kWeld - "Next level" DIY battery spot welder

Batteries, Chargers, and Battery Management Systems.
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tatus1969
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Mon Jul 17, 2017 4:32 pm

I wasn't happy with the lifetime of my regular Turnigy 3S/5Ah/50C packs. I know that my usage profile for welding with them was far from daily life duty, I think during my abuse test with the cookie can it was more or less 50% duty cycle at 1kA. I have ruined two packs until they both showed noticable swell. They are still usable, and pulse current is still at 900A, but I am aware that this literally playing with fire, and I wouldn't copying this to anyone.

Hence, I decided to order one of these, and make a test under "realistic" usage conditions for welding:

[edit: incorrect link removed by moderator, correct link listed below]

These are rated at 130C (pulse), which is 650A (!). Let's see what they will deliver in practice.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Mon Jul 17, 2017 4:36 pm

liveforphysics wrote:Nice board and nice idea leveraging the burst current of a hobby pack.
In my limited experience, spot weld quality and repeatability seems to hinge greatly on consistent electrode angle and pressures, as well as surface prep.

The same electrical pulse delivered can make a tidy weld or just burn holes or not make a weld depending on the above mentioned factors.
I didn't really make this observation. Yes, if you don't push firmly enough, then you get a nice fireworks instead of a weld, but whenever this didn't happen in my experiments (one too many...), the welds were quite reproducable. That is still to be confirmed by you guys, but I think the idea of delivering constant energy instead of constant pulse time is probably making quite a difference.
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Mon Jul 17, 2017 5:06 pm

Tatus1969, the battery you linked to is a 6S. You have clearly done a lot of research on every aspect of this. Do you have a preferred charging system for a 6S pack?

Of course, many builders around here already have an RC charger, but I am curious what charging system you like?

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

Post by tatus1969 » Mon Jul 17, 2017 5:15 pm

spinningmagnets wrote:Tatus1969, the battery you linked to is a 6S. You have clearly done a lot of research on every aspect of this. Do you have a preferred charging system for a 6S pack?

Of course, many builders around here already have an RC charger, but I am curious what charging system you like?
oh, I didn't see that. I linked that picture from the 3S product page. Hobbyking apparently didn't take the effort to take more pictures.

To be precise: I purchased this one here.

https://hobbyking.com/en_us/catalog/pro ... tore=en_us

I'm offline-charging them with a SkyRC RS16.
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Mon Jul 17, 2017 7:04 pm

Thanks!

3S it is....

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Re: low cost DIY battery spot welder

Post by sn0wchyld » Mon Jul 17, 2017 9:29 pm

tatus1969 wrote:Most software parts are prepared, the weld control loop already works with 10us cycle time and ADC conversions running with DMA. Really nice microcontroller architecture, you set up everything, and then it will continuously update an array in memory with conversion results.

While waiting for the boards to arrive next week I have machined electrode holders from 6x12x35mm brass. What do you think about it (these are not the final screws yet)?
IMG_20170702_123949.jpg
IMG_20170702_124000.jpg
would it be better if the current path didn't have to go through the relatively thin section of brass that connects the 'wire bolt' section to the 'clamp bolt' section? ie only have the slot cut through the clamp section half way, so only 1 side flexes to pinch rather than both? or alternatively combine the pinch bolts and the wire bolts, so your wire bolt is being held to the flat section of your clamping area?

hope that makes sense...

