kWeld - "Next level" DIY battery spot welder

Batteries, Chargers, and Battery Management Systems.
Seakane   1 mW

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

Post by Seakane » Apr 27 2020 11:02am

spinningmagnets wrote:
Apr 26 2020 5:50am
I recommend that you try a calibration with a different 12V car battery, and see if you get the same results.
I have not tried another battery for comparison, but it is on my list for today. Thanks for the suggestion.

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tatus1969   1 kW

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

Post by tatus1969 » Apr 27 2020 12:12pm

Seakane wrote:
Apr 27 2020 11:01am
Is it okay that my R value is lower than the manual's range?
Yes, that mistake is actually not with you but the manual. That number is from the previous electrode design and I haven't been able to make up the time to update it. Your result is spot on.
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Re: kWeld - "Next level" DIY battery spot welder

Post by JoelR » Apr 27 2020 3:39pm

I'm up and running with my kWeld using the recommended Turnigy Graphene 5.0Ah 75C https://hobbyking.com/en_us/graphene-50 ... s-75c.html . Results thus far have been absolutely amazing. Now I get it. Wow!! :-)

I've noticed that after a row of 12 welds @50J on .2mm x 8mm nickel strip using the super convenient automatic mode (another wow!) that the probes and leads get pretty warm and so does the battery. I don't have a good feel yet for how warm is too warm and thus time for a cool-down.

Similarly, I see there's an adjustable low voltage alarm for the input battery but I don't know what I should set it to to protect the battery for a long service life.

How do others monitor and care for their LiPo input batteries?

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

Post by SubnetMask » Apr 27 2020 4:53pm

tatus1969 wrote:
Apr 27 2020 6:23am
SubnetMask wrote:
Apr 25 2020 9:46am
@tatus1969, what are your thoughts on Headway LiFePo4 cells and the kWeld?
Yes these are much safer and can be used. You'll need to run the calculations with regards to voltage (should be ~ 10 to 15V) and the pack's internal resistance (~ 3 to 5 milliohms) however, and that's where it becomes tricky. The cell ESR numbers can be unknown, measured poorly, or tweaked for marketing. If you can afford experimenting (starting with low cell count to avoid overcurrent) then there's nothing against that approach. I don't know however how well they can withstand the repeated abuse from being short circuited by the welder, as that could drastically reduce their lifetime.
Just so I'm clear - even though the kWeld can go down to 4v, suggesting that these in a 2s arrangement should work, they would really need to be in a 4s arrangement because the kWeld would actually want the voltage higher than 6v on batteries?


Unrelated to that, just a thought - if you ever do another PCB redesign or adjustment, perhaps move the connector for the foot switch closer to the edge and use a socket like this with this plug to allow easy disconnection of the foot switch while the kWeld is enclosed in the case. With the current setup, if you wanted to remove the foot switch, or if you had the connector jumped for 'permanent' automatic mode, you'd have to take it out of the case to disconnect the foot switch or jumper.

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

Post by eee291 » Apr 28 2020 3:07am

Why would you want to disconnect it anyways? I always roll up mine when I'm done with it. You could also solder a barrel plug inline if you really needed to remove it every time you use the thing.

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

Post by ossivirt » Apr 28 2020 4:38am

I quess it would be neat for storage to disconnect it but since it leaves electrodes and battery leads still hanging there its not that big deal. And making plugs for high power wires is more expensive and reduces performance :roll:

Or you can just make nice box/case for it that has place for welder, pedal etc and has nice foam inside like if you would buy expensive tools 8)

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

Post by garolittle » Apr 28 2020 7:07am

JoelR wrote:
Apr 27 2020 3:39pm
I'm up and running with my kWeld using the recommended Turnigy Graphene 5.0Ah 75C https://hobbyking.com/en_us/graphene-50 ... s-75c.html . Results thus far have been absolutely amazing. Now I get it. Wow!! :-)

I've noticed that after a row of 12 welds @50J on .2mm x 8mm nickel strip using the super convenient automatic mode (another wow!) that the probes and leads get pretty warm and so does the battery. I don't have a good feel yet for how warm is too warm and thus time for a cool-down.

Similarly, I see there's an adjustable low voltage alarm for the input battery but I don't know what I should set it to to protect the battery for a long service life.

