kWeld - "Next level" DIY battery spot welder

Batteries, Chargers, and Battery Management Systems.
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tatus1969   1 kW

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 21 2020 4:09am

Seakane wrote:
Apr 20 2020 11:35pm
Okay held the knob for the "open" part of the test and got the following values:

Offs: 62
Std: 5.6
And: Ok
No problem :-) And what was the result of the SHORT part?

Seakane wrote:
Apr 20 2020 11:35pm
Still don't know why my resistance value was off from spec at -0.02 milli Ohmes, but judging by the lack of concern here, I think I will forge ahead.
As I said, that was the result from a welding pulse, and *not* from a calibration step. Of course it measures zero then, as you were holding the probes together without anything inbetween. And of course it cannot push energy into 'nothing' which is why it terminated the pulse after 200milliseconds of attempting.
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Re: kWeld - "Next level" DIY battery spot welder

Post by Seakane » Apr 21 2020 1:15pm

No problem :-) And what was the result of the SHORT part?
Timeout
n=000001
E=-23.2J
t200.00m
I= 1344A
R=-0.02m
T= 29.4C

On a lark I made a couple welds on a dead cell and am getting pretty excited about using this thing in earnest. First pack will be for my 6 year old daughter's Oset trials bike. The stock lead acid batteries weigh more than she does!

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Re: kWeld - "Next level" DIY battery spot welder

Post by Timotee » Apr 21 2020 3:12pm

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

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 22 2020 2:06am

Seakane wrote:
Apr 21 2020 1:15pm
Timeout
n=000001
E=-23.2J
t200.00m
I= 1344A
R=-0.02m
T= 29.4C
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.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 22 2020 2:16am

Timotee wrote:
Apr 21 2020 3:12pm
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
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.
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Re: kWeld - "Next level" DIY battery spot welder

Post by john61ct » Apr 22 2020 2:45am

Might be fine for a very small number of cells.

Need more Ah as well as more robust circuitry.

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Re: kWeld - "Next level" DIY battery spot welder

Post by JoelR » Apr 23 2020 1:24am

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

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Re: kWeld - "Next level" DIY battery spot welder

Post by john61ct » Apr 23 2020 2:23am

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

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 23 2020 4:23am

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.

:warn: :warn: 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.
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Re: kWeld - "Next level" DIY battery spot welder

Post by flippy » Apr 23 2020 5:10am

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.
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Re: kWeld - "Next level" DIY battery spot welder

Post by wutang » Apr 23 2020 8:40am

hi guys, any idea why I'm getting only around 1000A with these batteries (2S, 7500mAh, 90C rated)? https://hobbyking.com/de_de/turnigy-nan ... roved.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)
setup.jpg
setup.jpg (218.87 KiB) Viewed 1101 times
any idea how to squeeze out a bit more out of this setup? or should I buy another battery?

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BVH   1 kW

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Re: kWeld - "Next level" DIY battery spot welder

Post by BVH » Apr 23 2020 9:59am

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.

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Re: kWeld - "Next level" DIY battery spot welder

Post by wutang » Apr 23 2020 10:16am

BVH wrote:
Apr 23 2020 9:59am
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.
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

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Re: kWeld - "Next level" DIY battery spot welder

Post by BVH » Apr 23 2020 10:44am

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.

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 23 2020 11:18am

wutang wrote:
Apr 23 2020 10:16am
hi guys, any idea why I'm getting only around 1000A with these batteries (2S, 7500mAh, 90C rated)?
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 wrote:
Apr 23 2020 10:16am
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
If the battery's ESR would be the only factor then that would be the case, but the welder also contributes ~ 3 milliohms here.
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Re: kWeld - "Next level" DIY battery spot welder

Post by wutang » Apr 23 2020 11:27am

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)

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Re: kWeld - "Next level" DIY battery spot welder

Post by JoelR » Apr 23 2020 1:27pm

tatus1969 wrote:
Apr 23 2020 4:23am
:warn: :warn: 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.
That would be a great way to learn what has worked for people. Thank you, Frank.

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Re: kWeld - "Next level" DIY battery spot welder

Post by SubnetMask » Apr 24 2020 4:42pm

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?

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Re: kWeld - "Next level" DIY battery spot welder

Post by ossivirt » Apr 24 2020 5:25pm

SubnetMask wrote:
Apr 24 2020 4:42pm
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?
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..

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Re: kWeld - "Next level" DIY battery spot welder

Post by SubnetMask » Apr 25 2020 9:46am

ossivirt wrote:
Apr 24 2020 5:25pm
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..
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?

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Re: kWeld - "Next level" DIY battery spot welder

Post by Seakane » Apr 25 2020 11:57pm

tatus1969 wrote:
Apr 22 2020 2:06am
Seakane wrote:
Apr 21 2020 1:15pm
Timeout
n=000001
E=-23.2J
t200.00m
I= 1344A
R=-0.02m
T= 29.4C
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.
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

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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Apr 26 2020 5:50am

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

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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 27 2020 6:17am

Seakane wrote:
Apr 25 2020 11:57pm
R = 2.37mR (typically between 2.5 and 3.0. Any problem with my value?)
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.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Apr 27 2020 6:23am

SubnetMask wrote:
Apr 25 2020 9:46am
@tatus1969, what are your thoughts on Headway LiFePo4 cells and the kWeld?
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.
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Re: kWeld - "Next level" DIY battery spot welder

Post by Seakane » Apr 27 2020 11:01am

tatus1969 wrote:
Apr 27 2020 6:17am
Seakane wrote:
Apr 25 2020 11:57pm
R = 2.37mR (typically between 2.5 and 3.0. Any problem with my value?)
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.
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?

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