Author Topic: kWeld - "Next level" DIY battery spot welder  (Read 89616 times)

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Offline carracing111

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #525 on: April 08, 2018, 05:50:48 am »
I join the waiting list!

I have a couple of questions:

Kweld is capable of handling 2000A and the set of capacitors only 1000A. Is it possible to use two sets of capacitors in parallel?
I've thought about this to get solder thicker nickel strips or maybe to achieve a faster welding frequency, 4 seconds is a long time! With my current car-audio capacitors (6 in parallel), I perform 1 welding every second approximately.

I have 12 Maxwell BCAP0350 capacitors, would they work with your protection board or is the ESR too high (3.2 mOhms)?

I recently received the welder Kweld. It must be said that it looks impressive! I'm looking forward to trying it! It will work with a pneumatic welding head in the same way that I have running my current Arduino Spot Welder. When I do I will comment on how it works!

I am very satisfied with my current welding system, although I am limited to 0.15mm nickel. I hope to get to weld at least 0.25mm strips with Kweld!

Regards.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #526 on: April 08, 2018, 08:38:36 pm »
I join the waiting list!
great  :-+

Kweld is capable of handling 2000A and the set of capacitors only 1000A. Is it possible to use two sets of capacitors in parallel?
I've thought about this to get solder thicker nickel strips or maybe to achieve a faster welding frequency, 4 seconds is a long time! With my current car-audio capacitors (6 in parallel), I perform 1 welding every second approximately.
I've started with conservative numbers while waiting for the PCBs, and I'll make an update as soon as I have them. I've measured around 1200A with my hand-wired mockup, but the PCB will have less thick power tracks (the first attempt will be standard 35um double-sided). 1200A is already enough to weld 0.3mm pure nickel without slots (that needs approximately 90-100J). It is possible to reduce the wiring resistances of the connected welder by using lower gauge wires, which should allow to go up even higher.

The 4-second repetition rate is based on thermal limitations of the capacitors themselves, as they heat up from their own ESR. They have a large thermal mass (time constant is in the order of 5 minutes), which means that you can do much quicker bursts, as long as the charger can keep up with that. The 4-second rate is meant to keep the thermal equilibrium below the maximum. And that is with convection cooling, without a fan. Adding that will improve the situation significantly, which is why I added support for that (hysteretic on-off control to keep it simple). You can safely use supercaps up to their rated voltage, but they don't like high temperatures. (This is information that I got when having had Nesscap engineers visiting us some years ago, especially confirming the first statement. You don't need to have a voltage safety margin.)

I have 12 Maxwell BCAP0350 capacitors, would they work with your protection board or is the ESR too high (3.2 mOhms)?
If you combine enough of them (I'd say 3S3P, maybe 4S2P), then you can overcome their higher ESR. But they have a different pinout and cannot be mounted directly on the kWeld-cap board.

I recently received the welder Kweld. It must be said that it looks impressive! I'm looking forward to trying it! It will work with a pneumatic welding head in the same way that I have running my current Arduino Spot Welder. When I do I will comment on how it works!
Great, I'm curious!

I am very satisfied with my current welding system, although I am limited to 0.15mm nickel. I hope to get to weld at least 0.25mm strips with Kweld!
See above  :D
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Offline carracing111

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #527 on: April 08, 2018, 09:55:54 pm »
Perfect, thanks for the quick response.

I will order two boards without condensers plus a full board.
I could try 4S3P with my capacitors. I guess I can make some kind of adapter, so that the pins of my capacitors match.

I attach a couple of photos of my current capacitor configuration and with the welding head that will inherit my new Kweld!

If someone is interested in a head like mine, I can send detailed photos, explain how it works and offer a good price.

Regards

Arduinospotweldercap" border="0



20180330_122252" border="0
 

Offline branadic

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #528 on: April 09, 2018, 02:33:25 am »
If the fully assembled board works as expected I'm in with one complete board, to replace my 12V 17Ah Pb battery.

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Prema 5000 | Prema 5017 SC | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #529 on: April 09, 2018, 08:05:46 pm »
I attach a couple of photos of my current capacitor configuration and with the welding head that will inherit my new Kweld!
That looks very solid, how do you charge the capacitors?

