Spare Parts Resistance Welder

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wvg_ca

Active Member
just thought I'd share a spare parts contraption that I built quite a while ago, for a much different purpose then, but works great for model railroading..
It's a resistance welder, not a soldering type, an actual metal welder for small scale hobby usage..
I use it to make replacement handrails, steps, weird braces, and other spur of the moment contraptions..
Made of two 100k 35v caps in parallel, fed through a switch and a 1k 1w input resistor to make it easier on my little 1amp variable supply..
then an scr fed from a 7805 from the main rails, through an old probe head, with a push button trigger mounted on the probe..
easy to use, attach the neg to a ground plate, brass is nice, won't stick, I use steel, the little bit of stick holds parts in place better, line up the two wires, and a quick push on the button, and they're welded together..
I use small 0.017 steel blackened wire for most things, they were origionally some kind of wire ties for tagging items, or for larger sizes I use 0.023 mig welding wire.. cheap, 25 bucks gets you a 50 lb spool...:)
It's took me maybe an hour to assemble the unit, but you can make many small wire items like handrails very quickly, and don't need to go down to the LHS ...
The steps in the photo were replacements for an old cheapy Tyco tank car, and it'll get 'upgraded' with some old blue box trucks, and KD #5's, a shot of flat black Krylon will a bit of durability , and some decals and weathering, and another low cost piece of rolling stock..

I use about 15v for smaller sizes, up to maybe 25v for larger wire with multiple weld points, like the photo below..
My supply is only 1a, max 30v, so an old train transformer may should be enough to drive this welder..

if you really need a schematic, I'll post one..
..enjoy..
 
Last edited by a moderator:

Hillwilliam

Layout Poor
Resistance Welder

I'd sure like a schematic. Might have enough parts except for the cowpastures lying around to build one. Might have to raid a stereo amp for the biggies. :D

edj
 

UP2CSX

Fleeing from Al
Cool! A miniature welder with a Philco meter. That's some real scrounging. :) Nice job on that tank car ladder. I'm an electronic idiot but I'd like to see a schematic too, just so I can see how you did it.
 

wvg_ca

Active Member
ok, rough schematic..easier [and faster] to do by hand..:)
caps are fairly large, appx 5" high..a large coffee cup size [medium at Robins], or one 'jumbo coffee' size..
meter [depending on type] can be anywhere, across caps is easiest..even your multimeter.. just to see when the caps are charged, and fine tune what you need for voltage to get a good solid weld, most times it will break one of the wires next to the weld before the weld itself lets go..:)
If it blows the wires apart, it's too high..make sure you put some pressure on the probe when you hit the 'juice button'..:)
old probe came from old multimeter of some kind, switch and small parts from junk box, caps came from old [huge] printers at local scrap metal yard, need an scr about the size of the last joint of your little finger to handle the load, or larger, whatever can be found locally..mini push button from radio shack or princess auto, whatever,
don't really need the 7805 regulator if you can't find one, it will work ok without it as long as you run minimum 5v in, I use from 15 to 25 normally..you can just draw from the + side of a cap to the push button...through maybe a 1k resistor so it's easier on the switch..
 

Hillwilliam

Layout Poor
Resistance Welder

Many thanks for the schematic. I've got a MIG welder out in the shop but that's a bit overkill for modelling.

Having never used one of these, I am wondering how much heat is introduced surrounding (think plastic ties) the joint. It appears this may be a solution to connecting feeder wires from the buses too.

Thanks again.

edj:)
 

wvg_ca

Active Member
the current induced heat is very localized and momentary...I can pick up something like the steps pictured immediately after a weld, and there is very little warmth in the joint..
I never tried soldering feeder wires to track, but I assume if the wire was a copper similar to the track itself, it should weld ok, ???
I'll try some tonight and see what it does..
 

Hillwilliam

Layout Poor
I believe the copper percentage in N/S rail is somewhere between 55 and 75% copper so the feeder wires should fall into the solderable category.

Thanks

edj
 

wvg_ca

Active Member
tried a bit of welding wires to rails..
works ok, so it seems anyways...
good with either 32gau solid, or kynar [wire wrap] wire, fair on stranded, if off a bit or no pressure, lose a small portion of the strands, they just kinda disappear..:)
pretty good wit 0.017 steel wire to Atlas turnout rails [older code 100]..
 




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