kWeld - "Next level" DIY battery spot welder

Batteries, Chargers, and Battery Management Systems.
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tatus1969
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Thu Nov 09, 2017 6:40 am

JumperJackFlash wrote:Could you get the covers injection molded and produced in lots? I'd be happy to pay extra for a cover for my welder as would most of your potential customers (I believe :D ).
I general a good idea, but the production volumes aren't yet enough. Manufacturing the required mold tools will cost in the order of 5000€-10000€. I plan to sell the 3D printed cases for around 40€. The break even would therefore be 125-250 housings.
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Re: kWeld - "Next level" DIY battery spot welder

Post by Merlin » Thu Nov 09, 2017 5:39 pm

at this moment i think IF you make this KWELD able to weld 0,1 copper you could probably sell to more ppl.(not that easy probably but sounds/reads like you have the skills to do it =)
all copper welder atm are DIY Mods of DIY welders.

building hi Power batterys is so much "easier" with copper. no need for 3x 0,2nickel stripes to prevent the bottleneck for the (Highpower-low-RI)cell(s)-pack
3 times less work.
did i said that i like copper? :mrgreen:

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Sat Nov 11, 2017 5:12 am

Merlin wrote:at this moment i think IF you make this KWELD able to weld 0,1 copper you could probably sell to more ppl.(not that easy probably but sounds/reads like you have the skills to do it =)
all copper welder atm are DIY Mods of DIY welders.

building hi Power batterys is so much "easier" with copper. no need for 3x 0,2nickel stripes to prevent the bottleneck for the (Highpower-low-RI)cell(s)-pack
3 times less work.
did i said that i like copper? :mrgreen:
I'll make another attempt at 2kA and see if I can weld a 0.1mm copper sheet to a battery. My last attempt was at 1000A, and I tried to weld together two sheets of copper. But that is not realistic as I realize.
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Re: kWeld - "Next level" DIY battery spot welder

Post by nieles » Sat Nov 11, 2017 5:36 am

tatus1969 wrote:
JumperJackFlash wrote:Could you get the covers injection molded and produced in lots? I'd be happy to pay extra for a cover for my welder as would most of your potential customers (I believe :D ).
I general a good idea, but the production volumes aren't yet enough. Manufacturing the required mold tools will cost in the order of 5000€-10000€. I plan to sell the 3D printed cases for around 40€. The break even would therefore be 125-250 housings.
for high volume tooling you are right. but they can do aluminium moulds for lower volume production. have a look: https://www.protolabs.com/services/inje ... n-molding/

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Re: kWeld - "Next level" DIY battery spot welder

Post by Merlin » Sat Nov 11, 2017 8:15 am

as i dont have the skills,
willow and RTL have experience in welding copper.
maybe they can help you?

(both 2 posts in this link here)

https://endless-sphere.com/forums/viewt ... 8#p1326348

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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Sat Nov 11, 2017 8:59 am

IF you make this KWELD able to weld 0,1 copper you could probably sell to more
Trust me, kWeld cannot keep their parts in stock already, due to the brilliant design, so...if you think you can do better? the time to display your better-design is now!

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Re: kWeld - "Next level" DIY battery spot welder

Post by Merlin » Sat Nov 11, 2017 5:37 pm

:?: what are u talking about? :?

i dont have the skills. i think i wrote it twice.
did i said something wrong or bad?

if you are able to read, maybe read again where i have answered only on tatus post....
oh wait...ill help you and quote that for you and paint it red.....
tatus1969 wrote:
JumperJackFlash wrote:Could you get the covers injection molded and produced in lots? I'd be happy to pay extra for a cover for my welder as would most of your potential customers (I believe :D ).
I general a good idea, but the production volumes aren't yet enough. Manufacturing the required mold tools will cost in the order of 5000€-10000€. I plan to sell the 3D printed cases for around 40€. The break even would therefore be 125-250 housings.
man, that was just to help selling more of them. i buyed his welder (full kit) one minute after his -new batch- newsletter mail.

never expected a post like this from a "mod".... :roll:

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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Sat Nov 11, 2017 7:31 pm

I apologize, I did not intend to offend you.