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

Post by JimFritzMI » Mon Jul 17, 2017 11:09 pm

Two quick questions: 1) Would you consider changing the firmware to allow a dual pulse? There is a significant increase in weld quality from everything I have read and seen. 2) How are you doing the update via usb, I ask because I don't have access to a Windows machine and couldn't justify one for software updates alone. We only run Linux around these parts. LOL

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Re: low cost DIY battery spot welder

Post by tatus1969 » Tue Jul 18, 2017 3:41 am

sn0wchyld wrote: would it be better if the current path didn't have to go through the relatively thin section of brass that connects the 'wire bolt' section to the 'clamp bolt' section? ie only have the slot cut through the clamp section half way, so only 1 side flexes to pinch rather than both? or alternatively combine the pinch bolts and the wire bolts, so your wire bolt is being held to the flat section of your clamping area?

hope that makes sense...
I've read your text several times, but I am afraid I don't fully get it :?
I've extracted the idea to slot the tube on one side only, and will try that first once the last ebayer hopefully will have delivered by this weekend. If that works out regarding plastic strain of the construction, that'll be the best solution. I want to make sure that you don't need pliers or a hammer to replace electrodes.
The cable end will be crimped, not bolted. When that is done properly, you achieve a very reliable cold weld.
JimFritzMI wrote:Two quick questions: 1) Would you consider changing the firmware to allow a dual pulse? There is a significant increase in weld quality from everything I have read and seen. 2) How are you doing the update via usb, I ask because I don't have access to a Windows machine and couldn't justify one for software updates alone. We only run Linux around these parts. LOL
I'm prepared for that, and I want the community decide if that is desirable also with my system. It's just a few lines of code, but I am convinced that my energy control approach does not require that. If all energy goes into the weld spot (and not, for example, the electrode contact), then it should not make a difference if there is corrosion, a bad contact between nickel strip and battery, or whatever. The right amount of energy is always delivered to the right place.

Regarding firmware update: you need a USB to serial converter (3.3V logic level, not RS232 levels!!) and a terminal. The update will use YMODEM protocol, as simple as it can get.
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Re: low cost DIY battery spot welder

Post by sn0wchyld » Tue Jul 18, 2017 5:59 am

hahah yea thought it might not be clear... something like this:
quick holder.JPG
(60.67 KiB) Downloaded 15 times
please excuse the crudeness, just threw it together to make the point

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Re: low cost DIY battery spot welder

Post by tatus1969 » Tue Jul 18, 2017 9:20 am

sn0wchyld wrote:hahah yea thought it might not be clear... something like this:
quick holder.JPG
please excuse the crudeness, just threw it together to make the point
Thanks for that picture, now I can relate your post much better. I thought that it would related to my new holder design in this post: https://endless-sphere.com/forums/viewt ... 0#p1304850

Your picture made clear to me that you relate to the original holder design that I presented in the videos. That is already outdated, there was too much machining involved, and it was to clunky.

BTW: don't undervalue your drawing, it served its purpose well and every boss would reward you for not putting more effort in it than necessary.
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Re: kWeld - "Next level" DIY battery spot welder

Post by parabellum » Tue Jul 18, 2017 12:34 pm

tatus1969 wrote: JimFritzMI wrote:
Two quick questions: 1) Would you consider changing the firmware to allow a dual pulse? There is a significant increase in weld quality from everything I have read and seen. 2) How are you doing the update via usb, I ask because I don't have access to a Windows machine and couldn't justify one for software updates alone. We only run Linux around these parts. LOL


I'm prepared for that, and I want the community decide if that is desirable also with my system. It's just a few lines of code, but I am convinced that my energy control approach does not require that. If all energy goes into the weld spot (and not, for example, the electrode contact), then it should not make a difference if there is corrosion, a bad contact between nickel strip and battery, or whatever. The right amount of energy is always delivered to the right place.

Regarding firmware update: you need a USB to serial converter (3.3V logic level, not RS232 levels!!) and a terminal. The update will use YMODEM protocol, as simple as it can get.
I think, double pulse is only important on timing controlled spot welding to avoid not enough energy passing trough dirty/resistive spot. Kweld is energy controlled and independent of timing, so every weld spot sees same amount of energy passing trough, needed for metal fusing where time frame could vary. Right?

