6pence Resistance Spot Welder

Place for dealers to post items for sale.
User avatar
pguk   100 W

100 W
Posts: 107
Joined: Mar 16 2012 4:30pm
Location: North England, birthplace of the Industrial Revolution

Re: 6pence Resistance Spot Welder

Post by pguk » Jan 25 2017 1:47pm

Use of EEPROM I think would be the main step change from how I have it working at present. The ability to store last used settings and reload the same on power up. Users report my own experience which is that it takes a little while - a few practice welds - to arrive at a place where you're happy to get going on the pack. Once you have settings which work well, these will change little as long as the setup is the same. If you go to thicker nickel or perhaps brass or copper, or change the weld current source, then settings will change significantly.

Long button press to give fast scrolling value would be great. Especially if the device were to prove useful in driving an MOT style welder down the line where longer times may be required.

Also important, from an operators point of view, is to keep the ability to tweak parameter values 'on the fly', without having to switch out to 'configuration mode' involving too much pushing of buttons.
6pence spot welder https://endless-sphere.com/forums/viewt ... 31&t=81274
"It is all nice and proper, but only an idiot would think that the father is sixpence to the good on the transaction." C.S. Lewis' Mere christianity

Valld   10 mW

10 mW
Posts: 23
Joined: Dec 06 2016 8:03am

Re: 6pence Resistance Spot Welder

Post by Valld » Jan 26 2017 2:42pm

Hi guys,

Time for me to share my experience with the 6pence spot welder. Below are a few photos that speak more than words, so I will try to be as short as possible.

Let me start with special thanks to Paul who was very helpful and assisted me big time with building the power board. The control board arrived relatively quickly in less than a month from UK well packed and I didn't pay any tax.
IMG_20170119_101701.jpg
homemade power board front, all elements sourced from aliexpress
IMG_20170119_101715.jpg
back side, beefy 3 watts resistors, only ones I could get locally
IMG_20170125_211926.jpg
general view of my setup, no box yet
IMG_20170125_211945.jpg
closer view
IMG_20170125_212007.jpg
No copper wire in Botswana, electrodes homemade from 2mm thick copper sheet (same as the drain and souce sides of the power board) hammered into the cable and crimped with modified cable lug
The welder works beautifully from the first moment. Only have 0.15mm pure nickel strip. I did play with the pulse times and the difference is noticeable, but even with 1-1-5 (default settings) I'm getting strong and nice weld. On 2-1-15 I'm able to weld 3 strips together.

I live in Botswana, it's a country with very small population (2 million) and non-existent market for electronic components, so I had to order all the parts for the control board from Aliexpress. I have no idea if the MOSFET's and diodes are genuine, but the welder works. What surprised me most is that I didn't blue up the FET's after soldering them to the thick copper bar with my 60 Watts soldering iron. It took well over a minute to heat the bar and another 30 seconds to properly flow the solder around every FET. The board looks ugly, but I'm happy how it works.

The only problem I had was last night. I connected the two battery terminals of the welder, then turned on the power to the control board and the display didn't lit up. About two seconds after that I heard a pop. Immediately disconnected everything and found that the schotkky diode blue up and separate in two parts. Turned back on the control board and it started properly. Changed the diode, plugged in everything back and it worked like nothing happened.....

I'm wondering if there is some proper order of powering everything, maybe I should first start the control board, then connect the battery terminals?

I need an advice. I'm planning to build a 14s10p battery pack with Sanyo GA batteries. Do you guys think I can do that with 0.15mm nickel strip? The battery is designed in a way that there will be at least 2 series connections between the cells in the sub packs and 3 parallel between the sub packs. Thicker nickel strip is hard to source even from Aliexpress and I already have about 20 meters 8mm x 0.15mm.

Even if I had built the control board, I ordered from Paul one of his power boards, to be sure I have a working welder when the batteries arrive, and to appreciate his hard work and dedication.

User avatar
pguk   100 W

100 W
Posts: 107
Joined: Mar 16 2012 4:30pm
Location: North England, birthplace of the Industrial Revolution

Re: 6pence Resistance Spot Welder

Post by pguk » Jan 26 2017 4:34pm

Hey Valentin

Good lookin', Lookin' good !!

It was always the vision to enable the garage builder to get a tool for minimum outlay. You have proved one can build a capable power board with parts from aliexpress assembled with hand tools and a 100w soldering iron.

