kWeld - "Next level" DIY battery spot welder

[tatus1969]

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.

[tatus1969]

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.

[anishkgt]

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.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D

[Kjelt]

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.

[tatus1969]

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...]

[tatus1969]

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.

[SirJMD]

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.

[plazma]

All specs are better with that LiPo. Internal impedance is very low.

[SirJMD]

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.

[SvanGool]

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".

[tatus1969]

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.

[tatus1969]

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

[tatus1969]

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 :-)

[SvanGool]

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.

[SirJMD]

And so it begins..!

[tatus1969]

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.

[Kjelt]

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?

[SirJMD]

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.

[SirJMD]

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.

[tatus1969]

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.

[Fraser]

I purchased a Turnigy 5000mAh LiPo pack this week. I also purchased the pretty much essential Turnigy fire containment bag in which the LiPo will live.

For me, I thought it would be nice to have the large 15Ah or 36Ah Pb Gel 12V battery for static use in the lab, but also to have the option for more mobile use using the LiPo battery option. Occasional use will hopefully not stress it too much.
O
Whilst I understand the desire to develop this welder to meet many different needs, I would like to avoid the situation lampooned with early LED digital watches in many cartoons...... that is to say, the nice compact watch on your wrist and the huge power source pulled along behind you on a cart !  In my world, small is beautiful The super capacitors seem pretty compact these days but it appears the demands for charging them quickly lead to a quite bulky power supply. Batteries charge more slowly so no need for a large PSU, yet they have large capacity to keep delivering current pulses via the kWeld before needing a recharge. In 'amateur' use this seems desirable.

Fraser

The kWeld is a very neat and compact welder solution that can operate away from utility mains. This is wonderful for portable use away from the lab, or just where you do not want a bulky mains power supply.

IMHO, the beauty of the kWeld design is that it is a well formed 'welding core' , a bit like the thermal imaging 'core' format with which I am more familiar. It may be integrated into a welding system that suits each user. A superb option for those of us who wish to customise and experiment

Good luck with the development of the supercapacitor solution, I hope that it provides decent performance whilst not making the welder unwieldy or oversize. It is great to read of your experimentation though as I have no practical knowledge of the modern supercapacitors being discussed here.

If it is not too rude a question, why are people so keen to use the supercapacitors instead of battery power sources ? Lower ESR ? Higher current tolerance ? , it certainly isn't low cost

Best Wishes to all my fellow kWeld owners and especially to Frank, the father of the kWeld 

[Kjelt]

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?

Ah ok clear I thought it was about the output cables.
It is hard for me to measure such low resistances even with a 4 wire multimeter.

What I intend to do now is to use the 1meter 8awg you supplied only for the output wiring (2x50cm) to the electrodes and use a 16mm² cables from a carstartercable set I just bought to the input with clamps attached. That way I can power the kWeld with a carbattery or supercaps or whatever by just clamping it up instead of using connectors.

At the moment I have no powersource which can provide 1500A.
The labsupply is "only" 70Amps and needs more rework than thought (it was rewired by the previous owner to get out of spec) so that will be something I am going to do the coming week.

I am awaiting the trials and errors you are conducting to buy the correct number and type of supercapacitors.
I do have a small leadbattery I could use for just testing if the kWeld works but that will not suplly enough current just a test to see the system powers up and works. I could also use the powersupply as it is now and test it (it will short the caps of the supply and not have enough current but for a test I know that everything works).

Last but not least the kWeld gets a standard boxhousing with transparent lid but mechanical work will also take time.

[Fraser]

I bought a couple of LiPo cell monitors and balancing units for my kWeld battery. They are cheap but effective for keeping an eye on the state of the LiPo before, during and after use  Useful little gadgets.

One has a large display and several useful functions whilst the other has fewer functions but shows all cell voltages on the same screen for easy monitoring. The cell balancer is also a useful facility to have.

I recommend one of these for those users electing to operate from a LiPo battery pack as they have a low voltage warning alarm that may be set to your needs per cell. There are plenty available on eBay.

Fraser

[anishkgt]

 and these are more common.

http://www.ebay.com/itm/RC-Lipo-Battery-Low-Voltage-Alarm-1S-8S-Buzzer-Indicator-Checker-Tester-LED-Best-/282397825614?hash=item41c038da4e:g:7bUAAOSw14xWKh-Q
Small and has an audible alert when a desired voltage has occurred. The buzzers can be replaced with a relay and wire it up to cut-off the load when the pre set voltage has reached.

[Fraser]

Indeed, there are many versions around and most are very cheap.

When effectively abusing a 3S LiPo battery it seems a very good idea to keep an eye on its cell balance and general health

My only concern with a "cut-out' circuit using one of these is whether the cut-out would trigger during the very high current draw of the welding operation ? You could end up with spurious and annoying 'trips' of the welder.

Fraser