kWeld - "Next level" DIY battery spot welder

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

Post by progrock » Nov 21, 2017 9:19 am

It's actually just Bosch's 18v 6.3ah battery packs (a relatively new product, that works with most bosch 18v tools, except is apparently too large to fit some of them.) Here's the battery on bosch's site: https://www.boschtools.com/us/en/boscht ... -178152-p/ and here's a link to one on amazon https://www.amazon.com/Bosch-GBA18V63-C ... B01N6VIHUR

What's great is, while amazon apparently is selling each battery for close to $90... I've been getting them consistently off ebay for around $105 for 2 shipped. Originally I was buying them in a pack of two with a charger for about $120 (got so many chargers I've been selling them for $20... which seems to make people pretty happy, and brings my cost to $50 a battery pack). Originally had to do that, since all the sellers selling just the 2 batteries at a good price were in California, where I'd have to pay tax, and would bring the price to almsot the same as the 2 batteries plus charger. Each pack contains 10 x Sanyo 20700A cells (30A continuous per a cell, 3100mAh) in a 5s2p configuration, the plastic holder their in is Bosch's "CoolPack 2.0" designed to keep them from overheating (and holds them very securely)... plus the copper I heard is laser welded on. And as I just found out, what I originally thought was hardly a BMS (didn't see balancing wires), is apparently a full featured BMS, with a flexible circuit (similar to a laptop display's cable) that is attached to each parallel group through the side of the cell, underneath the circuit board. I'm making use of the batteries (as configured), copper, battery holder, and even the top/bottom caps (they have a nice formed rubber insulation that even accounts for the slightly different heights of the positive vs negative sides of the parallel groups, which not only protects with a bit of shock absorbance, but keeps even pressure across the batteries, forcing the copper to make solid contact across the entire surface).

I need to buy a good digital micrometer, BUT, my digital calipers (which are relatively cheap bt appear to work) measures the copper at .10mm , which seems right (but the first battery of both the positive and negative sides has 2 layers, and the negative side is attached to some pretty thick braided copper, and the positive side has a much thicker copper tab attached that is about 0.85mm thick. Both the braided copper and the thicker copper tab are attached to the thin copper by some form of much higher power welding (no solder or extra material, but they have a seriously strong/solid connection... as well as the same kind of connection to the BMS... I couldn't even pry the positive side off of the BMS with any of my tools, had to cut the end off in order to remove the BMS).

These are by far the best built battery packs I have seen, and I'm currently constructing a 20s2p pack by connecting 4 in series (planning to beef up the copper by pressing thicker chunks of copper across each section)... goal is to have a 3000w battery pack for my Cyclone, for my usual short trips I plan to use it on, that is as light as possible while still capable of easily producing the 3k watts. Ironically, ended up not even needing a spot welder for this build.. but will for my next one.

Here's a some photos of the batteries as I removed the last pieces I won't be using, showing all the parts I mentioned (the 4th one shows the BMS directly, while the 2 following it show the balancing 'cable', that also contains the 4 LEDs + button to show current batttery charge:

https://drive.google.com/file/d/11iWsbf ... sp=sharing
https://drive.google.com/file/d/1f-hJ2i ... sp=sharing
https://drive.google.com/file/d/120tmFI ... sp=sharing
https://drive.google.com/file/d/1UcbNHz ... sp=sharing
https://drive.google.com/file/d/1pZ1oGK ... sp=sharing
https://drive.google.com/file/d/16PGL8g ... sp=sharing
https://drive.google.com/file/d/1wOumrJ ... sp=sharing

My apologies for such a long post, wanted to explain all the details of the battery clearly. BTW, I read a blog's teardown report of these, which is where I heard the copper was laser welded... not very sure about whether or not it's true (I know they have very consistent welds that are clearly done by an automated system)... but I'm trying to see if Bosch will let me know in better detail what their process is to weld the copper (if they are will to say).... could provide some useful information. Obviously the slotting is rather important.

BTW, these cells are POWERFUL... I shorted across a single parallel group, and it took a chunk off of my VERY solid Wiha screwdriver (after 5 years of use/abuse, the only sign of damage on this driver)... and that's just 1 single group of 2 cells at about 4V.

