kWeld - "Next level" DIY battery spot welder

Ive been thinking how to get the max chooch and repeatability for cheap as possible i imagine this has been asked but its a massive thread.

Some rc chargers got a maintenance cycle on them i know the ichargers do and the end voltage is adjustable so could it balance a capacitor bank the 300w/10amp per cell would give a fast enough turn around for every few second pulses and the chargers screen a visual indication of when caps ready to pulse the kweld.

Theres even a discharge function so if i dont forget once finished i can bleed the caps down before handling for storage.

Does this work for getting full power am i missing something ?
 
Hooked up the same 6s 4ah hobbyking panther graphene lipo. No weird static noises from the kweld this time. Get to the SHORT! part of the setup. Hit the foot switch and get a reeaaly big spark from the lipo EC5 connector. Oops its a cold solder joint. Bullet connector is undamaged so resolder and try again. This time get a huge spark from the electrodes and see a couple of tiny craters on the tips. Sanded down the rough spots with some 2,000 grit paper and generally freshened up the tips to a bright copper appearance.

I'm done trying to weld with 22.2v.

Have some 100ah lifepo4 cells here. I'm going to connect 4 of them and see how that goes. Hopefully no scary sparks this time. :shock:
 
I've posted this a long time ago. I use 2ea, 3S/6000 mah Turnigy Panthers in Parallel. I calibrate using only one because it will error to over-current, then put them back in parallel.

https://hobbyking.com/en_us/turnigy-graphene-6000mah-6s-75c-lipo-pack-w-xt90.html?utm_source=google&utm_medium=cpc&utm_campaign=google_us_shopping&countrycode=US&gclid=CjwKCAjwmv-DBhAMEiwA7xYrd7xtsTvc2AT4ZYIJaJ9xafe1e834PYWhLmS3CTOq0Q9iQ-F57H1NxhoCTHYQAvD_BwE&gclsrc=aw.ds
 
Would a better quality LiPo (with lower discharge resistance, say 150A continuous real-world) possibly trigger that overcurrent condition?

So maybe choosing LiPo that can "only" handle 80-100A discharge might be a better fit?
 
Note I asked these related Q's a while back

john61ct said:
So what are the pack specs to get top output power?

Voltage range?

Actual peak vs continuous maximum amps drawn?

What are the specs that might get to be "too much"?
Click to expand...
 
I don't want to put words in his mouth but I remember way back in this thread, I believe the builder of the Kweld, Tatus may have posted something to the effect that the higher the input Voltage, the less current flow, or something like that and that a 3S LiIon, (not LFP) was the sweetspot. His capacitor bank has a low Voltage input maximum and that should tell us something. I was just doing some spot welding on 18650's using .15mm tabs and using only between 20 and 25 Joules and getting that 1750 Amp current I mentioned above.

I was getting the same results with the 65C rated Turnigy Grapheen 3S/6000 that I believe was the predecessor of the 75C Panther as I have not seen them available in quite some time.

I think some of those top rated SMC Lipo's that Joe is testing over on RCGroup would trip the overcurrent error when used in singular.
 
you dont need volts, you need amps. amps create heat, volts does not. volts just helps the amount of energy pass tru.
 
So apparently 2500A peak is too much, reco maximum is 2000A.

Presumably that is for a **very** short burst.

The Odyssey PC series apparently works well, the little 28Ah version is discussed above

but presumably the bigger G31 100Ah, being lead, would also not risk discharging too fast.

So long as a charge source was able to keep it up over 50% SoC, that would give a nice big buffer, and last for many years.

So long as the size and weight weren't too much, some portability scenarios the little one would be better.

 
Hello Forum,

my name is Wolfgang, I am from Austria and I'm new to this forum.

The last years I welded my packs with a Sunkko 709AD spot welder, which I modified to ensure that I can weld
0,15mm Nickel-sheets. Now I want to step up to a better solution with real spot welding instead of "resistance welding".
Therefore I thought about purchasing the kWeld for this task.

I still have some questions about the system and I hope you guys can answer it for me or tell me, if I'm right or wrong:

-) With a LiPo-Battery as power source for the welder, the voltage of the battery will slowly decrease during
the use of the welder. Because of this, the welder has to longen the pulse to get the same amount of Joules
into the welding point. This is related to Ohm's law -> voltage of battery is decreasing, resistance is (nearly) the same,
so the current will also decrease. This is not beneficial, because we want a pulse which is as short as possible.

-) The kCap as alternative to the LiPo on the other hand has the advantage of a constant voltage and so constant current and
welding duration at each welding spot, because the caps are charged in the pause between the welding.
So this would be more beneficial and to be preferred. Also you don't have to care about the handling and storage
so much as with LiPo-cells.

-) The constant voltage on the kCap at each welding spot is only assured, if the external supply can charge the caps to their
desired voltage in time, so either longer pauses or higher charge current.
If for example one welding impulse is taking 1000A for 20ms, then whis would be 20As of charge
taken out of the caps. If I charge the caps then with a charging current of 10A, this would mean the pause has to be minimum
2 seconds before the next welding pulse.

