Author Topic: kWeld - "Next level" DIY battery spot welder  (Read 185184 times)

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Offline anishkgt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #275 on: August 30, 2017, 07:55:21 pm »
Oh don't bother 18650 cells. You'd need a lot of them compared to just one lipo.


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Offline plazma

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #276 on: August 30, 2017, 08:35:53 pm »
Oh don't bother 18650 cells. You'd need a lot of them compared to just one lipo.


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18650 cells can have very different chemistries and current ratings. Show me a similar volume LiPo with better current rating than the Sony cell.
 

Offline anishkgt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #277 on: August 30, 2017, 09:01:11 pm »
Well I was talking about the size to capacity ratio. They can have different chemistries but the burst amps is what makes the difference. A lipo is good at it.


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Offline plazma

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #278 on: August 30, 2017, 09:07:28 pm »
Looks like my first message got truncated to half. The Sony cell can give 35A continuous and 100A max. for 6s. A 2s10p pack would give 1000A 7.2V max. I also wrote the cell type Sony US18650VTC5A.
 

Offline SvanGool

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #279 on: August 31, 2017, 12:01:14 am »
Nope I've not tested it to that extreme.  But I can if one can guide me.

You would need a normal large electrolytic capacitor of e.g. 22000uF/16V, like http://www.mouser.com/ProductDetail/Cornell-Dubilier/229TTA016M and a storage oscilloscope to show you a few milliseconds when you connect the power supply you proposed (rating 12V/100A). Connect the oscilloscope to the capacitor and set it to trigger just above 0V and then connect the power-supply to the capacitor (matching polarity of PSU and cap). Do you use thick wiring between PSU and cap.

The picture on the oscilloscope should look similar to this, when your power supply would operate, as desired, for ultra-capacitor usage:



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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #280 on: August 31, 2017, 08:22:39 am »
Nope I've not tested it to that extreme.  But I can if one can guide me.

You would need a normal large electrolytic capacitor of e.g. 22000uF/16V, like http://www.mouser.com/ProductDetail/Cornell-Dubilier/229TTA016M and a storage oscilloscope to show you a few milliseconds when you connect the power supply you proposed (rating 12V/100A). Connect the oscilloscope to the capacitor and set it to trigger just above 0V and then connect the power-supply to the capacitor (matching polarity of PSU and cap). Do you use thick wiring between PSU and cap.

The picture on the oscilloscope should look similar to this, when your power supply would operate, as desired, for ultra-capacitor usage:
I would be surprised if they would have a current limiting circuit. I had ordered one 1kW model yesterday and will check that. But they do have remote voltage sensing, and this can eventually be turned into a constant current supply in combination with a beefy measurement shunt and an opamp circuit.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #281 on: August 31, 2017, 08:25:10 am »
another question: does anyone know how the matching connectors for these are called, and where they can be ordered? I don't want to solder directly to the PSU.

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Offline anishkgt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #282 on: August 31, 2017, 08:27:49 am »
Hard to find the connector for that separately as these are attached to the server itself. You will have to solder it that is how I use them. Maybe you could check with supplier or check with any local IT company for any scrap servers that would fit.


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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #283 on: August 31, 2017, 08:40:22 am »
another question: does anyone know how the matching connectors for these are called, and where they can be ordered? I don't want to solder directly to the PSU.
That will be extremely difficult, perhaps you can measure the pitch between the individual traces (you can see the sliding of the connectors) and buy a standard card edge connector of the right width and remove the pins that are not used or might become a short hazzard.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #284 on: August 31, 2017, 09:00:52 am »
another question: does anyone know how the matching connectors for these are called, and where they can be ordered? I don't want to solder directly to the PSU.
That will be extremely difficult, perhaps you can measure the pitch between the individual traces (you can see the sliding of the connectors) and buy a standard card edge connector of the right width and remove the pins that are not used or might become a short hazzard.
found them, they are using these: https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

these ones are even better: https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545 [EDIT: these have four positions too many...]
« Last Edit: August 31, 2017, 09:35:09 am by tatus1969 »
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #285 on: August 31, 2017, 09:44:01 am »
Looks like my first message got truncated to half. The Sony cell can give 35A continuous and 100A max. for 6s. A 2s10p pack would give 1000A 7.2V max. I also wrote the cell type Sony US18650VTC5A.
I only have incomplete data on these, can you share the information that you have? I didn't know that they should be good for 100A pulse. My experience though is that most Liion cells are optimized for energy density, whereas Lipos are optimized for power density:
US18650VTC5A:                        2.9kW/kg (35A cont, 3.7V, 45g)
Turnigy nanotech 3S/5Ah/130C: 8.1kW/kg (325A cont, 11.1V, 442g)

Afaik, Lipos can currently only be beaten by supercapacitors.
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #286 on: August 31, 2017, 09:54:00 am »
I bought some Sony 18650 cells for my RC car. The specs got me thinking if they would be good for this application. Max. 100A per cell for <6s. 35A max. continuous. The model is Sony US18650VTCA. In a 2s10p setup it would give max. 1000A 7.4V.

