kWeld Spot Welder Questions 2018.09.27

kWeld Spot Welder Questions 2018.09.27

Most of the questions are for tatus1969 (Frank), the originator of the kWeld system. However, anyone's comments to any of the questions will be greatly appreciated.

Since the original thread :

kWeld - "Next level" DIY battery spot welder
Post by tatus1969 » Jun 22, 2017 6:26 am
https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039&hilit=kweld

is very lengthy (18 pages as of Sept 27, 2018) and hard to search. So I decided to start another thread as a summary of questions important to newbies (including me) before acquiring such system (or any other spot welders) and DIYing own battery pack.

I am interested in buying a set of kWeld for my DIY Li-Ion battery pack(s) welding, here are the questions :

I made my first pack 14s7p out of old notebook 18650 cells using Vruzend caps (no welding + no soldering) and it runs fairly well considering some of the cells might be over 10-yrs-old. Of course, I get terrible figures of 0.3-0.4V with sometime even 0.7-0.8V sag from the pack. I manage to run over 1000km out of it in about 3 months already. I've learned quite a bit. So, it is about time to get the real thing.

Requirements :

1) Wanna spot weld nickel-plated copper strip, may be 0.2-0.3 mm thick for my 14s7p triangle pack. While another 14s5p bar pack is with W-shaped nickels for a readily available battery holders from Aliexpress. I am thinking of welding double layers of 0.2mm nickel.

Is the kWeld capable of doing that ? I don't find it listed in your spec.

2) I prefer a stationary welding unit since I don't have Li-Po batteries and car batteries are too heavy and too bulky to work with. I have several spare switching power supplies 12V 30A (per pic.1).

Pic 1 : switching power supplies 12V 30A




May be I can parallel them to get higher amps needed with the help of ultra caps ?

3) From kweld's web : https://www.keenlab.de/index.php/shop/

What parts of kWeld kit do I need ? Ultra Capacitors ? How many of each ? Prefer to have all of the necessary parts (including nuts, bolts, etc) so I don't have to run around to find them. And from your suggestion, I will work it out to get a complete list. Please advise.

4) What else of extra work / assembling do I need to do to get this kWeld ready to weld my battery pack ?

5) I have a hard time sourcing those pre-cut to shape nickel-plated copper strip or even copper strip alone, may be 0.2-0.3 mm thick, with pre-slit channels in-between the welding spots. My laser-cut shop said it is hard, I wonder if possible, to laser-cut copper sheet. All I can find on-line are nickel, plated or pure strips. Pic.2 shows one of the shape PaulID posted which looks great to me. A simple single slit channel should be OK. Or should I have a big sheet of copper then plate it with nickel, before laser-cut it into desire shape. So laser cut will see it as nickel instead of copper - LOL. Too much of works just for a better conductivity.

Pic.2 : PaulID pre-cut strip with slit channels




6) Does anyone know what is the minimum effective thickness of nickel layer on that nickel-plated copper strip (for spot welding) ? So I can specify that when I have the plating shop do it for me.

If I cannot find that ready-made copper strip, I might have to buy a roll of copper sheet and manual-cut it with scissors into different shapes to cover the whole positive and negative terminals of each of the 7-p battery group (of the 14s7p triangle pack) without the pre-slit channels. Here is what I mean ...

Pic.3 from eric1565 nickel sheet




7) For the slits, I'm thinking about hammering 0.2 copper sheet (might be nickel-plated) with a chisel to get the desire slit channels ? Any better method ? Or I will have to hammer copper sheet like crazy to get 14s7p = 196 pos+neg slits.

Will this scissors-cut copper sheet (without the pre-slit channels) get a good result from welding with kWeld ?

8) Please recommend source to buy these pre-cut copper strips (similar to PaulID's) or how to DIY.

Thanks for the owner's of the pictures reference here.

Any comments will be appreciated.

I believe the easiest way to install a slit is to use a Dremel with a thin abrasive disc for cutting. I have done that before with successful results.