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

Post by fechter » Nov 21, 2017 3:19 pm

Here is a little info on welding copper tabs from Sunstone.
https://sunstonewelders.com/applications/batteries/
They say their welder can do up to .020" copper. Of course it's not cheap, but if they can do it, so can we. They have an interesting coaxial electrode design, which I suppose concentrates all the heat on a single spot instead of two.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Nov 22, 2017 3:39 am

fechter wrote:
Nov 21, 2017 3:19 pm
Here is a little info on welding copper tabs from Sunstone.
https://sunstonewelders.com/applications/batteries/
They say their welder can do up to .020" copper. Of course it's not cheap, but if they can do it, so can we. They have an interesting coaxial electrode design, which I suppose concentrates all the heat on a single spot instead of two.
I checked the user manual of their 400J device. They actually have some numbers in there, indicating that the weld current is between 5kA and 10kA depending on output wire gauge. That matches my experience, the maximum of 2kA of the kWeld is not yet enough to weld copper (at a confidence level that I would want to have). You need much more instantaneous power to overcome the much better electrical and thermal conductivity of copper. But I'll keep investigating this when time allows.
progrock wrote:
Nov 21, 2017 9:19 am
It's actually just Bosch's 18v 6.3ah battery packs
Wow, that really is a showcase of modern construction techniques. They must be using welders from another planet... And they seem to have directly crimped the braid to the fuse tabs, relying on high pressure cold welding. And I also really like how they did the temperature monitoring by just sticking the flex cable to one of the cells. Awesome.
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Re: kWeld - "Next level" DIY battery spot welder

Post by fechter » Nov 22, 2017 9:31 am

tatus1969 wrote:
Nov 22, 2017 3:39 am
Wow, that really is a showcase of modern construction techniques. They must be using welders from another planet... And they seem to have directly crimped the braid to the fuse tabs, relying on high pressure cold welding. And I also really like how they did the temperature monitoring by just sticking the flex cable to one of the cells. Awesome.
Looks like possibly ultrasonically welded.

Separate topic: what do you use to measure weld current? I don't seem to have anything that will work at that high a current. I might be able to stack a bunch of 10 mOhm resistors (which I have) in parallel to make something around 1 mOhm.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Nov 22, 2017 11:25 am

fechter wrote:
Nov 22, 2017 9:31 am
what do you use to measure weld current? I don't seem to have anything that will work at that high a current. I might be able to stack a bunch of 10 mOhm resistors (which I have) in parallel to make something around 1 mOhm.
I have a 600uR / 150A precision shunt. Before I purchased that, I was using a known length and cross section of copper wire (using the welder's output leads), and measured the voltage across it using a scope. I was off by 20%, but it was good enough for a first estimate.
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Nov 22, 2017 5:51 pm

Yeah, that totally sums it up, it is a fantastically well done pack. And goof call, I totally forgot to point out the temp sensor on the flexible balancing pcb/cable. I'm just amazed that these packs can be acquired brand new for just about $50 each consistently. Their charger is also cool, it has a blower fan that pumps air through the pack as they charge.

I'm very much considering building a simple breakout board where I can connect up to 6 of those balancing/temp sensing cables (prob need a few extensions), and then connect it to a standard BMS' balancing cable... would eliminate the need to wire up my own balancing lines... which is one of the only thing I needed to solder to the copper between the batteries. I think I might also include one of the 1-6s mini voltage displays (been wishing I could find a 20s, but this would sole that problem), and have something like a multiplexer to be able to manually rotate between each 5s pack and check the individual voltages... and maybe something similar with the temp sensors. All in all, wouldn't require much, would be really cheap to make (a few dollars a board really... and that's at a low quantity)... and would definitely cleanup and simplify these 20s packs I'm making. Not to mention, would be a fun project to get some practice with designing PCBs, and on a very easy level, so a good place to start.

