kWeld - "Next level" DIY battery spot welder

[ossivirt]

I thought i posted this but I don't see it so i guess not. Wanted to ask, if i am understanding the math on calibration in the manual correctly it seems like wire size matters. I was going to use 4AWG for the connection to the battery but is the calibration expecting 8AWG in particular? If so is there any kind of conversion calculation i can easily do or is it better to just stick with 8AWG

Wire size chances resistance and therefore welding current depending your setup. Wire lenght chances how bad the inductive kickback from weld pulse is. Shorter wire is means less kickback. If wires are longer than original you need to chance the wire lenght value wich sets welders over current limit lower to protect itself. Thats how I understand it anyway..

 

[LordKitsuna]

I thought i posted this but I don't see it so i guess not. Wanted to ask, if i am understanding the math on calibration in the manual correctly it seems like wire size matters. I was going to use 4AWG for the connection to the battery but is the calibration expecting 8AWG in particular? If so is there any kind of conversion calculation i can easily do or is it better to just stick with 8AWG

Wire size chances resistance and therefore welding current depending your setup. Wire lenght chances how bad the inductive kickback from weld pulse is. Shorter wire is means less kickback. If wires are longer than original you need to chance the wire lenght value wich sets welders over current limit lower to protect itself. Thats how I understand it anyway..

ah ok, i was not clear on if the wire size would change the math for the wire length or not sounds like regardless of wire size i should put in the true total length. thanks

 

[LordKitsuna]

Hopefully this is the last fairly basic question I'll have in a while I just hooked up my new battery cables adjusted my cable length in the settings and did a calibration.

Resistance was slightly lower as expected however the value "std" almost doubled. Whereas my original calibration was std=26.7 my new value is 45.7. Is this a sign of anything wrong? Or is this expected for going from 8 AWG to 4 AWG cable. I'm not really sure what that value is meant to represent so I don't have a good idea of when or if I should expect it to change. The I= was within margin error so basically didn't change.

I'm also having a bit of trouble trying to figure out if I have my cable lengths correct. The default setting appears to be 1 m but as far as I can tell that is wildly inaccurate for the complete kit cable lengths. I have added much longer battery cable and as far as I'm able to measure both the electric cable plus my battery cables is 26 in which comes out to 0.66 m at least according to Google. I am sadly cursed with American useless units in my head. Although it won't let me set below one meter either so is it basically just an anything below that doesn't matter

Edit: after making sure all connections were tight and redoing calibration std is back down to 29.2 which leaves the only question left about the cable length

 

[john61ct]

There is no rulebook that is waiting to be discovered, a lot of people seem to get the best results for their situation by trial and error.

Get it set up according to the standard recommendations, practice on scrap materials, set your baseline benchmarks to compare to.

Then try your variations, maybe incrementally, and see the results.

That way you can ask very specific questions to solicit advice.

 

[LordKitsuna]

There is no rulebook that is waiting to be discovered, a lot of people seem to get the best results for their situation by trial and error.

Get it set up according to the standard recommendations, practice on scrap materials, set your baseline benchmarks to compare to.

Then try your variations, maybe incrementally, and see the results.

That way you can ask very specific questions to solicit advice.

maybe i worded poorly but i thought this was fairly specific questions. The manual says that making sure wire length is correct is important to not damage the unit but it seems like the wire length included in the full kit does not add up at all. the manual says it accounts for 1m total but when i measure what came in the kit its nowhere near 1m and even after extending my wire i am still under 1m as far as i can tell.

so it makes sense that i would want to make sure i am not doing something wrong here, or if the total length is fine for anything at or below 1m

 

[spinningmagnets]

Swapping to thicker welding cables will lower resistance slightly, which allows them to run a long time without getting hot.

Longer cables will increase inductance, which is best to avoid, if possible. The factory cables are the longest practical length, with a safety margin included.

Shorter cables are not necessary, but it doesn't hurt to have cables that are shorter and fatter.

 

[LordKitsuna]

Swapping to thicker welding cables will lower resistance slightly, which allows them to run a long time without getting hot.

Longer cables will increase inductance, which is best to avoid, if possible. The factory cables are the longest practical length, with a safety margin included.

Shorter cables are not necessary, but it doesn't hurt to have cables that are shorter and fatter.

ok thank you for that clarification, the way the operating manual is worded made it sound like i should have had 1m of total cable out of the box but with your post and some thought i think it means to say the wire length setting accounts for 1m of cable regardless of if its under that. which is what i was unsure about.

 

[ossivirt]

Original cables are shorter than 1m but that is partly because when you connect lipo there is x ammount of wiring integrated to the lipo brick. Same for sla when you put your favorite connector + short cables with battery terminal clamps. And like said above having shorter wire is a lot better than little too long..