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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Sun Nov 12, 2017 5:53 am

Merlin wrote:as i dont have the skills,
willow and RTL have experience in welding copper.
maybe they can help you?

(both 2 posts in this link here)

https://endless-sphere.com/forums/viewt ... 8#p1326348
Thanks for this link! I learned two things from cross reading:
- slotting the copper helps
- the BOSS welder can do the job

As kWeld has roughly twice the total MOSFET chip size, and it is tested to be reliable at 2000A weld current (does anyone know the limit of the BOSS welder?), I am quite confident now that I just had done the wrong test. I didn't realize the importance of being able to weld copper at that time.
nieles wrote: for high volume tooling you are right. but they can do aluminium moulds for lower volume production. have a look: https://www.protolabs.com/services/inje ... n-molding/
I know them, but haven't checked their prices yet. Would you have a guess (as I don't want to make an enquiry there now, because the design is not "mold ready" yet)?
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Sun Nov 12, 2017 4:14 pm

Oh man, I feel kinda dumb right now. I've been wondering about the slotting... but my first thought was kinda the opposite of what it does. I was thinking it would reduce the amount of current the spot welder could produce... thinking that would be a negative. But it makes so much more sense now, the current flow being hurt in this case, is the flow you basically don't want, instead it's forcing more of it from the nickel/copper to the battery. I'm just amazed (mostly at my stupidity, but also out how simple and seemingly beneficial this is).

I wonder what's the best way to put a slot in the middle of a piece of nickel/copper (or even on the edge), without warping/bending the metal... keeping it as flat as possible seems like a good idea.

edit: haha, just read bottom of that post, which was exactly the one idea I was thinking... though was hoping for another tool or something that would work better, but using a cutting disc on a dremel was all I could come up with, since it shouldn't bend the surrounding metal

edi2: BTW, I've also heard that nickel plating the copper makes it a bit easier to weld (haven't tested myself yet, but kinda makes sense)... and obv nickel plating will also help protect the copper from oxidation. And nickel plating is really easy, just need some pure nickel (if you make your own nickel acetate, could also buy some direct, but really easy to make yourself), vinegar, a jar (or similar), and a power source with some alligator clips. I actually made a nickel acetate solution the other week, but likely need to find a different container if I was going to plate any piece of copper larger than a couple of inches. I used this technique (but I'm sure there are plenty of others, but this is def easy enough) http://www.instructables.com/id/High-Qu ... l-Plating/

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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Mon Nov 13, 2017 7:33 am

Here's a guy welding multiple sheets of copper together with a home-made capacitive discharge spot welder...

He states that the reason he has succeeded so easily, while others have failed is primarily due to his electrodes. Instead of copper or tungsten, he's using graphite tips (taking hollow copper rods/pipe and using chunks of graphite in the end of them). But, he's built a "pinch" style spot welder, which may also have something to do with it, either way, seems to be worth a try, and it's cheap enough to make the electrodes.

I've been reading a lot of these DIY spot welders, and similar things... definitely wanna make a super/ultra capacitor bank for powering these. I like those Maxwell supercaps you recommended (wish arrow would stock maxwell, but oh well, mouser works).... I'm definitely interested if you have a PCB design for the protection board to link them in a 3s2p config. I've been considering having a go at trying to design a board myself... but I have about 30 min of watching someone use eagle as my experience right now... so... I think it's safe to say you could probably do better in your sleep. Though I probably could look around the internet for a design as well... but if you already have one, any chance I could get the design files to get some boards printed?

