6pence Resistance Spot Welder

[Storapa]

Right Folks,

My spot welder is finished. I've powered up the brain with the plug in 12v supply. Everything looks spot on. I need to cover some of the connector junctions with heat-shrink and put the whole thing into an electrical enclosure.

Was it difficult for a novice? Not really. The only issue was soldering the busbars. If I did it again, I would borrow a proper iron. Paul was very helpful answering my questions etc.

I haven't tested it yet, as I am not sure what to do about the battery that I built. I think I will try and find a big lead acid battery for the initial test.

I'm off on holiday for a week now, so rather frustratingly I will need to put it to one side until I get back. I have nickel strip, copper coated nickel strip, cells etc, all waiting to go.

Right, that's it for now.

Finished SpotWelder.jpg (92.61 KiB) Viewed 3922 times

[Animalector]

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Single handed operation. One hand to hold the nickel one hand on the probe foot switch to make the magic happen

Andy

[Valld]

Time for update My batteries from Tumich just arrived this Saturday! I tested all of them by discharging all of them (4x4) in my SkyRC MC3000 charger from 3.5V to 3.3V at 1A discharge rate. Each cycle took 20 minutes and the process took me a full day. All 150 came in perfect condition, no damaged, no defective cells and all of them at pretty much the same voltage - 3.50xx Volts.

Guys, I need an advice from someone with more experience. Something strange is going on when welding nickel strips. I'm able to weld 0.15x8 mm thick strips to each other with 1:1:5 ms (the default) and for 0.2x8 mm I need 2:1:35 ms or more. This is 600 % more power needed for only 25% thickness increase. Please advice if this is normal. I'm using new, fully charged 72Ah, 650A battery. When I weld 0.2mm strips with 35 ms I barely notice the weld is done, quiet and no sparks, when I tried the same settings with the 0.15 strips it made a huge holes in both strips with a fountain of sparks and quite noisy.... I'm not sure why such a big difference, it feels like two completely different materials, but I did the water/salt/vinegar test on both with no rust at all and the metal looks and feels the same way, so I believe both are pure nickel. Is my car battery too weak for 0.2mm strip? I can probably get a second battery in parallel, but really didn't want to....

[spinningmagnets]

The the thicker the nickel strip, the more vital it is to have the central slot. If your nickel strips don't have them, then you might try using a Dremel with a thin abrasive disc, that has worked for me in the past.

[pguk]

Great photos folks, thanks for taking the time

@valld
35ms sure seems a long time, I'm sure you would benefit from slotted nickel as Ron suggests, as all of the weld current is forced to go down and across the cell end and return on other side of the slot. Although I can't speak from experience on this.

I took delivery of another batch of 20 power boards. They are through allpcb.com and have 1oz copper this time, not 2oz as previously. This is okay because we are adding lots of copper to the board and not relying on board foil to carry any current. I have shifted the Schottky diode a little further away from the FETs to fix the issue where we had a short when stacking the boards using metal pillars. However I would still recommend using plastic pillars for stacking (M3).

[Animalector]

We did some welding today and I found little difference between having slots and not having slots... The Times I had blow through was when I lacked sufficient pressure on one of the tips or was too close to the edge of the positive surface.

Settings 1, 1, 17 for the negative side
And 1, 1, 12 for the positive side

Here you can see with slots and without.. one thing I did notice was a need to reduce the secondary for the positive side. Slightly different material perhaps? Or maybe in my failed attempts I was just to close to the edge of the nipple.

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[miffi]

I've got one of these kits on the way. Looking forward to putting it together. I hope I can solder the copper bus bars with a soldering gun as my iron is too small. Maybe one of those 100watt cheapo stained glass irons could do it with the right tip. Time will tell!

[Storapa]

Morning All,

After much fiddling about, my spot welder is now working. The build, in reality was very simple and it worked as soon as it was plugged in. No fuss, just a nice spot weld. I decided to use a regular lead acid battery for the time being, as there are mixed views wrt to my lithium pack. I will test it at some point though.

Right, photos.

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Settings,

P1 - 1.00

P2 - positive side - 14

P2 - negative side - 12

The strip is 0.15mm nickel.

I think the welds look ok. I could maybe back the time off a little. All tabs pull material when pulled from the cells. The weld is very good.

Any feedback would be gratefully received.

[Valld]

Final update . My pack is ready and fully operational. Real life always turns out different that the tests.... I made the rust test for all my nickel strips again, but this time I only soak them in salt water solution for about 10 minutes and then left them outside during the night. In the morning I got my answers to the weird difference in welding times for 0.15 and 0.20 mm strips. All 0.15 strips that I have turned out to be nickel plated steel! The good news was the 0.5kg 0.2 strip that I bought last didn't have any rust on it, so definitely the good stuff. That explains why I had a very different welding times between the two types of material. Looks like steel strips are much easier to weld than pure nickel. That was a good lesson.

Now to the actual job. The weld times between 0.2 nickel and battery terminals was easier than what I experienced during my tests between two 0.2 nickel strips. The explanation is probably the same a above - weld is easier between nickel and steel. All I needed to weld the whole pack was between 17 and 20 ms secondary pulse and 1.5 initial. I tried making slotted strips and it took forever to make the slots, just to shave about 5-6 ms of the second pulse, so I decided to not do it. Instead, as you can see in the photos below, I used a generous amount of strips. I got sure to use at least two connections per battery (good for at least 14Amps) and at least 4 or 5 connections between the 10cell packs - good for 28-35 Amps.Some of the series strips are doubled and tripled, which is not visible on the photos....