Regarding order of power up. Yes, it's safer to power on control side first. This way you can be sure all the FETs are clamped off before connecting battery cables.

https://m.youtube.com/watch?v=1r2tkwUnNv4
Re sourcing good nickel. There is info on here somewhere listing good sources. Here is a YouTube link to a guy who did a corrosion test on two lots of nickel sourced from china, both listed as pure nickel. Only one is the real thing. I got stung twice before finding this. I ordered from 'Bring good things to life'. When it arrived I did the test myself - and it was pure nickel.
Last edited by pguk on Jan 27 2017 5:36am, edited 1 time in total.
6pence spot welder https://endless-sphere.com/forums/viewt ... 31&t=81274
"It is all nice and proper, but only an idiot would think that the father is sixpence to the good on the transaction." C.S. Lewis' Mere christianity

User avatar
fechter   100 GW

100 GW
Posts: 14637
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: 6pence Resistance Spot Welder

Post by fechter » Jan 26 2017 8:38pm

Valld wrote:Hi guys,

I need an advice. I'm planning to build a 14s10p battery pack with Sanyo GA batteries. Do you guys think I can do that with 0.15mm nickel strip? The battery is designed in a way that there will be at least 2 series connections between the cells in the sub packs and 3 parallel between the sub packs. Thicker nickel strip is hard to source even from Aliexpress and I already have about 20 meters 8mm x 0.15mm.
Nice job on the welder circuit. Looks great.

There are a few topics somewhere discussing pack building techniques. You might get some ideas if you check them out.
Here's one, but there are a few: https://endless-sphere.com/forums/viewt ... 14&t=68005

Depending on how much current you plan to draw, two series strips may not be enough. The best is to have one series connection for each parallel cell. You really only need one parallel connection this way and it doesn't normally carry much current.
"One test is worth a thousand opinions"

Valld   10 mW

10 mW
Posts: 23
Joined: Dec 06 2016 8:03am

Re: 6pence Resistance Spot Welder

Post by Valld » Jan 29 2017 2:50pm

Thanks for the link fechter and Paul, very useful information there! I'm sourcing some 0.3mm nickel, should be OK with even only 2 to 3 connections between the sub packs and I don't have to make many layers.....

mudflap5   10 W

10 W
Posts: 90
Joined: Jul 28 2013 8:24am
Location: DFW Area Texas

Re: 6pence Resistance Spot Welder

Post by mudflap5 » Jan 29 2017 9:23pm

joby1 wrote:
mudflap5 wrote:Recently finished a 20S12P battery using the 6pence welder. The welder worked very well, although it took a few attempts to get the pulse timing right. I think timing has a lot to do with the size and capacity 12 volt battery, using a very large deep cycle marine battery for this build. The nickel strips were .25mm thick. The power board was built with the FET's bolted to an old heat sink from a burned up controller, and using the flyback and avalanche diodes. Made the welding tips from 4 guage solid copper wire. Here is a picture of the pack and the welder is in the background.
trying to wrap my head around pack design,
in the post it says 20s10p, is that battery not a 24s10p?

I am counting batteries and getting confused.. :)

thanks
Joby
It is 20S12P. 12 cells welded in parallel for a group of 12 cells. 20 groups (of 12 cells) are welded in series. 20S12P.

m.mitchell   1 µW

1 µW
Posts: 2
Joined: Jan 29 2017 6:06pm

Re: 6pence Resistance Spot Welder

Post by m.mitchell » Jan 30 2017 3:21am

RenderedContent-29A8FAC0-F094-4DD4-9DEB-03C25DBB5A05.JPG
Back of unit
RenderedContent-29A8FAC0-F094-4DD4-9DEB-03C25DBB5A05.JPG (66.08 KiB) Viewed 1010 times
RenderedContent-863F8E39-394F-4A31-A360-00907AAFEAB6.JPG
Side view
RenderedContent-863F8E39-394F-4A31-A360-00907AAFEAB6.JPG (165.21 KiB) Viewed 1010 times
RenderedContent-D323EB3A-A458-4974-BC82-1309312CA317.JPG
Front of mosfet
RenderedContent-D323EB3A-A458-4974-BC82-1309312CA317.JPG (143.75 KiB) Viewed 1010 times
Just finish my version of this spot welder unit. Runs very cool and each mosfet got its own heatsink and also the big diode on the back. Just got to make a housing now.

User avatar
pguk   100 W

100 W
Posts: 107
Joined: Mar 16 2012 4:30pm
Location: North England, birthplace of the Industrial Revolution

Re: 6pence Resistance Spot Welder

Post by pguk » Jan 30 2017 7:52am

Outstanding. Some hours gone into that? Any areas you found particularly tricky?