BTW, planning to start the design of the enclosure in fusion360 any day now... should be interesting, I haven't done any enclosures yet, but have had a few on my TODO list. Luckily enclosures are relatively straight forward/utilitarian... my current skill set is not half bad at functional designs (while I used mostly metal on my last 2 printer builds, I did design all the plastic parts I used for different pieces that would have required somewhat heavy machining to accomplish with metal). I also want to build electrode holders... possibly even try to make some nice ergonomic ones... though I need to do some more spot welding to figure out what's the best way I like to hold them (also, ergonomic designs are something I'm new at.... it's more artistic than having simple angles/curves and flat edges... but Fusion360 does have some convenient tools for doing this kind of stuff, so I wanna at least try). Once I get a basic idea going for those.. would be very interesting to get photos from people showing how they like to hold their electrodes... seeing hand/finger placement will make it easier to work out something.

And to those of you wanting injection molded parts.... give tatus a little break.... that shit is not easy, it takes a lot to design something, machine the molds, and produce them... a hell of a lot of work. I can understand wanting something a little cleaner than your standard home FDM printed parts.... but if that's the case, either find someone, or more likely find a 3d printing shop, that uses SLA or another non-FDM print method. They cost more, but come out much cleaner/smoother and more precise. Also, it's very possible to do post processing on FDM printed parts, when done right, the end result can have a look and feel very different from unprocessed parts (ie. sanding and coating/glazing can drastically improve things). As I said, I'm happy to make some designs that I will post for free, but have no plans of making nay money off them... so I personally don't plan on printing any for people. BUT, I might be willing to make a few to giveaway, or something. I also have printers capable of doing relatively large components in a range of materials... PC (PolyCarbonate), PETG, ABS... as well as flexible materials (TPU, etc.). Will see how things go, but might try to make use out of multiple materials at least for the electrode holders (about to set one up to do 3 different colors/materials at the same time... tho gonna take a little time before I can do flexible with others, but can always piece together separate parts).

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Mon Nov 13, 2017 9:29 am

progrock wrote:Here's a guy welding multiple sheets of copper together with a home-made capacitive discharge spot welder... He states that the reason he has succeeded so easily, while others have failed is primarily due to his electrodes.
I have attached some pictures of my copper welding attempts. The current was ~1500A.

At 100J, the 0.1mm (manually) slotted copper sheets will stick to the battery terminal, but it is relatively easy to pull it off again. And the remaining dips in the battery terminal don't show any weld residues.
IMG_20171113_151045.jpg
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At 150J, the copper sheets start melting from the current that goes the long route.
IMG_20171113_151039.jpg
IMG_20171113_151039.jpg (208.78 KiB) Viewed 215 times
And the battery got damaged as well, as you can see in this last picture. So the answer is: yes, the welder is capable to deliver the required power, but I'm still not convinced at all...
IMG_20171113_151039a.jpg
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progrock wrote: make a super/ultra capacitor bank for powering these. I like those Maxwell supercaps you recommended (wish arrow would stock maxwell, but oh well, mouser works).... I'm definitely interested if you have a PCB design for the protection board to link them in a 3s2p config. I've been considering having a go at trying to design a board myself... but I have about 30 min of watching someone use eagle as my experience right now... so... I think it's safe to say you could probably do better in your sleep. Though I probably could look around the internet for a design as well... but if you already have one, any chance I could get the design files to get some boards printed?
The 3S2P BCAP0310 configuration "only" delivers 1000A, this is not enough for copper. That would probably require 3S1P BCAP3000, but that is very expensive so I didn't investigate this further yet. I will design a capacitor protection board for the 3S2P, but I have another project running right now (motor controller) so that I cannot start this yet.
progrock wrote: BTW, planning to start the design of the enclosure in fusion360 any day now....
Great :-)
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Mon Nov 13, 2017 10:57 am

Hmm.. yeah I was doing the math before, I might have donesomething wrong, but just doing the simple straight forward equations, as if it was a perfect world 100% efficiency, cpas at max voltage, etc... I believe I got just under 2.5k A... 1k sounds much more realistic of what you would actually get. I was also looking at these: https://www.mouser.com/ProductDetail/Ma ... -E016-B02/ which I believe are on their own protection board already, but if I'm not mistaken, its no better than those, actually worse... costs more... and probably a bigger PITA if anything breaks.