For the positive and negative ends I used a split cable end with multiple solder connections to ensure smooth amp handling.

And now about the welder. All I can say is EXCELLENT! I finish all the welding in about 4 days, working a few hours in the evenings and preparing the strips at work during the day. Every welding session was limited to 150-200 welds by the heat build up on the welding cables/terminals and lasted 10-15 minutes with rest sessions of 5-10 minutes in between. I had 0 misfires and 0 blowouts. Ones a strip was attached with the first weld it was very fast to make the rest 20-30-40 welds. I touched the schottky diode a few times and it was slightly warm at worst. I used 17ms for the strip-battery terminal welds and 20-21 ms for second and third layer between the nickel strips. I tried a few times after the first weld to pry a strip and they were holding well. By the way, I never tried the power board that I bought from Paul, finished all the work with the board I made (photos in the first pages of this thread)

One more fact to share. I was able to charge the battery all the time during welding, no problem with this at all. I used SkyRC B6AC V2 charger and was able to monitor the battery voltage during welding. The whole pack (approximately 5000 welds total) used about 45 Ah to complete (3 nights by 15Ah to fully recharge). Now I have a nice 14S10P 52V battery pack about 33Ah capacity made with Sanyo GA batteries from Tumich.

I hope I did provide some useful information for anyone newbie like myself for their future DIY battery pack projects.

[notger]

Just got the parts for the 6pence welder.

Now i was searching for the rest of the needed parts in my workshop.
What do you think about what i have here ?

- 95AH 3 Year old car lead acid battery, still very "vital" ? could that be too strong ?
- 16mm² cables as weld and batteryclamp cables? should i double them to 32mm² ?

thanks in advance

Notger

[Storapa]

Right Folks,

I spent last night welding up my first pack (14s x 4p). It took just over an hour with just under 250 pairs of spot welds. Every weld was spot on.

IMG_1550.JPG (94.82 KiB) Viewed 3774 times

All I need to do now is attach my BMS, power leads etc.

I have a general question about the pack build, but will post that in a new thread.

[Valld]

Pack ready Will post some photos in a day or two with the whole bike, only left to complete the housing and mount it on the bike.

[Storapa]

Looks great.

Where did you get the heat shrink from?

[Valld]

ATOPELEC Store, Aliexpress. I bought everything necessary for the welder and battery pack from Aliexpress except the control board and electrodes for the welder and the battery cells, from Paull and Tumich in this forum respectively.

[Storapa]

ATOPELEC Store, Aliexpress. I bought everything necessary for the welder and battery pack from Aliexpress except the control board and electrodes for the welder and the battery cells, from Paull and Tumich in this forum respectively.

Cool. Thanks for the info.

[pguk]

- 95AH 3 Year old car lead acid battery, still very "vital" ? could that be too strong ?
No, it should fine I reckon.
- 16mm² cables as weld and batteryclamp cables? should i double them to 32mm² ?
Personally, I would double them up for a nice fat 32mm if you can.
Notger

@Storapa
You got some nice results there. What size is your lead acid battery, and how are you keeping it charged as you go along?

@Valld
Great to see you got there at last, and thanks for a detailed report of the build and all your experiences. Your pack looks sweet, I hope it serves you for a good long while to come

[riba2233]

Right Folks,

I spent last night welding up my first pack (14s x 4p). It took just over an hour with just under 250 pairs of spot welds. Every weld was spot on.


All I need to do now is attach my BMS, power leads etc.

I have a general question about the pack build, but will post that in a new thread.

Do you have insulation between series cells?

[Storapa]

@Storapa
You got some nice results there. What size is your lead acid battery, and how are you keeping it charged as you go?

Hi Paul,

Thanks for the remarks. I'm using an old 95Ahr Optima leisure battery. The voltage didn't really change whilst I was welding, so no charging was needed.

[Storapa]

Do you have insulation between series cells?

Other than the insulation that is around the cells, no. I've seen plenty of packs built in this fashion. Is there a problem with this method of construction?

[riba2233]

Yes, it's a big problem. Cells chafe over time from vibrations and can short each other, which can lead to fire.

[Storapa]

Yes, it's a big problem. Cells chafe over time from vibrations and can short each other, which can lead to fire.

I'm just about to rebuild a Trek BionX system battery that is constructed in a similar manner (hot glued cells). Have Trek got it wrong?

The Stealth guys use the same method of pack construction.

Am I missing something?

[riba2233]

Look, I've explained what could happen, it's easiest way for a pack to catch fire. You have been warned, and it's completely your responsibility

EDIT:

This is how I like to do it:

[Storapa]

So are you wrapping an extra layer of kapton tape around each cell?

Are you relying on the connections to hold the pack together?

[riba2233]

There is hot glue between the cells, maybe you can see some on the second picture. Yep, I just wrap kapton tape around each parallel group, and in the end that gives double layer of insulation, very resistant. Sometimes I use insulating (electrical tape, third picture) if I run out of kapton.

[fechter]

The shrink wrap that comes on the cells can also melt if the cells get too hot. If you get a short, there's a good chance for catastrophic fire.

It's a really good idea to place some extra insulation between the series sections. I'd recommend Nomex paper. Very thin, abrasion resistant and won't melt at high temperatures. Kapton doesn't melt easily but is pretty thin.