# today's projects, auto reverse & spot welder



## wvgca (Jan 21, 2013)

it's cold outside, so todays projects...
1] make a small auto reversing test track , for run in or ...
don't have room for a 4 foot ho circle,...
2] need some ladders, want them in fine scale steel for appearance, don't like gobs of glue..
so going to try to make a spot welder, not a resistance welder that needs a blob of solder, just straight metal to metal spot welding...

should have enough parts laying around so that these are readily 'do able' projects..??


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## DonR (Oct 18, 2012)

Did you get anywhere with your auto reverse track?

I tried to find a couple of threads here on the Forum
that discussed several ways of making it work but
failed so far. 

The most simple hookup uses a latching relay that reverses
the polarity for a DC loco. A short insulated track section
at each end sends power to the relay coil to activate the
reverse.

Don


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## wvgca (Jan 21, 2013)

super shuttle shift test track is complete, and works as hoped... very simple, one relay, one resistor, and two micro switches, that's the main parts ...an old cordless phone wall-wart for power for the relay, and an adjustable bench supply for loco power.. all parts bin supplies...
second photo is an akane brass 4-6-0 that was lubed, and ran back and forth at a slow 4 volt crawl for two hours ... no failures to auto reverse...

spot welder is validated working, just need to mount all components to base, maybe can find a small piece of plywood someplace, got to be some leftovers from the layout around, someplace ..


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## wvgca (Jan 21, 2013)

spot welder is complete, and works great... all from spare parts boxes, basically two big capacitors [100,000uf], a meter for charge voltage, and a probe end with microswitch [momentary] triggering an SCR... for 0.017 hard steel wire, a charge of 13 volts does an excellent spot weld, the wire next to the weld will break before the weld does..
the 0.017 wire that i use was originally meant to tie paper tags to metal parts.. it gives a scale 1 1/2" rung or upright on ladders , 0.024 steel wire is scale two inch and needs 16 volts on my setup.. no solder or CA blobs, super strong... and already has a corrosion resistant black oxide finish... a bundle of these wires two inches in diameter and ten inches long were two bucks at the local steel supply yard.. I don't expect to run out, ever ..


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## rrgrassi (May 3, 2012)

Great work! I wish I had the know how and the parts to do such a thing!


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## wvgca (Jan 21, 2013)

if you want, i can do a schematic.. not sure if you have a local surplus electronics shop??
radio shack wont have the caps or the scr...maybe not even the volt meter..


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## rkenney (Aug 10, 2013)

What are you charging your caps with?


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## wvgca (Jan 21, 2013)

i'm using a bench supply, variable to 28v, 1 amp, through a limiting resistor, to charge the spot welder, cycle time is 3 to 5 seconds, depending on final charge voltage, it takes me that long to line up the wire for the next weld anyways..


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## alman (Oct 22, 2012)

I would like to see a schematic for the spot welder !

PLEASE ! :smilie_daumenpos:


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## rkenney (Aug 10, 2013)

wvgca said:


> i'm using a bench supply, variable to 28v, 1 amp, through a limiting resistor, to charge the spot welder, cycle time is 3 to 5 seconds, depending on final charge voltage, it takes me that long to line up the wire for the next weld anyways..


Like this.


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## michael cuneo (Sep 5, 2013)

*reversing unit*

Hi I was wondering if you could post a diagram for this unit ? I really enjoy scratch building things and this is just one on my bucket list thanks Mike


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## rkenney (Aug 10, 2013)

Here's a video from you tube that builds a spot welder from a microwave power transformer.

http://www.youtube.com/watch?v=vrlvqib94xQ

It's a little bulky and most of us don't have a microwave layin' around.

I too would like to see a schematic for your spot welder.


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## wvgca (Jan 21, 2013)

pretty simple circuit, all from spare parts...
rough guess is 30 plus joules of energy, assuming 1/100 second of discharge
equates to 3500 plus watts, or instantaneous 200 amp welding current..
yep, if they are not held tightly pressed together, they vaporize..lol
just great fun....the cables jump when the scr is triggered...

'don't force it, just use a bigger hammer'


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## wvgca (Jan 21, 2013)

minor update to the spot welder project ..
I needed some 12ga stranded wire for another project today,
and picked up enough to update the spot welder from 16ga ..
makes a big difference, I didn't think I was losing that much
energy through the 16ga, but 12ga is a lot better


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## wvgca (Jan 21, 2013)

Tried it out on a brass United Ma&Pa today, works reasonably well, I still feel that the commercial units 
that run lower output voltage would work better, but this was inexpensive, and to my mind, 'good enough'









oops,, this should have gone in the resistance soldering station project thread, that's actually what i was working with ..
sorry for any confusion


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## gunrunnerjohn (Nov 10, 2010)

How well does it do in repairing brass? I'm curious if there's a way to fix stuff that comes loose on brass locomotives without having to do repainting.


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## wvgca (Jan 21, 2013)

I really don't know for sure ... but as a guess, if a small part comes off, a bit of surface prep only 
on the solder joint, there should be minimal repainting needed , mostly just on the visible mating edges ... 
I don't know how much the concentrated heat applied would damage the paint in the actual probe 
contact area ... but it would probably be necessary to remove 'some' paint to get a proper electrical 
contact, both the probe and return ...
I used expired solder paste, [ I don't have any fresh tubs] ,and thinned it slightly with acetone


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## gunrunnerjohn (Nov 10, 2010)

I've been gluing them back on with Loctite 380 Black Max. Carefully applied, it doesn't require repainting, and it makes a very secure bond once it's set. It would be easier if I could solder, but I've never figured out how to do the job without damaging paint.


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