 

[tatus1969]

I did extend the length of the battery cables using some 4AWG wire (just lazily by braiding them into then soldering together with the existing wire) but I assume that using that different size cable screws with the math so I'm going to need to just go get some proper cable at the length I want so I can calibrate it properly

When using the full 2kA, you cannot extend the battery leads as that introduces extra inductance. Please make sure to have read the user manual chapter discussing that.

I thought i posted this but I don't see it so i guess not. Wanted to ask, if i am understanding the math on calibration in the manual correctly it seems like wire size matters. I was going to use 4AWG for the connection to the battery but is the calibration expecting 8AWG in particular? If so is there any kind of conversion calculation i can easily do or is it better to just stick with 8AWG

The calibration only "looks" at the output side of the unit, it doesn't care how you wire up the battery. That said it is still wise to recalibrate when the amount of available current changes considerably (e.g. when using a different battery), because the current measurement itself isn't error free.

value "std" almost doubled

That is the standard deviation of a series of repeated measurements, as long as that is within limits the welder allows you to continue. It would complain otherwise, but that normally means that something is broken.

The default setting appears to be 1 m but as far as I can tell that is wildly inaccurate for the complete kit cable lengths

It is as accurate as you make it, as it is you who is expected to add up the pieces. The stock wiring is 1 meter exactly. The probe system is 0.8 meters. You do neither need to account for the probes nor for the electronics module itself, the system has enough margin for that. The battery also doesn't count, as its inductance is quite low because of its huge mass. If your battery leads are 26 inches (0.66 meters), then the number that you need to dial in is 0.66 + 0.66 + 0.8 = 2.12 meters. This will drastically reduce the allowed current. If you don't enter the correct number, you will damage the unit from overstress. Hence, my first comment above. Note that the wire thickness is (practically) irrelevant here, only the length counts.

 

[ijr9005]

i see the pulses 5 times, how much heat does this put into the cell, how does it compare to a compatent person solderig prepared cells fresh from the freezer, totallly disilusioned with welding high resistance nickel poorlly

 

[tatus1969]

i see the pulses 5 times, how much heat does this put into the cell, how does it compare to a compatent person solderig prepared cells fresh from the freezer, totallly disilusioned with welding high resistance nickel poorlly

pardon?

 

[spinningmagnets]

how much heat does this put into the cell?

I hadn't thought about putting the cells in the freezer, thats a brilliant idea.

For low cell heat, use the kWeld and the "copper nickel sandwich" method, even if you don't really need the high-amp copper series buses...the moment the weld-pulse is over, the heat of spot-welding is wicked away from the cell faster than if the bus was nickel...

Also, copper becomes soft enough for the weld-bead to solidly connect, at a lower temp than nickel.

 

[LordKitsuna]

I did extend the length of the battery cables using some 4AWG wire (just lazily by braiding them into then soldering together with the existing wire) but I assume that using that different size cable screws with the math so I'm going to need to just go get some proper cable at the length I want so I can calibrate it properly

When using the full 2kA, you cannot extend the battery leads as that introduces extra inductance. Please make sure to have read the user manual chapter discussing that.

I thought i posted this but I don't see it so i guess not. Wanted to ask, if i am understanding the math on calibration in the manual correctly it seems like wire size matters. I was going to use 4AWG for the connection to the battery but is the calibration expecting 8AWG in particular? If so is there any kind of conversion calculation i can easily do or is it better to just stick with 8AWG

The calibration only "looks" at the output side of the unit, it doesn't care how you wire up the battery. That said it is still wise to recalibrate when the amount of available current changes considerably (e.g. when using a different battery), because the current measurement itself isn't error free.

value "std" almost doubled

That is the standard deviation of a series of repeated measurements, as long as that is within limits the welder allows you to continue. It would complain otherwise, but that normally means that something is broken.

The default setting appears to be 1 m but as far as I can tell that is wildly inaccurate for the complete kit cable lengths

It is as accurate as you make it, as it is you who is expected to add up the pieces. The stock wiring is 1 meter exactly. The probe system is 0.8 meters. You do neither need to account for the probes nor for the electronics module itself, the system has enough margin for that. The battery also doesn't count, as its inductance is quite low because of its huge mass. If your battery leads are 26 inches (0.66 meters), then the number that you need to dial in is 0.66 + 0.66 + 0.8 = 2.12 meters. This will drastically reduce the allowed current. If you don't enter the correct number, you will damage the unit from overstress. Hence, my first comment above. Note that the wire thickness is (practically) irrelevant here, only the length counts.

Wow i feel like a special kind of stupid. I realize now that my mistake was I was not adding both directions of wire. Kind of embarrassing to have made such a simple mistake but thank you for correcting me. Unfortunately the default length for the battery cables can't even reach between the terminals on the battery I have. So I'm going to have to figure something out, out of curiosity would this be good situation for the kcap kit. Or to ask the question more directly does the super capacitor kit isolate the total wire length so that you only count between the caps and the welder.

