 1900 mah. The LiPo battery I use now is rated at 3000 mah. This is a considerable increase, not only in voltage but current rating as well.

YouTube Video

I found that I had too many spots, at one place, over lapping the velcro. This added too much height to the battery assembly. A slight moficiation was needed. This video shows the undated assembly.

YouTube Video

When you are finished with the modification, or you disconnect the battery pack for recharging, don't forget to reset the clock. 

I hope you find this modification as useful as I did.

Barry, KU3X