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

Post by tatus1969 » Tue Jul 18, 2017 12:52 pm

parabellum wrote:
tatus1969 wrote: JimFritzMI wrote:
Two quick questions: 1) Would you consider changing the firmware to allow a dual pulse? There is a significant increase in weld quality from everything I have read and seen. 2) How are you doing the update via usb, I ask because I don't have access to a Windows machine and couldn't justify one for software updates alone. We only run Linux around these parts. LOL


I'm prepared for that, and I want the community decide if that is desirable also with my system. It's just a few lines of code, but I am convinced that my energy control approach does not require that. If all energy goes into the weld spot (and not, for example, the electrode contact), then it should not make a difference if there is corrosion, a bad contact between nickel strip and battery, or whatever. The right amount of energy is always delivered to the right place.

Regarding firmware update: you need a USB to serial converter (3.3V logic level, not RS232 levels!!) and a terminal. The update will use YMODEM protocol, as simple as it can get.
I think, double pulse is only important on timing controlled spot welding to avoid not enough energy passing trough dirty/resistive spot. Kweld is energy controlled and independent of timing, so every weld spot sees same amount of energy passing trough, needed for metal fusing where time frame could vary. Right?
That is exactly the idea behind kWeld.
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Tue Jul 18, 2017 3:37 pm

There must be some value to the dual pulse, or it would not be the default method in industry. As I understand it, the very short first pulse burns off any oxidation and preps the two touching surfaces to ensure the precisely-timed main pulse provides a consistent result.

I think it is a concession to allow robots to spot-weld on an assembly line, where there is less scrutiny for the surface finish of each nickel strip that is presented for spot-welding. I don't think there is anything wrong with using a dual-pulse unit, but I have seen many adequate welds that were made with a single pulse. As long as the condition and surface finish of the parts are properly prepared and consistent, I am certain a single-pulse is adequate.

That being said, it sounds like it would not be difficult to modify the firmware to add that function.

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

Post by tatus1969 » Tue Jul 18, 2017 5:27 pm

spinningmagnets wrote:it sounds like it would not be difficult to modify the firmware to add that function.
I am working on the integrated firmware update functionality just right now, that will make these changes very simple. You only need one of these http://www.ebay.de/itm/FT232RL-FTDI-USB ... SwepJXVRoG , an adapter cable that will be available in my store (you can also solder it yourself easily), and a simple terminal program capable of YTERM file transfer.
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Re: kWeld - "Next level" DIY battery spot welder

Post by spinningmagnets » Tue Jul 18, 2017 6:50 pm

We don't even have the first version in our hands, and customers are already demanding upgrades! I hope this doesn't scare tatus1969 away!

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

Post by tatus1969 » Wed Jul 19, 2017 4:31 pm

spinningmagnets wrote:We don't even have the first version in our hands, and customers are already demanding upgrades! I hope this doesn't scare tatus1969 away!
No problem, I'm not frightened :wink: The firmware update functionality is required anyway, also if we wouldn't have this discussion. This is a new product, and I have tested it thoroughly, but I'm also a human.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Thu Jul 20, 2017 9:29 am

All the parts and tools for the new electrode system have arrived now. I will make a first complete build with video, but the first critical question is already answered: does the cable crimp work? See this picture of a cross section :D

Image

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

Post by tatus1969 » Thu Jul 20, 2017 1:19 pm

Here are pictures from the first build of the new electrode arrangement. The clamping mechanism works very well. I have done some welds with it, and it develops less heat than the previous design. I'll keep it like that and this is (or the parts for it) is what will be delivered when ordering it from the shop.

Image

Image

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

Post by parabellum » Thu Jul 20, 2017 2:35 pm

tatus1969 wrote: does the cable crimp work?
Nice cross section result, but what happened just over the crimp neck? Did it crack the tube?