100A from a 18650 sounds a bit too high. It's around 40C - many Lipo packs can't even handle that. I couldn't find the datasheet for the model you mentioned, but for US18650VTC5 the maximum discharge seems to be around 20A, or around 8C.
 

Offline plazma

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #287 on: August 31, 2017, 09:57:19 am »
All specs are better with that LiPo. Internal impedance is very low.
 

Offline SirJMD

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #288 on: August 31, 2017, 10:11:41 am »
Looks like my first message got truncated to half. The Sony cell can give 35A continuous and 100A max. for 6s. A 2s10p pack would give 1000A 7.2V max. I also wrote the cell type Sony US18650VTC5A.
I only have incomplete data on these, can you share the information that you have? I didn't know that they should be good for 100A pulse. My experience though is that most Liion cells are optimized for energy density, whereas Lipos are optimized for power density:
US18650VTC5A:                        2.9kW/kg (35A cont, 3.7V, 45g)
Turnigy nanotech 3S/5Ah/130C: 8.1kW/kg (325A cont, 11.1V, 442g)

Afaik, Lipos can currently only be beaten by supercapacitors.

I would be cautious about drawing that high current form li-ion cells. "Fun" things start to happen when the cells get hot.

Good quality 18650 cells can be a bit pricy, so in that regard I think the supercaps are the best option so far, if they can take the beating.
But we would have to include a management system for them, to protect against overcharging.
 

Offline SvanGool

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« Last Edit: August 31, 2017, 10:19:13 am by SvanGool »
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #290 on: August 31, 2017, 11:29:06 am »
Found them, they are using these: https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

these ones are even better: https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545 [EDIT: these have four positions too many...]

Be aware that the TE Standard Edge II card edge connectors have a contact rating of 3A  ???
I would take a look at TE "Crown edge" or "SEC-II".
There are 24 of them in parallel per pole, if load sharing works reasonably well then I am not too concerned.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #291 on: August 31, 2017, 01:08:15 pm »
I have data from a calibrated measurement (3% current accuracy, 3% voltage accuracy):

Setup:         
- kWeld current measurement calibrated with 0.5% shunt resistor         
- probes shorted as shown right (20mm open between holders)         
         
V   A   milliOhms   Where measured
2.72   1452   1.87   Probe system, measured between top of terminal screws
0.472   1451   0.33   Power switch, measured between terminal screws
1.12   1441   0.78   Fuse, measaured between terminal screws
0.272   1441   0.19   Battery plus cable, measured between terminal screw and cable end
0.272   1441   0.19   Battery minus cable, measured between terminal screw and cable end
4.88   1460   3.34   Total system resistance, measured between kWeld cable ends

« Last Edit: August 31, 2017, 05:05:04 pm by tatus1969 »
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Offline tatus1969

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #292 on: August 31, 2017, 05:16:35 pm »
But they do have remote voltage sensing, and this can eventually be turned into a constant current supply in combination with a beefy measurement shunt and an opamp circuit.
just found this thread https://endless-sphere.com/forums/viewtopic.php?f=14&t=47415 :-)
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Offline SvanGool

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #293 on: August 31, 2017, 08:44:30 pm »
But they do have remote voltage sensing, and this can eventually be turned into a constant current supply in combination with a beefy measurement shunt and an opamp circuit.
just found this thread https://endless-sphere.com/forums/viewtopic.php?f=14&t=47415 :-)
I have two DPS-600PB on the way. They can be put in parallel (load sharing) and decreased to 10.8V (which I could not find for other PSUs) for app. 80A. I think I also found a way to solve the potential cc/cv problem by putting a couple of parallel 12V/200W halogen lamps in series between PSUs and caps. Those lamps have a much higher resistance when they are on, which should be enough to start the PSUs.

The mod in the thread you found, only works from 8V up but the supercaps charger should be able to work from 0V up. Maybe a combination is possible by short-circuiting the lamps, by an additional MOSfet, when the voltage reaches 8V. But this is all (or partially) only necessary, when the PSU really switches off, when loaded by a plain supercap bank, let's first test when the goodies arrive :)

Edit: added last paragraph.