0.20mm thick copper is very flexible and easy to cut with stout scissors, nowhere near as stiff as 0.20mm nickel. I would suggest adding some type of support to the cells to ensure there is no structural stress on the copper bus plates.

The most important experiments that I am looking forward to the results are...nickel-plated copper bus - plates being spot-welded

If the desire for nickel-plating is only to protect the copper from corroding, then the plating thickness can be very thin.

If it is because you want copper buses, but also want them to be easily spot-weldable...then I suspect the nickel-plating must be fairly thick. Only testing will verify the minimum thickness for proper spot-welding.

spinningmagnets said:

I believe the easiest way to install a slit is to use a Dremel with a thin abrasive disc for cutting. I have done that before with successful results.

0.20mm thick copper is very flexible and easy to cut with stout scissors, nowhere near as stiff as 0.20mm nickel. I would suggest adding some type of support to the cells to ensure there is no structural stress on the copper bus plates.

The most important experiments that I am looking forward to the results are...nickel-plated copper bus - plates being spot-welded

If the desire for nickel-plating is only to protect the copper from corroding, then the a ting thickness can be very thin.

If it is because you want copper buses, but also want them to be easily spot-weldable...then I suspect the nickel-plating must be fairly thick. Only testing will verify the minimum thickness for proper spot-welding.

Click to expand...

Thanks for the tips spinningmagnets. I have a similar tool to Dremel and just bought some cutting discs. Will try that out soon. Also thinking about some punching tool like when we punch hole in leather belt...can be easy too.

spinningmagnets / tatus1969, I found this related and interesting :

Spot welding overlapping nickel strips
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96333&hilit=copper+strip

Come up with an idea, how about 2 platings :

Start by a base nickel strip - shape we like from on-line (should be easy), 0.1mm thick,
then plate it with copper 0.075 mm thick on each surface = 0.15mm copper thick,
then another thin 0.025mm nickel plate on each side. So we get, in cross section :

Pic 1 : cross section of double plating ni-cu-ni-cu-ni




The double plating with copper and nickel will be by industrial process, easily control with accurate result.
1st plating with copper 0.075mm thick is automatic on both side, front and back with same thickness.
2nd plating with nickel 0.025mm thick is likewise.
Total of 0.3mm thick strip with 0.15mm copper layer thick (0.075mm x 2).

Any comments ? Will this be good for kWeld ?

Brilliant idea! Definitely worth trying...

Once you divorce the bonding of any copper to nickel in the buses, from the operation that connects the cell-tip to the bus...it means you can do anything to them, even if they get so hot they glow.

One bad thing about ES :

Once I found something cool on ES and really wanna do it, as soon as I start searching for details, I always come across another cool thing. And that always another sound alternatives to what I was up to in the first place. So I ended up having to make hard decisions frequently on which (good) way to go. That makes me looks reluctant. LOL.

Like the saying "I wish I knew that...", after you did something you think is less superior to another thing you found out later.

This forum is really addictive and really is "Endless Sphere".

Here is another alternative non-welding DIY batt pack approach I just found :

N.E.S.E. the no solder module
Post by agniusm » May 03, 2017 10:48 pm
https://endless-sphere.com/forums/viewtopic.php?f=31&t=88051&hilit=3+D+printer&sid=c6362532c0b2906cf3ebbcb4f719918b

ichiban said:

1) Wanna spot weld nickel-plated copper strip, may be 0.2-0.3 mm thick for my 14s7p triangle pack. While another 14s5p bar pack is with W-shaped nickels for a readily available battery holders from Aliexpress. I am thinking of welding double layers of 0.2mm nickel.

Is the kWeld capable of doing that ? I don't find it listed in your spec.

Click to expand...

I have tested 0.1mm pure copper sheet, this does not work at all with kWeld even when slotting them. My theory is that both electrical and thermal conductivity of copper is far better than nickel or steel, and because of that reason you need a much higher output power than what kWeld can deliver. Afaik copper sheet spot welders deliver currents of 10kA and more. And you cannot use copper electrodes. You wrote that you have used Laptop cells. These wouldn't require copper strips. You only need copper for high discharge cells to cut down interconnect resistance, but in my opinion 0.3mm pure nickel would still be good for up to 20A per cell.

ichiban said:

2) I prefer a stationary welding unit since I don't have Li-Po batteries and car batteries are too heavy and too bulky to work with. I have several spare switching power supplies 12V 30A (per pic.1).

