kWeld - "Next level" DIY battery spot welder

[tatus1969]

is there a current limit

yes, 500mA as stated in the manual :-)

[dmxlights]

is there a current limit

yes, 500mA as stated in the manual :-)

I missed that bit 

Thank you for your quick replies Frank.

[dmxlights]

Hi Frank,

I was have a problem with my bench power supply current limiter cutting the supply.

I was reading the Kcap manual to find the model of the server power supply you use and then seen you listed a Meanwell power supply, which got me thinking. I have one which is a 12v @29A. I have check it to see what is the lowest it will go to which is about 9.5v-10v. I know that the kcap board will with 8.1v to 14v. I have set my meanwell power supply to about 11v and is working well. I have notice also the balancer led is on when the cap fist charge after switching on and once I do one weld it goes out and stays out. I did not notice when I was using the bench power supply.

[CM800]

Trying hard for an excuse to add one of these to my collection of toys (kweld+ kcap+ ksupply)

Have you done much wire to sheet or wire to pin bonding with this? What is the limit to the smallest thing you have welded reliably with this?

[tatus1969]

I was have a problem with my bench power supply current limiter cutting the supply.

What kind of problem?

I have set my meanwell power supply to about 11v and is working well.

Perfectly okay. But is this a current limiting type Meanwell? Hickup limiting models (most of them are) are not suitable.

I have notice also the balancer led is on when the cap fist charge after switching on and once I do one weld it goes out and stays out. I did not notice when I was using the bench power supply.

That's okay and their job :-)

Have you done much wire to sheet or wire to pin bonding with this? What is the limit to the smallest thing you have welded reliably with this?

Not self, but a number of users are doing that with the welder. Not sure though in which forum that was reported, could be either here or
https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039
https://forum.esk8.news/t/kweld-spot-welder/6926

[dmxlights]

I was have a problem with my bench power supply current limiter cutting the supply.

What kind of problem?

The power supply is a 25a and I think the current limiter has a fault which is cutting the supply straight when I switch it one with the cap board connected. I have just done a test if I power up the power supply first with out the cap board connected and ten turn it off and connect the cap board and switch it on its ok.

I have set my meanwell power supply to about 11v and is working well.

Perfectly okay. But is this a current limiting type Meanwell? Hickup limiting models (most of them are) are not suitable.

What do you mean by Hickup. The model of the Meanwell I have is NES-350-12. I seem to have no problems with it as I can power it on with the cap board connected.

I have notice also the balancer led is on when the cap fist charge after switching on and once I do one weld it goes out and stays out. I did not notice when I was using the bench power supply.

That's okay and their job :-)

Good to know it ok

[tatus1969]

The power supply is a 25a and I think the current limiter has a fault which is cutting the supply straight when I switch it one with the cap board connected. I have just done a test if I power up the power supply first with out the cap board connected and ten turn it off and connect the cap board and switch it on its ok.

Yes, sounds like a problem with the current limiter starting up into a dead short (like the empty kCap is).

What do you mean by Hickup. The model of the Meanwell I have is NES-350-12. I seem to have no problems with it as I can power it on with the cap board connected.

That's what 'normal' power supplies do when being presented with an overcurrent at their output. They turn off, wait, then retry. Your model is the other, current limiting type (datasheet -> protection -> overload -> protection type).

[dmxlights]

The power supply is a 25a and I think the current limiter has a fault which is cutting the supply straight when I switch it one with the cap board connected. I have just done a test if I power up the power supply first with out the cap board connected and ten turn it off and connect the cap board and switch it on its ok.

Yes, sounds like a problem with the current limiter starting up into a dead short (like the empty kCap is).

What do you mean by Hickup. The model of the Meanwell I have is NES-350-12. I seem to have no problems with it as I can power it on with the cap board connected.

That's what 'normal' power supplies do when being presented with an overcurrent at their output. They turn off, wait, then retry. Your model is the other, current limiting type (datasheet -> protection -> overload -> protection type).

Thank you Frank for your quick replies and I am going to build a case now for the meanwell and kcap and the Kweld boards so it an all in one case and it will be nice and neat.

The other thing I am sorry I did not buy the kweld and Kcap sooner

Thank you Frank for your replies and for making your kweld and other designs available for us to buy.