If the fully assembled board works as expected I'm in with one complete board, to replace my 12V 17Ah Pb battery.
The test PCBs will arrive in two days, I'll know very soon.
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Offline carracing111

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #530 on: April 10, 2018, 07:43:33 am »
Hi.

I charge the capacitors at 10V and 20A with a 60V, 20A power supply connected to another stepdown power supply (RD DPS5020)
At the moment it seems to work very well.

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Offline carracing111

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #531 on: April 11, 2018, 09:15:18 am »
I just tried Kweld with the supplied electrodes.
Everything seems to work fine, the calibration was successful although I believe that my capacitors are not able to supply the adequate power.

When I exceed 25J, after each welding Kweld restarts. It seems that the voltage falls below a minimum for a brief moment and this causes the restart.
With my old spot welder I do not have this problem since it uses an independent power supply. How can I solve this with Kweld? Is it possible to add an independent power supply?

I hope that with the supercapacitors works better.
I also need to set a power of 100J to get acceptable welds in pure nickel 0.15mm.

I have a feeling that Kweld needs a more powerful power supply.
Maybe the problem is in the added cable. My old welder connects directly to the capacitors and uses a much thicker electrode wire.

I have to continue testing but leaving aside the restart problem, the welds look great.

Regards
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #532 on: April 11, 2018, 07:02:13 pm »
I just tried Kweld with the supplied electrodes.
Everything seems to work fine, the calibration was successful although I believe that my capacitors are not able to supply the adequate power.
If you press and hold down the trigger switch when welding, then you should can read out the measured current. Use a low energy setting like 5J for that to obtain the current for fully charged capacitors.

The stock kWeld wires are optimized for the right current level with high current 3S Lipos. A significant part of the energy delivered by the power source is lost there. In your case, lower wire gauge will reduce that, allowing to use the stored energy more efficiently. How much Farad do the capacitors have?

The standard kWeld configuration with the Turnigy nanotech 3S has a system efficiency of approx 15%, which means that the power source needs to deliver 25J / 0.15 = 167J of energy per 25J pulse. It is important not to discharge the capacitors too deep, because weld power will drop with current raised to the power of 2. Your weld pulse should be as short as possible, in order not to allow heat spread away from the spot. You want the energy to stay concentrated in the small spot area. A good rule of thumb is to use 1/3 of the available capacitor voltage. When initially charged to 12V, you need at least a capacitance of C=2*167J / (12V^2 - (12V*2/3)^2) = 4.175F to achieve that.

When I exceed 25J, after each welding Kweld restarts. It seems that the voltage falls below a minimum for a brief moment and this causes the restart.
With my old spot welder I do not have this problem since it uses an independent power supply. How can I solve this with Kweld? Is it possible to add an independent power supply?
kWeld restarts when the input voltage drops below 3V approximately. But this also means, that the current flow has dropped down to a level that will probably not be enough to melt any more metal. This the reason why I think that it is does not make sense to add an auxiliary power input. It is possible though, you could directly attach a 12V supply to the electrolytic capacitor on the left, preferably with a series diode.


I hope that with the supercapacitors works better.
I also need to set a power of 100J to get acceptable welds in pure nickel 0.15mm.
The capacitor bank that I am developing has more than 200F, which means that there will be no significant voltage drop, even from big welds.

I have a feeling that Kweld needs a more powerful power supply.
Maybe the problem is in the added cable. My old welder connects directly to the capacitors and uses a much thicker electrode wire.
Yes, bigger wires help as explained above. The power switch has less resistance than any other similar device, but this advantage is being eaten up by the resistance of the 300A fuse. You could of course bridge that, but I wouldn't recommend it.
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Offline carracing111

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #533 on: April 12, 2018, 02:49:00 am »
The values of the tests are the following:

CAL:
OFFS = 67, R = 2.84mR

Test 5J in nickel of different thicknesses

Test 1:
E = 5J, T = 2.19m, I = 1357A, R = 1.17mR

Test 2:
E = 5J, T = 2.34, I = 1370A, R = 1.07mR

The capacitors are 0.5F. They come from a very cheap car-audio brand, I buy them on offer at € 10 each pair. With luck there will be 3F among the 6 capacitors.