Reminds me of our town's police station built in the Brutalist style sometime in the '70s.
https://en.m.wikipedia.org/wiki/Brutalist_architecture

Be a shame to hide it inside an enclosure
Thanks for posting :)
6pence spot welder https://endless-sphere.com/forums/viewt ... 31&t=81274
"It is all nice and proper, but only an idiot would think that the father is sixpence to the good on the transaction." C.S. Lewis' Mere christianity

Valld   10 mW

10 mW
Posts: 23
Joined: Dec 06 2016 8:03am

Re: 6pence Resistance Spot Welder

Post by Valld » Jan 30 2017 12:54pm

LOL! This looks like a piece of art! Really nice. I forgot to mention that I do not get any heat on the power board, even with rapid (as fast as I can) welding. I believe its not the heat that kills the FETs.

m.mitchell   1 µW

1 µW
Posts: 2
Joined: Jan 29 2017 6:06pm

Re: 6pence Resistance Spot Welder

Post by m.mitchell » Jan 30 2017 5:40pm

Hi,
It only took a few hours to make. I had a lot of bits laying about so just made a nice version of it. I did not find any of it tricky to do. Just one thing,if your soldering to think copper make sure you got enough heat on it for the solder to run well, or your have bad solder and not good for a good contact. I love the police station you put up lol, that did make me laugh. I know heat does not blow up FET but it just helps to keep everything cool plus I had no problems with it. Going well so far. I think I make a clear top housing so you can see my work of art lol or police station from the 70s lol.

Boobyjohn   1 mW

1 mW
Posts: 18
Joined: Jun 13 2015 1:03pm

Re: 6pence Resistance Spot Welder

Post by Boobyjohn » Feb 01 2017 12:23am

So I have been brewing on a fairly simple extension to this welder: "Probe" preparation welds.

The idea with this post is just to throw the idea out there. Hopefully, someone with more experience with spot welding will comment on the feasibility and utility of the proposal.

The electronic side of this will be a voltage divider circuit (which is just to series connected resistors) between the positive and negative terminals of the current source (which I assume is battery of some kind), and connected to the ADC (i.e., analog pin) on the Arduino chip. This will enable us to get "relative" voltage readings. By "relative" I mean that the ADC converts the input voltage to a value between 0 and 1023. It reads 0 if the input voltage is 0V, and 1023 if it is 5V or more. The ADC is capable of sampling the voltage at approximately 10 kHz (and maybe up to 77 kHz by doing low level magic in the code).

The idea is to measure the voltage sag of the battery during a pulse, and compare that with the voltage immediately before/some time after the pulse. This will enable us to:
1. Make probe welds, i.e., extremely short welds, that doesn't do any welding, but determines the resistance of contact surfaces which can then be shown to the operator. If the resistance is too high, too little pressure is on the weld terminals. If the resistance is too low, he is trying to weld thicker material and need to increase current.
2. Record max current during weld. If the current readings for two similar welds are similar, chances are that both welds are of similar quality. If the current readings deviate the lower current weld is probably not good. Thus the operator can find bad welds as he proceeds.
3. Preemptive weld abort. If the max current in the formation pulse is not within a given envelope, the main pulse is not fired. Thus, if the operator made some mistake that would result in a bad weld, the weld is aborted before any damage is done.


The voltage sag at the battery terminals should be very noticeable. If the battery has an internal resistance of 20 mOhm (which is typical according to a random post on the Internet i found), the voltage sag with 100A current is 0.02 * 100 = 2V. 2V difference on the battery side, will (after passing through the voltage divider and ADC) result in a change of voltage readout in the Arduino of more than 100 steps(ballpark figure, actual will depend on voltage divider parameters), or 10% of the resolution.

User avatar
fechter   100 GW

100 GW
Posts: 14637
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: 6pence Resistance Spot Welder

Post by fechter » Feb 01 2017 12:54am

If the sampling rate and processor speed were fast enough, you could have it automatically output a constant weld energy. Weld time would be calculated on the fly based on current and voltage. This would compensate for variations in probe resistance, etc., up to a point. Weld energy is voltage x current x time. We can easily vary the time.
"One test is worth a thousand opinions"

Boobyjohn   1 mW

1 mW
Posts: 18
Joined: Jun 13 2015 1:03pm

Re: 6pence Resistance Spot Welder

Post by Boobyjohn » Feb 01 2017 1:14am

@fechter
Processor and sampling is fast enough. The highest reported sampling rate is 75 kHz or a sample every 13 microseconds [1], and processor chugs along at 16 MHz. At these speeds, I think signal latency is going to be a factor as we approach these limits. Do you c the problem? :) Edit: Old physics joke, that isn't relevant here after all. If the signal wire 1 m, the delay, if limited by the speed of light, is just 3 ns.

