DIY Capacitive Discharge 18650 Spot Battery Welder #6





Introduction: DIY Capacitive Discharge 18650 Spot Battery Welder #6

About: I mainly take on projects I have seen here and put my own twist on them. I also like to take garbage or thrown out electronics and make something nice from them. I have no certain area of Expertise, I am new...

Here is the 6th Battery Tab welder I have created to date. Since my first MOT welder, I've been wanting to do one of these and I am happy I did! This one I decided to do with a Capacitor. The ProTip is how to make a simple Battery Tab welder from an Audio Capacitor(.6F and up) This has also ended up to be my favourite one of the 7. The welds it produces have no burns and the tabs are almost perfect when done. Hardly a sound when it fires. Great Little 3lbs welder!

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Step 1: Lay Out and Look Over All Your Part and Pieces Needed for the Build.

With any build, I like to make sure I lay out all parts and pieces I may need for the build to make sure there are no defect. Can be really frustrating to have everything together and find one part is defective.I made sure to test the KP100A, the Buck Converter, the Boost Converter and 2F Capacitor(.6F or 600,000uF actually). I typically test these parts as I get them from eBay or other stores. Most of the Items I purchased for this build came from eBay. The APC UPS case, I found at the local goodwill for around 5$ completed and working with an actually good 12V sealed lead acid battery 7.4Ah. During my inspection, I noticed the Cables I planned on using, with the Capacitor was not as advertised. They claim it to be 4 gauge, but you can clearly see its actually 8 gauge. At first, I thought this might be a problem, but I noticed in other videos, most Posters were using 8. I also later found out the Capacitor from the same package was only .6F and not 2F as advertised. When I contacted the seller, they did not act one bit surprised, but made the sell fair and offer me a rebate. All other parts and pieces tested good. Here are the Parts I used on this build. Please message me if you need a link for any of these parts.

Boss CPBL2 2 Farad Car Digital Voltage Capacitor Power Audio Cap + 4 Ga Amp Kit

DC-DC Converter Buck Regulator 5V-30V To 0.8-29V (XL4015) Constant Current/Voltage Power Supply Module

5A, LED Ammeter Voltmeter Display

250W DC Step-up Boost Converter Constant Current Power Supply LED Driver 10-50V

KP100A 1600V 100A Phase Thyristor Silicon Control SCR Rectifier

Round Rocker Switch 12V W/ LED light dot car auto rv boat toggle SPST


6 Gauge Solid Bare Copper Wire

50W 6Ohm LED Load Resistors

Schottky barrier diode 15Amp (low voltage loss)

10A 250V Panel Mount Chassis Fuse Holder Socket Base

2 x EBL 3.7V 3000mA (actually 2300mah) 18650 Li-ion Lithium-ion Rechargeable Batteries High Drain

Kester Solder 24-6040-0027 60/40 Stand 0.031

Gold High-Temperature Heat Resistant Kapton Tape Polyimide BGA

Kester 951 & 186 Liquid Flux

Mis. Shrink Tubing Sleeves

ON/OFF/ON 3 Positions SPDT Round Boat Rocker Switch 10A/125V 6A/250V

5.5/2.5 (5.5mm OD 2.1mm ID) DC Metal Barrel Jack Panel Mount x 2

M5 Bolts and Nuts set Mis from the local Hardware Store

Screw Terminal Barrier Connector Electrical Wire Connection 12Position Barrier Terminal Strip Block 10A—100A

Mis screws salvaged from other projects.

Gorilla Superglue, Wood Putty and Wood Glue from the local Hardware Store

Older APC UPS 500Watt for the case

Step 2: Draw Up the Schematics on the Wiring and Build.

I am not the greatest at writing up a schematic or Instructables for others to read. But it serves its purpose and works for me. I have found when I write one up, 9 out of 10 times, I end up revising it as I go along. But in the end, I try and save them all, just in case I have to repair later. Making a schematic will ensure no question to self when you decide to wire everything up. This is also when I decided that the UPS case would work perfectly, as I saw one used in another Youtube Video.I also like to lay out the face design. This is normally changed at the end, but it still gives me something to go off of when I decide to drill my holes. I also like to use graph paper for all my schematics. The great thing about the graph Paper, I can use exact measurement (or close to) when I write everything out. During the schematic and build Idea, I was inspired by 3 other Youtube Poster. "swipemagnetron, The Workbench and BuildYourDreams". Make sure to look them up on YouTube, they also have very detailed videos on Tab welders (Capacitor).