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

Post by JumperJackFlash » Nov 24, 2017 12:00 pm

fechter wrote:
Nov 22, 2017 9:31 am
tatus1969 wrote:
Nov 22, 2017 3:39 am
Wow, that really is a showcase of modern construction techniques. They must be using welders from another planet... And they seem to have directly crimped the braid to the fuse tabs, relying on high pressure cold welding. And I also really like how they did the temperature monitoring by just sticking the flex cable to one of the cells. Awesome.
Looks like possibly ultrasonically welded.

Separate topic: what do you use to measure weld current? I don't seem to have anything that will work at that high a current. I might be able to stack a bunch of 10 mOhm resistors (which I have) in parallel to make something around 1 mOhm.
The Bosch commercials say that the battery tabs were laser welded.

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

Post by progrock » Nov 25, 2017 4:14 am

Haha, thank you, I have not seen that commercial. OK, so who's building the at home laser welder?... I wonder what kind of power that would need, and what kind of laser. I've been planning to buy an engraving laser for a while now, that will attach to my 3D printer's X carriage... just haven't decided on the strength to get... seems like 500mW-17W are the practical options. Then, there's the CO2 laser engravers I've used many a time, usually a 60W (tho have also used a 120W)... primarily for cutting and/or etching plexiglass. I would not expect any of those to be able to accomplish the task of welding copper.... though I'm no expert.

I've also been trying to figure out if there's any practical (but at least somewhat accurate) way to measure/compare what just sandwiching copper on top of welded nickel on batteries will do. A recently new product I saw was doing pretty much exactly that, had your nickel more or less as usual (though it was 1 single nickel plate for each side of 2 parallel groups being connected)... then copper was held down with screws/washers (with insert nuts in between the batteries). I'm trying to replicate this to some degree, but really wouldn't be able to tell you much more than whether it works or not... I don't really know how (nor do I probably have the equipment) to truly measure what kind of max current it could handle (unless it's total garbage and can't handle much... but I'm thinking this shouldn't be half bad, especially with some thicker copper, if there's a flat enough surface t make a good connection)

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

Post by tatus1969 » Nov 25, 2017 4:32 am

progrock wrote:
Nov 25, 2017 4:14 am
OK, so who's building the at home laser welder?...
It'll probably need to be a capacitor discharge power pulse laser. As my welder is not yet powerful enough for copper and it has a weld pulse power of up to 4kW for nickel (2kA into 1mOhm), I'd say that the laser will need much more than that. And the losses due to the optical reflectivity of copper will further exaggerate that number. That will be a very dangerous laser that can seriously hurt you 8)
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Re: kWeld - "Next level" DIY battery spot welder

Post by progrock » Nov 25, 2017 10:05 pm

OK.. so basically, all we need to do is build the laser from Real Genius... how hard could that be ;)

Whole more power seems like the obvious solution for copper welding, I still want to see if there are other ways to make it possible, without requiring as much power. Obviously the slit in the metal is one step in the right direction, I'm wondering if there are other things that can be done. As I brought up before, there is an instructable that used graphite tips on the electrodes... BUT, I don't think their technique is likely to be viable here... none the less, I plan to try it out very soon.

But as for the additional power... still planning to build a circuit board to handle a bank of super capacitors. At least that should solve the issue of having the power to use... then just need a spot welder control that can handle the power... more mosfets than the designs I've seen most likely, but as you brought up, would also need to make sure that many fets can be driven from the gate control signal.

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

Post by fechter » Nov 26, 2017 2:39 pm

tatus1969 wrote:
Nov 22, 2017 11:25 am
I have a 600uR / 150A precision shunt. Before I purchased that, I was using a known length and cross section of copper wire (using the welder's output leads), and measured the voltage across it using a scope. I was off by 20%, but it was good enough for a first estimate.
I tried using a 6" length of 12ga solid copper wire with small sensing wires soldered at the ends. According to the chart, this should be about 0.8 mOhms. Based on this, I was seeing about 1.8kA during the pulse. I suspect the added resistance of the copper wire was reducing the current quite a bit as the cables weren't jumping as much as normal. So the tiny little graphene batteries seem to be doing around 2kA.