I did ponder hooking the mosfets up to the PWM, but I have no idea how they would respond to that kind abuse :) I do fear that the control loop would get very complex since the code would have to adjust for rate of change in current.

[1] http://www.instructables.com/id/Girino- ... illoscope/

User avatar
fechter   100 GW

100 GW
Posts: 14637
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: 6pence Resistance Spot Welder

Post by fechter » Feb 01 2017 10:13am

That looks fast enough. I generally run around 10ms pulses. So the trick would be to measure the weld current and voltage. It wouldn't need to be exact, just really repeatable. You'd enter the desired weld energy (Joules) and when the measured amount reaches this, it ends the pulse.

I'm not sure how useful or necessary this is. I've done thousands of welds with just time control and had very few bad welds. Most of the fails were when I got to close to the edge of the cell end button and it blew a hole through the tab.
"One test is worth a thousand opinions"

User avatar
pguk   100 W

100 W
Posts: 107
Joined: Mar 16 2012 4:30pm
Location: North England, birthplace of the Industrial Revolution

Re: 6pence Resistance Spot Welder

Post by pguk » Feb 02 2017 5:24am

This all sounds super clever :shock:
If the chip needs to run at 16MHz to do this stuff, I need to put a crystal back on the board. I was so chuffed when I found that the chip is capable of clocking itself, if you're happy at 8MHz. Less No of parts is a good thing - as fechter hints, I'm not sure of the gains of over engineering this switch.
I don't think these FETs would suit pwm. The last code revision I did was to give the operator choice to do a single pulse only, with regard to giving the FETs a super easy life. (Folks were blowing FETs before the diode mod was introduced by Okashira. After the introduction of a Schottky flyback diode, plus TVS diodes, plus change to the SMD MOSFETs, folks are no longer blowing FETs)
6pence spot welder https://endless-sphere.com/forums/viewt ... 31&t=81274
"It is all nice and proper, but only an idiot would think that the father is sixpence to the good on the transaction." C.S. Lewis' Mere christianity

Boobyjohn   1 mW

1 mW
Posts: 18
Joined: Jun 13 2015 1:03pm

Re: 6pence Resistance Spot Welder

Post by Boobyjohn » Feb 02 2017 1:16pm

@fechter

You *only* need to measure voltage sag. The rest will be consistent as long as the battery isn't exchanged.

Entering weld energy should be done by proxy, i.e., "that amount of time given this amount of sag". This cuts parts involved in half.
I'm not sure how useful or necessary this is. I've done thousands of welds with just time control and had very few bad welds. Most of the fails were when I got to close to the edge of the cell end button and it blew a hole through the tab.
Those are exactly the welds that could be aborted, without any damage to the tabs. Because you were too close to edge of the cell, the contact between tabs and the cell's terminal should be poor. The formation weld would then pull less current, and the logic could then prevent the main pulse from being fired.

FYI: This idea is not strictly my own. Some professional welding systems operate with an "envelope" of the current. If the current goes outside this envelope, the weld is aborted. The sources I have found, conclude that this gives more reliable welds.

@pguk
8 MHz is probably not as good as 16 MHz. But, if we are able to get 35 kHz sampling rate I guess that is more than enough anyway.

User avatar
fechter   100 GW

100 GW
Posts: 14637
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: 6pence Resistance Spot Welder

Post by fechter » Feb 02 2017 3:02pm

Good idea as long as the internal resistance of the source battery stays the same. It will tend to change slowly over time, which you could manually compensate for.

Automatically aborting the weld if it senses high resistance sounds like a good feature.
"One test is worth a thousand opinions"

Boobyjohn   1 mW

1 mW
Posts: 18
Joined: Jun 13 2015 1:03pm

Re: 6pence Resistance Spot Welder

Post by Boobyjohn » Feb 03 2017 1:01am

@fechter

I will just maintain a list of voltage sags for the last 20 (or so) welds and compute the average voltage sag using that list (first discarding highest and lowest value). If the voltage sag is more than 10% (or some other percentage) off, the main pulse is aborted.

Each time the pulse one parameter is changed, the list is flushed, so this system only kicks in after 20 (or so) welds. This way, the operator may get away with not configuring the feature at all.

