kWeld - "Next level" DIY battery spot welder

Batteries, Chargers, and Battery Management Systems.
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The Lightning Stalker   1 mW

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

Post by The Lightning Stalker » Jan 24 2018 9:41am

I'm in the market for ultracaps. Those Skels look good but they come in 10 packs and are weld only. I would need another welder to weld the ultracaps for my welder.

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

Post by spinningmagnets » Jan 26 2018 10:58pm

If anyone is having difficulty finding a small quantity of copper rod in 1/4-inch__0.25-inch diameter (roughly 6mm), I have purchased several feet, and can sell it by the inch, plus postage.

My local hardware store stocks solid copper wire in 6ga and 4ga as grounding wire for large junction boxes. This 6mm had to be ordered, and is considered 2ga.

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

Post by The Lightning Stalker » Jan 27 2018 9:34am

I don't know if these are new or if I just didn't notice them, but Thunder Power has some 120C stuff right now.
http://www.thunderpowerrc.com/CAR_BATTERIES/Reaper
The specs on these are getting pretty insane now.

Are there any plans for pulse arc capabilities on the kWeld? Of course it would need the proper solenoid tungsten holder. I'm thinking it could be useful for welding ultracaps etc.

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

Post by fechter » Jan 27 2018 8:18pm

Pulse arc is interesting. I did some experiments using a non-contact electrode and high voltage starter. I've never tried using a solenoid but it might work.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Feb 01 2018 5:38am

The Lightning Stalker wrote:
Jan 27 2018 9:34am
I don't know if these are new or if I just didn't notice them, but Thunder Power has some 120C stuff right now.
http://www.thunderpowerrc.com/CAR_BATTERIES/Reaper
The specs on these are getting pretty insane now.

Are there any plans for pulse arc capabilities on the kWeld? Of course it would need the proper solenoid tungsten holder. I'm thinking it could be useful for welding ultracaps etc.
The "4800mAh 2-Cell/2S 7.4V Reaper 120C LiPo, Shorty" sounds really promising, they state 1152A max burst discharge. But can someone tell them that Deans/EC3/EC5/Traxxas/XT60 connectors are all hopelessly underrated for a battery that is rated for 576A continuous?
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tatus1969   100 W

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

Post by tatus1969 » Feb 01 2018 5:40am

fechter wrote:
Jan 27 2018 8:18pm
Pulse arc is interesting. I did some experiments using a non-contact electrode and high voltage starter. I've never tried using a solenoid but it might work.
I want to make pulse arc welding experiments with kWeld, as I think that this is well in reach. Maybe it just needs a higher battery voltage.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Feb 03 2018 9:53am

I have received the first batch of laser-cut housing parts for kWeld. Here is a picture of the first build, they will be available in my shop soon. These are much more affordable than 3D printed housings (unless you have a printer yourself), so I stopped the development of those.
kWeld-lasercut-housing.jpg
kWeld-lasercut-housing.jpg (127.22 KiB) Viewed 1958 times
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Re: kWeld - "Next level" DIY battery spot welder

Post by andrew.box » Feb 03 2018 12:10pm

Wow, nice project. If you end up selling boards or kits please say so here. I bet we could get a number of people who'd reserve a board and parts. Also try the DIY power wall forums, those folks love spot welders.

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

Post by tatus1969 » Feb 04 2018 5:43am

andrew.box wrote:
Feb 03 2018 12:10pm
Wow, nice project. If you end up selling boards or kits please say so here. I bet we could get a number of people who'd reserve a board and parts. Also try the DIY power wall forums, those folks love spot welders.
I actually sell them: www.keenlab.de
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Re: kWeld - "Next level" DIY battery spot welder

Post by andrew.box » Feb 05 2018 11:04am

Cool, thanks! I'm currently wasting all my money on a Volt module based battery backup portable inverter project, but I may want to pick one of these up eventually. They look like great quality little spot welders and price is reasonable.

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

Post by okashira » Feb 12 2018 3:55pm

I just ordered one for some testing. :-)
How soon will it ship?
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Feb 13 2018 6:42am

okashira wrote:
Feb 12 2018 3:55pm
I just ordered one for some testing. :-)
How soon will it ship?
Shipping is planned in week 9, but I am not sure if I can keep that because I have trouble with foreign customs at my board assembly service location. I will keep you updated.

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

Post by bigbore » Feb 13 2018 3:11pm

I'm almost ready to turn my Kweld on for the first time. These are the massive 4AWG cables with 10mm diameter brass electrode holders. The electrodes I'm going to try for the first time are made with 3mm copper rode.