Step 3: Dry Fit All Bigger Components

When building something like this, you are not 100% sure it will fit, until you actually place all parts where they might fit. I am not 100% sure of the terminology or wording, but I like to call this Dry-Fit.(I used to work in Paint and Body..). It's good to make sure, that nothing will be in the way of any other part or wiring.With this build, I have noticed that the Capacitor is a little to big for the case, and I may need to place the bigger part of the SCR on the outside of the case. I will use a hole saw and cut a 3" round hole in the back of the case to fit the Capacitor. This should also let me know if it is getting hot during welds. I also figured out that the Buck Converter will fit perfectly where I planned on the face. All other smaller parts and pieces should seem to work where I might place them.

Step 4: Prep the Frame-Cut Out All the Holes in Case & Cut/Glue in Plaskolite (plexiglass) for Face.

After the dry-Fit, I made sure to measure with a ruler where each part would fit. I also used a 3" hole saw bit to cut the back piece where the Capacitor would hang out. When cutting these holes, I like to use a StepBit. After I measure and center the area I need to drill. I take a 1/16" drill bit and drill a starter hole. Followed up by a 1/8 drill bit. Then I finish it off with the StepBit. I will also wrap a piece of tape around the bit to mark the size of the hole needed. This ensures I do not go to deep when cleaning them out. I will also need to use my "DIY Mini Dremel" to clean out any dividers inside the case that might get in the way. I can use needle nose pliers to get most of it.

After I drill each hole, I will dry-fit the part to make sure it fits. Then I remove and save for the build. With the black tape I added to the glass, I decided to also add a peice of Black Carbon Fiber Film Wrap Vinyl to hide the wording on the face. I try and make sure the case is 100% prepped before I start my build.

Step 5: Prep the 2 Main Components &Set Voltage/Amps

I don't normally prep the components until assembly, but this one, I wanted to use Screw Terminal Barrier Connectors on all connections. This is to help me, encase the case is a pain to put back together. I also wanted the option of swapping out any of the DC converters if I needed to quickly with no soldering.I also figured since the parts are on the table, I could set the voltage and Amps as needed. I set the Buck Converter to 16V and 3.2Amps, and the Boost Converter I set at 25Volts(later changed to 30V)Amps full open. If I need a higher voltage on the Buck Converter, I drilled 2 small holes in the top of the case, where I could adjust as needed. I also added Connectors to the 50W 6Ohm LED Load Resistors

Step 6: Solder,Tin and Add Barrier Blocks to the Switch and DC Jacks.

Because of the way I have decided to build this, I also solder and tin the on/off/on switch, power switch for the LED, on/off rocker with led for the main power and both DC Jacks. With the On/Off Rocker, there is a tiny LED. This LED is normally meant for 12V systems. So I just add a 1k ohm 1/4watt resistor to it on the negative (in) side(3rd gold pin). This ensures I can use this with higher voltages. On the main front switch(on/off/on), the middle pin goes to the Capacitor. One side the 6ohm 50w Resistor and the other side is to the (power out) of the Buck Converter. This is when I decided to add the Schottky barrier diode 15Amp (low voltage loss). This protects the Buck converter from any backfeed or current. The rest of the switches and DC jacks are pretty basic.

Step 7: Make the Battery Pack-2 in Parallel

Just messing around, I knew i needed to make a battery pack for the SCR and small Voltmeter(Capacitor Voltage). With the SCR, I figured a 53 ohm 1/4 watt resistor should keep the amps below 150mA at 4.2-3.7V. So I decided to place 2 in Parallel because I saw a video with the same. With this one, instead of using a Tab Welder, or soldering the batteries. I used some old battery holders I had. Figured this would work great if I end up having to replace them. So Placed 2 together and used hot glue to hold in place, Than I soldered the wire and twisted them together for barrier blocks later. Then I added blue shrinkwrap after I added the EBL 18650s. Put the leads in a barrier block and this pack is ready to go. This was also a good time to test the TP4056 I will be using to charge this up.

Step 8: Mount All Panel Mount Switches, DC Jacks, Voltmeter and Buck Converter

Starting with the Buck Converter, I found a few scrap pieces of plexiglass and wood. I just measured where to drill for screws, and superglue the mount in place. After I tighten the screws, the Buck converter stay steady. I just use Adhesive on the little led to hold that in place. The rest was mainly snapping in the panel mount rocker switches and screwing in the other smaller parts.At the last minute, I decided to also add a panel mount fuse(10amp). A little dap of Hot glue on everything and it shouldn't move one bit.

Step 9: Combine All Wiring and Barrier Blocks According to the Schematic.

Keeping the schematic close by, I started combining wires according to the page. I wasn't to worry about cleaning everything up. I'll do that once I feel I have tested this and it has worked for a couple of month with no issues. I added a few zip-ties to hold them all together. I added the Capacitor and the wiring as it specified in my schematics and it fit where I figured it would. Ran the KP100A through the hole (negative side) and used an Allen wrench to tighten, the same on the other side with the positive lead.One of the last parts was the Boost converter connected to the Buck converter and the power switch in the back. Decided, this would be a great time to test. I Applied power and turn it on. Everything worked as expected. A few Dabs of hot glue here and there to hold wire back and mount the boost converter. I was ready to put the case together. With a little wiggling, I was able to get it together and screw in the back part that holds it all together. Placed the battery in the little holder on the bottom and snapped it in place. Everything seems to go together well.