User avatar
fechter   100 GW

100 GW
Posts: 14637
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: 6pence Resistance Spot Welder

Post by fechter » Feb 03 2017 11:48am

That's a great approach. Slow changes in the source battery would be compensated for.
"One test is worth a thousand opinions"

User avatar
pguk   100 W

100 W
Posts: 107
Joined: Mar 16 2012 4:30pm
Location: North England, birthplace of the Industrial Revolution

Re: 6pence Resistance Spot Welder

Post by pguk » Feb 04 2017 5:40am

'More reliable welds' has to be a good thing. It can be alarming when you get a mis-weld, and then you're nervously waiting for the next time it may happen.
6pence spot welder https://endless-sphere.com/forums/viewt ... 31&t=81274
"It is all nice and proper, but only an idiot would think that the father is sixpence to the good on the transaction." C.S. Lewis' Mere christianity

Valld   10 mW

10 mW
Posts: 23
Joined: Dec 06 2016 8:03am

Re: 6pence Resistance Spot Welder

Post by Valld » Feb 04 2017 5:01pm

Welder completed. I had a faulty invertor getting dust for years and decided to use its box. One of the most annoying things with my first designs was that the weld cables were not fixed to anything stable and the whole system was moving when I was moving the cables, so I just mounted the cable terminals to the box with their own bolts. Now when I want to use the welder, I just press it down on top of my battery terminals and it stays snug and stable. The only minus is that it fits only this battery (most probably), but its brand new 72Ah 650a good (for Botswana) battery. I bought it to replace the battery (35Ah) for my petrol generator which died a few months ago. So if I need it I can always pull out the welder and use it in the generator. The Schtkky diode was always on my way and I never found a good place to install it stable and with no direct contact with the weld cables, and I finally found a good place for it. Below are some photos, I used the invertor terminals to connect the Schottky and weld cables on the outside. The small switch on the top right I connected to the negative on the control board input power, so I now have on/off switch and the pedal and power to the control board are on the right side of the box. I used a piece of the top of the box to make the control board panel and the hole I can use for storing the nickel strip. My batteries just started their long trip from Poland, so I'm on standby for 2-3 months. By the time they arrive you guys may develop some new features to the already great device :). Some photos below:
Attachments
IMG_20170204_145705.jpg
IMG_20170204_150912.jpg
IMG_20170204_145602.jpg
IMG_20170204_150858.jpg
IMG_20170204_145732.jpg
IMG_20170204_150439.jpg

Valld   10 mW

10 mW
Posts: 23
Joined: Dec 06 2016 8:03am

Re: 6pence Resistance Spot Welder

Post by Valld » Feb 04 2017 5:06pm

And some more :
Attachments
IMG_20170204_145219.jpg
IMG_20170204_145740.jpg
IMG_20170204_091920.jpg
IMG_20170204_145248.jpg

User avatar
fechter   100 GW

100 GW
Posts: 14637
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: 6pence Resistance Spot Welder

Post by fechter » Feb 04 2017 5:37pm

Looks great!

Got any old batteries you can test with? I'd like to hear how the welds turn out.
"One test is worth a thousand opinions"

Valld   10 mW

10 mW
Posts: 23
Joined: Dec 06 2016 8:03am

Re: 6pence Resistance Spot Welder

Post by Valld » Feb 05 2017 1:31am

Sure, the welds are beautifull! No heat buildup on the boards, no cable kicking, very little or no sparks if the electrodes are perpendicular to the tabs. The left is with the default settings, the right one with 8ms second pulse. I only have 0.15mm nickel strip ( pure, tested). I'm able to weld 3 strips together at ones with second pulse of 10ms.
Attachments
IMG_20170123_171704.jpg

User avatar
pguk   100 W

100 W
Posts: 107
Joined: Mar 16 2012 4:30pm
Location: North England, birthplace of the Industrial Revolution

Re: 6pence Resistance Spot Welder

Post by pguk » Feb 06 2017 5:36am

Cool Valld - thanks for posting.
Did the power board I built arrive with you yet? I'm interested to hear how it performs with the large batt you have there in comparison to your own build.
Been busy taking photos of a complete build this weekend (will post later). It has control board mounted on top of power board with a bracket for switches and connectors attached. This way no enclosure is needed and it can be strapped on top of the battery when in use. I have to make weld cables up, then I can do some testing.
6pence spot welder https://endless-sphere.com/forums/viewt ... 31&t=81274
"It is all nice and proper, but only an idiot would think that the father is sixpence to the good on the transaction." C.S. Lewis' Mere christianity

Post Reply