Edit: I also measured the battery voltage during the pulse. It went from about 12v to about 6v. This gives about 6 mOhms internal resistance for each pack (I have 2 in parallel). If you stacked a bunch of those things in parallel, you could get some serious amps.

I just zip tied the welder board to the top of the batteries for now. The board is bigger than the batteries. This thing will fit in your pocket.
Img_0579.jpg
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Re: kWeld - "Next level" DIY battery spot welder

Post by The Lightning Stalker » Nov 26, 2017 6:55 pm

progrock wrote:
Nov 25, 2017 4:14 am
Haha, thank you, I have not seen that commercial. OK, so who's building the at home laser welder?... I wonder what kind of power that would need, and what kind of laser. I've been planning to buy an engraving laser for a while now, that will attach to my 3D printer's X carriage... just haven't decided on the strength to get... seems like 500mW-17W are the practical options. Then, there's the CO2 laser engravers I've used many a time, usually a 60W (tho have also used a 120W)... primarily for cutting and/or etching plexiglass. I would not expect any of those to be able to accomplish the task of welding copper.... though I'm no expert.
Oh this ha ha ha. This takes me back to my laser days. You are talking thousands of dollars investment in parts alone. The huge learning curve and putting it all together would be a total nightmare. Then the eye hazards of such a laser is just beyond words.

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

Post by progrock » Nov 26, 2017 9:13 pm

Yeah.. I can assure you I don't expect anyone to build a home laser welder... was more pointing out how weak the available lasers are.

Fechter, i just ordered a 6AH 65C (130C burst) 3S Turnigy Graphene from Hobbyking yesterday... should be a step up from my current 5AH 60C (120C burst) Turnigy Heavy Duty. Was originally looking at the 5Ah 65C nano-tech.... but hoping these new Graphene batteries are even better, plus the 20% more AH shouldn't hurt. They are on sale right now at Hobbyking for $47.62... and if you add another $2.38, the sale also includes free shipping. Two of those in parallel would be pretty damn serious... though not sure if these welders would handle that without blowing FETs. But the 1 should be more than enough for any kind of nickel I'll be welding.

Here's a link if anyone is interested in the sale https://hobbyking.com/en_us/graphene-60 ... -xt90.html

BTW, in the process of designing a holder for my BMS, as well as some form of a case for the accompanying battery pack (wasn't planning on making it a "full" case for the battery... More like a scaffold to go around the battery, and clamp them together. Using 4 of those Bosch battery packs sandwiched together. If all goes well, will make a post of the whole process of modifying the batteries, and putting them in series, as well as release the 3d models of the design to print. Plannign on using Polycarbonate for the exterior of the case, it's much stronger than most filaments, so can use less... gonna reinforce it with some M3 threaded rods... which will also creating the clamping pressure I am looking for... then gonna have a thin layer of semi-flexible TPU designed as inserts for the battery and the BMS.

I'm gonna try to work out the design for the kWeld case I'm trying to make after this (tho prob won't have it complete till I have one in my hands to test out the fit, etc). I'm thinking about using a similar technique with it, utilizing some TPU to add a little flexibility/cushion for protection (will also release a design without it, for those who can't print flexibles). Ordered some plastic modeling putty and some spray primer and paint (already got XTC epoxy, and plenty of sandpaper)... should be able to do some post processing to make the thing look very legit... hopefully.

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

Post by macribs » Nov 28, 2017 11:31 am

progrock wrote:
Nov 07, 2017 6:13 am
Oh, I totally forgot... while I still would love to be able to weld some thin copper... I did see a somewhat cool idea to utilize nickel + copper (where you only weld the nickel).... check out these new battery holders: https://www.aliexpress.com/store/produc ... 57299.html


Now, I've been using 20700's lately... but this battery holder/pack design has got me thinking. I;ve actually been using brass knurled insert nuts (also available as copper) very often in my personal 3d printed designs (I find it much easier usually than attempting to use regular hex nuts, especially compared to some of the semi-complex 'pocket/slot' designs some people use for hex nuts)... I think I'm going to try to work out some designs similar to this battery holder (reusing it's unique design ideas... and hopefully improving on them) and make some parametric battery holders where it would be easy to use any size cylinder battery (primarily 18650, 26650, 20700 and 21700... tho adjustable to other dimensions as well) and be able to setup whatever number of rows/columns, as well as whatever number of parallel cells. I'll share my designs on here and thingiverse... and will take any recommendations people have for improvements/variations.

