kWeld - "Next level" DIY battery spot welder

Any thoughts on using my NOCO GB70 Jump starter as a power source?

The unit specs are:
2000 peak Amps
56WHr Lipo (5000mAH @ 11.1v nominal)
and this funny J3S rating of 15,700 (Joules in 3 seconds).
The Joules number seems to indicate a continuous amps of about 450A

Seakane said:

Timeout
n=000001
E=-23.2J
t200.00m
I= 1344A
R=-0.02m
T= 29.4C

Click to expand...

I repeat, this is *not* the result of a SHORT calibration step. That step uses a 10ms interval. Is it possible that you have a shorting link in the foot pedal terminals? That is not allowed during calibration.

Timotee said:

Any thoughts on using my NOCO GB70 Jump starter as a power source?

The unit specs are:
2000 peak Amps
56WHr Lipo (5000mAH @ 11.1v nominal)
and this funny J3S rating of 15,700 (Joules in 3 seconds).
The Joules number seems to indicate a continuous amps of about 450A

Click to expand...

Iny my opionion most of this is marketing BS. These start engines, as that requires maybe 500A for a few seconds, but I'd expect that the internal circuitry would blow more or less instantly when being presented with kWeld load currents.

Might be fine for a very small number of cells.

Need more Ah as well as more robust circuitry.

Hello! I'm anxiously awaiting the delivery of my kWeld later this week. I've been reading tons of posts about power supplies and would like to get some advice.

I don't have much infrastructure to charge large LiPo batteries such as the recommended Turnigy Graphene units. I could buy a proper LiPo charger plus a battery but would rather start with a 12v car starter battery and use the various 12v chargers I already have. Space and portability are not important in my case. Cost and low risk of a battery catastrophe are.

From what I've read, a 65Ah starter battery will work. However, when I search for 65Ah lead acid batteries, most results are for AGM / SLA batteries that are more costly than standard flooded lead acid batteries. Instead, these are rated in Cranking Amps and Cold Cranking Amps. Since the advice is to use a new battery with low internal resistance, I'd like to buy a new battery but first need to know more specifically which battery models will work. For example, the battery for my Subaru Crosstrek is called a "group 35" and has 640 Cold Cranking Amps and 800 cranking amps (via Costco's Interstate Batteries page) and costs $79. If this is sufficient, I'll buy one since it also fits my car. If not, can someone recommend and exact lead acid battery that will work?

Thanks in advance for your help!

Joel
Redmond, WA

All batteries made from lead have much higher resistance than any LI oned

I haven't used Pb batteries myself, but have collected feedback from other users on the kWeld product page. A 65AH battery (the 'normal' size for cars, likely also your Subaro) seems to be in the 1000A region, and larger 100AH models are around 1400A.

Can I make a poll from you guys using the welder with a starter battery? If you tell me model / age / reported current by kWeld, maybe along with a picture, then I would share that info for others.

i used it with a set of 4 60Ah thundersky/winston cells that i used for years in my previous car and it faulted out as the amps was WELL above 2000.

so, dont use those.

hi guys, any idea why I'm getting only around 1000A with these batteries (2S, 7500mAh, 90C rated)? https://hobbyking.com/de_de/turnigy-nano-tech-ultimate-7500mah-2s2p-90c-hardcase-lipo-pack-roar-brca-approved.html

based on the specs they should be able to deliver (continuos?) 675A, so I was hoping for more than 1000A

so anyway, the specs from calibration are:
R=2.21m
I=1057A

the battery has (based on iCharger 1010b+ measurement) 25m internal resistance - this seems quite high, so I guess this might be the problem (but no idea how accurate the charger is)

it's setup like this - so original kWeld battery cables + original cables from battery connected (i.e. around 20 cm more cable) (I'm using soldered bullet connectors - 10mm size)


any idea how to squeeze out a bit more out of this setup? or should I buy another battery?

