Introduction: USB Rechargeable Soldering Iron: Solderdoodle Pro

Picture of USB Rechargeable Soldering Iron: Solderdoodle Pro

Please click below to visit our Kickstarter project page for Solderdoodle Pro 2.0 and pre-order a production model!

Solderdoodle Pro is a portable, cordless, USB rechargeable soldering iron. It is based off my original Open Source project: "Solar Powered Soldering Station"

Specifications for the Battery and Circuit, including Gerber files, can be found at

After learning how to use 3D printers, one of my friends asked if there was such a thing as a USB soldering iron and I said that I had instructions to build one, but the battery was external. I then realized that I could create my own case design on a 3D printer and put the battery, charge controller, and other parts inside as one single unit! It worked! .stp files for the case are provided below.

Solderdoodle Pro Specs:

Solderdoodle Specs:
* Time to Fully Charge Solderdoodle @ 5V 1A: 3 hours

* Capacity: 3350mAh/3.6V * Type: NCR18650B Lithium-Ion

* Diameter: 1.5 inches * Length: 7.2 inches

* Charge Cable Length: 5 feet * Weight: 96g (3.4 oz)

* Input Cable - Male USB 2.0 Type A to Micro Connector

* Input - Current: 450 to 1300mA | Voltage: 5 to 6 Volts

* Output - Current: 1400mA | Voltage: 2.5 to 4.2 Volts

* Body Material: High Temperature Plastic

* Battery Life Under Typical Use: 5 years

* Replaceable battery * Provides over an hour of soldering

* Solder up to 24 gage thick wire (Flux recommended for lead-free applications, thicker wire, or large ground planes)

* Heats up to over 700ºF (371ºC) in just 30 seconds

* For use with leaded solder and lead-free solder

*WARNING: Be careful when handling any Lithium-Ion battery because shorting the battery can cause burns. Always wear safety goggles. Please use recommended battery and circuit components because of the higher 2000mA max battery charge current involved. 3D printed parts may warp under high temperatures.

FCC Compliance: NOT Required because the circuit frequencies are below 1.7MHz

Step 1: Materials, Tools, and Files Required

Picture of Materials, Tools, and Files Required

Here is a list of the materials, tools, and files required.


QTY Description

1 Weller BP645 Soldering Iron

1 Lithium-Ion Charge Controller Circuit (Schematic, Gerber Files, etc. can be downloaded at The main IC components are the Maxim MAX8903G charge controller and MAX1790 DC-DC step-up converter circuits)

1 NCR18650B 3350mAh Unprotected Panasonic Lithium Ion Battery (If lower cost is necessary, try the Panasonic NCR18650A battery with a slightly less capacity of 3070mAh. Make sure it's unprotected and check the battery part number carefully. Protected batteries have added length with a built-in circuit, which may affect performance. Reference Other brands of batteries are NOT recommended because the charge controller current to the battery can be as high as 2000mA and the Panasonic NCR18650 chemistry can handle it. If you need to use other brands, make sure that they meet the same specifications, chemistry, and can handle up to 2 Amps of charge current. Using batteries that don't meet these specifications can lead to dangerous battery damage.)

1 Green 5mm Straw Hat LED

2 Hirose 2-pin connector DF3-2S-2C

2 Hirose 4-pin connector DF3-4S-2C

8 Hirose Socket 24-28 AWG Crimp Pin DF3-2428SCC

1 5' USB Male-1/8" Headphone Jack USB 2.0 Type A Cable

1 1/8" Headphone Jack female connector attached to a small PCB with a .16" hole for mounting

1 1" Wide Kapton Tape Roll

2 1" Kapton Tape Disc

1 1" Diameter Piece of Heat Shrink Tubing 2.7" Long

2 1/16" Piece of Heat Shrink Tubing 1.0" Long

1 Roll of solder wire

1 3D Printed case (Files available on previous page. These files are designed for FDM printers where the screw holes are oversized to compensate for closing up of the holes. If printed on SLS or other types of machines, the screw holes may be too big and the screws may just fall out.)