If these designs work out, I'll likely have less need for welding copper in the first place (**tho, one major reason I want to weld copper is that I have some battery packs that I want to use that have copper laser welded on them, sadly 1-2 of the packs, while partially disassembling, had 1 of their copper tabs detach from 1 cell.... so I would really liek to be able to reattach those... it's 0.1mm thick copper, hoping it may be possible.)
A flexible modular base design that let end user choose type of cells, # of p etc would be awesome. That would make for a sturdy bese for any battery, leaving no mechanical stress on the spot welded tabs. If you could supply plated copper too so end user could bolt on copper for carrying the current that would be the holy grail of DIY battery building.

Structural sane pack from the battery holders. Nicely welded nickel strips to each cell to avoid prolonged heat to battery yet ensure optimum contact points to each cell that does not degrade or corrode over time. Add a bolt on plated copper bus bar with better conductivity to carry the current. Li ion for the people. Repairable. And able to deliver maximum amp without producing extended heat in pack.

Maybe you should start a dedicated thread on this idea. That way people can easily keep up, post ideas, and we can follow from the side lines how this project comes along. Well worth a dedicated thread.

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

Post by tatus1969 » Nov 29, 2017 6:33 am

fechter wrote:
Nov 26, 2017 2:39 pm
I tried using a 6" length of 12ga solid copper wire with small sensing wires soldered at the ends. According to the chart, this should be about 0.8 mOhms. Based on this, I was seeing about 1.8kA during the pulse. I suspect the added resistance of the copper wire was reducing the current quite a bit as the cables weren't jumping as much as normal. So the tiny little graphene batteries seem to be doing around 2kA.

Edit: I also measured the battery voltage during the pulse. It went from about 12v to about 6v. This gives about 6 mOhms internal resistance for each pack (I have 2 in parallel). If you stacked a bunch of those things in parallel, you could get some serious amps.

I just zip tied the welder board to the top of the batteries for now. The board is bigger than the batteries. This thing will fit in your pocket.
That sounds very good. I just orderd one of these: https://hobbyking.com/en_us/graphene-60 ... -xt90.html for testing.
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Re: kWeld - "Next level" DIY battery spot welder

Post by The Lightning Stalker » Nov 30, 2017 9:49 pm

As you may be aware, the C rating on these lipos is quite often grossly inaccurate. This is well known amongst drone pilots. Tests have shown the graphene cells to perform on-par or even slightly under quality lipos in some cases, even those with lower C ratings. These are not short-circuit tests, mind you, but standard lipos are a little cheaper than graphene, even name brand ones in most cases. I'm not saying the graphines are bad, but the quality is inconsistent and the support from the companies selling them is either poor or nonexistent. Some of the more respected standard lipo brands are Pulse, Tattu/Gens Ace and Thunder Power. Thunder Power in particular is known to have excellent support, albeit at a price. I have a Pulse 5000mAh 35C I can try when the kWeld gets here. It has an XT60 on it though, so I don't expect it to perform very well due to that connector. Also it is a year old, and lipos have a finite lifespan.

I bought some ultracaps and they are here, but unfortunately they are the wrong ones for CD welding as the internal resistance is a little high. It looks like I need to buy better ultracaps and/or a different/better lipo. (I'm not unsoldering the XT60 on the Pluse since it's mostly for my RC stuff)

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

Post by fechter » Dec 01, 2017 12:09 am

I think you're right. The Graphene is most likely marketing BS and not really doing much for the cells. There well may be much less expensive ones that perform as good or better.
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Re: kWeld - "Next level" DIY battery spot welder