How do others monitor and care for their LiPo input batteries?
Exact same questions for me. : - )

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

Post by BVH » Apr 28 2020 10:31am

To reduce the heating up of the battery, parallel a second, identical battery when welding. You can also aim a small fan at the pack when working. It won't help cable heating though. When a Lipo is at 3.7 Volts per cell - resting, not under load, it is down to about 18-20% capacity remaining. Best not to drop below 20%. Depending on how fine you can adjust the alarm, (I have not used it) I'd set it to between 3.7 and 3.73 Volts Per cell. Also, don't leave a Lipo in a fully charged state for any length of time - even over night. It kills them. Best to leave it at "Storage Charge" which is about 3.75 Volts Per Cell when you're not using it.

Hopefully, you're using a balance charger so that all cells stay balanced.

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

Post by tatus1969 » Apr 29 2020 3:57am

JoelR wrote:
Apr 27 2020 3:39pm
leads get pretty warm and so does the battery. I don't have a good feel yet for how warm is too warm and thus time for a cool-down.
Please make sure the battery doesn't exceed 50degC in order not to further reduce its lifetime. In most cases, the necessary cooling periods for the electrodes are enough to ensure that, but it is worth double checking.
JoelR wrote:
Apr 27 2020 3:39pm
Similarly, I see there's an adjustable low voltage alarm for the input battery but I don't know what I should set it to to protect the battery for a long service life.
@BVH, fully agree. But there is a second option - you can set the undercurrent cutoff (menu "MinCurr") such that, as soon as the current drops to lets say 80% nominal, the welder will abort.
SubnetMask wrote:
Apr 27 2020 4:53pm
perhaps move the connector for the foot switch closer to the edge and use a socket
Thanks, and that's on the list among other things for a redesign. At the moment I don't have much time for this, in favor of other projects. I'm working on something big actually, a novelty. :)
SubnetMask wrote:
Apr 27 2020 4:53pm
Just so I'm clear - even though the kWeld can go down to 4v, suggesting that these in a 2s arrangement should work, they would really need to be in a 4s arrangement because the kWeld would actually want the voltage higher than 6v on batteries?
The battery needs to push enough current through the loop, it's literally Ohms law. More voltage means more current for a given resistance. On the other hand, too much voltage requires additional resistance and therefore waste of power. With the stock cabling, a welding pulse typically needs about 5 volts at the kWeld's input terminals, the rest is 'lost' in the battery. That's where the 12V "sweet spot" comes from.
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Re: kWeld - "Next level" DIY battery spot welder

Post by garolittle » May 06 2020 1:20pm

Just received my new Kweld unit and I’m almost ready to start. Has anyone used these Tungsten electrodes from Sunstone? This was the closest size I could get to the 5 mm electrodes that came with the kit. Any feedback is welcome. Thanks
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » May 06 2020 8:19pm

Nothing wrong with tungsten electrodes. Be aware they have a much higher resistance than the copper electrodes, so they will get very hot. The benefit of tungsten is that it has a very high melting point, so if the copper electrodes are sticking to the work, the tungsten will not.

A third option is to buy electrodes that are half-copper and half tungsten. Slightly lower price, too.

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

Post by garolittle » May 06 2020 9:28pm

spinningmagnets wrote:
May 06 2020 8:19pm

A third option is to buy electrodes that are half-copper and half tungsten. Slightly lower price, too.
Did not think of that idea. Makes perfect sense. Do you have a recommended source? I will do some research as well. As always thanks for sharing your knowledge. Gary.

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

Post by SubnetMask » May 07 2020 9:24am

Got my kWeld yesterday and got it all together, just waiting on the power source now.

For the power source, I ordered two Turnigy Nano-tech 5000mAh batteries, with the intent to run them in parallel to reduce the 'abuse' on each battery, but I've read what seem to be conflicting information. I've read posts saying that you can't calibrate it with both attached, but it'll work fine. I've read that a single pack should be around 1300-1500A, so if two only increases by 50%, that's still bringing it real close to the 2000A limit, if not over. And I've seen pictures in a thread that Frank has posted in of the same setup I have/had planned - a Y cable with a XT90 on one end of each for the batteries and the other end of both soldered to a XT150 to power the kWeld. Is running the two packs in parallel going to be OK for the kWeld?