Click to expand...

The kCap capacitor module "wants" a voltage of not more than 8.1V. The required current depends on the repetition rate that you want to achieve when welding. I have made some calculations in the kCap manual (https://www.keenlab.de/wp-content/uploads/2018/08/kCap-manual-r1.0.pdf).

Most standard PSUs are not directly suitable, because they either aren't adjustable to the correct voltage, or don't have current limiting. You have to consider that an empty capacitor is equivalent to a short circuit at the PSU's output, which causes it to shut down from overcurrent. These capacitors behave in fact more like small rechargeable batteries, which is why you basically need a charger instead of a PSU. That charger will regulate a constant ouput current, up to the point where 8.1V is reached. It then switches to regulating that constant voltage This is called CC-CV operation (constant current - constant voltage).

In the manual, I suggest a 20A "buck" or "step down" converter. This does the CC-CV method and can be supplied from a suitable PSU like yours. But there's still one caveat: once the capacitor is charged, it acts as a power supply by itself. If you then unplug your PSU, then the capacitor will maintain voltage at the PSU output, delivered backwards (!) through the buck converter. A powerful diode between PSU and buck conveter will prevent this from happening, if it is a problem for the PSU. As you cannot know that, and the PSU will likely break if it has that "problem", it is better to add this diode anyway.

ichiban said:

May be I can parallel them to get higher amps needed with the help of ultra caps ?

Click to expand...

Yes, you can parallel kCaps as you like, but more of two in parallel is not recommended as you will get too close to the 2000A current limit of the welder. Please note that kCaps cannot be arranged in series, withoug adding extra balancing circuitry (which is, in the simplest case, some power resistors).

ichiban said:

3) From kweld's web : https://www.keenlab.de/index.php/shop/

What parts of kWeld kit do I need ? Ultra Capacitors ? How many of each ? Prefer to have all of the necessary parts (including nuts, bolts, etc) so I don't have to run around to find them. And from your suggestion, I will work it out to get a complete list. Please advise.

Click to expand...

For the stationery system, you need the kWeld kit, and one kCap module. Assemble the modules, add a charger (this is your task, I am working on a solution here as well, but this project is currently on hold in favor of others), and you can start welding. I highly recommend to enclose both units, as accidental short circuits can be dangerous, and will also likely damage them if you touch circuitry.

ichiban said:

4) What else of extra work / assembling do I need to do to get this kWeld ready to weld my battery pack ?

Click to expand...

Just basic mechanical tools, please check the kCap manual above and also the kWeld assembly (https://www.keenlab.de/wp-content/uploads/2018/07/kWeld-assembly-manual-r5.0.pdf) and operation manuals (https://www.keenlab.de/wp-content/uploads/2018/07/kWeld-operation-manual-r3.0.pdf).

Very glad to hear from you and thanks for the answers tatus1969. Hope that will benefit many new DIYers too.

Just try to make new packs after learning some from old laptop pack. Forgot to mention that I am aiming towards new cells : LG MJ1 3.4Ah/10Amax (for better range), or, LG HG2 2.9Ah/20Amax (for better power). Just the matter of ordering them any time.

The 2-Pack I am planning :

1) 14s7p = 98 cells Triangle in a DIY 3D printed box (designing)
2) 14s5p = 70 cells in an AliExpress aluminium tube, under the downtube (improvised from behind-seat-tube box)

So now I have 2 packs and 168 cells to weld. Both packs will be used together in parallel for my mountain climbing mission. It will be 50+km with 3000+m in elevation rise, wet and cold. Should be early next year. I have approx 1.5 months to finish all these. After that, the 14s5p can be above the downtube as a normal operation or move to my next build.