The 90C on the label is a complete lie. The absolute best Lipos available are the Graphenes and some of those will do a sustained 40-45C. After that, inter-cell and connector solder joints begin to melt. You will be lucky to get about 25 to 30C out of it. Buy a second one and run in Parallel and you will probably reach where you want to be.

BVH said:

The 90C on the label is a complete lie. The absolute best Lipos available are the Graphenes and some of those will do a sustained 40-45C. After that, inter-cell and connector solder joints begin to melt. You will be lucky to get about 25 to 30C out of it. Buy a second one and run in Parallel and you will probably reach where you want to be.

Click to expand...

wouldn't it then trigger the overcurrent protection? if one already pushes over 1000A I guess in parallel it would be over 2000A ... for now I'm OK with the 1000A, but at least I know that in the future I have to stick with the recommended batteries

It might trigger overcurrent if you run them in Parallel while calibrating the unit as my 2 Panthers in Parallel did. So calibrate with one, weld with 2. That's what I do with zero problems. This was suggested to me by the builder of the KWeld some time ago.

wutang said:

hi guys, any idea why I'm getting only around 1000A with these batteries (2S, 7500mAh, 90C rated)?

Click to expand...

Yours is a 2S model, the 1400A figure is for a comparable battery with 3 cells in series. That's why your current is lower. The ESR measurement is certainly way off, these packs have a few milliohms only.

wutang said:

wouldn't it then trigger the overcurrent protection? if one already pushes over 1000A I guess in parallel it would be over 2000A ... for now I'm OK with the 1000A, but at least I know that in the future I have to stick with the recommended batteries

Click to expand...

If the battery's ESR would be the only factor then that would be the case, but the welder also contributes ~ 3 milliohms here.

thanks, I suspected that the int.res. measurement was off (with that resistance it wouldn't be able to push 1000A)

for now I'll stay with one battery (usually doing 0.15 nickel), unless I find a good deal on similarly rated one (so I can run them in parallel)

tatus1969 said:

Can I make a poll from you guys using the welder with a starter battery? If you tell me model / age / reported current by kWeld, maybe along with a picture, then I would share that info for others.

Click to expand...

That would be a great way to learn what has worked for people. Thank you, Frank.

I've been working through this thread reading up on the unit and will be ordering one, probably next week, but I have one question that I haven't really seen the answer to. Is the 'kSupply' able to be used to run the kWeld instead of using a battery pack, or is it just meant to charge/power the kCap module?

SubnetMask said:

I've been working through this thread reading up on the unit and will be ordering one, probably next week, but I have one question that I haven't really seen the answer to. Is the 'kSupply' able to be used to run the kWeld instead of using a battery pack, or is it just meant to charge/power the kCap module?

Click to expand...

Its meant to charge kCap module. Welder needs 800-2000Amps to work properly and I dont know any powersupply that can do that other that supercaps and lipo/sla batteries. Atleast at reasonable price..

ossivirt said:

Its meant to charge kCap module. Welder needs 800-2000Amps to work properly and I dont know any powersupply that can do that other that supercaps and lipo/sla batteries. Atleast at reasonable price..

Click to expand...

Thanks, I kind of suspected that was the case but wasn't 100% positive. I did actually end up reading more on it a handful of pages after I posted the question.

Now I just will need to figure out what to power it with.

