If it is not too rude a question, why are people so keen to use the supercapacitors instead of battery power sources ? Lower ESR ? Higher current tolerance ? , it certainly isn't low cost
Best Wishes to all my fellow kWeld owners and especially to Frank, the father of the kWeld
I've started testing the kWeld - with sparks going everywhere.
At 50J I burned straight through the nickel strips. At 14.6J I get strong welds but still sparks going everywhere, even though I press down on the electrodes rather hard. Peak current was just over 1400A.
14.6J
6,74ms
1.03 mOhm
1428A
With the calibration it set an offset of 66 and a resistance of 1.95 mOhm.What kind of nickel strip do you have, is it 0.1mm? And is it maybe nickel plated steel? (You can test it with a Dremel with cutting disc, if it is pure nickel then you won't see any sparks.)
The numbers are consistent though, as 1428^2 * 1.03e-3 * 6.74e-3 = 14.15J. Current and weld spot resistance are also typical, and if you can verify the pulse time for correctness then I think that the system works as it should.
What kind of pulse is the kWeld making? Single large pulse?
I know that commercial spot welders utilizes a dual pulse. Would that be possible with the kWeld?
i have been trying to learn some of the background "science" of this nice project by tatus1969 from googling
and here is also a version of LTspice simulation, i added a C2 n some diodes to deal with the kick back which i assume is what was mentioned in 1 of the posts as being a danger? it appears due to the very high current, the simulation seem to say the kick back could go over 1kV? not sure about this but maybe someone else can comment on this.
the cable specs are "stretched" to simulate what if lengths.
the simulation is somewhat fun, its a somewhat "non-destructive" way to find cable parameters that fit a certain current/weld output profile
(the txt file needs to be renamed to *.asc for LTspice)
What kind of pulse is the kWeld making? Single large pulse?
I know that commercial spot welders utilizes a dual pulse. Would that be possible with the kWeld?kWeld is single pulse - I currently keep my position that it doesn't need double pulse technique, because the implemented energy metering is superior. Of course it is very simple to change the behaviour in the firmware... I'm happily up to the discussion.
EDIT: I think that double pulse is necessary in conventional welders because when pulse time is kept constant, then delivered weld spot energy depends on the weld spot resistance. That can vary when there is bad contact due to corrosion or weak contact force. I made the constant energy approach to get rid of these factors.
... It trickle charges the capacitors because it goes into overcurrent shutdown at ~100A every 25ms ...
Simple fix there Kjelt is to retap with a recoil tap and put in a M5 insert, which uses almost the same diameter and which will recover most of the diameter and most of the strength. Not as good conductivity wise as it is stainless steel as opposed to brass
The brass hollow rod is pretty commonly available on eBay. It might be better to just buy a length and start again ?
I've heard that the first pulse's purpose is to remove oils and other impurities, so the second pulse can perform the actual weld.
I'm by no means an expert in that area, but it sounds plausible. I'm not sure how to test it in practice.
Removed my post since it was my own stupid mistake. The taps were placed back in different order so I found just out while putting everything back that it was an M6 tap instead of an M5 tap I used.
Since now one piece of the electrode brass pipe is damaged I have to find another way to construct the electrodes.
using a pair of the XT-150 (or similar bullet connectors) at the probe tip
The drawback of using the XT-150 connectors for the probe tip mounting may be the connection resistance that it may introduce. They are gold plated and oxidisation resistant though.
Heatsink with 5mm hole down the centre. The outer diameter is a little too large though. You get the idea though
I'm curious if I can use this LiTiO (6S):
https://www.ev-power.eu/LTO-technology/Lithium-Titanate-Oxid-Battery-Cell-LTO-2-4V-30AH.html?cur=1
Price may not be competitive but my idea is:
- use 6S LTO battery pack in my car as a secondary battery (should have good cold temperature performance for cold starts)
- make this battery removable from car and use it as a occassional portable powersource (for kWeld...)
- charging would be done in car from alternator
I've heard that the first pulse's purpose is to remove oils and other impurities, so the second pulse can perform the actual weld.
I'm by no means an expert in that area, but it sounds plausible. I'm not sure how to test it in practice.Yes, and another rationale is to soften the nickel strip and let it sink to the battery tab through the tip pushing it down.
My experience is that I get consistent welding results from kWeld, no matter how hard I push down the electrodes. I also made welding tests on batteries from I which I had dremele'd away existing strips, which is dramatically changing their surface structure, and I still get the same results. I made some tests with solder flux in the path, and I already though about artificially aging/oxidizing some material. I'm most curious of the feedback on this topic from other kWeld builders.
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
ops, this is now re-arranged.
thanks for the correction
now even the short battery lead is making quite a ton of voltage spikes
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.