« Last Edit: August 31, 2017, 11:44:44 pm by SvanGool »
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #294 on: September 01, 2017, 07:53:23 am »
And so it begins..!

 
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #295 on: September 01, 2017, 04:01:52 pm »
I've got some first results from using Maxwell capacitors. Four of them are enough for 90 joules into a 1 milliohm weld spot. My requirement was 100 joules, and that is not reached yet.

But their ESR is surprisingly low, I measured only 1.5 milliohms per cell, in contrast to the 2.2 milliohm in the datasheet.



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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #296 on: September 01, 2017, 05:40:50 pm »
Does that mean you need five supercaps or is the voltage then too high?

I am doing the crimp on the cables at the moment, first time I used the hydraulic Amp tool from 1983 i inherited from a friend.
But I find the AWG8 cables a bit thin and 1m too short for my electrode holder that needs to move up and down. So just thinking what about car starter / booster cables. They are available in 500A (25mm2), 700A (35mm2) even 1000A (50mm2) and have fully isolated crocodile clamps that can easily be attached to the supercaps and/or powersupply.

Any thoughts?
 

Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #297 on: September 01, 2017, 06:33:20 pm »
I've started testing the kWeld - with sparks going everywhere.

At 50J I burned straight through the nickel strips. At 14.6J I get strong welds but still sparks going everywhere, even though I press down on the electrodes rather hard. Peak current was just over 1400A.

14.6J
6,74ms
1.03 mOhm
1428A

With the calibration it set an offset of 66 and a resistance of 1.95 mOhm.
 

Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #298 on: September 02, 2017, 09:36:14 am »
I've done some more testing and it feels like it shoots much more juice than the setting says.

At just 5 joule I get strong welds where the tabs can only be removed with pliers, with the tabs being ripped apart. At 50 joule it becomes a handheld arc welder.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #299 on: September 02, 2017, 10:19:27 am »
I've started testing the kWeld - with sparks going everywhere.

At 50J I burned straight through the nickel strips. At 14.6J I get strong welds but still sparks going everywhere, even though I press down on the electrodes rather hard. Peak current was just over 1400A.

14.6J
6,74ms
1.03 mOhm
1428A

With the calibration it set an offset of 66 and a resistance of 1.95 mOhm.
What kind of nickel strip do you have, is it 0.1mm? And is it maybe nickel plated steel? (You can test it with a Dremel with cutting disc, if it is pure nickel then you won't see any sparks.)

The numbers are consistent though, as 1428^2 * 1.03e-3 * 6.74e-3 = 14.15J. Current and weld spot resistance are also typical, and if you can verify the pulse time for correctness then I think that the system works as it should.

Does that mean you need five supercaps or is the voltage then too high?
No, the voltage is 10.5V now, which is barely enough for the kWeld to be used without an auxiliary logic supply. I want to use as few capacitors as possible to find the optimum price/performance point. These are 10€ each, and everyone counts :-) I don't consider throwing parts on a problem as good engineering. The kWeld power switch will also receive a detailed evaluation in which I will reduce the number of transistors, and at the same time bring the current to its limits. I tried to simulate these things, but it is difficulty to find a realistic model especially for the inductive kickback. Just modeling the current sharing between diode and MOSFETs is almost impossible, the existing models are not accurate at these current levels.

I am doing the crimp on the cables at the moment, first time I used the hydraulic Amp tool from 1983 i inherited from a friend.
Great  :-+

But I find the AWG8 cables a bit thin and 1m too short for my electrode holder that needs to move up and down. So just thinking what about car starter / booster cables. They are available in 500A (25mm2), 700A (35mm2) even 1000A (50mm2) and have fully isolated crocodile clamps that can easily be attached to the supercaps and/or powersupply.
Have you found time to read the operation manual? I am discussing this topic there. You need to find a tradeoff between cable length and ohmic resistance. There are two limits that may not be exceeded: maximum current, and maximum inductive kickback energy.

The system basically short-circuits a capable power supply, and all that's in the way is the loop resistance. I don't remember how are you going to supply the system?

Edit: just took this picture. kneel down at this beautiful piece of art. The two transformers are just 20x25x25mm each, there are only five output caps, the entire power stage (except PFC and input capacitors) is just 70x60x35mm, and it's rated for 12V / 82A.

« Last Edit: September 02, 2017, 10:40:37 am by tatus1969 »
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