Related to what to power it with, I read a post or two about the headway LiFePo4 38120 cells, and the feeling was they were 'junk'. Why is that? Those cells are 'rated' at 200A each, but from what I've gathered, it seems they're quite capable of delivering 300A+ in a dead short, so based on that and the voltage specs for the kWeld, it seems like a 2s4p or 2s5p (should be around 1200A or 1500A, respectively) arrangement of them should work well. And then there is the safety factor - those LiFePo4 cells are a TON safer than LiPO cells. You can abuse them and over charge the heck out of them (NOT saying you should, of course) and while going too far over you'll destroy them, but unlike other chemistries, while it might get unpleasant, they more than likely won't burst into flames and burn your house down (I've seen video where testing a LiFePo4 cell, not a headway, and MASSIVELY overcharging it for 10+ hours resulted in it just bulging and outgassing, while a (re-purposed Tesla) pack made up of 18650's, which are arguably 'slightly' more stable than LiPO, had a cell burst into flames due to an accidental out of balance over charge condition which resulted in a runaway that caused most of the pack to go up). You have to get really stupid with LiFePo4's to even get to the point of rupturing them, causing them to vent gasses. I'd really rather go with a LiFePo4 headway arrangement over a LiPO pack if I can get the cells at a reasonable price, due to the safety margin, unless, of course, for some reason, the really won't work.

It seems like, in no particular order, the overall safest options are lead acid, LiFePo4 and the kCap module.

@tatus1969, what are your thoughts on Headway LiFePo4 cells and the kWeld?

tatus1969 said:

Seakane said:

Timeout
n=000001
E=-23.2J
t200.00m
I= 1344A
R=-0.02m
T= 29.4C

Click to expand...

I repeat, this is *not* the result of a SHORT calibration step. That step uses a 10ms interval. Is it possible that you have a shorting link in the foot pedal terminals? That is not allowed during calibration.

Click to expand...

Well. I may have a bad case of the dumb =/. Not sure why I struggled with that so much.

Open:
Offs = 63
Std = 3.6

Short:
R = 2.37mR (typically between 2.5 and 3.0. Any problem with my value?)
Std = 30.0
I = 1379A
T = 19.6C

Battery is a mildly used lead-acid starter battery rated 750 CCA and a current voltage of 12.82v.

Aaron

I recommend that you try a calibration with a different 12V car battery, and see if you get the same results.

Seakane said:

R = 2.37mR (typically between 2.5 and 3.0. Any problem with my value?)

Click to expand...

Looking good, but you shouldn't get such varying results. Please check all nuts and bolts, also the electrode set screws (but be careful there as they thread into copper). You might also want to clean the electrode tips with sand paper. Make sure to get absolutely no sparks during the SHORT step, and press the conical areas of the tips together hard while triggering.

SubnetMask said:

@tatus1969, what are your thoughts on Headway LiFePo4 cells and the kWeld?

Click to expand...

Yes these are much safer and can be used. You'll need to run the calculations with regards to voltage (should be ~ 10 to 15V) and the pack's internal resistance (~ 3 to 5 milliohms) however, and that's where it becomes tricky. The cell ESR numbers can be unknown, measured poorly, or tweaked for marketing. If you can afford experimenting (starting with low cell count to avoid overcurrent) then there's nothing against that approach. I don't know however how well they can withstand the repeated abuse from being short circuited by the welder, as that could drastically reduce their lifetime.

tatus1969 said:

Seakane said:

R = 2.37mR (typically between 2.5 and 3.0. Any problem with my value?)

Click to expand...

Looking good, but you shouldn't get such varying results. Please check all nuts and bolts, also the electrode set screws (but be careful there as they thread into copper). You might also want to clean the electrode tips with sand paper. Make sure to get absolutely no sparks during the SHORT step, and press the conical areas of the tips together hard while triggering.

Click to expand...

Sorry. I have communicated poorly. My R value is 2.37mR. The manual suggests that I am outside the normal range of 2.5 - 3.0. I have not been getting varying test results.

Is it okay that my R value is lower than the manual's range?

spinningmagnets said:

I recommend that you try a calibration with a different 12V car battery, and see if you get the same results.

Click to expand...

I have not tried another battery for comparison, but it is on my list for today. Thanks for the suggestion.

Seakane said:

Is it okay that my R value is lower than the manual's range?

Click to expand...

Yes, that mistake is actually not with you but the manual. That number is from the previous electrode design and I haven't been able to make up the time to update it. Your result is spot on.