It is assumed that with 100J I could weld nickel of 0.3mm and this power is the one I need to weld nickel of 0.15. It seems that the capacitors deliver enough power (1370A), or not?

At the moment I do not intend to weld thicker nickel and the solderings to 100J in nickel of 0.15mm serve me.
The problem is that if I add Kweld in my welding head and restart it to each solder, then the power will be mismatched again, and I would have to reconfigure the soldering iron after each solder! That's why I've thought about adding a small independent source of energy.

Can you think of a better solution?

When will the supercapacitors be ready?

Thank you
« Last Edit: April 12, 2018, 02:52:54 am by carracing111 »
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #534 on: April 12, 2018, 05:02:28 am »
The current level is very good, but as the capacitance is only 3F, this means that the voltage will drop very quickly, and the power that they can deliver into a weld is limited. You wrote that you are charging them to 10V. When they get discharged to 5V during a pulse (current will be only half at that moment), then the delivered energy is 0.5 * 3F * (10V^2 - 5V^2) = 112.5J. With an assumed system efficiency of 15%, this means that you should be able to reliably weld with up to 17J (kWeld setting). This is just enough for 0.1mm pure nickel, but thicker material needs bigger capacitors.


It is assumed that with 100J I could weld nickel of 0.3mm and this power is the one I need to weld nickel of 0.15. It seems that the capacitors deliver enough power (1370A), or not?
Your current capacitors have too little capacitance to hold up voltage during the pulse. They drain too quickly, and the current drops linearily with the voltage of course. Power into a resistive load (the weld spot) is proportional to current to the power of two, so that drops even quicker. So the answer is no, it is not enough for 0.15mm nickel.

At the moment I do not intend to weld thicker nickel and the solderings to 100J in nickel of 0.15mm serve me.
For 0.15mm nickel, the required energy should be 20-30J (estimated, I don't have that available), not 100J.

The problem is that if I add Kweld in my welding head and restart it to each solder, then the power will be mismatched again, and I would have to reconfigure the soldering iron after each solder! That's why I've thought about adding a small independent source of energy.
As I described, you can add an aux power supply if you like. But I would not recommend to discharge the caps to such a low voltage during a pulse, as described above and in my previous posts. Limit yourself to 17J and see what nickel thickness you can do with that. If you go higher, the results will not be as repeatable as you would expect, which is because the pulses get too long, current gets too low, and heat gets spreaded around the spot too much.

Can you think of a better solution?
Add more capacitance. I gave you a formula in my last post that allows you to calculate how much you need based on the pulse energy that you want.

When will the supercapacitors be ready?
I will receive the PCBs for the first prototype tomorrow, and the further timing depends on the results that I get.


I've made a quick simulation to visualize how quickly the output power from your capacitors drops. You can see that after just 4 Milliseconds, you are down from 13.6kW to 4.1kW:
« Last Edit: April 12, 2018, 05:10:13 am by tatus1969 »
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Offline carracing111

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #535 on: April 12, 2018, 05:57:40 am »
Thank you very much for all the explanations, I am learning a lot!

I will wait for the arrival of your capacitorsto continue the tests.

What I do not quite understand is because my Arduino Spot Welder works well with my capacitors. I can make good welds in 0.15mm nickel between 10-12ms. Maybe shorter pulses would be better but I think 10-12ms is within an acceptable range.

Regards
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #536 on: April 12, 2018, 07:53:42 am »
What I do not quite understand is because my Arduino Spot Welder works well with my capacitors. I can make good welds in 0.15mm nickel between 10-12ms. Maybe shorter pulses would be better but I think 10-12ms is within an acceptable range.
Have you wired up kWeld with the same beefy wires that you have been using with the Arduino welder? If not, then it would be like comparing apples and oranges. The losses in the stock kWeld cables are too high when you connect it to a limited power source like your capacitors. Both kWeld and the Arduino welder use a MOSFET switch, so you can expect the same welding result for the same pulse duration with both welders, and with the same wiring and power source.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #537 on: April 13, 2018, 05:44:25 am »
The supercapacitor PCBs arrived today, and I went to populate one. One remark if you are going to solder your own BCAP0310 parts: I used my 150W soldering iron for that task, the solder joints pull a lot of heat from the tip.