Quick Note: Not sure if you watch the video, or noticed the Multimeter. Make sure to constantly test for continuity. This will also ensure you did not miss any connections.

Step 10: Capacitor Charging and Discharging With a Test Check List

Before I add the leads, I wanted to run this through a quick checklist to make sure it is working correctly. Light on the back seems to be working when I power the unit on. Using my smaller Bench Power Supply. I turn the amps up full blast(5amps max) and 21V. I planned on using a Dell 19.4V 3.33amp laptop adapter, but for now, I can use the Bench power supply. On the front, I flip up(on) the little switch on the left, this turns on the smaller LED, that gives me the Capacitors voltage. Turning on the switch in the back and the Buck Converter light up. I had the On/off/On switch to "off", so it was doing nothing. I press the switch down(single line) and the Capacitor started to charge. Once the red light came on the Buck Converter the Cap voltmeter showed 15.8V.(.2 went through the diode) Charged perfect. But the charge took 30 seconds. That was great! At 3amps, this should be about right for 2F. Till I realized, the amps was turned down to 1A on the Bench supply. With a little more testing I came to find out the cap was only .6F at best. But it should still work. The only problem with a smaller Cap. I would have to wait a little longer inbetween welds, or it may overheat. With a bigger Cap, you have more lead way. I plan on getting a bigger one in the future. Last parts I needed to check is the discharge. I Turn everything off with the cap charged. Flip the switch on the front up(2 lines) and it started to discharge quickly. The 6ohm 50watt resistor is perfect for this. Everything, but the (2F to .6F), of the Capacitor, tested right. Looks like my project is almost completed.

Step 11: Complete the Build by Adding the Simple 6 Gauge Electrodes

Finally, to wrap this build up,I am Using bigger Terminal Blocks(inside coper piece) and 6 gauge solid copper, that I sharpened with the "DIY Mini Dremel" for the electrodes. Then I used Kapton tape and shrink wrap to hold it all together. Kapton tape works very well for this. The switch or trigger is only to use till I get the foot pedal from TEMco. This was a really Fun Build and the welds it produces are Great. Unfortunately, I do not have video or pictures of the welding but plan on making a video later on comparing all my welders, where I really think this one will dominate. I left the electrodes longer, so I could apply the perfect amount of pressure when welding. During my research, this seems to be the deciding factor on your welds. In less than 2 welds, I had the pressure down. I may add rubber handles to these later on, but great as they are.I am sure there will be more tinkering.Once my pedal gets here, it will make welding even easier. This tends to get a little warm if you do not wait the correct time inbetween welds. But it normally takes a few of them before this happens. I am fully satisfied with this welder and I have 7 to compare it to.

Please let me know if you have any questions. I normally answer back pretty quick. Thanks for reading my instructable and don't forget to vote. If you watch my video, please like subscribe and share. My Next Instructable is a very simple welder I made in less than a few hours(after the case was dry or set in 48hrs, Of Course..LOL)



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    8 Discussions


    3 months ago

    I like your idea of connecting the SCR (what you youngsters call thyristor) directly to that low voltage capacitor terminal to keep the series resistance low. You probably know energy in a capacitor increases as the square of the voltage ( Joules = C x V x V / 2 ) So I fail to see why you choose a low voltage to make a simple tab welder..

    I hear you, plan a video of the welder in action in the future But there are NO pictures of any welded parts which suggests this project is not an effective welder..

    You do get an A+ on presentation and picture quality..

    Yes, I agree with you the video (34 minutes) is too long to watch and not see a capacitance weld or discharge at the end.. I suspect some problems might be that the power resistor will melt the plastic case, too low a voltage, and there is no heat sink on the SCR..

    3 replies

    Thanks for your comments, and I do value your feedback. Me Not showing the welder in action, could also mean, that this video was done a few months back with the intention of having a showdown of sorts(as I explained). While you can assume all you want, I can assure you this is a top-notch welder as long as you have the patience to wait inbetween welds. I am in no way shape an expert at filming and these were done in the begging of my journey. This welder has proven to give me the best welds to date, next to my 12v Battery Tab welder. If you have followed me outside of Instructables, then you know I have 7 welders total. And I use them Daily on certain projects.

    I would never ever(NEVER EVER) cover anything up, I have absolutely NOTHING to hide. Not sure why you would get that impression of me. I try and make sure I leave even my mistakes in my videos and tutorials, so people know when I make a mistake. The actual plan at the time was to have a showdown of welders. I have made these welders in just about everyway I could think of, except the China Circuit I have seen showing up here and there.