[muvideo]

Hello,
after 3 months finally I was able to start building and testing kweld.
I bought the 650F maxwell supercaps with round studs for power supply and now I'm verifying if my build is workable.
The power supply consists of 4 of these supercaps in series, they are connected trough aluminium plates with holes
tight enough to be interference coupled with studs. I heated them and pressed on studs while hot.
[attach=2]
[attach=1]
For balancing the caps I rushed simple discrete circuits, testing them and are workin ok for now.
Super cheap all around, I tried to use what I had around.
[attach=3]
Total voltage is about 8.9V, balancers keep the capacitors to slighly more than 2.2V.

Cal result is giving 1426A and 1.99mOhm, is this what I should expect or I'm leaving too much resistance around?
Now caps are connected directly to kweld but I need to easily disconnect them.
What connector should I use between kcap and power supply?
I've seen XT150 [attach=4] or EC8 [attach=5] around, are them any good?

Edited: add images

[tatus1969]

@muvideo, awesome and thanks for sharing. Heat shrinking the busbars is an option that I hadn't thought of. I'd give the caps more voltage however, they are rated at 2.7V and that will help push the current further. The numbers you get is what I had estimated. EC8 and XT150 should be comparable, but either case you'll need to accept a bit of current loss.

[wizard69]

HI Guys & gals;

I've just started reading this thread from page one to 19 or so and frankly need to take a break.   However I have some questions.

• The abbreviation "MOT" comes up a  lot.   It appears this relate to a transformer based power source, but "MOT" is not ringing a bell, so are there any hints to what this means.
• I'd be very reluctant to implement the Lithium Polymer battery solution as I have no faith in the safety of those batteries in this sort of use.   However why not use the batteries to charge some capacitors and then split the current draw between them?   Or some variant of that with the goal of keeping battery current much lower.
• On the stationary capacitor based implementation would not a simple electronic switch be enough to separate the charging power supply from the capacitor bank during discharge?   I'm thinking simple here to keep complexity down.

The only type of captive discharge welder I have had experience with was one designed for thermocouple welding.    Power there was controlled by a simple pot that I imagine was adjusting the charge voltage on the cap.    that is an assumption on my part because I've never actually taken the welder apart, but it behaves like an SCR based capacities discharge welder.  This seemed to work really well for what that device was doing and had good control over the power delivered to the weld.

As for other types of welding , the one thing I learned there is that there are many many variables!!!   It can be rather hard controlling for all of them but in all cases cleaning is godly.   As such one thing everybody should consider is a good wipe down of the surfaces to be welded.

[tatus1969]

The abbreviation "MOT" comes up a  lot.   It appears this relate to a transformer based power source, but "MOT" is not ringing a bell, so are there any hints to what this means.

Microwave oven transformer. If you want to go through the hassle of disassembling and rewinding one of those. That's how the Sunkko devices work.

I'd be very reluctant to implement the Lithium Polymer battery solution as I have no faith in the safety of those batteries in this sort of use.   However why not use the batteries to charge some capacitors and then split the current draw between them?   Or some variant of that with the goal of keeping battery current much lower.

Can be done, but raises the question of how to connect a charged battery to an empty ultracaps, without putting it on fire from the huge current surge. You'd need some kind of resistor+relay precharge solution, but other than that this approach is viable. I went a different route - my kCap module is strong enough to deliver enough current on its own.

On the stationary capacitor based implementation would not a simple electronic switch be enough to separate the charging power supply from the capacitor bank during discharge?   I'm thinking simple here to keep complexity down.

That's exactly what kCap does, and I've also added a diode to prevent backfeeding into the supply. Although 'simple electronic switch' isn't exactly the right wording when dealing with 70 amperes of charging current.

The only type of captive discharge welder I have had experience with was one designed for thermocouple welding.    Power there was controlled by a simple pot that I imagine was adjusting the charge voltage on the cap.

That's the standard approach, but kWeld works differently: it measures the amount of energy put into the weld spot, and terminates when the set goal is reached. This makes the welds much more repeatable as it accounts for process variations.

For capacitors, that would not be as important as their stored energy is more or less equivalent to the energy dumped into the spot, but there is another problem: ultracaps that have a low enough ESR to deliver enough current also have a lot of capacitance. You don't want to use very high voltage (to overcome higher ESR), as that also increases the risk of arcing (kWeld has protection against this as well). Using the high capacitance caps at very low voltages, in contrast, would introduce too much variation from changing spot resistance.