Post by bigbore » Dec 01, 2017 9:50 am

The best LiPo battery I have is a 5S2P that I built some years ago for my fast electric Offshore, it’s made of 10 of the Turnigy 5000mAh 1S 40C that were available on HK. Now the best I find are these 20C https://hobbyking.com/en_us/turnigy-500 ... -cell.html
Next time I will need a lipo battery I will look for some single cells like Turnigy 5000mAh 40C

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

Post by macribs » Dec 01, 2017 10:39 am

There was some great test results popping up on those HK graphite cells the first year or so after launch. One of the things I noticed most was the fact that there seemed to be more consistent result among those graphite lipoly bricks. Cells purchased on different dates tended to show similar results as earlier tests. For me that is an indicator of better production run as well, and that is a good thing. People buying other branded bricks at different dates and production rund have noticed larger discrepancies.

I am not praising those bricks, but I think if you first choose to go lipoly graphite could be a thing to look into.

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

Post by tatus1969 » Dec 04, 2017 6:32 am

I'm happy to announce the release of kWeld firmware rev2.0. It is backwards compatible with the existing rev2 modules as well the new rev3 ones that are on the way to me.

New features:
- added support for hardware revision 3
- added support for rotary encoder
- added configuration menu
- current limit is now calculated from adjustable cable length
- made auto mode firing delay adjustable
- added adjustable battery undervoltage detection
- improved open circuit detection when welding

The binary can be downloaded from this page:
https://www.kicksurfer.de/index.php/kweld/

For those of you who already have the firmware update tool in hands: I'm sorry but I haven't found the time to include the update procedure in the operating manual yet. I am busy shipping out the current production batch by the end of this week, and I will update the manuals thereafter.

For now, I only have this short description, if something is not obvious please let me know:
1. Connect the small adapter board to the USB adapter so that the connectors on the adapter are facing up, and the LEDs on the USB adapter are visible (i.e. "natural" position, components on both boards facing up)
2. Connect the assembly to kWeld with the short cable (goes out to the right), use a mini USB cable (not included) to connect to PC, if necessary install drivers (http://www.ftdichip.com/Drivers/VCP.htm)
3. Find the new serial port via Windows Device Manager
4. In extraputty (http://www.extraputty.com/), establish a serial connection with this COM port and 115200 / 8N1 / no handshake
5. Power up kWeld, then type in a small "k" in the console
6. Bootloader must respond now
7. Now type a small "y"
8. Now make a YMODEM transfer with the firmware file via the extraputty menu (Files Transfer -> YMODEM -> Send)
9. Wait for the transfer to complete, it should then read an "OK"
10. Now trigger kWeld restart by typing a small "a"

For those who have added the encoder to their kWeld rev2: you need to type "v3" into the console when kWeld is running normal (not in firmware update mode). (There will be no echo.) This enables encoder use. Typing "v2" instead switches back to potentiometer mode. The firmware does a reset in each case and restarts.

Here is a short description of the new configuration menu:
1. for rev2 (potentiometer) systems, turn dial all the way left and press trigger switch to enter the menu // for rev3 (encoder) systems, push the dial know instead
2. turn the knob to choose from one of the available options:
"CAL": enter calibration function (as known)
"Mode": select between manual and auto trigger modes
"TrgDelay": [default 0.5s] adjust trigger delay in auto mode
"DefaultE": [default 10.0J] adjust set energy level after power-on (only when using encoder)
"CableLen": [default 1.0m] enter the total length of the power wiring (add up all conductor segments), the firmware calculates the correct current limit from that (using the inductive kickback formula from the operating manual). This provides correct protection in case you are using longer wires than standard
"LoBatt": [default 0.0V] sets battery warning voltage level (set to 0 if you don't want to use it)
"Exit": leave the menu
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Dec 04, 2017 6:35 am

fechter wrote:
Dec 01, 2017 12:09 am
I think you're right. The Graphene is most likely marketing BS and not really doing much for the cells. There well may be much less expensive ones that perform as good or better.
Maybe Turnigy has not the best stability in production quality, but they seem to spend significantly more material for the same capacity. I have the 3S / 6Ah battery here now, I think I can test it next week.
Resistance is futile - We Are The Watt.

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