Getting the balancer to work properly took just a little longer than I anticipated, as it needed a few tiny (almost unnoticeable) tweaks:


Err, is it really already 10pm? What have I done during the last five hours? :o

Anyway... ready now for a full load test:

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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #538 on: April 13, 2018, 07:35:45 am »
Looks  8)
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #539 on: April 14, 2018, 01:10:56 am »
I am currently running an endurance test of the entire system, including the server PSU, the charger running at full power (average power delivery is around 500W), the new capacitor module with cooling fan (Scythe SY1225SL12SH), and the welder.

The system generates a 50J welding pulse into an artificial load once every two seconds. This is the maximum that the capacitor module can do continuously. It's steady state temperature is 58.5°C, which leaves enough headroom to their rated 70°C (room temperature is 25.0°C).

Without the fan, the capacitors are limited to a continuous repetiotion rate of once every 4 seconds. But as mentioned, this is the maximum average over several minutes of use, their thermal capacity is quite high and the welding electrodes heat up way quicker (I am currently working on improving this), so it is okay to make a series of welds as quickly as it can be handled.

Without a charger, the welding current measures 1050A. With the mentioned charger connected in parallel, the current is 1250A instead, as the charger helps to stabilise the capacitor voltage by delivering an additional 80A during the pulse. When using a different charger with less current, the results will be somewhere inbetween.

The 1050A is good enough for up to 100J welds or 0.3mm pure nickel strips. As the capacitors do not drop in voltage during the pulse (due to their high capacitance), the pulse duration is approximately linear: 5J = 3ms, 30J = 25ms, 100J = 94ms (each into a weld spot resistance of 1.2 mOhms).

Please let me know if you would like to get any other number that I haven't measured yet.

I plan to let the test make at least 10,000 pulses because I want to know if the capacitors experience any sort of damage or degradation from their use in this exotic application. Current pulse count is 2373, and there is no sign yet that the current would start dropping.

Here is a picture of the setup. This is actually a custom design that I am doing for a client project. The final setup will use two welders simultaneously (attached to the same one capacitor module) in an automated system.

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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #540 on: April 17, 2018, 03:54:03 am »
Endurance testing has finished after 10,000 pulses, and the capacitors held up very well! Here is how the weld current developed throughout the test. The starting current with fresh cells is 1250A. I have extrapolated the curve, and it would hit the 1000A mark after roughly 40,000 pulses. This is at full load and running the capacitors at a permanent temperature of approx 55°C (25°C ambient temp).

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Offline bicycleguy

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #541 on: April 23, 2018, 10:47:27 am »
..
Thanks  :D It is performing extremely well. Even when doing a full pull (1kA for 200ms) the MOSFETs don't get even slightly warm. I am considering doing a test row by removing one after another to see how much I overdid it. ...

Hi, looks nice.  Did you ever try removing some MOSFETs
 

Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #542 on: April 27, 2018, 04:39:23 am »
Perfect, thanks for the quick response.

I will order two boards without condensers plus a full board.
I could try 4S3P with my capacitors. I guess I can make some kind of adapter, so that the pins of my capacitors match.

I attach a couple of photos of my current capacitor configuration and with the welding head that will inherit my new Kweld!

If someone is interested in a head like mine, I can send detailed photos, explain how it works and offer a good price.

Regards

https://preview.ibb.co/hZaJ4x/20180330_122252.png

Where did you get the pneumatic head? And price?
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #543 on: May 02, 2018, 06:04:24 pm »
Just wanted to let you know that the capacitor module is now available for pre-orders at https://www.keenlab.de/index.php/product/kweld-ultracapacitor-module/! I expect to be able to deliver by beginning of June. The production batch size for this first round is not too big, and I expect not to be able to build up regular stock yet.
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #544 on: May 02, 2018, 06:11:05 pm »
Hi, looks nice.  Did you ever try removing some MOSFETs
I did intensive robustness testing at current levels above its rating (which is 2000A), where I purposely destroyed a welder. kWeld failed after a few hundred pulses at 2800A. This is equivalent to an overload of a factor 2, because ohmic losses are proportional to the current squared. It was actually a MOSFET that failed, and this is the reason why I consider the number of paralleled transistors to be appropriate.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #545 on: May 03, 2018, 03:49:28 am »
Just wanted to let you know that the capacitor module is now available for pre-orders at https://www.keenlab.de/index.php/product/kweld-ultracapacitor-module/! I expect to be able to deliver by beginning of June. The production batch size for this first round is not too big, and I expect not to be able to build up regular stock yet.
Old news I ordered it already  :)  8)
 