For pack#1 :
Pic1 : 14s7p Triangle box (designing)





Pic2 : Dense type cell holders using these :
18650 battery 10P 13P holder for 10S 36V 13S 48V battery pack 2*10 2*13 plastic holder 18650 lithium battery bracket
https://www.aliexpress.com/item/18650-battery-10P-13P-holder-for-10S-36V-13S-48V-battery-pack-2-10-2-13/32847248791.html?spm=a2g0s.13010208.99999999.268.4b183c00oNHWec







For pack #2 : 14s5p under downtube

Pic3 : 14s5p downtube box (improvised from behind-seat-tube box)

Free Shipping Ebike battery box Electric bicycle battery case for DIY battery pack With free 18650 cell holder 36V batteries box
https://www.aliexpress.com/item/lithium-battery-case/839303110.html?spm=a2g0s.13010208.99999999.271.b83c3c00XFyD28







Pic4 : 14s5p cells' holders & strips (downtube) seller confirmed 0.15mm pure nickel
https://www.aliexpress.com/item/18650-lithium-battery-holder-5P13S-5P14S-W-type-battery-holder-and-pure-nickel-strip-For-13S/32858584596.html?spm=a2g0s.13010208.99999999.274.b83c3c00XFyD28

Re: my stationary welding unit, from your suggestion, I will be using that 12V 30A
switching PSU together with a charger capable of CC-CV. I will not forget that diodes to prevent bite-back from cap. Here is the charger, 0-50V/ 15A I have and plan to use :

Pic5 : 50V15A buck supply

DPS5015 15A Constant Voltage current Step-down Programmable digital Power Supply buck Voltage converter color LCD voltmeter
https://www.aliexpress.com/item/DPS5015-15A-Constant-Voltage-current-Step-down-Programmable-digital-Power-Supply-buck-Voltage-converter-color-LCD/32797129142.html?spm=a2g0s.9042311.0.0.394e4c4dj6xqwg


View attachment 1


Since it is easy, cheap and programmable.


Questions :

Now the 2 packs contain 3Ah and above cells 14s7p and 14s5p :

1) So, is the kWeld capable of welding 0.3mm nickel-plated copper strip like I post above ? I can buy ready-made pure nickel strip then DIY plate it with copper and nickel later.
Or at least double layered 0.15mm pure nickel strips (no slits - weld one layer at a time) ?

Pic6: sketch 0.3mm ni-cu-ni-cu-ni





2) What is the max thickness pure nickel strip kWeld can weld ?

Tatus1969, please comment on any issues since your feed back is valuable to the

new guys even if it is not relate to kWeld directly.

Anyone feel free to comment on any aspect they seems fit.

Thank you for your time and sincerely appreciate that.

I figure that :

+ For non-weld/non-solder type batt assembly : they fit for :

(a) you don't know the right way to go yet so buying a welder is a big decision - several hundred $ and might use it for once in years
(b) you might want to disassemble later, though disassembling the pack might be pain in the rear part (some kits). I'm using this kits too. :lol:

+ For welding : when you are certain about cells quality and your welding and don't think disassembly is needed. They are more permanent and have better electrical connections.

For new DIYers with limited knowledge on this subject, we try to go the path that will not cause pain in the future. But in the learning process, we might step into some traps and have to fix it, frustratingly.

It is not apple to apple comparison but it's the nature of consumer that we have choices and wanna go the least resistant path.

Let me know if I misunderstood something.

ichiban said:

DPS5015 15A

Click to expand...

Should be perfect!

ichiban said:

1) So, is the kWeld capable of welding 0.3mm nickel-plated copper strip like I post above ? I can buy ready-made pure nickel strip then DIY plate it with copper and nickel later.
Or at least double layered 0.15mm pure nickel strips (no slits - weld one layer at a time) ?

Click to expand...

As I wrote, even 0.1mm pure copper doesn't work. You need a lot more current to weld this material. I don't have nickel-plated copper to test here, but I don't give that high hopes. It should probably be very thick nickel plating, because that is the only material that will melt.

ichiban said:

2) What is the max thickness pure nickel strip kWeld can weld ?

Click to expand...

kWeld has been designed to spot weld nickel or nickel-plated steel of up to 0.3mm thickness.

