I posted a few days ago that I had bought a K-weld spot welder. It arrived yesterday so I started assembling the welder immediately.
I got a super cap board as well so I can run from a PSU instead of LIPO packs. I have a 12v, 17a Meanwell PSU just sitting on the shelf so it was an obvious choice for the welder.
I got the clear plastic cases for both modules.
First a few pics of welder. The kit comes in lots of good quality zip lock bags and was really well packaged for shipment.
Attention to detail is generally very good.
The welder board is nicely made and what I got has all the latest fixes that have been discovered since these spot welders were first made.
This is well published that the welder uses an STM32 for control.
The mosfets and busses are nicely done.
The super cap box is pretty nice and all of it interlocks together.
The welder case is not great IMHO. You need to super glue it together. The board mounts to the base via 4 screws and stand-offs. Otherwise the entire shell just falls apart if it's not glued together. Careful gluing is required! After gluing, the entire top of the case comes off the bottom as a single piece.
The fully assembled welder on my PSU. I think I will get rid of the longer wires and work out how to mount the bullets from the super cap module into the case wall. That will let me plug in the welder module directly into the wall of the super cap module which will make the whole welder a good bit more compact.
My changes done so far: (Things I wish the welder had in it already)
1. The 8 awg cables between the super cap board and the welder are about 6" long. They bolt down to both boards. I won't be using the welder day in and day out so there are times when I'll stick it on the shelf for a while. I'll need to take it apart for storage. I cut the wires at the welder screw lugs. I then soldered 8mm bullets to the screw lugs. This lets me disconnect the super cap module from the welder module.
2. The foot switch wires end at a screw terminal block on the welder board. Again...I'll need to take things apart for storage. I used a 4 pin JST connector and used 2 pins in parallel for each wire from the foot switch. There's no real current load here. 2 pins each is just for long term reliability.
This is the connector on the foot switch.
3. I haven't done it yet, but I'm going to add 8mm bullets at the welding cables so they can be disconnected from the welder module. I may also make up added sections of cable so the welding pen cable lengths can be a bit longer.
By default the energy setting was at 10 juels. This was a lot better than my Chinese welder and the welds were a better. They were still fairly weak and I could pull of the nickel strip from the 18650 without a lot of trouble. I'm using .2mm. I kept playing with the energy setting to see what would happen. 80 juels was too much and blew a hole through the cell. I then tried 70 juels which was better, but it still compromised the nickel strip. 60 juels however was just right. What you are seeing below is 3 welds at 70 and the right most one is at 60. AT 70 juels, the nickel strip has spots blown through it, but the weld is very strong. 60 made a great weld that did not blow through the nickel strip. I needed pliers to tear off the strip from the cell.
I did run into a couple of complications:
1. The super caps will charge up at 500 amps if you let them. I needed to limit current draw from my PSU so it wouldn't over load and shut off. This is something that I think should be an option for the kit. A precharge board between the power source and the super cap module so you can charge the caps gracefully.
2. The super cap board has no way to discharge gracefully. A precharge board could also incorporate a large resitor that can discharge the capacitors gracefully. An accidental short across the power wires would probably blow the connectors off. Whatever metal thing they shorted across would also be badly pitted or destroyed.
3. While they are charging, the super caps get pretty hot and you will want to add a fan on top of them to keep them cool. This needs to be part of the super cap modules. They get far too warm! I scrounged a 2.5" 3 wire PC fan and that worked nicely.
4. My PSU delivers 17 amps. More than that and it detects an over load and shuts off to protect itself. I made up a bank of 8 3 ohm resistors in parallel to limit current to the super caps. It took 20 minutes to charge them at this current rate. Of course these caps are 310 farads each and you have 2 in parallel and 3 in series. It's going to take a good while to charge that much capacitance.
5. Something that isn't clear is the operating voltage. you have 3 super caps in series or 2.7v x 3 = 8.1v. However in the manual it says nothing about the super cap max voltage. The manual says 30v max. Surely this is not good for the caps to run them at higher than their rated voltage! I turned down my Meanwell PSU as low as it will go.
6. There is no way to turn off or disable the welder. About all I can do is unplug the foot pedal. Be careful as you have crazy amounts of current at the welding pens and they weld just about anything.
I did something like 20 or 30 welds on junk cells tonight. The welding pens never got slightly warm. Getting the welder calibrated is very easy. In settings I made 2 changes. I had to set battery voltage and I set current from 800 to 900 amps. Other than that the welder worked flawlessly and required no other set up.
After this initial bit of use, I'm going to take apart the covering on those 3 20S packs I just made and reweld them with the K-Weld. It did a far better job! I'm pretty happy with the weld results. The cells do not get hot at all while being welded and the weld spots are very strong. At $400, it''s not cheap, but the weld quality is very good and highly controllable. To me it was a worthwhile purchase. It will get used quite a lot in the next few months.
