Author Topic: kWeld - "Next level" DIY battery spot welder  (Read 196872 times)

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Offline pcm81

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #725 on: November 20, 2020, 04:58:05 am »
Wanted to bump this thread up, because i just did something amazingly crazy with kweld.
So, i am running just from the recommended  Turnigy Nano-tech 5000mah 3S 65~130C Lipo Pack  After doing a good job polishing the tips of the stock probes i bumped the KWELD up to100J, created a stack of 7 pieces of 0.15mm thick pure nickel strips, with bottom strip longer than the top 6. Placed one probe on the bottom strip and another probe on the top, held the top probe down firmly and pressed the pedal. The  100J of energy, rushing through the nickel at 1300A and actually welded all 7 nickel strips. That is 0.15*7-1.05mm on nickel welded together.
Goes to show, if you put some thought into your current path and let the kweld do its thing, it can do a lot more than any rational individual ever need to do in their lifetime.
 
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #726 on: November 20, 2020, 09:04:13 am »
Specs:
Capacity: 5500mAh
Configuration: 3S2P / 11.1V / 3Cell
Constant Discharge: Up to 140C
Discharge Cable: 12AWG
5.5Ah * 140C = 770 amperes "burst". Still uses "skinny" 12AWG?? No way. Spec wise it seems that it would be appropriate, but overall it sounds fishy to me. The 'standard' Turnigy battery is current back in stock, better use that proven solution.

I would like to mount the Kweld and other components in a large metal case, with the Kweld mounted flush with the front panel . I know I would have to extend the control knob and the LCD screen, and likely shield the LCD area. What would I look for if I want to extend the LCD so I can panel mount it (likely 1") , what is the LCD and socket referred to as .
The LCD is a NewHeaven NHD-0108HZ-FSW-GBW, the connectors are Samtec BBL-111-T-E / SL-111-TT-12.

I've ordered the kweld with the kcap module. I'm planning on charging the caps with my 60v 5A bench power supply through a murata rbq-8.2/45-d48 isolated DC-DC converter to use as much of available power as possible. Do you think that is a good alternative?
60V*5A=300W, and the brick can keep up with that. The brick's datasheet states *both* hickup-style short circuit protection *and* output current limiting. Not sure which conditions apply for which scheme, but hickup-style protection is not suitable as that is exactly what the empty ultracaps represent. In that case the brick might not be able to start up properly.
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Offline pcm81

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #727 on: November 21, 2020, 03:43:56 am »
I would like to hear some opinions on my Kweld build before i actually build it. Any feedback or recommendations would be appreciated.

I am looking to make a "package" build, may be inside a small pelican case or similar enclosure. The build will consist of Kweld, 1 or more turnigy 130C batteries, or possibly a custom 4S Li-ion cell bank and a Tenergy Li charger.
I would like to push 1300Amps.

My questions/options are:
1. Do i need a mechanical disconnect between charger and battery power leads? Not sure how charger would react to 1300 amp pulse coming out of the batteries into kweld... If disconnect is needed to protect the charger, do i need it on both power and ground lines? How about on balance lines?
1.5 can i charge the li-ion battery with KWeld connected or do i need to disconnect it from charger/battery circuit with additional set of switches?
1.75 If i do not need to disconnect charger from battery when using kweld, can i actually use kweld while charging? Again, not sure about the whole inductive energy from pulse interaction with charger especially while it is charging the battery.
2. Is switching to 6AWG or even 4AWG a good idea or not worth it? Looking to have flexibility of longer leads but heavier gauge wire is going to require longer bend radius, reducing the flexibility added by additional length.
3. I am looking to add options such as ground clamp, to basically be able to do single point spot welding on larger "somewhat structural" materials, like nickel covers for wire routes etc, not "real structural" welds. What would you recommend for good quality disconnects to be able to swap between electrode sets? I am NOT trying to replicate the functionality of a MIG or TIG Tack/spot welder, just trying to enable myself to use kweld in as wide of a range of applications as possible. At work (aircraft company) we use very basic, but expansive, AC tack welders for this type of work. The energy output of those is measured in percent... so no where near the accuracy and flexibility that Kweld can provide.