Offline parasole

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #546 on: May 05, 2018, 02:45:19 am »
Here is my power bank setup, 100pcs of 10000uf cheap capacitors, provide perfect weld at 12.6V...
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #547 on: May 05, 2018, 03:12:01 am »
Here is my power bank setup, 100pcs of 10000uf cheap capacitors, provide perfect weld at 12.6V...
That is 1F in total, and when you charge them to 12.6V and allow them to discharge to 8V (I won't recommend to go lower, because current drops proportionally, hence output power drops quadratically), this corresponds to an energy delivery of 47 joules. I typically calculate a ballpark system efficiency number of 15% (the remaining 85% is lost in capacitor ESR, cabling, fuse, and welder switch), this allows you to weld with a pulse energy of up to 7.1 joules. This is just enough for 0.1mm nickel, but I doubt that you can do 0.2mm or 0.3mm with your setup.
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Offline parasole

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #548 on: May 05, 2018, 06:29:54 am »
That is 1F in total, and when you charge them to 12.6V and allow them to discharge to 8V (I won't recommend to go lower, because current drops proportionally, hence output power drops quadratically), this corresponds to an energy delivery of 47 joules. I typically calculate a ballpark system efficiency number of 15% (the remaining 85% is lost in capacitor ESR, cabling, fuse, and welder switch), this allows you to weld with a pulse energy of up to 7.1 joules. This is just enough for 0.1mm nickel, but I doubt that you can do 0.2mm or 0.3mm with your setup.

Sure you are right in your calculations, I just shared my experience and it serves me well. Having 100 caps helps greatly to reduce the ESR and operate with safe currents on individual capacitors. In the attempt to minimise the losses, I use quality awg6 welding cables and no fuse. Instead, I do charge the bank by using automotive bulb which provide quick recharge (about 5-7 sec, just enough time to prepare next welding position) and safety in case of any eventual FET failures and power sourse shorts.
The bank is dischaged to about 5V and provide robust and repeated result with 0.15mm I have used for my battery. I did not try thicker nickel since did not have it, however the way out is quite simple, or more capacitance or little bit more voltage, there is some room for it with 16V capacitors.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #549 on: May 06, 2018, 12:46:57 am »
That is 1F in total, and when you charge them to 12.6V and allow them to discharge to 8V (I won't recommend to go lower, because current drops proportionally, hence output power drops quadratically), this corresponds to an energy delivery of 47 joules. I typically calculate a ballpark system efficiency number of 15% (the remaining 85% is lost in capacitor ESR, cabling, fuse, and welder switch), this allows you to weld with a pulse energy of up to 7.1 joules. This is just enough for 0.1mm nickel, but I doubt that you can do 0.2mm or 0.3mm with your setup.

Sure you are right in your calculations, I just shared my experience and it serves me well. Having 100 caps helps greatly to reduce the ESR and operate with safe currents on individual capacitors. In the attempt to minimise the losses, I use quality awg6 welding cables and no fuse. Instead, I do charge the bank by using automotive bulb which provide quick recharge (about 5-7 sec, just enough time to prepare next welding position) and safety in case of any eventual FET failures and power sourse shorts.
The bank is dischaged to about 5V and provide robust and repeated result with 0.15mm I have used for my battery. I did not try thicker nickel since did not have it, however the way out is quite simple, or more capacitance or little bit more voltage, there is some room for it with 16V capacitors.
The calculations result from my experiments, and findings that I came to with a customer here in Germany who was using 5 x 1F (huge) electrolytic audio capacitors. Even they don't provide enough energy for one 50 joulse pulse to weld 0.3mm nickel.

If you use 6AWG and no fuse, then this helps improving the efficiency and explains why you can do 0.15mm nickel.

Please don't get me wrong, I don't want to critizise your impressive design, just want to share my experience with smaller capacitors.
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