Battery Spot Welder (CD Welder) || DIY or Buy - YouTube

In a previous project video I showed you how to create a battery pack out of

18650 lithium ion batteries.

Back, then I utilized a rather riskier and not recommended methods of connecting the battery cells together.

By soldering the nickel strips directly to them.

This can be dangerous because you heat up the battery quite a bit which according to its data sheets can lead to problems.

So even back then I tried an immediately failed at doing some DIY spot welding.

With the two salvaged microwave transformers which I had lying around from another failed wedding video.

But since I want to create a bigger battery pack in the near future

I'm in dire need of a battery spot welder and truth be told I almost bought a cheap one for around 200 euros.

Which seems to be capable of doing the job without a problem.

But before buying I wanted to try the DIY route and see whether I could create my own battery spot welder.

Which is the subject of this DIY or by episode.

And spoilers I will fail terribly.

Let's get started!

[music]

When it comes to spot welders

Then we can either use a big transformer in combination with some power electronics

To create small energy pulses with the length of a couple of milliseconds

Or we can create a CD welder aka a capacitive discharge welder

This method still uses power electronics to create millisecond pulses of energy

But the main power source are this time capacitors.

As you might know if capacitors get connected to a voltage source then they get charged up

and can also hold this charge for a while

and if you short the capacitor leads with a nickel strip

then we get an energy burst which in this case is not enough for welding though

Since the 220 microfarad capacitor only held an energy of zero point zero two four seven five joules.

But if we instead utilized super capacitors with a capacity of whopping 100 farads

connect six of them in series

Utilize Kapton tape to create a poor man's capacitor bank and charge the pack up to 15 volts

Then we successfully stored around

1875 joules of energy

Which should be plenty for spot-welding.

That means it was time to create the control circuitry around the capacitor bank

As electrical switches I went with IRL 2505 N channel MOSFETs,

which can handle up to 104 amps

Thus I used one for the charging process of the capacitors and three in parallel to discharge the capacitors during welding.

Additionally I utilized four TCO four 4420 MOSFET driver ICs

Which already ends the power electronics part for this project.

For he control electronics I went with an Arduino Nano as the brains of the organization,

a 128 by 64 OLED display so that we can see what pulse time is currently used and whether the capacitors get charged up

a rotary encoder to adjust the port's time and initialize the charging of the capacitors

and finally a pedal for sewing, to which I soldered one channel and the ground cable of an audio cable

So that I can connect it to the circuits through an audio jack in order to activate the discharge pulse.

To those main components I then added some complimentary ones

and started turning this theoretical composition of components into a proper schematic

through the free on-line circuit design software called Easy EDA

Not only did I make sure to connect all the components to the correct Arduino pin and counterpart

But also make sure to utilize the correct package with included PCB footprint

Because once the schematic was complete. I did not feel like connecting this big number of components to one another on a piece of perfboard

Instead I click the convert to PCB button and started arranging all the PCB footprints of the components

Once I was happy with the layouts I then started tracking the copper traces on the top and bottom layer

at the end I placed thicker copper traces for the power electronics and

created a solid copper region for the ground potential

and with that being done, I exported the Gerber files and ordered five of the PCBs through JLC PCB.

Which was not only affordable, but also only took one week for them to arrive.

Now even though the PCBs look like they would work without a problem, there still was a problem.

Which was that I did not use to correct footprint for the DC jack.

So I had to enlarge the holes, which did work out eventually.

That means it was time to first [solder] all the SMD capacitors to the PCB

and afterwards all the through-hole components which all and all took roughly around 30 minutes.

And if you're wondering for what the big 10 ohm power resistors is used

Then let me tell you that it is used to slowly charge the capacitors while providing feedback voltage to the Arduino.

So that the microcontroller knows when to stop charging.

Only problem was that the feedback voltage can easily exceed 5 volts,

which the 5 volt Arduino certainly does not like.

So as an afterthought I interrupted the feedback copper trace

and added a 2 kilo ohm/1 kilo ohm voltage divider to lower the voltage.

And with that being done the hardware was complete, and it was time to program the microcontroller

Now I will not go into too much detail on how I created the [code].

Since I already talked about interfacing each one of the utilized components in previous videos.

Let me just say that I used an external interrupt for the rotary encoder,

pin change interrupts for the push button and the paddle button and a super simple delay function to create the welding pulse.

So after uploading the code, connecting the capacitor bank and a DC voltage of 15 volts to the circuits

It was time for testing and as you can see the rotary encoder control works.

Charging the capacitors is possible

and even the pedal switch created a precise pulse according to what we have set with the rotary encoder

Beautiful, right?

Well here begins the depressing part, since the capacitor bank was always connected to the welding terminals

no matter whether there was an impulse or not

The problem was, which I found out after too many hours of troubleshooting

the missing reference potential from the discharge MOSFETs

Which I could not add as an afterthought because that would have shortened out the main power supply.

So all in all this project was a big bummer for me.

But it shows beautifully that buying a product can often saves you a lot of nerves.

Now for me going back to the schematic and fixing this problem is not worth it.

Since welding projects seemed to be my kryptonite.

But if you want my project information to fix it or see a functioning CD welder

then simply have a look in the video description.

As always, thanks for watching.

If you enjoyed watching my failed attempt, then don't forget to like, share and subscribe

Stay creative, and I will see you next time! With a functioning project...hopefully.