kWeld - "Next level" DIY battery spot welder

[ealex]

Hello

I've recently got my unit (version 3.3) and I'm trying to make a case out of MDF.
It's basically a 3 layer box that will hold the batteries at the bottom and the unit on top.

Is there any chance you can share the PCB hole patterns ? It's the last part of the build - everything else is modeled and assembled

(edit - typing errors)

[anishkgt]

Aren't the supercaps rated for a specific current, here i think its 240A. Though the short circuit current is about 1200A, which should never be used for operation. How do you control or limit the current draw ? each cap in parallel is 240A x 2 = 480 and that multiplied 3 times is about 1400A and those series would be lower.

[socke]

Hey,

where do I get the schematics? I've scrolled through this thread for a while and googled for it but didn't find anything. Even on the website where the kit is sold I've seen no schematics. The website was btw "hard" to find as well (had to google for it, didn't find any link in the first post of this thread).

Best regards!

[tatus1969]

Aren't the supercaps rated for a specific current, here i think its 240A. Though the short circuit current is about 1200A, which should never be used for operation. How do you control or limit the current draw ? each cap in parallel is 240A x 2 = 480 and that multiplied 3 times is about 1400A and those series would be lower.

These ratings are related to their thermal limits, you can exceed them in pulse applications. I was worried that there could be internal hot spots and did long time tests of several 10,000 pulses under full sustatined load (water cooled 1mOhm resistor as load, and lots of fan cooling) and found them to be rock solid.

Is there any chance you can share the PCB hole patterns ? It's the last part of the build - everything else is modeled and assembled

Attached.

where do I get the schematics? I've scrolled through this thread for a while and googled for it but didn't find anything. Even on the website where the kit is sold I've seen no schematics. The website was btw "hard" to find as well (had to google for it, didn't find any link in the first post of this thread).

I'm afraid but kWeld is neither open source HW nor SW. And thanks for that reminder, I know that part is a mess... someone throw a bucket of time over to me :-)

[ealex]

@tatus1969 - thanks
i'll make some photos of the set-up tomorrow, when I have some daylight available.

[ealex]

I've finally managed to get everything together and start working on a small pack:
Everything is on a clear table - batteries + high power stuff don't go well with my cluttered bench


I've used 2 turnigy 3S 2200mAh cells in parallel.
They seem to stand the abuse - they are barely warm when the electrodes get unpleasantly hot 32 welds at 50J, with 1300A average


This is how a weld looks, on 5mm wide, 0.3mm thick nickel strip.

It seems a little bit to hot, but I've tested on some scrap cells and the weld is strong and the cells are not melted trough

And a microscope photo of another weld:


You can see the electrode angle and a little bit of metal flowing away (maybe add some flux - Rossman style)

(edit reason - I can't get the hang of this editor)

[tatus1969]

You can see the electrode angle and a little bit of metal flowing away (maybe add some flux - Rossman style)

I had actually tried that in the past, this completely eliminates coloring actually.

[tatus1969]

Good news for you guys in Australia and around: Andrew from hiketech.au is starting to sell keenlab products here! https://hiketech.com.au/index.php?route=product/category&path=111

He's also working on introductory videos, and I'd appreciate if you'd support him by watching and recommending them (given that they are good - haven't seen them yet ;-)

His YT channel is: https://www.youtube.com/channel/UC7MuS242JIeOQYY_8V9U89g

[tatus1969]

Seems to be newstime today... More good news, I finally managed to order new/redesigned kCap ultracapacitor modules and have started offering them for pre-order: https://www.keenlab.de/index.php/product/kweld-ultracapacitor-module/ (will also be available from the above US/AU resellers)!

They now feature protection against overcharging (MOSFET switch) and also prevent backfeeding into their supply (by an ideal diode circuit), which now allows the use of any kind of current limited power supply with any voltage between 8.1V and 14V. The product page lists these options in more detail.

[tatus1969]

I got notified about an ebay auction of 800x BCAP0650P (new unopened, dated 2007, mix of laser weldable and threaded posts), tempted to purchase them. Anyone interested in these? I'd test them and sell for 6€ a piece.