BTW, not sure what your problem is with copper, just built this pack with the boss spot welder and a 3s 120C lipo, no problems:

Image

Large version:
bosch_battery_copper1.jpg
(215.91 KiB) Downloaded 2 times
...OK, before anyone starts flamming... YES, my welding skills are that spot on.... no way was this done at the Bosch factory with a laser.

What's really interesting is the "flaw" I've seen with basically 90% of the batteries. As you can see in the photo, the top right corner cell isn't spot welded down (and doesn't have a slot). After carefully inspecting a dozen of these (on both sides... so 24 batteries without the slots), I think maybe 2 of them are welded down (barely)... some don't even look like there was an attempt... but most you can see there was one, but it clearly didn't work. So guess that slot really does make a difference. BTW, I'm not fully aware of their welding technique.. I just know that the one really well done teardown of these, the guy said they were laser welded. Also, I'm pretty sure these are 0.1mm thick... BUT I don't have a legit micrometer to confirm that (been on my to buy list for quite a while now, and TBH my digital calipers aren't that good to begin with, they work, but I don't trust any small measurements).

Anyway, thought the photo might help a bit... I find it interesting how they just do 1 weld per a battery, and even more interesting that pretty close not all of them have the 1 failed weld on each side. I suppose the interesting thing there is, I have used these batteries with my Bosch power tools (as I'm sure MANY other people have as well), and I haven't heard any bad reviews about that I would connect to these missing welds... the batteries seem to work perfectly fine anyway. I'm assuming it's because the top and bottom covers go on nice and tight (4 screws on each is what holds the battery together, that and just the 1 piece plastic body, and some glue), the covers also have a semi soft rubberish surface (presumably to help take some of the impact when they are dropped, but might also help with forcing the copper to make clean contact with the top/bottom of every battery.... makes you wonder how important the welds are to begin with, haha).

I gotta say tho, these are some nice looking battery packs, much cleaner than others I've taken apart (clearly made by machines and not by hand). But, these consistent welds with this kind of copper should be the goal of any high power battery spot welder.
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Mon Nov 13, 2017 10:59 am

Oh, and as I mentioned before... you should try nickel plating the copper, and then see what results you get (and def use the slots).

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Mon Nov 13, 2017 4:10 pm

progrock wrote: I was also looking at these: https://www.mouser.com/ProductDetail/Ma ... -E016-B02/
Look at it's ESR, 22mOhms. That is way too much :wink:
progrock wrote: BTW, not sure what your problem is with copper, just built this pack with the boss spot welder and a 3s 120C lipo, no problems
8)
progrock wrote: What's really interesting is the "flaw" I've seen with basically 90% of the batteries.
...
I find it interesting how they just do 1 weld per a battery, and even more interesting that pretty close not all of them have the 1 failed weld on each side.
...
I gotta say tho, these are some nice looking battery packs, much cleaner than others I've taken apart (clearly made by machines and not by hand). But, these consistent welds with this kind of copper should be the goal of any high power battery spot welder.
...
Oh, and as I mentioned before... you should try nickel plating the copper, and then see what results you get (and def use the slots).
Thanks, very interesting - and a bit odd. But I don't have much time to continue this investigation right now, maybe the one or other kWeld owner has better luck?
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Mon Nov 13, 2017 4:40 pm

Yeah, the ESR was way too high, totally killed the calculated amps. I'll play around with some technique when I get a chance. Building a pair of those DIY android welders... won't mind abusing one of them to see if I can get something to work. Not too optimistic with the graphite tips, but still wanna try them out... will also talk to rojitor, he succeeded with copper welding 0.1mm with a 4s and the boss welder, and also said nickel plating helped a bit I believe. If that can do it, def possible... especially with a nice setup of super caps.

