kWeld - "Next level" DIY battery spot welder

[ebooosted]

Hello Guys, I'm enjoying my Kweld but also having some issues at the moment, hope some of you experts could point me to the right direction:

When I make the calibration procedure I get the message "Overcurrent" the spot welder does not weld at all if I try to weld after the failer calibration , I was told the current is too high, over 2000A, however I don't know how to fix this. It's important to highlight that I've been using this spot welder for 2 months without issues with the same Graphere 75C LiPo battery.

 

[BVH]

This could be the same issue I posted about just a page or so back. Your Panther can provide over 2000 Amps during calibration so the unit senses overcurrent and fails to complete the calibration process. Without the calibration process being completed and a value stored, the welder will not go into welding mode. It is programmed this way. But once calibrated, you can indeed use this Panther to weld with. So calibrate with a smaller pack and then use the Panther to weld. Maybe you originally calibrated with a different pack and later began using the Panther? This procedure solved my problem. I weld with 2 each, 3S/6000 mAh Panthers but calibrated with a lesser pack. When calibrating with the two Panthers, I'd get 1996 Amps and the overcurrent error. "CAL" would always appear on the screen.

 

[tatus1969]

I'm copying my email response to him here:

"I’m not sure what this could mean. This battery shouldn’t give you more than 1400A. Can you please check if all bus bar bolts are tight? Maybe disassemble it and clean the surfaces.

This could also mean that one of the MOSFETs is blown. Do you have a magnifying glass that you can use to check if there are cracks in their packages? These will often be between the black plastic top and the large metal tab. If that is the case, then I’ll of course take care in terms of a warranty case."

 

[BenjAZ]

I've got two Lipo batteries and I'm not sure if any is good enough to use the the Kweld.

a) 4s (14.8V) 16,000mAh 10C (this would make 160A continuous)
b) 6s (22.2V) 5,800mAh 25C (145A continuous)

Could I use any of this batteries with this spot welder?

Thanks

 

[tatus1969]

a) 4s (14.8V) 16,000mAh 10C (this would make 160A continuous)
b) 6s (22.2V) 5,800mAh 25C (145A continuous)

They are both likely produce enough current, a because of its high capacity, and b because of its high voltage. But this also depends on their brand and age, because of their internal resistance.

I can't really recommend either, because their current ratings aren't high enough. I have made some comparison tests, and Lipos that are too weak tend to either swell quickly, or even have their cell interconnects break. Only the ones that I have linked in the kWeld page on keenlab.de got my approval after these tests. Customers are using other similar models and brands with success, but they all have 300A+ rated current in common.

 

[BenjAZ]

Thanks for your explanation, I'll get one of the recommended lipos and will test with these as a backup.

Thanks

 

[Acido]

I need a power supply for my kCap capacitors, which one do you guys use?
And if you made one can you link the parts used please?

I've been working on a solution for that in the past, but had to pause this in favor of design projects for customers. The kCap power supply project got "lucky" now because a customer needs it as well. I'm very close to making a first series production order and add it to the shop, and have a few prototypes on my desk that I could sell.

I tried powering the welder with a portable car jump starter thats "rated" for 1900A at 12V but it is more 800A, and unusable for welding...
I have 10 battery packs in line waiting for me to fix my welder and people are starting to get a little angry..
If you could sell me one of those chargers to power the capacitors that would be amazing

 

[Acido]

Hello Guys, I'm enjoying my Kweld but also having some issues at the moment, hope some of you experts could point me to the right direction:

When I make the calibration procedure I get the message "Overcurrent" the spot welder does not weld at all if I try to weld after the failer calibration , I was told the current is too high, over 2000A, however I don't know how to fix this. It's important to highlight that I've been using this spot welder for 2 months without issues with the same Graphere 75C LiPo battery.