-) I have read that the kCap is only capable of delivering around 1000A of welding current when it is charged to around 8,2V.
The stored charge in the cap at 8,2V and the given 206F would be around 1690As, so much more than needed for one welding spot
and so the voltage on the caps shouldn't drop too much during the welding. Because of the 3S2P-configuration of the kCap
the voltage can not be increased to get more welding current out of it.
If the kCap-board would be changed to a 4S2P-configuration, then it should be possible to get around 1300A welding current.
Or change to a 6S1P-configuration and using ultracaps with lower ESR to get higer current.
The reason that I want an increased welding current is, that I have read in the manual, that with the kCap a maximum of
0,15mm nickel sheets is possible to be welded. But if I'm buying such a tool, then I would want some "spare power" and
also be capable of welding 0,2mm.

-) The input range of the kCap is stated with 8,1-14V at max. 70A and the caps are charged to 8,0 to 8,3V.
Is there on the input side a step down converter if the input voltage is higher than 8,3V, so that also the real charging
current of the caps is than higher (because of the step down of the voltage), or is it just a decoupling of the input
after the caps are charged?

-) Is anybody using a ultra-capacitor-bank as power source of the kWeld, which is capable of handling over 1500A?
With an selfmade balancing circuit for getting the same voltage level on all caps which are in series?


I hope you can help me and thanks in advance for your answers
Wolfgang
 
the Kcap has balancing on board. you only have to feed it 8V. i use a mean well HRP-300-7.5. it works perfectly even when doing rapid fire welding. but you are not faster then the recharge speed.

unless you are really on the ragged edge with copper and/or phat nickel 0.3 welds you dont need to worry with the kweld/kcap combo. it can do 1000A+ even with pretty long leads wich is more then plenty.

i dont think you understand how the kweld differs from a regular welder. the kweld works with joules, not amps. the weld remains the same even with a drop in voltage/current. the kweld compensates as it looks at the energy, not the amps.

the main result you notice with lower amps is mostly that your welding tips get faster too hot to hold. :wink:
 
Hi Flippy,

thanks for rour reply and your answers.

flippy said:
the Kcap has balancing on board. you only have to feed it 8V. i use a mean well HRP-300-7.5. it works perfectly even when doing rapid fire welding. but you are not faster then the recharge speed.
Click to expand...

Yes I have read it about the balancing of the kCap, which is OK and necessary.
The HRP-300-7.5 has 40A of current delivery, so I also think this enough for constand welding.
The question what I'm interested in here is, what the input electronics of the kCap looks like and how it is handling higher input voltages.

flippy said:
unless you are really on the ragged edge with copper and/or phat nickel 0.3 welds you dont need to worry with the kweld/kcap combo. it can do 1000A+ even with pretty long leads wich is more then plenty.
Click to expand...

OK thanks.
Do you use the original AWG8 wires or bigger ones?
How much length do you have added to your cables?

flippy said:
i dont think you understand how the kweld differs from a regular welder. the kweld works with joules, not amps. the weld remains the same even with a drop in voltage/current. the kweld compensates as it looks at the energy, not the amps.
Click to expand...

Yes I understand this function principle, that's why I have written about the longer spot impulse at lower amps to get the same amount of Joules to the welding spot. That longer impulse is the compensation of the kWeld to get the same amount of Joules.

flippy said:
the main result you notice with lower amps is mostly that your welding tips get faster too hot to hold. :wink:
Click to expand...

That is one of the points why I think (thought), that I want more current in a shorter time:

-) Welding tips stay cooler (less resistance, better to touch)
-) Welding tips stay cleaner (not so much copper from the tips is "taken" away)
-) Welding cables stay cooler (less resistance)

If the comlete system gets warmer, the overall resistance is increasing and so the welding current will decrease, which needs then longer impulses. This will keep going and the temperatures will rise faster and so on.

I know that this is maybe only a theoretical problem which doesn't exist with everybody, because of a maybe slower welding rate, less welding Joules used and so on.

I just thought, why first not to (nearly) fully understand the system before I buy it and then work with it. :wink:

Thanks for your input and looking forward to your answers.

Cheers
Wolfgang
 
Holy cow! It's been a long time since I looked at the KWELD thread. 53 pages...geez!
I have a free imgur account and for whatever reason you can't post images in thread from it. Best I can do is post the URLs and let you go look at the pics.