Various Lengths 26 AWG Standard Red and Black Stranded 4 Amp Max Wire Listed Below:

1 6.10" Black Wire .06 strip one end .20 strip the other end

1 8.00" Red Wire .06 strip one end .20 strip the other end

2 3.00" Black Wire .06 strip one end .20 strip the other end

1 3.00" Red Wire .06 strip one end .20 strip the other end

1 1.50" Red Wire .06 strip one end .20 strip the other end

1 4.10" Black Wire .06 strip one end .20 strip the other end

1 4.10" Red Wire .06 strip one end .20 strip the other end


QTY Description

1 Small phillips screw driver

1 Power Core Battery Fixture

1 Wire Strippers 24-26 gage range

1 Wire Crimper 20-24 gage range

1 Tape Measure

1 Third Hand Soldering Clamp

1 Soldering Iron

1 Heat Gun

1 Scissors

Step 2: Battery Assembly

Picture of Battery Assembly

Insert the NCR18650B battery in to the Battery Fixture with the positive side facing up. The fixture will align the Red and Black wires as you solder. Do not touch the soldering iron to the fixture because it can melt. You might be able to solder the battery without the fixture, but it is much harder and you would still need something to keep the battery from falling over. The fixture can be used for other battery projects too.

Place the .20" stripped end of the long Red wire in the trench labeled +RED and solder the Red wire to the battery. Try to solder to the battery quickly because too much heat to the battery may damage it. If there is any solder sticking out, smooth it out with the soldering iron.

After soldering, tilt the fixture and push the battery out from underneath with your finger. Turn the battery upside down and insert the battery in to the fixture with the Red Wire in the +RED trough and the negative end of the battery facing up. Crimp the end of the Red wire with the Hirose Pin and insert the pin in to port 1 of the Hirose 2-Pin connector. You want to attach the connector at this point because it is dangerous to leave a dangling bare end of a battery wire exposed and can potentially cause a short or burns if it touches the negative end of the battery.

Place the .20" stripped end of the long Black wire in the trench labeled -BLK and solder the Black wire to the battery. The negative end of this battery usually requires more heat to solder because there's more surface area in contact with the mass of the battery, but try to solder quick. If there is any solder sticking out, smooth it out with the soldering iron.

After soldering, crimp the end of the Black wire with the Hirose Pin and insert the pin in to port 2 of the Hirose 2-Pin connector. Tilt the fixture and push the battery out from underneath with your finger. Bend the black wire straight down over the edge of the negative end of the battery and guide the red wire to loop around along the side of the battery. The effect should be that the Red wire coming down from the positive end of the battery is 120º apart from where the Black and Red wires meet. This wire geometry allows for the positive and negative wires to come out from the same side and gives the snug fit.

Wrap a piece of 1" wide Kapton tape once around the middle of the battery to hold the wires down. Place a 1" Kapton tape disc at each end of the battery and fold the edges over the side of the battery. Then slide the 1" Heat Shrink Tube over the battery with the tube flush with the positive end of the battery. All the tube slack should be sticking out the negative end. Now use a heat gun to shrink the tube to complete the battery assembly.

Step 3: Cable Assembly

Picture of Cable Assembly

Unscrew the Weller soldering iron and remove all the parts. Solder the 3" black cable to the coiled wire on the heating element. Then solder the 1.5" red wire to the metal spring where the AA battery would touch. Crimp the connector to the other ends of the wire and connect the Hirose 4-Pin connector to the wires as indicated below:

Red Wire pin to port 1

Black Wire pin to port 4

Now solder the 3" black wire to the female headphone jack terminal that corresponds to where the base of the male jack would be. Then solder the 3" red wire to the female headphone jack terminal that corresponds to where the base of the male jack would be. Crimp the connector to the other ends of the wire and connect the Hirose 4-Pin connector to the wires as indicated below:

Red Wire pin to port 2

Black Wire pin to port 1

Finally, solder the .20" stripped end of the short black wire to the short leg of the LED (cathode) and solder the .20" stripped end of the short red wire to the longer leg of the LED (anode). Slide the 1/16" heat shrink tube over the LED legs and use a heat gun to shrink the tube. Crimp the Hirose pin to the ends of the wires. Attach the Hirose 2-Pin connector with the Red Wire to port 2 and the Black Wire to port 1. Bend the LED 90º.


You can run Solderdoodle at higher temperature by soldering the Red output wire to the C4 capacitor, which is connected to pins 23 and 24 on the Maxim chip. This bypasses the DC-DC converter and runs at higher power because DC-DC converters aren't efficient with low resistance loads.

Step 4: Soldering Iron Assembly

Picture of Soldering Iron Assembly

After printing the new soldering iron case, take one half of the case and place the heating element, metal spring, LED, and headphone jack in the locations shown in the image.

Lay the battery in the rear of the case.

Wrap a piece of Kapton tape around the circuit to make sure that it doesn't touch any metal and short.

Connect the heating element cable to the USBOUT port on the circuit.

Connect the headphone jack cable to the USB IN6V port on the circuit.

Connect the battery cable to the BAT port on the circuit.

Connect the LED to the LED port on the circuit.

Tuck the wires in away from any protrusions so that they don't get crushed when the two halves of the case are screwed together.

Now add the LED window and switch in the locations shown in the image.

Place the other half of the case on top while looking inside to make sure the cables are not being crushed.

Place the two long screws in the rear screw holes and the short screw in the screw hole near the heating element. Screw the screws in with a screwdriver.

Test to make sure the power turns on when the switch is activated and charges correctly when plugged in to a USB port.

CONGRATULATIONS! Your done building the Solderdoodle!

Click here for Safety and Troubleshooting on next page -->

Step 5: Safety and Troubleshooting

Picture of Safety and Troubleshooting

This test shows that the quality of the Solderdoodle is very high.

Solderdoodle only turns on by sliding the safety switch and pressing the spring loaded button down, so I taped it down and let it run with a temperature sensor touching the tip. I took photos of the test and plotted it in a chart, which are shown above. You can see that the temperature is above 700ºF for a full hour and only starts to decline after 1 hour 20 minutes. The battery is completely drained after 2 hourss. Under normal use, the power button isn't held down this long, so it should last much longer during normal use.


Do Not leave Solderdoodle in direct sunlight. Keep it covered or in the shade. Heat from the sun can cause the charge circuit and battery to get very hot, stop charging, degrade the battery, and shorten its lifespan.

Acceptable Temperatures: Solderdoodle is designed to be operated in temperatures between 0º and 45º C (32º and 149º F).

Storage: Store the Solderdoodle in room temperature. Solderdoodle should be recharged about once a year to prevent over discharge.

For best results, fully charge Solderdoodle before using.


Solderdoodle LED doesn't light up when charging from my laptop:

1) This can occur if Solderdoodle is completely drained and goes in to a trickle charge mode. Keep Solderdoodle plugged in for about 15 minutes and the LED charge light should turn back on.

2) Some older laptops have a low current limitation in their USB ports and will disable the USB port if the current exceeds the limit. Try plugging Solderdoodle in to another USB port.


Solarcycle (author)2016-06-15

Solderdoodle is now available for purchase at

SamusAran28 (author)2014-12-31

Great instructable! Will be making soon!

Solarcycle (author)2014-09-21

Only 59 hours left in the Solderdoodle Pro Kickstarter campaign! Be the first to own one! Shipping in March or sooner!

turbiny (author)2014-09-10

Anyway to buy the parts and assemble it myself

Solarcycle (author)turbiny2014-09-21

I will have parts available to purchase after my Kickstarter campaign has ended. No other company will sell the parts only.