    A 6ohm 50-watt resistor will take 18 volts from a .6F capacitor all day long and not break a sweat. It never gets a smidgen warm. The SCR, is only powering a .6F cap at 18V at the most. Both the resistor and the SCR can handle all the way up to 2F easily! The only heat generated is by the leads and the Cap itself, if you discharge to fast and do not wait in between welds. If you check the other Youtubers Video's I mentioned. You will also see they have had no issues using the same components. It doesn't take to much energy to create a clean weld. believe or not?

    The reason I chose to make a low voltage welder, was to show I could. There is no actual reasoning, this is DIY and every once and awhile you see something and want to try building it for yourself. Not every DIY is for something intentional. Sometimes, you just feel like doing something. If you check my Google+ profile, you will see other welders I have completed. I plan on releasing those videos as time permits. With the plan on doing the caparison Video as soon as I finish my 7th and 8th welder(both low powered)

    But again, I do value you feedback and I can't wait to see your Capacitor welder when it is done! I will add you here on Instructables! Thanks for your comments!

    So, I like that "Sometimes, you just feel like doing something" approach.

    I went back and studied your circuit layouts with more detail and you are Correct that power resistor will not really warm up at all.. Old guard me just shakes at not mounting Dale style resistors to a metal plate :-)

    You obviously have extensive experience in electronics.. It was the stud SCR that initially drew me to your ible and I did not review your Google profile.. I enjoy learning new ways and accept your assertion of working low voltage tab welding and sorry to have doubted your veracity.

    Included are some pictures of old 110 amp and up stud SCRs through to a 700 amp hockey puck SCR that will probably never get used by packrat me..

    What thickness tabs and metal are you welding ?


    I learn everything from Experienced Members like you 200%. I'm an old Roughneck from Texas/New Mexico and old Millwork Manufacturer Manager/Carpenter from Seattle. I wanted to start building those really neat Bluetooth Speaker Boom Boxes, and along my journey, somehow, ended up building Power Supplies, Soldering Stations and Tab Welders like Crazy. (Still, have all my parts saved for my first Bluetooth build last year...LOL)1 year later, and I still value everything anybody can teach me. 200% You will probably find me on YoutTube asking those Experienced builds questions after question after question. I OCD research every little part and piece. Newbie here!!

    The person I got the idea for the old APC UPS case, used a Hockey Puck Style for his and he gets pretty close to the same results. I think he even got one of those fake 2F caps, that's actually only 0.6-0.4F also. He uses a LM317 psu and the APC transformer to power his. The guys I got the idea of using Buck and Boost Converter uses the same 100amp SCR. But he has since upgraded his system to a bigger meaner machine. Both guys used the same type of system with the same result. I wasn't sure if I could post the link to both video's, but I posted both names to look up. They both have some really great content on Capacitor welders.

    What I have found with the Capacitor welder, and this might be because of its small Capacity. I can only do the Pure Nickel Strip at about 0.15mm x 0.08MM Safley(or to my personal standard and I am picky). If I try Nickel Plate, it sticks and it normally sticks great, I am just not 100% confident so I don't even bother using it anymore(it works great with my other welders). If I find, I need a thicker piece for amp draw, I will just double up the strip and go over it 2 times. or I lay a bead of solder across the strip and then add the second strip(not sure if this right, but it works?).

    Currently, I am in the middle of a smaller PowerWall and it takes up a lot of my time. But while I test Batteries, I try and catch up on my videos(1 year worth) I also have 2 other welders I am planning. both very small and both very powerful. Hopefully as soon as I finish this powerwall.

    Thanks again for the comments and Thanks for taking a second look! I really really appreciate it!


    3 months ago

    To be honnest, I don't know how to work without a schematic. I'm an electronician and I'm used to draw each and any connection to be able to understand the behaviour. Moreover, with a clean schematic, the printed board is easy to make. Here, for example, I don't know how the thyristor is driven.

    1 reply

    I apologize, I am in no way an Electrician. If you look at the Schematic/Pictorial I created. You will see a blown up written out picture of the CSR. It is connected by a 3.7V battery, a resistor to keep the amps below 150mA and a Momentary Button. Power from the cap is released when the Monetary button is pressed. Because there is no longer power after the press/weld, the CSR closes.

    Your schematics are much closer to what is called a pictorial. Both are useful, but should not be confused.

    1 reply

    I have written both types, but I never really knew what I should call this version. I know with Circuits, I would draw out a schematic and with a Build like this, I would simply add smaller Pictures to represent the component used. I always thought a Pictorial was a little more detailed. I noticed most DIYer would just simply call theirs a schematic also, and I figured I would just do the same. To me, it was not quite a pictorial, and Not quite a schematic.Thanks for the comment.