My KWELD setup:

I have 2 supercap modules in parallel behind my KWELD. I've shortened all the wires between the modules to the minimum needed to make them bolt up to each other with the plastic covers on. I wanted to eliminate any resistive losses I could. I guess 6 awg wire would have helped to, but I used 8 awg...like it came with. I started with a single 20 amp meanwell PSU turned down to 9v. It took several minutes for it to charge up the 2 banks of super caps. Then I could spot weld for about 2 minutes. Then wait like 5 minutes for the PSU to charge the caps again. This got tedious pretty fast! I then bought a single 50A Meanwell PSU and set it to 9v. Recovery time was much reduced, but I could still weld faster than the PSU could keep the super caps charged. I bought a second PSU and I run them in parallel for about 100 amps at 9v DC. So far I have not been able to weld faster than they can keep the super caps charged up. BTW...I've been running my super caps a little over voltage since I got the KWELD in 2019. They have been fine. 3v each isn't really a problem and they never get warm. My fans hardly ever run.

https://imgur.com/RUAVVwI

Here's my dual Meanwell 100 amp PSU setup. I saw someone else do this with resistors and diodes and I copied them. The resistors are dual purpose. There's a large rocker switch in front that can bypass the resistor bank as needed. The resistor bank serves as a gentle way to charge up the super caps. Without it, they can easily charge faster than 100 amps and that will overload the PSU's and they will shut down. The resistor bank is of sufficient resistance that at 9v in, they charge the super caps at about 60 amps. They get warm...hence the heatsink off an oooooold Intel CPU. Close the rocker switch and the PSU current is direct to the super caps. At the end of the day, I like to discharge my super caps. I open the rocker switch, disconnect the negative wire from the PSU's and connect the yellow discharge wire to the negative side of the super caps. The 4 diodes are in parallel and prevent any back feeding into the PSU's as plus and minus of the super caps are now shorted across the resistor bank to discharge them.

https://imgur.com/htoEOts

I built this LTO pack for it, but have yet to need to be portable so it has been tried out, but never really used. It's 3S4P for about 44Ah. The LTO cells can dump 350 amps each so no problems keeping up with the KWELD. It has to feed through the super caps as they are bolted to the KWELD via their wires. I can charge the LTO pack directly from the dual PSU's or use it inline with them. Again the slightly over charging of the cells is not a problem.

https://imgur.com/rydcggF

I have been welding .2mm nickel just last month and the setup keeps up with my joule setting and current requirements just fine. I'll be building a new pack with .3mm nickel soon so that will up the current demand. I think it will still keep up with me, but we will see. The only thing I want to stop welding for is to cut nickel or because the weld pens are too hot.

I want to do one other thing to my setup. The weld cables are a bit short at times. I want to replace the 8 awg wires with 6 awg and then make them longer. It won't be hard to calculate the length in 6 awg needed to match the resistance of the 2 8 awg wires and I'll gain a bit of length in the process. Welds should be identical to what they were in the 8 awg wires.
 
you can use a single HRP-600-7.5 and dump the resistors. it would also make it much more efficient as you are not burning up most of the power as heat. hell, even a HRP-400-7.5 would suffice, especially with dual kcap. the 600W pushes 80A just fine and the HRP series current limits itself.

ps: if you just link to the images directly it works fine:

RUAVVwI.jpg


htoEOts.jpg


rydcggF.jpg
 
Excellent result. Imho, the 0.10mm copper is adequate for the high-amp 18650's, but there are 21700's that can do bigger amps, so for me, the science says that 0.15mm copper can do it all.

Could you please test 0.15mm nickel-plated-steel over 0.15mm copper? Its cheaper, easier to cut, and more readily available.
 
Any recommendations on protection circuits to use for managing a bank of 3s maxwell bcap0650 ultracaps as a power source with the kweld?

Balancer boards are easily available, but advice would be appreciated on protecting the psu and particularly the ultracaps from excess voltage/kickback.
 
Having the usual KWeld vs Maletrics debate in my head and suspect I will go KWeld as I like buying lab toys but that is not my question...

I have a lot to get one with doing two OSF TSDZ2 builds and custom batteries so the quickests and easiest route seems to be go with a recommended 3s lipo and charger (£80 ish) but I was wondering how many welds could I expect before needing to charge and how long before I kill the cells?

i have car batteries around for the farm but suspect none will be suitable, even some big truck batteries but i hate lumping around those.

that leaves the only other option as the kcap route - 160 euro with case, 60 euro regulator + a £20 HP psu - saw one for sale locally which must be an omen or I could use a powerful ATX psu or long HP server supply I have in my parts boxes. I also have a bench PSU but i think from memory it is 10A so would take a while to charge the kcap I am guessing? Might be 20A, has been a while since i had it out but i remember paying quite a bit for it as I had a research contract and needed something with decent power.
 
Jatem said:
Any recommendations on protection circuits to use for managing a bank of 3s maxwell bcap0650 ultracaps as a power source with the kweld?

Balancer boards are easily available, but advice would be appreciated on protecting the psu and particularly the ultracaps from excess voltage/kickback.
Click to expand...

you dont need protection. any half-decent power supply can deal with it. i am using a simple HRP-300-7.5 for years now.
 
So assuming your PSU is sufficient to support your welding rate using the kcaps, in theory continuously, for hours at a time,

it's either kcaps or battery, no advantage to using both?

IOW, is there any point to using LiPo batteries other than portability, getting away from the mains plug?
 
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