Solarcycle (author)2014-07-25

Solderdoodle now melts lead-free solder!

Solarcycle (author)2014-07-23

Solderdoodle Improved for Higher 700ºF Temperature!

I bypassed the 5V DC-DC converter and wired the heating element directly to the charge controller output and Solderdoodle was able to reach over 700ºF! I added photos of the improvements. I even used the Solderdoodle to modify the existing circuit! Solderdoodle specs will be updated to reflect the higher performance.

Solarcycle (author)2014-07-17

Uploaded a new revision for the 3D printed case. It only needs 2 screws now, has a better fit, and has the "ON" "OFF" text near the power button.

Solarcycle (author)2014-07-15

This is just the prototype, the new production version will have an improved design aesthetically and electrically. The prototype was built with parts I had on hand at the time.

Apolo8 (author)2014-07-10

That is not an instructable but a show and buy

Solarcycle (author)Apolo82014-07-13

This is not even a product yet. Solderdoodle is DIY Open Source Hardware and you can even built it yourself!

AJMansfield (author)2014-07-06

These already exist...

Solarcycle (author)AJMansfield2014-07-07

Solderdoodle lasted over an hour with the power button held down the entire time according to the test I just did. It's now recharging on my laptop.

AJMansfield (author)Solarcycle2014-07-08

"Lasts over an hour" ... Has enough power to keep the LED lit for an hour, sure. Sustain temperatures needed to melt solder, I don't think so.

Solarcycle (author)AJMansfield2014-07-08

This test I did proves that Solderdoodle melts solder for hours.

vforgione (author)2014-07-06

Wouldn't Weller be a bit ticked off that you ripped apart one of their products to make it your own? I'm just wondering if there's a worry of patent infringement. Good luck to you.

Solarcycle (author)vforgione2014-07-06

Weller does sell heating elements separately on their website, so basically that's what I'll be doing. If anything, it helps boost their sales of soldering irons for people to hack. For whatever reason if Weller gets mad, which is unlikely, I would just have to design my own heating element.

vforgione (author)Solarcycle2014-07-07

Sweet! Looks like you have a good plan.

Solarcycle (author)vforgione2014-07-07

I just called Radio Shack and they have no problem with their soldering iron tip being used in another soldering iron:

I would imagine that other off-the-shelf parts are treated the same.

Solarcycle (author)2014-07-07

Updated case design is available. It has a better fit than before.

ndjalva (author)2014-07-07

WHY in the world would you or anyone want to put your little wallwart or computer power supply to do nothing other than melt some metal. The power supply for your little computer is running on. Juse the tool as it was designed and be happy.

BurgersBytes (author)2014-07-06

Why not just adapt the Weller unit to hold the 18650 battery? One would replace 3 AA. Then you would not need a 3D printer.

Solarcycle (author)BurgersBytes2014-07-06

The 18650 battery and charge control circuit doesn't fit in the Weller case, I tried that already.

wblakesx (author)2014-07-06

Kudos. Best of luck.

Solarcycle (author)wblakesx2014-07-06

Thanks! I'm still refining the case design, so stay tuned for updated revisions!

neilh (author)2014-07-05

Hmm. I don't see the specific PCB on the site mentioned, could you perhaps clarify where the exact files are please. Great write up.

Solarcycle (author)neilh2014-07-05

The link on the site labeled "DOWNLOAD POWER CORE CIRCUIT FILES" should have all the PCB files. Power Core is the USB solar charger circuit I used for another project and I'm now using it in the Solderdoodle.

cudy789 (author)2014-07-02

Very good innovation off of the soldering iron, and best of all, portable! Great job!

Solarcycle (author)cudy7892014-07-02


About This Instructable




Bio: After being laid off in 2009, I got rid of my car to save money. The difficult transition from a car to a bicycle led ... More »
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