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

Post by garolittle » May 07 2020 10:45am

SubnetMask wrote:
May 07 2020 9:24am
Is running the two packs in parallel going to be OK for the kWeld?
That is what I am going to do this weekend. Will post the results.

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

Post by flippy » May 08 2020 5:43am

SubnetMask wrote:
May 07 2020 9:24am
Got my kWeld yesterday and got it all together, just waiting on the power source now.

For the power source, I ordered two Turnigy Nano-tech 5000mAh batteries, with the intent to run them in parallel to reduce the 'abuse' on each battery, but I've read what seem to be conflicting information. I've read posts saying that you can't calibrate it with both attached, but it'll work fine. I've read that a single pack should be around 1300-1500A, so if two only increases by 50%, that's still bringing it real close to the 2000A limit, if not over. And I've seen pictures in a thread that Frank has posted in of the same setup I have/had planned - a Y cable with a XT90 on one end of each for the batteries and the other end of both soldered to a XT150 to power the kWeld. Is running the two packs in parallel going to be OK for the kWeld?
do not charge the battery beyond 4V, that should keep the amps under 2k.
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Re: kWeld - "Next level" DIY battery spot welder

Post by BVH » May 08 2020 12:57pm

wrong thread

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

Post by tatus1969 » May 11 2020 4:29am

SubnetMask wrote:
May 07 2020 9:24am
For the power source, I ordered two Turnigy Nano-tech 5000mAh batteries, with the intent to run them in parallel to reduce the 'abuse' on each battery, but I've read what seem to be conflicting information. I've read posts saying that you can't calibrate it with both attached, but it'll work fine. I've read that a single pack should be around 1300-1500A, so if two only increases by 50%, that's still bringing it real close to the 2000A limit, if not over. And I've seen pictures in a thread that Frank has posted in of the same setup I have/had planned - a Y cable with a XT90 on one end of each for the batteries and the other end of both soldered to a XT150 to power the kWeld. Is running the two packs in parallel going to be OK for the kWeld?
kWeld has overcurrent protection (2000A), but if the battery is way too strong then it can't react quickly enough anymore. Two of them in parallel will be borderline but may work, but I suggest to start with 50% charge state (reduced voltage). When running at high amperage, make absolutely sure not to extend the cables. The single-battery calibration trick actually works, because it requires directly shorting the probes whereas regular welding has additional resistive material in the path.
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Re: kWeld - "Next level" DIY battery spot welder

Post by garolittle » May 12 2020 9:42pm

Got new Kweld. Awesome machine. Followed setup instructions for calibration but I do not get a resistance reading after pressing the electrodes firmly together and pressing the knob when the “Short” message is displayed. I can feel the pulse but instead of an IR rating it just displays “10J”. Any ideas? Looking forward to using this awesome machine. Thanks. Gary

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

Post by tatus1969 » May 13 2020 3:36am

garolittle wrote:
May 12 2020 9:42pm
Got new Kweld. Awesome machine. Followed setup instructions for calibration but I do not get a resistance reading after pressing the electrodes firmly together and pressing the knob when the “Short” message is displayed. I can feel the pulse but instead of an IR rating it just displays “10J”. Any ideas? Looking forward to using this awesome machine. Thanks. Gary
Can be either an incorrectly wired foot switch (check that you get an 'open' when it is not pressed), or insufficient power from the battery (it aborts calibration with undercurrent when below 800A). In any case, keep the trigger pressed during the steps as described in the manual to get diagnostic data.
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Re: kWeld - "Next level" DIY battery spot welder