EDIT:
4. Does it make sense to play with alternate electrode material like tungsten or graphite? I realize it has higher resistance than copper, but it also has higher melting temperature... While low resistance contact between electrode and nickel strip should result in minimal heating and damage to the copper electrode, it is still right ontop of the weld bead and basic thermal conduction will still heat it up. If we ignore the lower cost of copper, are there better options for the electrode set?

5. the power supply leads in KWELD kit have the ground wire shorter than power wire. What is the requirement driving this? My current configuration has the li-ion battery wire connected to the KWELD leads, so ratio of power wire lengths is now different than original ratio of supply wire lengths. In my final configuration i will probably have to build my own supply cables. Is there a specific ratio of supply cable lengths i should aim for? Or does this all come down to resistance hence if i use 6AWG for ground leg and 8AWG for  power leg i do not need to worry about supply cable length ratio?
« Last Edit: November 21, 2020, 04:39:49 am by pcm81 »
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #728 on: November 24, 2020, 10:04:14 am »
1. Do i need a mechanical disconnect between charger and battery power leads? Not sure how charger would react to 1300 amp pulse coming out of the batteries into kweld... If disconnect is needed to protect the charger, do i need it on both power and ground lines? How about on balance lines?
1.5 can i charge the li-ion battery with KWeld connected or do i need to disconnect it from charger/battery circuit with additional set of switches?
1.75 If i do not need to disconnect charger from battery when using kweld, can i actually use kweld while charging? Again, not sure about the whole inductive energy from pulse interaction with charger especially while it is charging the battery.
I had made measurements with the ultracaps (kCap) in the past, and these see only a small fraction of the inductive kickback voltage - typically 2 to 3 volts. The Lipos have a higher internal resistance, so the peak is probably higher here but if you want to be sure then you should probably make measurements with an oscilloscope. Whether that is okay for the charger will also depend on the model. I know of a few people that are using the welder with Lipo and a permanently connected charger, none of them reported me failures.

2. Is switching to 6AWG or even 4AWG a good idea or not worth it? Looking to have flexibility of longer leads but heavier gauge wire is going to require longer bend radius, reducing the flexibility added by additional length.
The thicker the more current and the less heat you'll get, there are only practical limits (plus of course the 2000 ampere limit of the unit when restricting the lead length to 1m total). Keep in mind that lower gauge leads will *not* reduce their inductance (practically spoken, of course there is a relationship but that doesn't contribute much).

3. I am looking to add options such as ground clamp, to basically be able to do single point spot welding on larger "somewhat structural" materials, like nickel covers for wire routes etc, not "real structural" welds. What would you recommend for good quality disconnects to be able to swap between electrode sets? I am NOT trying to replicate the functionality of a MIG or TIG Tack/spot welder, just trying to enable myself to use kweld in as wide of a range of applications as possible. At work (aircraft company) we use very basic, but expansive, AC tack welders for this type of work. The energy output of those is measured in percent... so no where near the accuracy and flexibility that Kweld can provide.
I'd say XT150 minimum.

4. Does it make sense to play with alternate electrode material like tungsten or graphite? I realize it has higher resistance than copper, but it also has higher melting temperature... While low resistance contact between electrode and nickel strip should result in minimal heating and damage to the copper electrode, it is still right ontop of the weld bead and basic thermal conduction will still heat it up. If we ignore the lower cost of copper, are there better options for the electrode set?
I haven't done that but there are users experimenting with this - you might also want to check out the other forum threads
https://forum.esk8.news/t/kweld-spot-welder/6926
https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039