[wizard69]

Microwave oven transformer. If you want to go through the hassle of disassembling and rewinding one of those. That's how the Sunkko devices work.

Thanks for that one!!!!   After 19 pages I didn't get the connection so to speak.

Also thanks for the rest of the response.   Looks like I have another 10 or more pages to read, you have one very interesting spot welder here.

[bobmutch]

tatus1969


Hi Frank, love the changes to the kCap V2, you product is tops. I bought a used kWeld and it is an above the crowd product!

We were having a discussion over in Keith's FB group about whether a 4S or 8S battery pack that has the same CDR in amps will produce the best welds.

So 4S or 8S of 3.2Vn LFP cells that have 360A CDR and 720A burst (the same as your recommended LiPo 3S 6Ah 60/130A pack). Will they product the same quality weld if set up optimally on the kWeld?

You show your range for the kWeld input as 4V to 30V and the ideal range as 5V to 15V. Is this ideal range have to do with efficiency of the kWeld or is it related to weld quality?

We discussed this before and you noted as the battery is discharged and the SOC hits ~40% the weld time will be longer to get the same Joules there will be less amps and hence less heat and the weld will be of poorer quality *IF* the Joules setting was originally set up optimally for a specific weld, when the battery was fully charged. Is that correct?"

thanks bobmutch

[pcmeiners]

Just purchase a KWeld. Plan on using 20 Maxwell BCAP0100 P270 T07 100F 2.7 capacitors in a 5s4p (balanced) setup which I could knock down in size if necessary. I figure the 5S will give 13volts, and the 4P, will provide low resistance. Each series set of caps will have it's own board, so I have leeway on how I mount them in a box. Also I ordered 6 gauge, bare copper,very high strand silicone cable, again due to keeping resistance low,  I also want to increase the cable length possibly to 4 feet.
At this point I could easily have a 4S or 3S and P1-P4 . I could vary the charge I give the caps, keeping the caps at lower or much lower than 13 volts. IAlong with this I have copper washers and my have access to copper bolts

As to the cable I really did not want 2680 strand cable, would have preferred half that strand count as it still would be quite flexible; there were more choice with tinned copper much fewer with bare copper. With the number of strands I worried about oxidation, so once I get the cable together I will seal the connects with liquid tape and water tight shrink tubing.
Frank I see you have used 6 ga, cable , I was wondering about that, I like the Teflon guards.
Aside from being careful initially bring up the power via the KWeld control is there anything inheritably wrong with the above, other than if I should create a dead short without flash gear ? 


Thanks for reading

[tatus1969]

Hi Frank, love the changes to the kCap V2, you product is tops. I bought a used kWeld and it is an above the crowd product!

We were having a discussion over in Keith's FB group about whether a 4S or 8S battery pack that has the same CDR in amps will produce the best welds.

Sorry, I must have missed the notification on this, just seeing it now.

Thanks for the Kudos :-)

The optimal voltage is given when it is enough to push the required current through the combined electrical resistances. The welder and its cabling contributes roughly 3.2 milliohms, and a typical weld spot has 1 milliohm. For 1500A of current, this would require 6.3 volts at the welder's input terminals. All extra voltage must be 'lost' by the battery's internal resistance. This is why I recommend 3S, which leaves enough headroom for this. This also means that a battery with higher voltage *must* have a higher internal resistance, in order to stay at the same current level. This again means that it will dissipate more power and heat up more.

is there anything inheritably wrong with the above

Sounds perfect to me! Just make sure not to overshoot in terms of current. You can easily achieve this by starting with lower charge voltage on the caps. And keep the leads between caps and welder as short as possible (-> inductive kickback).

[pcmeiners]

Thank for the reply...

Kit was just delivered. Have a Sorenson lab supply so I can dial in the voltage for now, will
keep it low, hopefully there are no issues with it, it did work with my 2F electrolytic cap bank
Is 3 feet # 6 gauge on the welding leads OK, or should they be shorter,  ?, purposely ordered the 6 gauge so I could gain a little length on the electrode leads, will the extra length cut down on the power at the weld.   Not well versed on electronics. Just tried the Shonsin 6 gauge wire, looks like I can get it into to the electrodes, most excellent.