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Re: kWeld - "Next level" DIY battery spot welder

Post by Buk___ » Tue Nov 14, 2017 1:50 am

tatus1969 wrote:At 150J, the copper sheets start melting from the current that goes the long route.
IMG_20171113_151039.jpg
And the battery got damaged as well, as you can see in this last picture.
A few thoughts:
  1. Place your welder probes closer to each side of the slit.
The purpose of the slit is to interrupt the direct path between the probes to cause the path of least resistance to be down into the cell terminal and back up.
Moving the probes closer to the slit makes the path through the terminal (with its higher resistivity) shorter, whilst leaving the shortest path through the lower resistivity copper the same length.
  • Move the probes as far towards the open end of the slit as possible.
Same reasoning as above.
  • Make the slit as narrow as possible.
Ditto.
  • Wire wool both contact surfaces immediately before performing the weld.
(If you aren't already.) To remove finger oils, oxides and other surface contaminates.
  • Press hard.
My experience with spot welding was in a car factory where we applied several hundred pounds per square inch to 3/4^2" contact points.

The most interesting stuff I was involved with was the "continuous" spot welding of the two halves of 20g steel petrol(gas) tanks.
The welded component was a 1/4" flange around the edges of the two halves of a pressed steel tank.
The electrodes consisted of two 2" diameter copper wheels that were motor driven (in opposite directions) and clamped to either side of the two flanges held in a jig.
As the wheels moved along the flange, the pulses of current through them produced overlapping spot-welds that produced a fuel-tight seal around the tank.

The critical part was varying the speed of the motors according to the resistance measured during the last pulse. the higher the resistance measured, the smaller (narrower) the weld spot produced. so the slower the motor had to move to ensure overlapping welds.

(Interesting aside: By explaining the process and the requirements to achieve best speed to the roll-weld operators; we achieved hugely increased productivity. By explaining that the speed of weld rig motion was entirely dependent upon the cleanliness & flatness of the mating surfaces, we reduce the re-work rate by nearly 90%, because the operators realised that spending 20 or 30 seconds more on surface prep, could save them 2-3 minutes per tank. And with a fixed speed production line that meant they spent 20%+ more time sitting waiting for the next tank to arrive, during which they could play chess, read books or any other pass time they might choose.

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Sun Nov 19, 2017 6:13 am

I totally underestimated the demand, and ran out of stock by just pre-orders in less than a week. I plan another batch right after having received the current one. I'll inform again through the newsletter. But in order help me estimate the demand, I have just implemented an "inform me on availability" button for the sold out products that puts you on a waiting list when you click it.
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Sun Nov 19, 2017 7:30 pm

Congrats on the sales... glad I ordered when I did.

Been on the look out for some super capacitors with extremely low ESR (Kinda funny considering I almost don't even care about the Farads for the most part, tho seems like with super caps the higher the F the lower the ESR). I think I found a good solution... especially for you, since I think they are located in Germany (haven't checked shipping rates to the US yet). The company Skeleton Technologies makes a handful of super capacitors with the lower ESR's I've seen. In general, I haven;t been able to find any capacitors with lower than 2mOhm ESR for under $50 each (at least non in stock, and usually closer to $60 each)... that was until now. The downside is, depending on which capacitors, would either have to order a box of 20, or a box of 10 (the larger ones are sold in 10's). But this wouldn't be so bad if a few people wanted to go in... I'm thinking pretty much any of these could be ran in a 3S1P config, and produce the power we were hoping for, especially the 1200F+ models.