I used the same lipo and the internal connections broke inside of it and it became useless.
So if it blows your not the only one

 

[tatus1969]

I tried powering the welder with a portable car jump starter thats "rated" for 1900A at 12V but it is more 800A, and unusable for welding...
I have 10 battery packs in line waiting for me to fix my welder and people are starting to get a little angry..
If you could sell me one of those chargers to power the capacitors that would be amazing

I'm still working on the charger. There was a stability problem that required me to contact the manufacturer of a chip that I am using. They couldn't help me for two weeks now, but I managed to find the problem myself a few days ago. New parts to test arrived yesterday, and if they work then I want to offer my (very) limited prototypes to beta testers.

 

[Martin73]

The incorrect cable length settings ("CableLen") on the spot welder might cause the Overcurrent message. The longer the cable is set, the lower amperage is triggering it. I had mine set at 1.2m and it would not pass over 1700 A. I corrected it to 1m and I can pass calibration at 1865 A.

 

[Martin73]

I need a power supply for my kCap capacitors, which one do you guys use?
And if you made one can you link the parts used please?

I use 0-30 V 0-10A regulated power supply UC3010 from Amazon. Works great for me to charge the supercaps back. I'm not doing too many welds though.
I built my own supercap bank using Eaton XV series 400F caps. I was surprised 6s were not giving me enough amperage. I had to use 6s 4p to get over 1800 A when charged to 16.0V.

What amperage are you guys getting with kCap ?

 

[tatus1969]

The incorrect cable length settings ("CableLen") on the spot welder might cause the Overcurrent message. The longer the cable is set, the lower amperage is triggering it. I had mine set at 1.2m and it would not pass over 1700 A. I corrected it to 1m and I can pass calibration at 1865 A.

Please don't do that. This limitation is there on purpose. If you have 1.2m cable, then current above 1700A may damage the welder.

 

[tatus1969]

What amperage are you guys getting with kCap ?

kCap will be around 1100A with kWeld. This is enough for 0.2mm pure nickel, and 0.3mm works but could use more power. It is 3S2P Maxwell BCAP0310, which was the best cost/performance tradeoff that I could find. A 5S2P configuration would deliver 1700A, but the additional caps would make the unit much more expensive so I opted against that.

 

[Martin73]

What amperage are you guys getting with kCap ?

kCap will be around 1100A with kWeld. This is enough for 0.2mm pure nickel, and 0.3mm works but could use more power. It is 3S2P Maxwell BCAP0310, which was the best cost/performance tradeoff that I could find. A 5S2P configuration would deliver 1700A, but the additional caps would make the unit much more expensive so I opted against that.

I made a mistake with the selection of my caps. I cheap-ed out and I didn't realize the importance of ESR in spot welding application. At the end I paid too much for my 24 caps to achieve 1800A.
Today I would go with BCAP0650 which has 0.8mOhm ESR. In your case you could do 3S, which is comparable in price and performance to your selection of 3S2P of BCAP0310 with 2.2 mOhm.

 

[specing]

Being the cheapskate that I am, I am now wondering why you people (kWeld, malectrics,..) use bus bars? They are an unnecessary cost when you can just take a thick stranded cable, peel 10 cm off of it and distribute the strands evenly to each MOSFET. This also gets rid of connector crimping and the added resistance there. Btw: A few days ago I was scouring random tech shops and I saw that circuit breaker mounts could be suitable to mount the mosfets (though the openings have a ~5mm inner diameter).

 

[spinningmagnets]

Distributing the thick stranded cable to each mosfet requires a certain amount of hand-work, and I'm not entirely sure of how that could be done. If that was a requirement for assembling this kit, then I suspect that many customers would be reluctant to order it, since the "ease of assembly" has frequently been stated as a feature that encouraged them to actually purchase it.

Placing an order for bus bars is as simple as clicking an option from a supplier, in order to add them to a kits. For the customer/assembler, it is but a moment's work to bolt them down onto the provided traces. There has been feedback from customers over the past year or so, and as a result, we now find ourselves at the version-4, however...the cost of the bus bars has not been an issue so far.

If you wish to purchase a kit without the bus bars (and you intend to add some fat stranded cable in the appropriate places), I am sure that you can contact the retailer and work out a price that deducts the wholesale cost of the bus bars.

