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Old 14th May 2024, 4:51 pm   #1
Uncle Bulgaria
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Default Spot welding resistance wire?

I've been musing on this as I consider repairing a toaster. It's a DeLonghi four slice with a break in the element right in the middle. To access it would require removing all the edge frames (lots of bent-tab-in-slot fixings) and disconnecting the wires from the OK element sections to move them out of the way.

They're all flattened wires spot welded together, and spot-welded to the PCB connections so reconnecting would mean a lot of silver soldering.

Has anyone managed to redo this sort of micro spot welding at a domestic scale? I have seen some references to do with people making lithium battery banks, but whether that's just advertising I don't know.
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Old 14th May 2024, 7:23 pm   #2
Ed_Dinning
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Default Re: Spot welding resistance wire?

I believe Elektor mag were recently advertising a small spot welder for use on batteries etc, should work nicely for your task

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Old 14th May 2024, 8:13 pm   #3
David G4EBT
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Default Re: Spot welding resistance wire?

Quite tricky would be my guess. Too much current and the metal is vaporised - too little and it doesn't weld.

These might be worth checking out:

'Mini Spot Welder, Handheld Battery Spot Welder Pen, Integrated Spot-Welding Machine for Industrial Assembling Battery Packs':

https://www.amazon.co.uk/dp/B09SB9Z8...T1zcF9kZXRhaWw

https://www.amazon.co.uk/Welding-Han.../dp/B08X4QZ3PT

Youtube Video:

'Repair Attempt - Super Cheap Spot Welder'

https://www.youtube.com/watch?v=Zk_ir69kB5Q
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Old 14th May 2024, 8:18 pm   #4
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Default Re: Spot welding resistance wire?

I recently borrowed one of the little lithium battery spot welders, to weld some approx.23swg thermocouple wires onto a capillary tube (don't ask!).

It did the job fine, I started low and it did not weld, then turned it up a couple of notches and there was a brief incandescent glow and when I took the probes away it had welded it all together.

It was this type of thing with separate electrodes.

https://www.amazon.co.uk/Battery-Wel...y%2C176&sr=1-6
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Old 14th May 2024, 10:49 pm   #5
Buzby123
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Default Re: Spot welding resistance wire?

Our DeLonghi 4-slot toaster had exactly the same problem.

I opened it up, looked at the slot-and-tab construction, spot-welded joints, and thought too much trouble.

Now it's just used as a 2-slot toaster.
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Old 14th May 2024, 10:59 pm   #6
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Default Re: Spot welding resistance wire?

A TIG machine which goes low enough in current can do the job, but an active-when-hot flux is needed to clean the surfaces of the metals. Good mechanical cleaning-polishing helps a lot and I did get a brazing type Borax flux to work. You definitely need high-frequency arc start. Forming thermocouples becomes easy with a bit of practice.

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Old 15th May 2024, 9:26 am   #7
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Smile Re: Spot welding resistance wire?

Hi,
I've seem to remember somewhere that a spot weld could be accomplished by discharging a large-ish capacitor across the workpiece via electrodes.
I don't know any details, but a possibility?
Cheers, Pete.
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Old 15th May 2024, 9:45 am   #8
McMurdo
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Default Re: Spot welding resistance wire?

I tried the capacitor method before using the little spot welder but never had much luck. As soon as the electrodes are brought together there's a discharge and it just blows a bit of the metal away. The spot welders from amazon have a contact detection circuit that waits a couple of seconds after seeing the circuit, giving you enough time to add just enough pressure, so then the current turns on and off and the job's done.

I used to go and fix spot welders (old ones from the late 70's) used for making brake shoes and they had a multi-level current control that did a pre-heat discharge, a delay, a main weld discharge, a cooling delay then a release. Somewhat bigger than required for a toaster element as they had water cooled electrodes but I suspect these little amazon jobbies have a similar system as some of them come with a tiny LCD screen that allow programming of this type of weld.

All a bit over the top for a toaster I suppose unless you're making an industry of it
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Old 16th May 2024, 10:03 pm   #9
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Default Re: Spot welding resistance wire?

In my limited experience the capacitor discharge method produces an enormous peak current, but it is too short to really do the job well
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