Thanks
Paul Meiners

[tatus1969]

Is 3 feet # 6 gauge on the welding leads OK, or should they be shorter

The stock system deliberately uses only 10cm long leads to the battery. Just check out the kWeld operating manual, that has a section that discusses this topic -> inductive kickback. Keep in mind that AWG size doesn't matter here, it is all about the total length of the leads that carry current.

[pcmeiners]

Will check out the manual thanks. Mis-read the links
Computer IT people have a gene which hinders reading manuals until frustration sets in. 

To Ultracap users, check out the voltage charge/temperature versus the lifetime of ultracaps….

https://www.capcomp.de/en/capacitors/ultracap-lifetime.html

[mtj1982]

Hi. Great thread and lots of informative stuff.

I have decided to go with the kweld for my hobby projects. Im building a lawnmower battery pack by reusing the old bms from the the old battery. I will also build myself a battery for a coming ebike project.

Im ordering the kweld spotwelder and the ultracapacitor bank. I have 2 new and unused DPS-1200FB power supplies. Would there be any advantage of combining those two in parallel to provide up to 200A to the capacitor bank? I was thinking of also get ting the ksupply to keep things safe. I READ in this thread that it is  possible to modify some of the connectors on the ksupply to fit the DPS-1200FB and avoid shorting it out.

Hope to hear from someone
Martin all the way from Copenhagen, Denmark

[tatus1969]

I have 2 new and unused DPS-1200FB power supplies. Would there be any advantage of combining those two in parallel to provide up to 200A to the capacitor bank?

Keep in mind that the capacitors need a charger that limits the current, any of these PSU's will just see a dead short and shut down when you'd directly connected the empty cap. kSupply delivers up to 70 amperes, so it doesn't make sense to provide more power than necessary. And the current kCap design also has a (MOSFET based) disconnect switch that is limited to this amount of current.

[pcmeiners]

For anyone interest in a Fujitsu DPS-800GB-3, as the edge card fingers match what is needed for the Ksupply. I order a couple of these, the seller designates these as "used" but they are new, as the edge card was never inserted into a machine (no scuffs). If you buy truly used you get dust, and well used fans, even reconditioned,  not worth it if you can find something cheaper. PIA to order fans, no less cost/shipping.

https://www.ebay.com/itm/GENUINE-DPS-800GB-3-FUJITSU-800W-SWITCHING-POWER-SUPPLY-UNIT-/264344561203

[mtj1982]

Thanks for the reply.

I found this battery online in stock with Hobbyking. Do you think it would work with the kweld as a mobile/transportable setup next to the stationary workbench setup psu > ksupply > kcap > kweld? In that case would I need to hookup the battery to the ksupply > kcap > kweld or directly to the kweld? The battery specs are as follows:

Features:
• ROAR approved
• Precision matched cells
• Capable of up to 140C discharge rate
• Low internal resistance
• Longer cycle life
• Turnigy quality
• High energy density (lightweight and high capacity)

Specs:
Capacity: 5500mAh
Configuration: 3S2P / 11.1V / 3Cell
Constant Discharge: Up to 140C
Pack Weight: 416g
Pack Size: 139 x 47 x 37mm
Discharge Connector: XT90
Balance Connector: JST-XH-4P
Discharge Cable: 12AWG

Included:
1 x 5500mAh 3S2P (11.1V) hardcase lipo pack
https://hobbyking.com/en_us/turnigy-rapid-5500mah-3s2p-140c-hardcase-lipo-battery-pack-w-xt60-connector-roar-approved.html

[pcmeiners]

I would like to mount the Kweld and other components in a large metal case, with the Kweld mounted flush with the front panel . I know I would have to extend the control knob and the LCD screen, and likely shield the LCD area. What would I look for if I want to extend the LCD so I can panel mount it (likely 1") , what is the LCD and socket referred to as .

Thanks

[multifrag]

Hello tatus1969,

I've ordered the kweld with the kcap module. I'm planning on charging the caps with my 60v 5A bench power supply through a murata rbq-8.2/45-d48 isolated DC-DC converter to use as much of available power as possible. Do you think that is a good alternative?