Post by SubnetMask » May 13 2020 4:24pm

tatus1969 wrote:
May 11 2020 4:29am
SubnetMask wrote:
May 07 2020 9:24am
For the power source, I ordered two Turnigy Nano-tech 5000mAh batteries, with the intent to run them in parallel to reduce the 'abuse' on each battery, but I've read what seem to be conflicting information. I've read posts saying that you can't calibrate it with both attached, but it'll work fine. I've read that a single pack should be around 1300-1500A, so if two only increases by 50%, that's still bringing it real close to the 2000A limit, if not over. And I've seen pictures in a thread that Frank has posted in of the same setup I have/had planned - a Y cable with a XT90 on one end of each for the batteries and the other end of both soldered to a XT150 to power the kWeld. Is running the two packs in parallel going to be OK for the kWeld?
kWeld has overcurrent protection (2000A), but if the battery is way too strong then it can't react quickly enough anymore. Two of them in parallel will be borderline but may work, but I suggest to start with 50% charge state (reduced voltage). When running at high amperage, make absolutely sure not to extend the cables. The single-battery calibration trick actually works, because it requires directly shorting the probes whereas regular welding has additional resistive material in the path.
Thanks Frank - when you say 'make absolutely sure not to extend the cables', I assume you mean ANY cable, including the inputs? If so, I'm guessing that rather than make a 'Y' (Or really more of a 'V' cable) with two XT90's on one end for the packs and a XT150 pair on the other to join up with the stock cables with the XT150's, I'd be better off creating this cable as short as possible with XT90's on one end for the packs to ring terminals on the other where they join to replace the stock 8AWG cables? In doing so, I assume I should also adjust the cable length in the settings to match whatever the round trip end sup being from the packs to the electrodes and back?

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

Post by garolittle » May 13 2020 7:25pm

tatus1969 wrote:
May 13 2020 3:36am
garolittle wrote:
May 12 2020 9:42pm
Got new Kweld. Awesome machine. Followed setup instructions for calibration but I do not get a resistance reading after pressing the electrodes firmly together and pressing the knob when the “Short” message is displayed. I can feel the pulse but instead of an IR rating it just displays “10J”. Any ideas? Looking forward to using this awesome machine. Thanks. Gary
Can be either an incorrectly wired foot switch (check that you get an 'open' when it is not pressed), or insufficient power from the battery (it aborts calibration with undercurrent when below 800A). In any case, keep the trigger pressed during the steps as described in the manual to get diagnostic data.
Thank you sir. It worked. It was the foot switch. Measured 2.29 milliohms during calibration. Thanks for the response. Gary

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

Post by garolittle » May 13 2020 7:46pm

My question is very similar to subnetmask .... Can I use the XT90 “parallel” connector as shown in the pictures below? I have not plugged in the paralleled battery packs to the Kweld unit yet. Wanted to ask the question before I made the move. :-)
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SubnetMask   1 mW

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

Post by SubnetMask » May 13 2020 8:32pm

My guess is that the XT90 on the leads into the kWeld (as well as the parallel adapter) would have trouble with the current. What gauge wire is used from that XT90 to the kWeld? It's not going to blow up or melt down just plugging it in, but doing welding could result in 'some heat'. My original plan was to use 10ga wire from each XT90 and join the two at a XT150 connector pair that would connect to the stock provided 8ga wires (the battery packs have 10ga wires, so a heavier gauge from each battery to where they join will have minimal benefit if kept short); possible alternate plan would be to join the two at ring terminals right on the kWeld.

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

Post by garolittle » May 13 2020 10:01pm

SubnetMask wrote:
May 13 2020 8:32pm
What gauge wire is used from that XT90 to the kWeld? ... possible alternate plan would be to join the two at ring terminals right on the kWeld.
8AWG Wire used from the XT90 connector leading into the Kweld. Your alternative plan sounds interesting. Really appreciate the comments and ideas.

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

Post by tatus1969 » May 14 2020 3:05am

XT90 is already too weak to carry the current from a single battery (~1400A). In fact, given the ratings of these batteries, both AWG10 and XT90 are not appropriate. Running up to 2000 amps through them will probably cause them to melt -keep in mind: 41% more current results in doubled conduction loss. If you don't want to swap the battery connectors, the best compromise is to run separate cables with ring lugs to the welder.

The 1.0m limitation is important because otherwise you'd need to dial in the extra length into the welder, and it would then reduce its current limit - not good if you intend to run it close to 2000A. All pieces of wire count, although my initial calculations never included the length of the battery cables themselves, nor the bus bars, nor the electrode system. There is some safety margin in the design, and I have made destructive tests at 2800A (this again corresponds to doubled stress). Still, the less stress the better, so every piece of wire that you can shorten is worth it.
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