5. the power supply leads in KWELD kit have the ground wire shorter than power wire. What is the requirement driving this? My current configuration has the li-ion battery wire connected to the KWELD leads, so ratio of power wire lengths is now different than original ratio of supply wire lengths. In my final configuration i will probably have to build my own supply cables. Is there a specific ratio of supply cable lengths i should aim for? Or does this all come down to resistance hence if i use 6AWG for ground leg and 8AWG for  power leg i do not need to worry about supply cable length ratio?
That's purely mechanical - the positive mounting "post" is a bit recessed on the board.
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Offline Uho

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #729 on: December 02, 2020, 05:14:51 pm »
I read all 30 pages of the forum with great interest. I am very sorry that I have already spent money on Chinese spot welding. It would be better to buy from you. My welding does not contain any protection. I don't want to change transistors often. Suppressors and diodes I will put in addition. But this is not enough. I want to make a small board based on comparators to track currents below 600A and above 1200A. So that she just turns off the driver. I have a few questions.
1. Does the IR44252 work well enough. He has a current of 0.3A.
 2. What pause is needed before starting to measure the voltage across the transistors. The tension does not rise instantly.
3. What are the voltage levels at a current of 1200A on transistors? Tee counted the voltage according to Ohm's formula or real measurements.
I have seen only one oscillogram of voltage measurement across transistors. And I didn't understand everything. If this is not a commercial secret, please answer my questions.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #730 on: December 03, 2020, 10:00:11 am »
I read all 30 pages of the forum with great interest. I am very sorry that I have already spent money on Chinese spot welding. It would be better to buy from you. My welding does not contain any protection. I don't want to change transistors often. Suppressors and diodes I will put in addition. But this is not enough. I want to make a small board based on comparators to track currents below 600A and above 1200A. So that she just turns off the driver. I have a few questions.
1. Does the IR44252 work well enough. He has a current of 0.3A.
 2. What pause is needed before starting to measure the voltage across the transistors. The tension does not rise instantly.
3. What are the voltage levels at a current of 1200A on transistors? Tee counted the voltage according to Ohm's formula or real measurements.
I have seen only one oscillogram of voltage measurement across transistors. And I didn't understand everything. If this is not a commercial secret, please answer my questions.
Not sure what your plan is. Do you want to extend your Chinese spot welder? This is probably a transformer based AC current system, where switching is done by SCRs and not MOSFETs.
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Offline Uho

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #731 on: December 03, 2020, 10:33:32 am »
I have 3000F capacitor spot welding. I bought capacitors separately. I can use either two or four capacitors in series. I bought a separate control board and DC-DC 20A. Order is still in transit. I am planning to charge capacitors current  up to 10A. I have not yet decided whether it is necessary to disconnect the charge of the capacitors during welding. If two capacitors are enough, then I plan to use such a balancer circuit. Attached the diagram. The Chinese do not put up any protection. There are many reviews about the combustion of transistors. Therefore, I want to make a current limitation 1200A.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #732 on: December 04, 2020, 10:12:35 am »
Attached the diagram.
Your circuit should have a resistor between opamp output and transistor bases to limit their current in case of strong capacitor imbalance. Not having that means that base current is only limited by the opamp's drive capability. And is it your intention that the transistors dissipate all the excessive energy? Make sure they are big enough then and have good cooling. Also, have you considered the stability aspect of your circuit? I'd add provision of bandwith and gain limiting components of the opamp when making the design so that you can play with that. Or make a simulation with all parasitics as well as the actual chosen components to check the dynamic stability.

There are many reviews about the combustion of transistors. Therefore, I want to make a current limitation 1200A.
I see. You want to interrupt current as soon as it hits the limit, right? IR44252 should be good enough, but make your calculation of the injected power into the MOSFET die based on flowing current (=1200A) and turn-off slope (better do actual measurement with a scope). The resulting energy should not exceed the maximum avalanche energy of your chosen MOSFET. Do *not* multiply by the number of MOSFETs, because the turn-off energy may be dissipated by just one of them when they switch differently.
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