Thanks for your fast response, tatus1969

Your answers play a key role in my decision making and progression of this project. Things get much clearer now though there are quite a lot of complicated work for me with most of the parts still to be ordered and time is running.

Any other comments from anyone will be greatly appreciated.

tatus1969 said:

Most standard PSUs are not directly suitable, because they either aren't adjustable to the correct voltage, or don't have current limiting. You have to consider that an empty capacitor is equivalent to a short circuit at the PSU's output, which causes it to shut down from overcurrent.

Click to expand...

Please I have a stupid question. What if I get a really huge PSU? Like, 5V 100A PSU? Will your capacitor module still short it and cause it to shut down?

Megavvolt said:

What if I get a really huge PSU? Like, 5V 100A PSU? Will your capacitor module still short it and cause it to shut down?

Click to expand...

That won't make a difference. As these capacitors have a really huge capacitance of hundreds of farads, connecting them to a PSU is like short circuiting it for seconds. The current surge can exceed 1000A depending on the total electrical resistance of the circuit. You need something that limits the current, in your case to 100A.

Frank, can a resistor be added between a PSU and the kCap? I am certain this would slow down the amount of time needed to "refill" the kCap between each weld, but it may be a worthwhile option, if it is possible...

tatus1969 - thanks!
spinningmagnets - yeah but it looks like that resistor would have to dissipate ~250W.

tatus1969 said:

You need something that limits the current, in your case to 100A.

Click to expand...

Ok I have another question. How close to the max voltage should I get to use the welder at full power?
Suppose I get this charger; will the 7.2V setup enable me to weld 0.3 nickel strips to my batteries, or do I need to get as close to 8.1V as possible?

I'm not very smart when it comes to electronics so please forgive me my next question:
I see that some people here buy two of your ultracap modules and put them in parallel to use with your welder; does that mean that one ultracap module is not enough to fully utilize your welder's capabilities? If so, why did you decide to make those modules the way (2p3s) that underpowers your welder?

spinningmagnets said:

Frank, can a resistor be added between a PSU and the kCap? I am certain this would slow down the amount of time needed to "refill" the kCap between each weld, but it may be a worthwhile option, if it is possible...

Click to expand...

yes, but that's significantly increasing the recharging speed, especially when the capacitors are almost full (like after one welding pulse). You can then add another, smaller value resistor in parallel via a relais, plus maybe a third even smaller, plus a third relay that completely shorts them. All these need to be controlled by a circuitry that switches them based on charge state. (That's basically the same old fashioned style that electric railways used to accelerate from a stop.)

I was working on a cheap solution with ebay/Aliexpress components, but the only results that I got so far is blown components. When they rate something for 20A, then you can expect that it can do 5A in reality. In the end, it is an illusion to think that you get away cheaper by using that stuff.

I have good news, as I managed to redesign the kCap supply module. Parts and boards are ordered, and if the redesign doesn't show any more flaws then I'll make a small production batch. --> https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039&p=1427356#p1427356

Megavvolt said:

Ok I have another question. How close to the max voltage should I get to use the welder at full power?
Suppose I get this charger; will the 7.2V setup enable me to weld 0.3 nickel strips to my batteries, or do I need to get as close to 8.1V as possible?

Click to expand...

It scales linearly, 11% less voltage means 11% less current. As power is voltage x current, this means that you lose 22% of output power. 0.3mm nickel might be problematic with that reduction.

Megavvolt said:

I'm not very smart when it comes to electronics so please forgive me my next question:
I see that some people here buy two of your ultracap modules and put them in parallel to use with your welder; does that mean that one ultracap module is not enough to fully utilize your welder's capabilities? If so, why did you decide to make those modules the way (2p3s) that underpowers your welder?

Click to expand...

These capacitors are quite expensive, so I made a cost/performance tradeoff. A 2p5s module would have allowed to use a 12V charger and would have delivered more current, but I opted against the additional 60€. But I wouldn't call the current solution underpowering the welder, as you can weld 0.3mm nickel as reliably as when using a Lipo. Using two of them in parallel rather extends its capabilities.

tatus1969 said:

A 2p5s module would have allowed to use a 12V charger and would have delivered more current, but I opted against the additional 60€.

