Back in June of 2017 I moved out of my parent's house and started renting my own. One of the many things that changed was my workspace. I went from a 12' x 13' room to a 4' desk which meant I had to make some changes. One of the major changes was switching from a soldering / hot air rework station to a TS-100 as my main iron. I ended up falling in love with this little thing but I still didn't have a way to make it mobile. That is where this little circuit comes in. I designed this circuit to fit onto a Dewalt 20v Max battery and provide power to my iron, as well as protect the battery and charge my phone.
Step 1: Supplies
I actually ended up making a kit for this project. If you are interested you can buy one here: https://goo.gl/X6EB9e
If you're purchasing the kit it will come with everything you need including instructions and an optional 3d printed case so feel free to stop reading here. (Or continue to see how the rest of us build it)
So now that I got my shameless plug out of the way, let's get started. This Instructable will be forgoing the 5v regulator for charging phones as buck converters can be finicky to work with (especially on breadboards).
These are all of the parts you will need for the battery protection circuit:
2x - Tab connectors for plugging onto the battery https://goo.gl/uUPTNX
1x - 100UF 25V Capacitor https://goo.gl/8ot59d
1x - 2.5x5mm Power jack for plugging your iron in https://goo.gl/EikcyX
1x - 3' Power cable https://goo.gl/6PeuMr
1x - slide switch https://goo.gl/YGuxcZ
1x - 15v Zener diode https://goo.gl/CRdySZ
1x - N-Channel FET https://goo.gl/xW8Nkt
2x - NPN Transistors https://goo.gl/A2ZvhZ
1x - 3mm LED https://goo.gl/yfDEDt
1x - 820 ohm 2w resistor https://goo.gl/zmJm82
1x - 1k 1/4w resistor https://goo.gl/WPUuiu
1x - 1M 1/8w resistor https://goo.gl/gtNNks
2x - 100k 1/8w resistor https://goo.gl/7jejwj
1x - Prototyping Board https://goo.gl/Dz41hF
Step 2: Testing the Circuit
One of the most helpful steps that I like to do before soldering a circuit is breadboarding. This isn't strictly necessary but in my experience setting everything up on a breadboard helps visualize the circuit you're about to build. If you have a breadboard handy, check out the schematic (first photo) and build it up. If you don't have one handy, however, feel free to check out the second and third photos.
Step 3: Soldering the Circuit
Once you have the breadboard built up, It's easy to decide how you want to solder it to the perf-board. Unfortunately, I don't have an example photo as I have been working with printed PCBs but I can offer a few tips that I've found along the way.
1. You are most likely going to have to drill out some of the perf-board holes in order to get the prongs to fit correctly. Keep in mind:
- The prongs (battery connectors) should be spaced ~22.5mm apart.
- The prongs are under stress when you plug/unplug the battery... It wouldn't hurt to add a little JB Weld for strength.
- B+ on the battery is +20v and B- is GND. See 1st Image.
- Don't mess with the center pins. They are used to balance-charge the battery pack.
2. Static is bad and can cause electronics to do odd things.
- Keep the main parts of the circuit close together. (ex: Don't run 3' of wire from the zener diode to the first transistor.)
- If possible, make a case for your circuit. (even just a shield would be good)
3. This is made for soldering irons, not your oven.
- Don't use this circuit with things that take a ton of power. There is no thermal protection in the Dewalt batteries so an excess of current can heat them up.
- This isn't a 9v. Don't lick the circuit.
Step 4: How Does This Work?
Congratulations! You now have a perfect little power supply for your TS-100 soldering iron! Now that you built it, how does it work? (This may be slightly technical.)
The voltage from the battery hits the zener diode. If the voltage of the battery is over 15v, the zener breaks down and starts to let electricity through. After about 15.25v, there is enough current to trigger the first transistor. This transistor pulls the second transistor's gate low which turns off the current flow through it. Because there is no connection to ground, the 100k resistor pulls the MOSFET gate high which turns on the power to your iron. (The capacitor is just to smooth out any oscillation when the battery is low.)
I hope you guys enjoyed this Instructable! Make sure to stay safe while soldering. If you liked this idea or have any suggestions, don't forget to leave a comment!
Also, If you want to buy the kit version of this with the 5v USB charger part of the circuit included, make sure to check it out here: https://goo.gl/X6EB9e