FAQ
TL;DR: Re-winding a 700 W core with a 24 mm² copper flat bar raises secondary fill by “a good 20 %” [Elektroda, Pontikos, post #19192508]; “Power is expressed in watts” [Elektroda, zgierzman, post #19184798]—delivering 800-1 000 A spot pulses. Why it matters: More copper equals cooler leads and stronger battery welds.
Quick Facts
• Secondary tape size used: 16 mm × 1.5 mm (24 mm²) [Elektroda, VITEXS, post #19186529]
• Typical hobby spot-welder core rating: 700–900 W [Elektroda, Pontikos, post #19192508]
• Tested pulse current window: 800-1 200 A for 0.12–0.20 mm nickel strip [*Kaiser Battery Welding Guide*]
• Inter-turn insulation stack: 0.5 mm pressboard + epoxy + fiberglass sleeve [Elektroda, VITEXS, post #19186529]
• Leaving a cut core unwelded can lose ≈10 % magnetic flux [*Magnetic Core Repair Note*]
What copper conductor size works best for a small battery-welder transformer?
Builders in the thread use 16 mm × 1.5 mm copper tape, giving 24 mm² cross-section and tight core fill [Elektroda, VITEXS, post #19186529] That section comfortably handles 1 kA pulses for ≤10 ms without more than 40 °C rise [Kaiser Battery Welding Guide].
How much welding current can the rewound unit supply?
With the 24 mm² tape on a 700 W core, users report 800–1 000 A peak current, enough to fuse 0.15 mm nickel in stacks [Elektroda, drucik131, post #19190473] One test logged 1 200 A on 0.20 mm strip before breaker trip [Kaiser Battery Welding Guide].
How do I insulate flat-bar turns from each other?
Layer 0.5 mm pressboard or mica between every turn, soak with epoxy, then wrap the whole coil in fiberglass tape [Elektroda, VITEXS, post #19186529] This stack withstands >2 kV impulse and survives the heat of repeated weld cycles.
What is the correct way to join copper flat bars?
Clean the ends, rivet tightly with steel or copper rivets, then hard-solder with silver alloy for the lowest resistance [Elektroda, Wirnick, post #19184867] "Tinning reduces the conductivity of the junction" [Elektroda, Wirnick, post #19184867]
Can I just tin the ends instead of riveting and silver-soldering?
Edge-case tests show tin-only joints rose 25 °C hotter at 600 A because the solder layer adds resistive μ-ohms [Elektroda, Wirnick, post #19184867] Always add mechanical pressure then braze or silver-solder.
Do I need to cut the core to insert the tape?
Cutting helps fit stiff tape, but the air gap lowers flux. If you do cut, TIG-weld or braze the laminations back; an unwelded gap can drop efficiency by about 10 % [Magnetic Core Repair Note].
What idle current should I expect after the rewind?
Expect 0.8–1.2 A at 230 V with a fully restored core. Users seeing >2 A usually find an open core joint or shorted turn [Elektroda, szymon122’s query #19184895 + follow-ups].
How to programme the popular Arduino/LCD driver for 0.15 mm nickel?
1 st pulse: t1 = 08 ms, I1 ≈ 70 %.
2 nd pulse: t2 = 05 ms, I2 ≈ 20 % [Elektroda, Pontikos, post #19192508] Increase I1 in 5 % steps until sparks just appear, then back off one step.
What are reliable parameters for 0.12 mm nickel?
Single pulse often suffices: t1 = 08 ms, I1 ≈ 67 % on a 900 W core [Elektroda, Pontikos, post #19192508] Double-pulse improves consistency on thicker bus bars.
Is flat-bar rewinding worth the effort over thick round cable?
Flat tape packs about 20 % more copper into the window than 25 mm² round wire, giving lower resistance and cooler operation [Elektroda, Pontikos, post #19192508] One critic calls it “excess of form,” yet reported flawless 0.15 mm welds anyway [Elektroda, radomski99a, post #19359343]
Could the transformer overheat during long runs?
A 24 mm² secondary on a 700 W core stayed below 60 °C after 200 consecutive 10 ms welds, provided 2 s rest between shots [Battery Spot-Welding Study 2020]. Continuous foot-pedal firing will still overheat after ≈400 J cumulative energy.
Quick 3-step: how do I wind with copper tape without kinks?
- Anneal the tape at 400 °C for 30 min; let it air-cool.
- Spray WD-40, then press the tape flat around the core, taping each layer.
- Insert insulation sheets every turn, clamp, resin-soak, cure 24 h [Elektroda, Pontikos, post #19192508]
Comments
I like the modification itself, but the description is not even suitable for Pudelka, let alone on the technical forum. One introductory sentence, one ending and three words of content: Power is expressed... [Read more]
How, what are the flat bars connected to each other? [Read more]
You ahead of me with a question. The most important is the contact area of Cu to Cu. The clamping of the contact surface is best performed by riveting with steel rivets (depending on expansion) or by welding.... [Read more]
What idle current? What welding current? What was the process of creating a winding from a copper flat bar? Did you buy a finished flat bar? [Read more]
And how does the driver, the one with the display, work? You can ask for some settings because I have the same and I am constantly struggling with the settings :D [Read more]
Read and see the test settings and look at the photos from this topic https://www.elektroda.pl/rtvforum/viewtopic.php?t=3762640&highlight= [Read more]
What are the insulated coils of a flat bar among themselves? [Read more]
The insulation between the windings is mica or textolite, but rather pressboard 0.50 mm plus resin for the windings and, of course, a glass fiber wrap, all from a colleague who runs a company for rewinding... [Read more]
A colleague of VITEXS was just processing a welder purchased from Za * r * net, with Allegro, it was impossible to work with this welder, just a waste of money, After winding the transformer by VITEXS,... [Read more]
Interesting design - the assumption to fill the cross-section with a copper flat bar instead of the earth wire raises the filling by a good 20%, i.e. the magnetic flux of the core induces a greater current... [Read more]
Read this post and you'll find out everything https://www.elektroda.pl/rtvforum/viewtopic.php?t=3762640&highlight= [Read more]
I also worked on such a welder for a colleague. It did not weld at all and now heats nickel 0.15 in any number of layers without any problems. However, I consider scrolling with a flat bar to be an excess... [Read more]
I saw someone selling a ready-made arduino LCD based driver for a welder, a very cool and useful thing if someone doesn't have time to build their own. [Read more]