Click to expand...

Well in reality, to save these 60€ I'd have to pay 65€ for your DC-DC converter and 20€ for the HP PSU (still much better than relying on a noname Aliexpress charger). I'd say a 2p5s module would make the kWelder really universal because one could buy any decent computer PSU and hook it up (well maybe add a 5-10ohm resistor on the 5V line of that PSU).

We could also use the HP PSU you mentioned without any further modifications (except for maybe you could sell the connecting board for it) because its output lines look really strange.

Then again, I'm a total idiot when it comes to electronics (or business for that matter), so please don't kill me if that's a stupid idea.

P.S. Oh. I am indeed an idiot. The ucaps module can't be hooked directly to a 12V PSU because it will get shorted.
I would still love to have an option with one fat 2p5s ucaps module not to have to buy two ucaps modules to fully utilize the kWelder's capabilities.

Megavvolt said:

P.S. Oh. I am indeed an idiot. The ucaps module can't be hooked directly to a 12V PSU because it will get shorted.
I would still love to have an option with one fat 2p5s ucaps module not to have to buy two ucaps modules to fully utilize the kWelder's capabilities.

Click to expand...

That's exactly the point (no, not that, you're not an idiot! ) You always need a charger of some kind. And a 5S2P is on my todo list since a while. Can't start that at the time being, too many projects.

Once I experienced how great it was using K-weld with the Li-Po battery power source recommended, all the looking up capacitors and step-down converters ground to a halt. For building a couple of batteries, even every weekend of the year, the Li-Po battery power source recommended will be all you could hope for; it works incredibly well, and you will need breaks more often than it needs to charge.

Does anyone use lead acid battery with the welder? I know it kinda defeats the benefits of small welder and lipos aren't that expensive but I just happen to have extra 120ah "heavy duty" battery and currently no use for any lipos. It probably says like 900or 1000 amps starting current.. It probably welds the thinner strips just fine but how about 0.3 mm or something similar? Does good lipo beat it 100-0?

ossivirt said:

Does anyone use lead acid battery with the welder? I know it kinda defeats the benefits of small welder and lipos aren't that expensive but I just happen to have extra 120ah "heavy duty" battery and currently no use for any lipos. It probably says like 900or 1000 amps starting current.. It probably welds the thinner strips just fine but how about 0.3 mm or something similar? Does good lipo beat it 100-0?

Click to expand...

I haven't tested this by myself, but I have several customers that are using the welder this way. It is all about the battery's internal resistance, as that's what defines the amperage that you achieve. The sweet spot is 1500A, you shouldn't go below 1000A, and the overcurrent protection trips at 2000A (at stock cable lengths, which you might need to exceed - this reduces the allowable current). My customers report that fresh 65AH batteries work well, but your 120AH model might be even too strong and trip the overcurrent protection.

tatus1969 said:

ossivirt said:

Does anyone use lead acid battery with the welder? I know it kinda defeats the benefits of small welder and lipos aren't that expensive but I just happen to have extra 120ah "heavy duty" battery and currently no use for any lipos. It probably says like 900or 1000 amps starting current.. It probably welds the thinner strips just fine but how about 0.3 mm or something similar? Does good lipo beat it 100-0?

Click to expand...

I haven't tested this by myself, but I have several customers that are using the welder this way. It is all about the battery's internal resistance, as that's what defines the amperage that you achieve. The sweet spot is 1500A, you shouldn't go below 1000A, and the overcurrent protection trips at 2000A (at stock cable lengths, which you might need to exceed - this reduces the allowable current). My customers report that fresh 65AH batteries work well, but your 120AH model might be even too strong and trip the overcurrent protection.

Click to expand...

Thank you for the information! Just as I thought that only way to be sure is to test it by myself because all the variables.. Leads may need to be little longer because terminals are opposite sides of the battery and it's very long battery. Also it's not brand new so ir is impossible to tell without measuring it. Kweld is on my Xmas for sure