If that's not how that works I may just have to look at other power sources which would not be the end of the world seeing as there are many good recommendations available already.

Edit:nvm i read the manual for the kcap i see that it should not be hooked to a battery. I will just have to explore other options then thanks for all the help

 

[john61ct]

I hadn't thought about putting the cells in the freezer, thats a brilliant idea.

Sorry if I'm obtuse

but that is sarcasm correct?

 

[spinningmagnets]

I've always spot-welded cells at room temperature. Putting them in a freezer is something that I was assured would not hurt them when I researched long-term storage of lithium cells. I had always heard that putting them where the temps were "cool", was better than storing it in a hot summer garage...but using a freezer sounded odd...

For some reason, I had never heard of cold-soaking them in a freezer before spot-welding. It's obvious now in hind-sight, but my old brain hadn't put 2 and 2 together yet, even though all the pieces were right there in front of me...

I'm very sarcastic with close friends, but with acquaintances, I try to be diplomatic.

 

[john61ct]

Aha well glad I asked!

So long as the heat gain is still minimized

I imagine the destructive effect on the internal materials does not go away just because they are frozen, in fact may be greater.

but yes I can see the inert materials bei g cold might give an extra second or so delaying the overtemp arriving

 

[LordKitsuna]

I would think freezing temperatures would be undesirable for most cells. But I could see chilling them in a refrigerator probably not being too bad while still giving you temperature Headroom compared to room temperature cells.

You might be able to take the separation even a step further and find a way to Simply "spot cool" before you spot weld. An ice pack or few drops of LN2 applied to the cap/end right before welding should chill the weld spot without requiring chilling of the entire cell. Well maybe not the LN2 that might create far too large a temperature gradient

 

[LordKitsuna]

I decided to play with the cable length. I realized i don't necessarily need the kweld to actually touch the table and i found that the absolute minimum length of cable i can use brings me to 1.12m which also puts me insanely close to max current

However this does still give me enough probe reach to spot weld a 14s7p battery without having to strain the probe cables. Now i just need to create a little platform i can mount to the side of the battery and attach the kweld too so that it's not hanging by the power cables.

Edit: ran calibration a few times and sometimes it says overcurrent so unfortunately it seems this isn't a good solution either and i will have to explore other power sources after all or at least a less powerful battery

 

[ossivirt]

Edit: ran calibration a few times and sometimes it says overcurrent so unfortunately it seems this isn't a good solution either and i will have to explore other power sources after all or at least a less powerful battery

You can also try to keep battery voltage little lower. Thats big battery so it will still weld many times even when nearly "empty". Or use 8avg battery wires will also loose couple amps..

 

[john61ct]

do you mean #8 AWG?

 

[ossivirt]

do you mean #8 AWG?

Yes sorry. Excuse my metric brain

 

[tatus1969]

Edit: ran calibration a few times and sometimes it says overcurrent so unfortunately it seems this isn't a good solution either and i will have to explore other power sources after all or at least a less powerful battery

You can lower the batt voltage just for calibration (the current there is higher because the work piece's electrical resistance is missing) then top it up again for normal use. Or use it at 50% in order not to risk random overcurrent abortions during welding, which would be embarrasing.

 

[LordKitsuna]

Alright so i drained the battery a bit and so far all has been fine, i still ride that line with calibration at 1894A but its not given me any issues on test welds.

More importantly my 0.2mm copper strips arrived and i have had really good results on a test cell. I was expecting to have to play around with this a lot but so far using 100J i can get some decently solid welds.

[youtube]2bM68vRFnIY[/youtube]

its not quite as hard fast as nickle but as you can see with only 2 weld spots (well technically i guess 4 since 2 probes) i can shake the cell around by the copper for awhile before it finally gives up and lets go. the cell cap does indeed get rather warm even just from 2 welds tho so i will likely start applying an ice pack to the cap right before welding. attempt to do some "spot cooling" for my spot welding :lol: with 3 or maybe 4 welds on a cell i don't see this being a problem unless i am missing something here.

 

[john61ct]

Why are you not going through a spot of nickel?

 

[Merlin]

its fancy using copper now. the bottleneck is still the cell itself.
i did alot of tests with 10-20A discharges on a single cell with nickel and copper in different thickness. copper is multiple times more conductive, thats true. but the heat comes from the cell not from the welds/nickel.
i didnt find any "real world" benefit of using copper again. even the voltage drop on single cells was 1:1 similar.
on battery packs and logged drag races.....no difference in the power of the pack.

some say "big players" on the market using copper in high power tools.
thats true. But the reson is money. copper is way cheaper than nickel.

well but thats to anyone on its own. iR matched cells + good layout with perfect current flow is more important for a longliving batterypack.

0.2 quality nickel sheets do the job just perfect.