Image
Image
Last edited by bigbore on May 09 2018 2:23pm, edited 1 time in total.

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

Post by spinningmagnets » Feb 13 2018 5:59pm

Those electrodes look good!

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

Post by bigbore » Feb 20 2018 9:41am

This is what Kweld looks like with 4AWG cables
Image

I’m very excited to find out what resistance I have after calibration. The length of the cables are the same as per manual with shorter electrodes holders but with this bigger wires I guess I can make them longer.
Last edited by bigbore on May 09 2018 2:24pm, edited 1 time in total.

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

Post by tatus1969 » Feb 21 2018 7:37am

bigbore wrote:
Feb 20 2018 9:41am
This is what Kweld looks like with 4AWG cables
What a monster! :wink:
bigbore wrote:
Feb 20 2018 9:41am
I’m very excited to find out what resistance I have after calibration. The length of the cables are the same as per manual with shorter electrodes holders
That'll probably depends most on your battery, I forgot what type you plan to use? The welder itself accounts for 0.33mOhm (switch path) + 0.78mOhm (fuse path) from terminal to terminal (actual measurement data).

EDIT:
bigbore wrote:
Feb 20 2018 9:41am
but with this bigger wires I guess I can make them longer.
Keep in mind that this also adds inductance, and to dial the total round trip length into the unit if you exceed EDIT: 1 meter.
Last edited by tatus1969 on Feb 21 2018 11:08am, edited 1 time in total.
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Re: kWeld - "Next level" DIY battery spot welder

Post by bigbore » Feb 21 2018 9:36am

tatus1969 wrote:
Feb 21 2018 7:37am
bigbore wrote:
Feb 20 2018 9:41am
I’m very excited to find out what resistance I have after calibration. The length of the cables are the same as per manual with shorter electrodes holders
That'll probably depends most on your battery, I forgot what type you plan to use? The welder itself accounts for 0.33mOhm (switch path) + 0.78mOhm (fuse path) from terminal to terminal (actual measurement data).
I will be using a 3S5P lipo made with very old zippy lipo 5000mAh 40C cells; this one
Image

Then from calibration il will get Ri+Rc1+Rc2+Rc3+Rc4+Rs. Is it correct?
Image

Also could you tell me the total length of both electrode cables you obtain with your electrode holders? I would like to know the length from electrode tip to the center of the ring cable shoe hole.
Last edited by bigbore on May 09 2018 2:25pm, edited 1 time in total.

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

Post by tatus1969 » Feb 21 2018 11:16am

bigbore wrote:
Feb 21 2018 9:36am
I will be using a 3S5P lipo made with very old zippy lipo 5000mAh 40C cells; this one
That looks like it has very low ESR, together with your thick wires you may exceed the 2kA limit. You'll see during calibration, maybe you need to reduce to 2S. Just guessing, anyway.
bigbore wrote:
Feb 21 2018 9:36am
Then from calibration il will get Ri+Rc1+Rc2+Rc3+Rc4+Rs. Is it correct?
Image
No, calibration only measures between the two output terminals of the module, that is Rc3+Rc4. But as Rc1/Rc2 should be extremely low in your case, you can estimate the battery ESR from the current that is displayed, and the other known values.

EDIT: here is the full picture of what I get with the Turnigy nanotech:
(milliOhms | Where measured)
1.87 Probe system, measured between terminal screws
0.33 Power switch, measured between terminal screws
0.78 Fuse, measured between terminal screws
0.19 Battery plus cable, measured between terminal screw and cable end
0.19 Battery minus cable, measured between terminal screw and cable end
3.34 Complete system, measured between kWeld cable ends
4.89 Battery ESR including leads and XT150 connector
bigbore wrote:
Feb 21 2018 9:36am
Also could you tell me the total length of both electrode cables you obtain with your electrode holders? I would like to know the length from electrode tip to the center of the ring cable shoe hole.
It is 0.4m each for both electrode wires, and 0.1m each for the battery wires. The total is 1.0m, not including the lengths through the module, those of the electrode holders and electrodes, and of the wires on the Lipo itself. I wasn't too accurate here, but there is quite some safety margin.
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Feb 21 2018 2:23pm

The listed 3S 130C 5000-mAh Turnigy Nanotech cells seem to be working fine for several builders. However, some potential customers have concerns about using LiPo, so I am investigating what an alternative power supply might look like.