 

[Merlin]

btw: building a highpower battery with 40T right now.
0.3 nickel. i have a 65C Graphene 6000mAh Lipo as Power source.

XT90 melted now. 5-6 welds and you cant touch your probes
took a fan to cool down everything. but melted anyway.

after replacing to XT150 i stepped up from 1350a to 1650a and got better welds.
but damn ....0.3 nickel isnt the best idea =)

 

[spinningmagnets]

I agree, I have read of builders using a double layer of 0.20mm, and were disappointed, rather than having twice the current capability.

The parallel strings can be connected by just about anything, and I am of the opinion that the higher the resistance, the better...to slow any current between the cells as they continuously equalize. All of the cells in a parallel string need to stay balanced against each other, but a 4mm narrow slice of 0.15mm thick nickel ribbon is more than enough IMHO.

Also, instead of forcing the current to go through a parallel strip to get to the series strip is a weak design. It adds unnecessary resistance. The series strips need to be bonded to the cells first to make sure the series current has the lowest resistance.

If the 0.20mm thick ribbon is not quite enough for the series current for your pack, I recommend bonding some copper to the nickel ribbon before you spot-weld it onto the cells, for the series current.

 

[tatus1969]

why you people (kWeld, malectrics,..) use bus bars?

The soft fact: I wanted to design kWeld such that everybody can assemble it - no soldering involved.
The hard fact: the bus bars are part of the current measurement circuit that kWeld needs for energy metering. A soldered wire would have varying ohmic resistance from copy to copy.

 

[tatus1969]

after replacing to XT150 i stepped up from 1350a to 1650a and got better welds.
but damn ....0.3 nickel isnt the best idea =)

Keep watching battery temps regularly, I recommend to not exceed 50degC.

 

[Taswegian]

Is there any merit in minimizing the length of the battery cables? (AWG10)

I will be replacing the XT90 with XT150 anyway so its no more work to cut them shorter.

Edit - I suppose going too short might risk too much heat conducting into the battery while soldering the XT150, not sure if this is an issue or if it is how short is too short.

 

[specing]

Heh. When I see "DIY" on something, I immidiately expect Velleman-style DIY where you are given a bag (box) of parts and wished good luck. Anyway, I did look for bus bars on Arrow, but the search comes up with either circuit breaker mounts or 1m long rods for >25 eur like https://www.arrow.com/en/products/210-133/wago-kontakttechnik-gmbh. I guess if you cut them up it comes to 5 eur per board and I'm left with 80 cm of useless bus bar


Okay. I'm probably going to write my own software and use simple timing at first.

Is there a thread for the malectrics's welder? I assembled an Arrow BOM for it at 16 eur https://octopart.com/bom-tool/S3bA133s comments welcome. (Well, that 16 eur does not include a foot switch, uart-to-usb instead of trimmer and display, battery clamps, thick wire, a stm32f072 devkit and a chinese perfboard to carry it all )

I picked the IRFB7437PBF fets because they are far cheaper at about 1 eur each (-60%), but offer half the avalanche energy ruggedness. The TVS diodes "should" protect them.

 

[spinningmagnets]

I have some nickel-plated copper wire (16-ga) that I can use to provide free samples for spot-welding tests

When comparing 16-ga round wire to flat ribbon, a slightly smaller size 17-ga is equal to 7mm wide X 0.15mm thick ribbon. However, copper is 4 times more conductive, compared to pure nickel.

Edit, the wire turned out to be stranded, each strand is .010-inch, or 0.025mm

 

[tatus1969]

Is there any merit in minimizing the length of the battery cables? (AWG10)

Yes and no: replacing them with 8AWG would help a lot (I was in fact discussing with battery manufacturers if they would be willing to make these - no). But the setup will always have a weakest spot (no pun intented 8)), and you don't want this to be the battery cells (or cell links).

 

[krebacz]

Hi,
What’s the wait time now? I’ve just ordered (#6151) and am wondering when I’ll get to play with this beauty thanks...