For a quick summary of the models, there are 5, all of them are rated at 2.85V ( a little step up from the usual 2.7V):

Code: Select all

Model    Farads   ESR(mOhm)   Price(box)   Qty   Price/1
SF0500      500       0.23*     412.00 €    20   20.60 €**
SF0750      750       0.21*     596.00 €    20   29.80 €**
SF1200     1200       0.11*     340.00 €    10   34.00 €**
SF1800     1800       0.10*     370.00 €    10   37.00 €**
SF3200     3200       0.09*     480.00 €    10   48.00 €**
* I used the "typical" <10ms DC ESR from the datasheet (which is the lowest value given, but likely the most relevant for this situation)
** I didn't look into shipping yet, I figure that depends on where they are being shipped (I'm assuming cheaper to Germany than the US), and this price is just for reference, haven't really found these for sale as singles, other than 1 on amazon that wasn't exactly cheap.

BTW, the "initial capacitance" is actually 5-10% higher than the ratings I listed (but as I mentioned earlier, I don't think the actual capacitance is that important for this.... of course we need enough to do a good amount of welds, but I'm pretty sure that's not even a concern with this high capacitance... PLUS, if I'm not mistaken, it's theoretically possible to have these charging during use... tho probably not very necessary)

Anyway, I figure either the SF0500's or even better the SF1800's (I figure it's with the $3 more than the SF1200) could be viable Super Capacitors to use in a 3S1P config most likely, and a little cheaper than others I've seen, with even lower ESR, and the extra .15V each doesn't hurt. Of course would have to get at least a box, but based on how quickly you're selling the welders, I'd be willing to bet there's enough of us to go through a few boxes. Though, one possible design flaw that may make these significantly less viable, is their terminal's... or almost, lack there of any. They appear to be similar to the positive ends of a button cap battery, which I'm assuming is far from ideal. I'd much rather have a pair of screw terminals on the same side, if possible.

Here's a link to Skeletontech's web store: https://www.skeletontech.com/ultracapacitor-webstore
And here's the datasheet: https://cdn2.hubspot.net/hubfs/1188159/ ... et-SCA.pdf

I've also been admiring the design this guy used: http://www.zeva.com.au/Projects/SpotWelderV2/

It would be very interesting to implement something similar to his (especially if I found a viable smaller capacitor... probably wouldn't make as much sense for large super caps like these). The core concept tho, having individual "break-away" PCBs with a number of small capacitors in series, and the MOSFETs to handle their power on each board... where it would essentially be up to the user to decide on how many of these to chain together (essentially put in parallel) to fit their power needs. Definitely seems like a cool concept, especially since you'd be able to add another board in if what you currently had wasn't doing the job. This kind of design wouldn't be too hard to accomplish with the more stereotypical android controlled welder, where the user sets pulse times, etc.... but I'm not sure how easy it would be to setup to work like your design. But it would be interesting if that could work... if you made your core control board capable of being hooked up to something like this (instead of just having the power source as changeable, having the mosfets as well). I just like the modular design, and the concept that it's almost infinitely expandable.... woudl even be cooler if their was an easy way to make each individual series of capacitors have an optional number in series (ie. be able to run 3 or 4 caps in series, depending on your needs)... basically having it so that the user could leave a spot empty (of course uniformly on all parallel boards), to add 1 more level of customization.

Anyway, I'm probably thinking too far... but jsut a simple 3S1P solution with any of the Skeletontech super capacitors could work out as a pretty sweet power solution for a welder, and so far, it's the cheapest solution I can find to create this high amount of power in short bursts (Tho technically, this thing could produce quite a bit even continuously... though I could only imagine that would require some serious cooling needs... also not something required for this kind of project).

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Re: kWeld - "Next level" DIY battery spot welder

Post by fechter » Mon Nov 20, 2017 12:34 am

I posted this in one of the other welder threads but thought it was relevant here. I got a pair of 2.2Ahr 3s Turnigy Graphene Lipo batteries and tried them with my welder. I was utterly amazed. After blowing holes through some test strips, I got the weld time dialed in. For thinner nickel strips like .2mm, I bet a single one of these packs would work.