I am currently thinking a hybrid pack that uses four high-current LiFePO4 cells (Headway 38120?), and a 12V capacitor bank. The impedance on the Headway cells is listed at a very low 4-mOhms, peak burst amps are 150A... If using six 2.7V Maxwell super capacitors, they are listed as 3.3-mOhms. [There are recently many 12V super cap banks being marketed right now as a car starter boost unit, to help a car battery on cold mornings]

Frank has mentioned that lower voltages might be slightly better (smaller inductance spikes?), and it is possible to build a power bank made only from six capacitors (one possible configuration is 3S X 2P for 8V). However, then you must find a power supply to keep the 8V Supercap bank charged. Some very large high-amp car battery chargers have a transformer with two coils on the output that can be configured by a simple switch to provide 12V at "X" amps, or 6V at "2X" amps.

We must find the best balance. Higher amps would cause more heat on the unit, but higher volts would cause more inductance? (I am still learning). If using a 4S Headway pack, the 12V car battery charger as a power supply could easily be found locally. However, adding super caps might make the jolts easier on the LiFePO4 cells.

I am open to any suggestions for a LiPo alternative that would work. The current default is to use one large new car lead-acid battery, or possibly two car batteries in parallel (still at 12V, but twice the amps).

edit, just ordered six Maxwell 350 Farad super caps (D cell size), 2.7V each, 3.2-mOhms...

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

Post by bigbore » Feb 22 2018 9:58am

As a LiPo alternative I would like to try a 4S4P made of LifePo4 A123 26650 like these:
http://www.batteryspace.com/A123-System ... 0-mAh.aspx

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

Post by fechter » Feb 22 2018 3:08pm

I tested a 10Ahr, 6s Lithium Titanate pack but it was pretty weak.

The 20Ahr A123 prismatic cells might be something to try.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tomjasz » Feb 23 2018 3:21am

bigbore wrote:
Feb 22 2018 9:58am
As a LiPo alternative I would like to try a 4S4P made of LifePo4 A123 26650 like these:
http://www.batteryspace.com/A123-System ... 0-mAh.aspx
While 12v LA batts are bulky, but I can pick them up for the core charge from battery sellers. When done return for money back. Married to a battery charger tender they last through a lot of welding, cheap.
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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

Post by tatus1969 » Feb 23 2018 9:39am

spinningmagnets wrote:
Feb 21 2018 2:23pm
Frank has mentioned that lower voltages might be slightly better (smaller inductance spikes?)
It's not about the inductive kickback, that only depends on flowing current and conductor inductance (inductance is a pure geometrical/material relation). The reasons why I try to keep the battery (or ultracapacitor) voltage as low as possible are this:
- to get higher voltage, you need add more cells in series, and this also causes their internal resistances to add up. But we ideally want to have a power source with "zero" resistance.
- the welder plus a typical weld spot have a combined resistance in the order of 5 milliOhms. If we want 1000A welding current, this means an ideal power source (no internal resistance) needs to have V = R*I = 0.005Ohms * 1000A = 5V. If that ideal battery would have 10V instead, then we would get too much current, 2000A. We don't want that much current, so in order to get back to the 1000A, we need to add another 5 milliOhm resistance. Like, I = V/R = 10V / (0.005Ohm + 0.005Ohm) = 1000A. But this resistance does not help us, it just dissipates unnecessary heat. Therefore, the rule: as little internal battery resistance as possible, and as little voltage as possible. It's in fact an optimization task.
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Feb 23 2018 10:23am

It's starting to look like the 12V car starter lead-acid battery truly is the best option for someone who does not want to use LiPo.

The 12V style is everywhere, but I recall there are 6V lead-acid starter batteries for older cars and golf carts (perhaps rare, and hard to find though...)

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

Post by tomjasz » Feb 24 2018 2:03am

spinningmagnets wrote:
Feb 23 2018 10:23am
It's starting to look like the 12V car starter lead-acid battery truly is the best option for someone who does not want to use LiPo.

The 12V style is everywhere, but I recall there are 6V lead-acid starter batteries for older cars and golf carts (perhaps rare, and hard to find though...)
Big and heavy, but with a battery tender they re an effective and very inexpensive alternative. I've found a couple of battery resellers. Crown Auto and such, that take batteries in and payout a core charge. I can buy a 12V LA for under $20. T9opping off with distilled water and sometime a bit of battery acid can make for a power source for hundreds of welds. And when they drop off, you can take back and either get the refund or another battery. Not all shops will do that but making good relationships. maybe offering your battery welding skills, can make for an effective barter. I've got a deep cycle marine sealed (troller) battery. It just rocks on and on 640CCA
Thanks Justin_le we're here thanks to you. All the best to the mods for their tireless work keeping it on an even keel.

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