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

Post by tatus1969 » Thu Jul 20, 2017 2:54 pm

parabellum wrote:
tatus1969 wrote: does the cable crimp work?
Nice cross section result, but what happened just over the crimp neck? Did it crack the tube?
I checked again - did I overlook something :shock: but no. This is partly black resisue from the new heavy duty crimp tool, and partly imperfections in the crimp insert's surface structure (a punched part).
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Re: kWeld - "Next level" DIY battery spot welder

Post by rachdatu » Sat Jul 22, 2017 6:53 am

Hello

Very interesting project.

Question: How long is going to last one of these batteries linked in this thread?
Some maths:
5000mAh, 3S, that's 55.5 Wh (5*3*3.7)
In joules: 55.5*3600=199800

Let's assume a 13s4p configuration, that's 52 batteries to weld.
6 welds per batterie on each side (2 layers of Nickel strips, 3 welds per layer).

50 joules per weld, that's a lot anyway.
So, 52*2*6*50=31200 joules for this battery pack.

Therefore, we could theoretically build 6 identical packs (199800/31200)
with one 5000mAh, 3s. Not bad !

Does that make sense?
Thanks

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

Post by tatus1969 » Sat Jul 22, 2017 7:01 am

rachdatu wrote:Hello

Very interesting project.

Question: How long is going to last one of these batteries linked in this thread?
Some maths:
5000mAh, 3S, that's 55.5 Wh (5*3*3.7)
In joules: 55.5*3600=199800

Let's assume a 13s4p configuration, that's 52 batteries to weld.
6 welds per batterie on each side (2 layers of Nickel strips, 3 welds per layer).

50 joules per weld, that's a lot anyway.
So, 52*2*6*50=31200 joules for this battery pack.

Therefore, we could theoretically build 6 identical packs (199800/31200)
with one 5000mAh, 3s. Not bad !

Does that make sense?
Thanks
That's theoretically correct, but the practical figures will be a lot lower. That 5Ah capacity is valid for a certain discharge current that is waaay lower than what we demand from it here. Also, a lot of the energy is lost in places other than the weld spot. The cabling and its joints are a large contributor to this. My guess would be that the energy efficiency of the entire system is not higher than maybe 10%.

You can use the system as a portable device, but it is also possible to charge the battery while operating the welder.

I am about to make a practical test and assemble a 6S2P battery with the welder, but that will not be this weekend because the new Lipo didn't arrive yet. In this test, I will measure the efficiency as well.

For me, the main rationale behind selecting a Lipo battery instead of other possibilities like a car battery or a large capacitor is size and cost. Of course the welder electronisc can also be used with all the others, I have not designed it specifically for Lipo batteries.
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Re: kWeld - "Next level" DIY battery spot welder

Post by tatus1969 » Mon Jul 24, 2017 5:39 pm

A quick progress update on this project:
- production of 25 copies electronic module is progressing well. I had a delay of one week here waiting for the microprocessors from Arrow, but the parcel is now at customs clearance here in Germany (there was some annoyance regarding export control restrictions, I had to calm Mr Trump that I will not be building any rockets from them). The PCBs have been manufactured in the mean time.
- I have completed the firmware update functionality. All that is needed for that is a terminal program that can talk YMODEM (extraPutty and TeraTerm do this job well), an adapter cable (will be added to the shop for a few €), and an Arduino style FT232 USB->UART adapter configured for 3.3V operation (I will also sell them via the shop for convenience).
- I have designed a housing for the welder, see these pictures and please tell me how you like it. I'll upload it so that anyone can print it. I'll not be selling them in my shop, as I don't have a 3D printer.

I still wait for the new battery and some parts to make a video showing the new stuff, hopefully by this weekend :D


Image

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

Post by cheapcookie » Mon Jul 24, 2017 6:54 pm

are you using skethup ? :roll: :roll: :roll: :roll: :evil:

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

Post by tatus1969 » Tue Jul 25, 2017 3:40 am

cheapcookie wrote:are you using skethup ? :roll: :roll: :roll: :roll: :evil:
Yes 8) I know that every construction engineer will facepalm me on that, but I like it very much. This one was completed in one afternoon.
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