[tatus1969]

The Maxwell caps arrived last week, I have got roughly 800 of them and have put them up in the shop: https://www.keenlab.de/index.php/product/bcap0650/

I am currently doing measurements with them, but so far they appear to be in perfect condition. Measured internal resistance is approximately 0.5 milliohms (!) at 50A test current, which is quite a bit lower than their rated "initial max" of 0.8 mR. Scope screenshots and my setup attached to the post. Capacitance is spot on, leakage current is ongoing (I need to wait a few hours to allow the voltage settle)

Very important: this is the laser weldable variant, which either needs a bit of creativity or a decent welder to attach bus bars or cables to them. Andrew from hiketech (my AU reseller) plans to do tests with his TIG welder, but if you are fine with this hardcore DIY route then a few of them in series (4S should be optimal) would make up a very decent pulse power supply for kWeld. Or, some other kind of project that needs lots of current - the combined short circuit current of all ~ 800 cells that I have here is 2,720,000 amperes 

[tatus1969]

quick update: still haven't received the kCaps yet, since the manufacturer realized a problem with wave soldering the capacitors: the conveyor belt is slanted, causing the caps to tilt. Solving this with a clamp that will sit on top of them. New expected arrival April 3.

And I want to share a new video with you, from a fellow guy in New Zealand: https://youtu.be/DX1U3UnCej0
I'm very impressed by his video, it is such good that it can even replace my kWeld assembly document.

[liyuqihxc]

Awesome design!
I have a question,between the edge of busbar and the mosfet is just a thin layer of copper pour right?

[tatus1969]

Awesome design!
I have a question,between the edge of busbar and the mosfet is just a thin layer of copper pour right?

Thanks :-) And your observation is correct. That works only because that copper path is extremely short and very wide. And it is very well cooled by the busbars. Calculating, simulating and experimentally validating that was part of the engineering that I put into that system.

[anishkgt]

in post #50, there is resistor R11 in series to GND from the drain pin of all MOSFETs. I presume this would be to balance the current send into the MOSFETs. Is that correct ?

[tatus1969]

in post #50, there is resistor R11 in series to GND from the drain pin of all MOSFETs. I presume this would be to balance the current send into the MOSFETs. Is that correct ?

How should a 22k resistor balance any considerable amount of current? That resistor has a different purpose, it is part of the 'auto' firing feature.

[anishkgt]

Oh rite. Was just curious.

[dmxlights]

Tatus1969,

I am going to build a case for the cap board and the kweld. I know the cap board has a connector for a fan do I need to use a 3 wire fan or can I use a 2 wire one.

Also can I extend the screen from the kweld board by ribbon cable or use an extension header to lift it off the board so it will be closer to the font panel of my case

[tatus1969]

I am going to build a case for the cap board and the kweld. I know the cap board has a connector for a fan do I need to use a 3 wire fan or can I use a 2 wire one.

If it fits then you can do that, the third tach pin is not used.

Also can I extend the screen from the kweld board by ribbon cable or use an extension header to lift it off the board so it will be closer to the font panel of my case

You can do that, but don't use long wire lenghts because the welding pulses generate lots of EMI and could cause data corruption.

[dmxlights]

Hi Frank,

Thank you for your reply.

It is nice to know that the 3 wire is not used and is there a current limit that can be drawn from the fan connector. I was think of putting 2 fans in the case one over the cap board and one over the kweld board.

I am only taking about 3cm of ribbon cable max to move the screen and I can shield it as well as I have foil tape as well.

I am already have 3 packs build just need shrink rap for battery packs.

[tatus1969]

is there a current limit

yes, 500mA as stated in the manual :-)

[dmxlights]

is there a current limit

yes, 500mA as stated in the manual :-)

I missed that bit 

Thank you for your quick replies Frank.

[dmxlights]

Hi Frank,

I was have a problem with my bench power supply current limiter cutting the supply.

I was reading the Kcap manual to find the model of the server power supply you use and then seen you listed a Meanwell power supply, which got me thinking. I have one which is a 12v @29A. I have check it to see what is the lowest it will go to which is about 9.5v-10v. I know that the kcap board will with 8.1v to 14v. I have set my meanwell power supply to about 11v and is working well. I have notice also the balancer led is on when the cap fist charge after switching on and once I do one weld it goes out and stays out. I did not notice when I was using the bench power supply.

[CM800]

Trying hard for an excuse to add one of these to my collection of toys (kweld+ kcap+ ksupply)

Have you done much wire to sheet or wire to pin bonding with this? What is the limit to the smallest thing you have welded reliably with this?

[tatus1969]

I was have a problem with my bench power supply current limiter cutting the supply.

What kind of problem?

I have set my meanwell power supply to about 11v and is working well.

Perfectly okay. But is this a current limiting type Meanwell? Hickup limiting models (most of them are) are not suitable.

I have notice also the balancer led is on when the cap fist charge after switching on and once I do one weld it goes out and stays out. I did not notice when I was using the bench power supply.

That's okay and their job :-)

Have you done much wire to sheet or wire to pin bonding with this? What is the limit to the smallest thing you have welded reliably with this?

Not self, but a number of users are doing that with the welder. Not sure though in which forum that was reported, could be either here or
https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039
https://forum.esk8.news/t/kweld-spot-welder/6926