I plan to run a steady 12.2v to the pack to keep it from discharging while welding, but I bet you could get quite a few welds out of a single charge.

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Mon Nov 20, 2017 9:35 am

progrock wrote:
Sun Nov 19, 2017 7:30 pm

Code: Select all

Model    Farads   ESR(mOhm)   Price(box)   Qty   Price/1
SF0500      500       0.23*     412.00 €    20   20.60 €**
SF0750      750       0.21*     596.00 €    20   29.80 €**
SF1200     1200       0.11*     340.00 €    10   34.00 €**
SF1800     1800       0.10*     370.00 €    10   37.00 €**
SF3200     3200       0.09*     480.00 €    10   48.00 €**
That is a very interesting find! They should be well suited in a 3S1P config, the only problem is that they are neither screw nor solder types. Their "price per ESR" is awesome!
progrock wrote:
Sun Nov 19, 2017 7:30 pm
I've also been admiring the design this guy used: http://www.zeva.com.au/Projects/SpotWelderV2/
I've seen that, quite impressive! The kWeld can be modded to drive external MOSFETs, but I haven't made explicit provisions for that. The new rev.3 module uses a 1.5A gate driver. That may still not be enough to drive such a huge amount of MOSFETs :-)
fechter wrote:
Mon Nov 20, 2017 12:34 am
I plan to run a steady 12.2v to the pack to keep it from discharging while welding, but I bet you could get quite a few welds out of a single charge.
Can you measure the weld current? Would be intestesting to see how they compare against the Turnigy nanotech's. When you connect a charger, be aware that the inductive kickback voltage is also present at the battery terminals to some degree. That may kill a Lipo charger.
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Mon Nov 20, 2017 1:59 pm

I know, the terminals are a killer... so sad considering the ESR / Price.... with some screw terminals, they would be close to perfect (I actually emailed them yesterday with that exact concern/question... I figure it's unlikely... but worth seeing if they plan to release a different version. I also asked how they rigged their higher voltage units... presumably they have the capacitors hooked up to PCB one way or another)

As for 1.5A gate driver.. wouldn't it be easy enough to boost that.. or simply use it to drive a SSR or similar to control the FETs? (haven't looked into what kind of delay/lag that may introduce... I suppose that could complicate things)

BTW, finished deconstructing the bosch battery packs I showed a picture of above (well down to what I plan to use, not fully apart). I discovered something, that makes a lot more sense now. Considering these are German engineered/built, I did not expect a sloppy manufacturing process where 1 battery on both sides was not spot welded. The one that appears not to be welded is because there is 2 layers of copper, the one underneath definitely is welded correctly. I also found out the BMS does indeed do balancing, there is a ribbon cable with a circuit through it that connects to the sides of the batteries underneath the BMS... it's a pretty damn clean solution compared to the others I have seen.

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Re: kWeld - "Next level" DIY battery spot welder

Post by fechter » Mon Nov 20, 2017 3:05 pm

tatus1969 wrote:
Mon Nov 20, 2017 9:35 am
fechter wrote:
Mon Nov 20, 2017 12:34 am
I plan to run a steady 12.2v to the pack to keep it from discharging while welding, but I bet you could get quite a few welds out of a single charge.
Can you measure the weld current? Would be intestesting to see how they compare against the Turnigy nanotech's. When you connect a charger, be aware that the inductive kickback voltage is also present at the battery terminals to some degree. That may kill a Lipo charger.
I'll see if I can find a way to measure the weld current. I don't have much rated for that high. For sure it's way, way more than I was getting out of a 24Ahr lead-acid battery.

Yes, you're right about the inductive kick to a charger. I plan to use a large inductor in series between the Lipo and the charger to isolate it. I'm also thinking of placing an inductor in series with the trigger switch input to keep induced voltages away from my microprocessor.
"One test is worth a thousand opinions"

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